Make it possible to stop road vehicles from slowing down in curves so "diagonal"...

[openttd-joker.git] / src / viewport.cpp

/* $Id$ */

/*
 * This file is part of OpenTTD.
 * OpenTTD is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software Foundation, version 2.
 * OpenTTD is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
 * See the GNU General Public License for more details. You should have received a copy of the GNU General Public License along with OpenTTD. If not, see <http://www.gnu.org/licenses/>.
 */

/**
 * @file viewport.cpp Handling of all viewports.
 *
 * \verbatim
 * The in-game coordinate system looks like this *
 *                                               *
 *                    ^ Z                        *
 *                    |                          *
 *                    |                          *
 *                    |                          *
 *                    |                          *
 *                 /     \                       *
 *              /           \                    *
 *           /                 \                 *
 *        /                       \              *
 *   X <                             > Y         *
 * \endverbatim
 */

/**
 * @defgroup vp_column_row Rows and columns in the viewport
 *
 * Columns are vertical sections of the viewport that are half a tile wide.
 * The origin, i.e. column 0, is through the northern and southern most tile.
 * This means that the column of e.g. Tile(0, 0) and Tile(100, 100) are in
 * column number 0. The negative columns are towards the left of the screen,
 * or towards the west, whereas the positive ones are towards respectively
 * the right and east.
 * With half a tile wide is meant that the next column of tiles directly west
 * or east of the centre line are respectively column -1 and 1. Their tile
 * centers are only half a tile from the center of their adjoining tile when
 * looking only at the X-coordinate.
 *
 * \verbatim
 *        ╳        *
 *       ╱ ╲       *
 *      ╳ 0 ╳      *
 *     ╱ ╲ ╱ ╲     *
 *    ╳-1 ╳ 1 ╳    *
 *   ╱ ╲ ╱ ╲ ╱ ╲   *
 *  ╳-2 ╳ 0 ╳ 2 ╳  *
 *   ╲ ╱ ╲ ╱ ╲ ╱   *
 *    ╳-1 ╳ 1 ╳    *
 *     ╲ ╱ ╲ ╱     *
 *      ╳ 0 ╳      *
 *       ╲ ╱       *
 *        ╳        *
 * \endverbatim
 *
 *
 * Rows are horizontal sections of the viewport, also half a tile wide.
 * This time the nothern most tile on the map defines 0 and
 * everything south of that has a positive number.
 */

#include "stdafx.h"
#include "core/math_func.hpp"
#include "core/smallvec_type.hpp"
#include "clear_map.h"
#include "tree_map.h"
#include "industry.h"
#include "smallmap_gui.h"
#include "smallmap_colours.h"
#include "table/tree_land.h"
#include "blitter/32bpp_base.hpp"
#include "landscape.h"
#include "viewport_func.h"
#include "station_base.h"
#include "waypoint_base.h"
#include "town.h"
#include "signs_base.h"
#include "signs_func.h"
#include "plans_base.h"
#include "plans_func.h"
#include "vehicle_base.h"
#include "vehicle_gui.h"
#include "blitter/factory.hpp"
#include "strings_func.h"
#include "zoom_func.h"
#include "overlay.h"
#include "overlay_cmd.h"
#include "vehicle_func.h"
#include "company_func.h"
#include "waypoint_func.h"
#include "window_func.h"
#include "tilehighlight_func.h"
#include "zoning.h"
#include "window_gui.h"
#include "linkgraph/linkgraph_gui.h"
#include "viewport_sprite_sorter.h"
#include "bridge_map.h"
#include "progress.h"

#include <map>
#include <vector>
#include <algorithm>
#include <tuple>
#include "depot_base.h"
#include "tunnelbridge_map.h"
#include "gui.h"
#include "core/container_func.hpp"

#include "table/strings.h"
#include "table/string_colours.h"

#include "safeguards.h"

Point _tile_fract_coords;


static const int MAX_TILE_EXTENT_LEFT   = ZOOM_LVL_BASE * TILE_PIXELS;                     ///< Maximum left   extent of tile relative to north corner.
static const int MAX_TILE_EXTENT_RIGHT  = ZOOM_LVL_BASE * TILE_PIXELS;                     ///< Maximum right  extent of tile relative to north corner.
static const int MAX_TILE_EXTENT_TOP    = ZOOM_LVL_BASE * MAX_BUILDING_PIXELS;             ///< Maximum top    extent of tile relative to north corner (not considering bridges).
static const int MAX_TILE_EXTENT_BOTTOM = ZOOM_LVL_BASE * (TILE_PIXELS + 2 * TILE_HEIGHT); ///< Maximum bottom extent of tile relative to north corner (worst case: #SLOPE_STEEP_N).

struct StringSpriteToDraw {
        StringID string;
        Colours colour;
        int32 x;
        int32 y;
        uint64 params[2];
        uint16 width;
};

struct TileSpriteToDraw {
        SpriteID image;
        PaletteID pal;
        const SubSprite *sub;           ///< only draw a rectangular part of the sprite
        int32 x;                        ///< screen X coordinate of sprite
        int32 y;                        ///< screen Y coordinate of sprite
};

struct ChildScreenSpriteToDraw {
        SpriteID image;
        PaletteID pal;
        const SubSprite *sub;           ///< only draw a rectangular part of the sprite
        int32 x;
        int32 y;
        int next;                       ///< next child to draw (-1 at the end)
};

/** Enumeration of multi-part foundations */
enum FoundationPart {
        FOUNDATION_PART_NONE     = 0xFF,  ///< Neither foundation nor groundsprite drawn yet.
        FOUNDATION_PART_NORMAL   = 0,     ///< First part (normal foundation or no foundation)
        FOUNDATION_PART_HALFTILE = 1,     ///< Second part (halftile foundation)
        FOUNDATION_PART_END
};

/**
 * Mode of "sprite combining"
 * @see StartSpriteCombine
 */
enum SpriteCombineMode {
        SPRITE_COMBINE_NONE,     ///< Every #AddSortableSpriteToDraw start its own bounding box
        SPRITE_COMBINE_PENDING,  ///< %Sprite combining will start with the next unclipped sprite.
        SPRITE_COMBINE_ACTIVE,   ///< %Sprite combining is active. #AddSortableSpriteToDraw outputs child sprites.
};

typedef SmallVector<TileSpriteToDraw, 64> TileSpriteToDrawVector;
typedef SmallVector<StringSpriteToDraw, 4> StringSpriteToDrawVector;
typedef SmallVector<ParentSpriteToDraw, 64> ParentSpriteToDrawVector;
typedef SmallVector<ChildScreenSpriteToDraw, 16> ChildScreenSpriteToDrawVector;

typedef std::vector<std::pair<int, OrderType> > RankOrderTypeList;
typedef std::map<TileIndex, RankOrderTypeList> RouteStepsMap;

const uint max_rank_order_type_count = 10;

enum RailSnapMode {
        RSM_NO_SNAP,
        RSM_SNAP_TO_TILE,
        RSM_SNAP_TO_RAIL,
};

/**
 * Snapping point for a track.
 *
 * Point where a track (rail/road/other) can be snapped to while selecting tracks with polyline
 * tool (HT_POLY). Besides of x/y coordinates expressed in tile "units" it contains a set of
 * allowed line directions.
 */
struct LineSnapPoint : Point {
        uint8 dirs; ///< Allowed line directions, set of #Direction bits.
};

typedef SmallVector<LineSnapPoint, 4> LineSnapPoints; ///< Set of snapping points

/** Coordinates of a polyline track made of 2 connected line segments. */
struct Polyline {
        Point start;           ///< The point where the first segment starts (as given in LineSnapPoint).
        Direction first_dir;   ///< Direction of the first line segment.
        uint first_len;        ///< Length of the first segment - number of track pieces.
        Direction second_dir;  ///< Direction of the second line segment.
        uint second_len;       ///< Length of the second segment - number of track pieces.
};

/** Data structure storing rendering information */
struct ViewportDrawer {
        DrawPixelInfo dpi;

        StringSpriteToDrawVector string_sprites_to_draw;
        TileSpriteToDrawVector tile_sprites_to_draw;
        ParentSpriteToDrawVector parent_sprites_to_draw;
        ParentSpriteToSortVector parent_sprites_to_sort; ///< Parent sprite pointer array used for sorting
        ChildScreenSpriteToDrawVector child_screen_sprites_to_draw;
        TunnelBridgeToMapVector tunnel_to_map;
        TunnelBridgeToMapVector bridge_to_map;

        int *last_child;

        SpriteCombineMode combine_sprites;               ///< Current mode of "sprite combining". @see StartSpriteCombine

        int foundation[FOUNDATION_PART_END];             ///< Foundation sprites (index into parent_sprites_to_draw).
        FoundationPart foundation_part;                  ///< Currently active foundation for ground sprite drawing.
        int *last_foundation_child[FOUNDATION_PART_END]; ///< Tail of ChildSprite list of the foundations. (index into child_screen_sprites_to_draw)
        Point foundation_offset[FOUNDATION_PART_END];    ///< Pixel offset for ground sprites on the foundations.
};

static void MarkViewportDirty(const ViewPort * const vp, int left, int top, int right, int bottom);
static void MarkRouteStepDirty(RouteStepsMap::const_iterator cit);
static void MarkRouteStepDirty(const TileIndex tile, uint order_nr);

static DrawPixelInfo _dpi_for_text;
static ViewportDrawer _vd;

static std::vector<ViewPort *> _viewport_window_cache;

RouteStepsMap _vp_route_steps;
RouteStepsMap _vp_route_steps_last_mark_dirty;
uint _vp_route_step_width = 0;
uint _vp_route_step_height_top = 0;
uint _vp_route_step_height_middle = 0;
uint _vp_route_step_height_bottom = 0;
SubSprite _vp_route_step_subsprite;
 
struct DrawnPathRouteTileLine {
        TileIndex from_tile;
        TileIndex to_tile;
        bool order_match;

        bool operator==(const DrawnPathRouteTileLine &other) const
        {
                return std::tie(this->from_tile, this->to_tile, this->order_match) == std::tie(other.from_tile, other.to_tile, other.order_match);
        }

        bool operator!=(const DrawnPathRouteTileLine &other) const
        {
                return !(*this == other);
        }

        bool operator<(const DrawnPathRouteTileLine &other) const
        {
                return std::tie(this->from_tile, this->to_tile, this->order_match) < std::tie(other.from_tile, other.to_tile, other.order_match);
        }
};

std::vector<DrawnPathRouteTileLine> _vp_route_paths;
std::vector<DrawnPathRouteTileLine> _vp_route_paths_last_mark_dirty;

static void MarkRoutePathsDirty(const std::vector<DrawnPathRouteTileLine> &lines);

TileHighlightData _thd;
static TileInfo *_cur_ti;
bool _draw_bounding_boxes = false;
bool _draw_dirty_blocks = false;
uint _dirty_block_colour = 0;
static VpSpriteSorter _vp_sprite_sorter = nullptr;

const byte *_pal2trsp_remap_ptr = nullptr;

static RailSnapMode _rail_snap_mode = RSM_NO_SNAP; ///< Type of rail track snapping (polyline tool).
static LineSnapPoints _tile_snap_points; ///< Tile to which a rail track will be snapped to (polyline tool).
static LineSnapPoints _rail_snap_points; ///< Set of points where a rail track will be snapped to (polyline tool).
static LineSnapPoint _current_snap_lock; ///< Start point and direction at which selected track is locked on currently (while dragging in polyline mode).

static RailSnapMode GetRailSnapMode();
static void SetRailSnapMode(RailSnapMode mode);
static TileIndex GetRailSnapTile();
static void SetRailSnapTile(TileIndex tile);

static Point MapXYZToViewport(const ViewPort *vp, int x, int y, int z)
{
        Point p = RemapCoords(x, y, z);
        p.x -= vp->virtual_width / 2;
        p.y -= vp->virtual_height / 2;
        return p;
}

void DeleteWindowViewport(Window *w)
{
        if (w->viewport == nullptr) return;

        container_unordered_remove(_viewport_window_cache, w->viewport);
        delete w->viewport->overlay;
        delete w->viewport;
        w->viewport = nullptr;
}

/**
 * Initialize viewport of the window for use.
 * @param w Window to use/display the viewport in
 * @param x Offset of left edge of viewport with respect to left edge window \a w
 * @param y Offset of top edge of viewport with respect to top edge window \a w
 * @param width Width of the viewport
 * @param height Height of the viewport
 * @param follow_flags Flags controlling the viewport.
 *        - If bit 31 is set, the lower 20 bits are the vehicle that the viewport should follow.
 *        - If bit 31 is clear, it is a #TileIndex.
 * @param zoom Zoomlevel to display
 */
void InitializeWindowViewport(Window *w, int x, int y,
        int width, int height, uint32 follow_flags, ZoomLevel zoom)
{
        assert(w->viewport == nullptr);

        ViewportData *vp = new ViewportData();

        vp->overlay = nullptr;
        vp->left = x + w->left;
        vp->top = y + w->top;
        vp->width = width;
        vp->height = height;

        vp->zoom = static_cast<ZoomLevel>(Clamp(zoom, _settings_client.gui.zoom_min, _settings_client.gui.zoom_max));

        vp->virtual_left = 0;
        vp->virtual_top = 0;
        vp->virtual_width = ScaleByZoom(width, zoom);
        vp->virtual_height = ScaleByZoom(height, zoom);

        vp->map_type = VPMT_BEGIN;

        Point pt;

        if (follow_flags & 0x80000000) {
                const Vehicle *veh;

                vp->follow_vehicle = (VehicleID)(follow_flags & 0xFFFFF);
                veh = Vehicle::Get(vp->follow_vehicle);
                pt = MapXYZToViewport(vp, veh->x_pos, veh->y_pos, veh->z_pos);
                MarkAllRoutePathsDirty(veh);
                MarkAllRouteStepsDirty(veh);
        } else {
                uint x = TileX(follow_flags) * TILE_SIZE;
                uint y = TileY(follow_flags) * TILE_SIZE;

                vp->follow_vehicle = INVALID_VEHICLE;
                pt = MapXYZToViewport(vp, x, y, GetSlopePixelZ(x, y));
        }

        vp->scrollpos_x = pt.x;
        vp->scrollpos_y = pt.y;
        vp->dest_scrollpos_x = pt.x;
        vp->dest_scrollpos_y = pt.y;

        w->viewport = vp;
        _viewport_window_cache.push_back(vp);
}

static Point _vp_move_offs;

static void DoSetViewportPosition(const Window *w, int left, int top, int width, int height)
{
        IncrementWindowUpdateNumber();

        FOR_ALL_WINDOWS_FROM_BACK_FROM(w, w) {
                if (left + width > w->left &&
                                w->left + w->width > left &&
                                top + height > w->top &&
                                w->top + w->height > top) {

                        if (left < w->left) {
                                DoSetViewportPosition(w, left, top, w->left - left, height);
                                DoSetViewportPosition(w, left + (w->left - left), top, width - (w->left - left), height);
                                return;
                        }

                        if (left + width > w->left + w->width) {
                                DoSetViewportPosition(w, left, top, (w->left + w->width - left), height);
                                DoSetViewportPosition(w, left + (w->left + w->width - left), top, width - (w->left + w->width - left), height);
                                return;
                        }

                        if (top < w->top) {
                                DoSetViewportPosition(w, left, top, width, (w->top - top));
                                DoSetViewportPosition(w, left, top + (w->top - top), width, height - (w->top - top));
                                return;
                        }

                        if (top + height > w->top + w->height) {
                                DoSetViewportPosition(w, left, top, width, (w->top + w->height - top));
                                DoSetViewportPosition(w, left, top + (w->top + w->height - top), width, height - (w->top + w->height - top));
                                return;
                        }

                        return;
                }
        }

        {
                int xo = _vp_move_offs.x;
                int yo = _vp_move_offs.y;

                if (abs(xo) >= width || abs(yo) >= height) {
                        /* fully_outside */
                        RedrawScreenRect(left, top, left + width, top + height);
                        return;
                }

                GfxScroll(left, top, width, height, xo, yo);

                if (xo > 0) {
                        RedrawScreenRect(left, top, xo + left, top + height);
                        left += xo;
                        width -= xo;
                } else if (xo < 0) {
                        RedrawScreenRect(left + width + xo, top, left + width, top + height);
                        width += xo;
                }

                if (yo > 0) {
                        RedrawScreenRect(left, top, width + left, top + yo);
                } else if (yo < 0) {
                        RedrawScreenRect(left, top + height + yo, width + left, top + height);
                }
        }
}

static void SetViewportPosition(Window *w, int x, int y)
{
        ViewPort *vp = w->viewport;
        int old_left = vp->virtual_left;
        int old_top = vp->virtual_top;
        int i;
        int left, top, width, height;

        vp->virtual_left = x;
        vp->virtual_top = y;

        /* Viewport is bound to its left top corner, so it must be rounded down (UnScaleByZoomLower)
         * else glitch described in FS#1412 will happen (offset by 1 pixel with zoom level > NORMAL)
         */
        old_left = UnScaleByZoomLower(old_left, vp->zoom);
        old_top = UnScaleByZoomLower(old_top, vp->zoom);
        x = UnScaleByZoomLower(x, vp->zoom);
        y = UnScaleByZoomLower(y, vp->zoom);

        old_left -= x;
        old_top -= y;

        if (old_top == 0 && old_left == 0) return;

        _vp_move_offs.x = old_left;
        _vp_move_offs.y = old_top;

        left = vp->left;
        top = vp->top;
        width = vp->width;
        height = vp->height;

        if (left < 0) {
                width += left;
                left = 0;
        }

        i = left + width - _screen.width;
        if (i >= 0) width -= i;

        if (width > 0) {
                if (top < 0) {
                        height += top;
                        top = 0;
                }

                i = top + height - _screen.height;
                if (i >= 0) height -= i;

                if (height > 0) DoSetViewportPosition(w->z_front, left, top, width, height);
        }
}

/**
 * Is a xy position inside the viewport of the window?
 * @param w Window to examine its viewport
 * @param x X coordinate of the xy position
 * @param y Y coordinate of the xy position
 * @return Pointer to the viewport if the xy position is in the viewport of the window,
 *         otherwise \c nullptr is returned.
 */
ViewPort *IsPtInWindowViewport(const Window *w, int x, int y)
{
        ViewPort *vp = w->viewport;

        if (vp != nullptr &&
                        IsInsideMM(x, vp->left, vp->left + vp->width) &&
                        IsInsideMM(y, vp->top, vp->top + vp->height))
                return vp;

        return nullptr;
}

/**
 * Translate screen coordinate in a viewport to a tile coordinate
 * @param vp  Viewport that contains the (\a x, \a y) screen coordinate
 * @param x   Screen x coordinate
 * @param y   Screen y coordinate
 * @param clamp_to_map Clamp the coordinate outside of the map to the closest tile within the map.
 * @return Tile coordinate
 */
Point TranslateXYToTileCoord(const ViewPort *vp, int x, int y, bool clamp_to_map)
{
        Point pt;
        int a, b;
        int z;

        if ( (uint)(x -= vp->left) >= (uint)vp->width ||
                                (uint)(y -= vp->top) >= (uint)vp->height) {
                                Point pt = {-1, -1};
                                return pt;
        }

        x = (ScaleByZoom(x, vp->zoom) + vp->virtual_left) >> (2 + ZOOM_LVL_SHIFT);
        y = (ScaleByZoom(y, vp->zoom) + vp->virtual_top) >> (1 + ZOOM_LVL_SHIFT);

        a = y - x;
        b = y + x;

        if (clamp_to_map) {
                /* Bring the coordinates near to a valid range. This is mostly due to the
                 * tiles on the north side of the map possibly being drawn too high due to
                 * the extra height levels. So at the top we allow a number of extra tiles.
                 * This number is based on the tile height and pixels. */
                int extra_tiles = CeilDiv(_settings_game.construction.max_heightlevel * TILE_HEIGHT, TILE_PIXELS);
                a = Clamp(a, -extra_tiles * TILE_SIZE, MapMaxX() * TILE_SIZE - 1);
                b = Clamp(b, -extra_tiles * TILE_SIZE, MapMaxY() * TILE_SIZE - 1);
        }

        /* (a, b) is the X/Y-world coordinate that belongs to (x,y) if the landscape would be completely flat on height 0.
         * Now find the Z-world coordinate by fix point iteration.
         * This is a bit tricky because the tile height is non-continuous at foundations.
         * The clicked point should be approached from the back, otherwise there are regions that are not clickable.
         * (FOUNDATION_HALFTILE_LOWER on SLOPE_STEEP_S hides north halftile completely)
         * So give it a z-malus of 4 in the first iterations.
         */
        z = 0;

        int min_coord = _settings_game.construction.freeform_edges ? TILE_SIZE : 0;

        for (int i = 0; i < 5; i++) z = GetSlopePixelZ(Clamp(a + max(z, 4) - 4, min_coord, MapMaxX() * TILE_SIZE - 1), Clamp(b + max(z, 4) - 4, min_coord, MapMaxY() * TILE_SIZE - 1)) / 2;
        for (int malus = 3; malus > 0; malus--) z = GetSlopePixelZ(Clamp(a + max(z, malus) - malus, min_coord, MapMaxX() * TILE_SIZE - 1), Clamp(b + max(z, malus) - malus, min_coord, MapMaxY() * TILE_SIZE - 1)) / 2;
        for (int i = 0; i < 5; i++) z = GetSlopePixelZ(Clamp(a + z, min_coord, MapMaxX() * TILE_SIZE - 1), Clamp(b + z, min_coord, MapMaxY() * TILE_SIZE - 1)) / 2;

        if (clamp_to_map) {
                pt.x = Clamp(a + z, min_coord, MapMaxX() * TILE_SIZE - 1);
                pt.y = Clamp(b + z, min_coord, MapMaxY() * TILE_SIZE - 1);
        } else {
                pt.x = a + z;
                pt.y = b + z;
        }

        return pt;
}

/* When used for zooming, check area below current coordinates (x,y)
 * and return the tile of the zoomed out/in position (zoom_x, zoom_y)
 * when you just want the tile, make x = zoom_x and y = zoom_y */
static Point GetTileFromScreenXY(int x, int y, int zoom_x, int zoom_y)
{
        Window *w;
        ViewPort *vp;
        Point pt;

        if ( (w = FindWindowFromPt(x, y)) != nullptr &&
                         (vp = IsPtInWindowViewport(w, x, y)) != nullptr)
                                return TranslateXYToTileCoord(vp, zoom_x, zoom_y);

        pt.y = pt.x = -1;
        return pt;
}

Point GetTileBelowCursor()
{
        return GetTileFromScreenXY(_cursor.pos.x, _cursor.pos.y, _cursor.pos.x, _cursor.pos.y);
}


Point GetTileZoomCenterWindow(bool in, Window * w)
{
        int x, y;
        ViewPort *vp = w->viewport;

        if (in) {
                x = ((_cursor.pos.x - vp->left) >> 1) + (vp->width >> 2);
                y = ((_cursor.pos.y - vp->top) >> 1) + (vp->height >> 2);
        } else {
                x = vp->width - (_cursor.pos.x - vp->left);
                y = vp->height - (_cursor.pos.y - vp->top);
        }
        /* Get the tile below the cursor and center on the zoomed-out center */
        return GetTileFromScreenXY(_cursor.pos.x, _cursor.pos.y, x + vp->left, y + vp->top);
}

/**
 * Update the status of the zoom-buttons according to the zoom-level
 * of the viewport. This will update their status and invalidate accordingly
 * @param w Window pointer to the window that has the zoom buttons
 * @param vp pointer to the viewport whose zoom-level the buttons represent
 * @param widget_zoom_in widget index for window with zoom-in button
 * @param widget_zoom_out widget index for window with zoom-out button
 */
void HandleZoomMessage(Window *w, const ViewPort *vp, byte widget_zoom_in, byte widget_zoom_out)
{
        w->SetWidgetDisabledState(widget_zoom_in, vp->zoom <= _settings_client.gui.zoom_min);
        w->SetWidgetDirty(widget_zoom_in);

        w->SetWidgetDisabledState(widget_zoom_out, vp->zoom >= _settings_client.gui.zoom_max);
        w->SetWidgetDirty(widget_zoom_out);
}

/**
 * Schedules a tile sprite for drawing.
 *
 * @param image the image to draw.
 * @param pal the provided palette.
 * @param x position x (world coordinates) of the sprite.
 * @param y position y (world coordinates) of the sprite.
 * @param z position z (world coordinates) of the sprite.
 * @param sub Only draw a part of the sprite.
 * @param extra_offs_x Pixel X offset for the sprite position.
 * @param extra_offs_y Pixel Y offset for the sprite position.
 */
static void AddTileSpriteToDraw(SpriteID image, PaletteID pal, int32 x, int32 y, int z, const SubSprite *sub = nullptr, int extra_offs_x = 0, int extra_offs_y = 0)
{
        assert((image & SPRITE_MASK) < MAX_SPRITES);

        TileSpriteToDraw *ts = _vd.tile_sprites_to_draw.Append();
        ts->image = image;
        ts->pal = pal;
        ts->sub = sub;
        Point pt = RemapCoords(x, y, z);
        ts->x = pt.x + extra_offs_x;
        ts->y = pt.y + extra_offs_y;
}

/**
 * Adds a child sprite to the active foundation.
 *
 * The pixel offset of the sprite relative to the ParentSprite is the sum of the offset passed to OffsetGroundSprite() and extra_offs_?.
 *
 * @param image the image to draw.
 * @param pal the provided palette.
 * @param sub Only draw a part of the sprite.
 * @param foundation_part Foundation part.
 * @param extra_offs_x Pixel X offset for the sprite position.
 * @param extra_offs_y Pixel Y offset for the sprite position.
 */
static void AddChildSpriteToFoundation(SpriteID image, PaletteID pal, const SubSprite *sub, FoundationPart foundation_part, int extra_offs_x, int extra_offs_y)
{
        assert(IsInsideMM(foundation_part, 0, FOUNDATION_PART_END));
        assert(_vd.foundation[foundation_part] != -1);
        Point offs = _vd.foundation_offset[foundation_part];

        /* Change the active ChildSprite list to the one of the foundation */
        int *old_child = _vd.last_child;
        _vd.last_child = _vd.last_foundation_child[foundation_part];

        AddChildSpriteScreen(image, pal, offs.x + extra_offs_x, offs.y + extra_offs_y, false, sub, false);

        /* Switch back to last ChildSprite list */
        _vd.last_child = old_child;
}

/**
 * Draws a ground sprite at a specific world-coordinate relative to the current tile.
 * If the current tile is drawn on top of a foundation the sprite is added as child sprite to the "foundation"-ParentSprite.
 *
 * @param image the image to draw.
 * @param pal the provided palette.
 * @param x position x (world coordinates) of the sprite relative to current tile.
 * @param y position y (world coordinates) of the sprite relative to current tile.
 * @param z position z (world coordinates) of the sprite relative to current tile.
 * @param sub Only draw a part of the sprite.
 * @param extra_offs_x Pixel X offset for the sprite position.
 * @param extra_offs_y Pixel Y offset for the sprite position.
 */
void DrawGroundSpriteAt(SpriteID image, PaletteID pal, int32 x, int32 y, int z, const SubSprite *sub, int extra_offs_x, int extra_offs_y)
{
        /* Switch to first foundation part, if no foundation was drawn */
        if (_vd.foundation_part == FOUNDATION_PART_NONE) _vd.foundation_part = FOUNDATION_PART_NORMAL;

        if (_vd.foundation[_vd.foundation_part] != -1) {
                Point pt = RemapCoords(x, y, z);
                AddChildSpriteToFoundation(image, pal, sub, _vd.foundation_part, pt.x + extra_offs_x * ZOOM_LVL_BASE, pt.y + extra_offs_y * ZOOM_LVL_BASE);
        } else {
                AddTileSpriteToDraw(image, pal, _cur_ti->x + x, _cur_ti->y + y, _cur_ti->z + z, sub, extra_offs_x * ZOOM_LVL_BASE, extra_offs_y * ZOOM_LVL_BASE);
        }
}

/**
 * Draws a ground sprite for the current tile.
 * If the current tile is drawn on top of a foundation the sprite is added as child sprite to the "foundation"-ParentSprite.
 *
 * @param image the image to draw.
 * @param pal the provided palette.
 * @param sub Only draw a part of the sprite.
 * @param extra_offs_x Pixel X offset for the sprite position.
 * @param extra_offs_y Pixel Y offset for the sprite position.
 */
void DrawGroundSprite(SpriteID image, PaletteID pal, const SubSprite *sub, int extra_offs_x, int extra_offs_y)
{
        DrawGroundSpriteAt(image, pal, 0, 0, 0, sub, extra_offs_x, extra_offs_y);
}

/**
 * Called when a foundation has been drawn for the current tile.
 * Successive ground sprites for the current tile will be drawn as child sprites of the "foundation"-ParentSprite, not as TileSprites.
 *
 * @param x sprite x-offset (screen coordinates) of ground sprites relative to the "foundation"-ParentSprite.
 * @param y sprite y-offset (screen coordinates) of ground sprites relative to the "foundation"-ParentSprite.
 */
void OffsetGroundSprite(int x, int y)
{
        /* Switch to next foundation part */
        switch (_vd.foundation_part) {
                case FOUNDATION_PART_NONE:
                        _vd.foundation_part = FOUNDATION_PART_NORMAL;
                        break;
                case FOUNDATION_PART_NORMAL:
                        _vd.foundation_part = FOUNDATION_PART_HALFTILE;
                        break;
                default: NOT_REACHED();
        }

        /* _vd.last_child == nullptr if foundation sprite was clipped by the viewport bounds */
        if (_vd.last_child != nullptr) _vd.foundation[_vd.foundation_part] = _vd.parent_sprites_to_draw.Length() - 1;

        _vd.foundation_offset[_vd.foundation_part].x = x * ZOOM_LVL_BASE;
        _vd.foundation_offset[_vd.foundation_part].y = y * ZOOM_LVL_BASE;
        _vd.last_foundation_child[_vd.foundation_part] = _vd.last_child;
}

/**
 * Adds a child sprite to a parent sprite.
 * In contrast to "AddChildSpriteScreen()" the sprite position is in world coordinates
 *
 * @param image the image to draw.
 * @param pal the provided palette.
 * @param x position x of the sprite.
 * @param y position y of the sprite.
 * @param z position z of the sprite.
 * @param sub Only draw a part of the sprite.
 */
static void AddCombinedSprite(SpriteID image, PaletteID pal, int x, int y, int z, const SubSprite *sub)
{
        Point pt = RemapCoords(x, y, z);
        const Sprite *spr = GetSprite(image & SPRITE_MASK, ST_NORMAL);

        if (pt.x + spr->x_offs >= _vd.dpi.left + _vd.dpi.width ||
                        pt.x + spr->x_offs + spr->width <= _vd.dpi.left ||
                        pt.y + spr->y_offs >= _vd.dpi.top + _vd.dpi.height ||
                        pt.y + spr->y_offs + spr->height <= _vd.dpi.top)
                return;

        const ParentSpriteToDraw *pstd = _vd.parent_sprites_to_draw.End() - 1;
        AddChildSpriteScreen(image, pal, pt.x - pstd->left, pt.y - pstd->top, false, sub, false);
}

/**
 * Draw a (transparent) sprite at given coordinates with a given bounding box.
 * The bounding box extends from (x + bb_offset_x, y + bb_offset_y, z + bb_offset_z) to (x + w - 1, y + h - 1, z + dz - 1), both corners included.
 * Bounding boxes with bb_offset_x == w or bb_offset_y == h or bb_offset_z == dz are allowed and produce thin slices.
 *
 * @note Bounding boxes are normally specified with bb_offset_x = bb_offset_y = bb_offset_z = 0. The extent of the bounding box in negative direction is
 *       defined by the sprite offset in the grf file.
 *       However if modifying the sprite offsets is not suitable (e.g. when using existing graphics), the bounding box can be tuned by bb_offset.
 *
 * @pre w >= bb_offset_x, h >= bb_offset_y, dz >= bb_offset_z. Else w, h or dz are ignored.
 *
 * @param image the image to combine and draw,
 * @param pal the provided palette,
 * @param x position X (world) of the sprite,
 * @param y position Y (world) of the sprite,
 * @param w bounding box extent towards positive X (world),
 * @param h bounding box extent towards positive Y (world),
 * @param dz bounding box extent towards positive Z (world),
 * @param z position Z (world) of the sprite,
 * @param transparent if true, switch the palette between the provided palette and the transparent palette,
 * @param bb_offset_x bounding box extent towards negative X (world),
 * @param bb_offset_y bounding box extent towards negative Y (world),
 * @param bb_offset_z bounding box extent towards negative Z (world)
 * @param sub Only draw a part of the sprite.
 */
void AddSortableSpriteToDraw(SpriteID image, PaletteID pal, int x, int y, int w, int h, int dz, int z, bool transparent, int bb_offset_x, int bb_offset_y, int bb_offset_z, const SubSprite *sub)
{
        int32 left, right, top, bottom;

        assert((image & SPRITE_MASK) < MAX_SPRITES);

        /* make the sprites transparent with the right palette */
        if (transparent) {
                SetBit(image, PALETTE_MODIFIER_TRANSPARENT);
                pal = PALETTE_TO_TRANSPARENT;
        }

        if (_vd.combine_sprites == SPRITE_COMBINE_ACTIVE) {
                AddCombinedSprite(image, pal, x, y, z, sub);
                return;
        }

        _vd.last_child = nullptr;

        Point pt = RemapCoords(x, y, z);
        int tmp_left, tmp_top, tmp_x = pt.x, tmp_y = pt.y;

        /* Compute screen extents of sprite */
        if (image == SPR_EMPTY_BOUNDING_BOX) {
                left = tmp_left = RemapCoords(x + w          , y + bb_offset_y, z + bb_offset_z).x;
                right           = RemapCoords(x + bb_offset_x, y + h          , z + bb_offset_z).x + 1;
                top  = tmp_top  = RemapCoords(x + bb_offset_x, y + bb_offset_y, z + dz         ).y;
                bottom          = RemapCoords(x + w          , y + h          , z + bb_offset_z).y + 1;
        } else {
                const Sprite *spr = GetSprite(image & SPRITE_MASK, ST_NORMAL);
                left = tmp_left = (pt.x += spr->x_offs);
                right           = (pt.x +  spr->width );
                top  = tmp_top  = (pt.y += spr->y_offs);
                bottom          = (pt.y +  spr->height);
        }

        if (_draw_bounding_boxes && (image != SPR_EMPTY_BOUNDING_BOX)) {
                /* Compute maximal extents of sprite and its bounding box */
                left   = min(left  , RemapCoords(x + w          , y + bb_offset_y, z + bb_offset_z).x);
                right  = max(right , RemapCoords(x + bb_offset_x, y + h          , z + bb_offset_z).x + 1);
                top    = min(top   , RemapCoords(x + bb_offset_x, y + bb_offset_y, z + dz         ).y);
                bottom = max(bottom, RemapCoords(x + w          , y + h          , z + bb_offset_z).y + 1);
        }

        /* Do not add the sprite to the viewport, if it is outside */
        if (left   >= _vd.dpi.left + _vd.dpi.width ||
            right  <= _vd.dpi.left                 ||
            top    >= _vd.dpi.top + _vd.dpi.height ||
            bottom <= _vd.dpi.top) {
                return;
        }

        ParentSpriteToDraw *ps = _vd.parent_sprites_to_draw.Append();
        ps->x = tmp_x;
        ps->y = tmp_y;

        ps->left = tmp_left;
        ps->top  = tmp_top;

        ps->image = image;
        ps->pal = pal;
        ps->sub = sub;
        ps->xmin = x + bb_offset_x;
        ps->xmax = x + max(bb_offset_x, w) - 1;

        ps->ymin = y + bb_offset_y;
        ps->ymax = y + max(bb_offset_y, h) - 1;

        ps->zmin = z + bb_offset_z;
        ps->zmax = z + max(bb_offset_z, dz) - 1;

        ps->comparison_done = false;
        ps->first_child = -1;

        _vd.last_child = &ps->first_child;

        if (_vd.combine_sprites == SPRITE_COMBINE_PENDING) _vd.combine_sprites = SPRITE_COMBINE_ACTIVE;
}

/**
 * Starts a block of sprites, which are "combined" into a single bounding box.
 *
 * Subsequent calls to #AddSortableSpriteToDraw will be drawn into the same bounding box.
 * That is: The first sprite that is not clipped by the viewport defines the bounding box, and
 * the following sprites will be child sprites to that one.
 *
 * That implies:
 *  - The drawing order is definite. No other sprites will be sorted between those of the block.
 *  - You have to provide a valid bounding box for all sprites,
 *    as you won't know which one is the first non-clipped one.
 *    Preferable you use the same bounding box for all.
 *  - You cannot use #AddChildSpriteScreen inside the block, as its result will be indefinite.
 *
 * The block is terminated by #EndSpriteCombine.
 *
 * You cannot nest "combined" blocks.
 */
void StartSpriteCombine()
{
        assert(_vd.combine_sprites == SPRITE_COMBINE_NONE);
        _vd.combine_sprites = SPRITE_COMBINE_PENDING;
}

/**
 * Terminates a block of sprites started by #StartSpriteCombine.
 * Take a look there for details.
 */
void EndSpriteCombine()
{
        assert(_vd.combine_sprites != SPRITE_COMBINE_NONE);
        _vd.combine_sprites = SPRITE_COMBINE_NONE;
}

/**
 * Check if the parameter "check" is inside the interval between
 * begin and end, including both begin and end.
 * @note Whether \c begin or \c end is the biggest does not matter.
 *       This method will account for that.
 * @param begin The begin of the interval.
 * @param end   The end of the interval.
 * @param check The value to check.
 */
static bool IsInRangeInclusive(int begin, int end, int check)
{
        if (begin > end) Swap(begin, end);
        return begin <= check && check <= end;
}

/**
 * Checks whether a point is inside the selected rectangle given by _thd.size, _thd.pos and _thd.diagonal
 * @param x The x coordinate of the point to be checked.
 * @param y The y coordinate of the point to be checked.
 * @return True if the point is inside the rectangle, else false.
 */
static bool IsInsideSelectedRectangle(int x, int y)
{
        if (!_thd.diagonal) {
                return IsInsideBS(x, _thd.pos.x, _thd.size.x) && IsInsideBS(y, _thd.pos.y, _thd.size.y);
        }

        int dist_a = (_thd.size.x + _thd.size.y);      // Rotated coordinate system for selected rectangle.
        int dist_b = (_thd.size.x - _thd.size.y);      // We don't have to divide by 2. It's all relative!
        int a = ((x - _thd.pos.x) + (y - _thd.pos.y)); // Rotated coordinate system for the point under scrutiny.
        int b = ((x - _thd.pos.x) - (y - _thd.pos.y));

        /* Check if a and b are between 0 and dist_a or dist_b respectively. */
        return IsInRangeInclusive(dist_a, 0, a) && IsInRangeInclusive(dist_b, 0, b);
}

/**
 * Add a child sprite to a parent sprite.
 *
 * @param image the image to draw.
 * @param pal the provided palette.
 * @param x sprite x-offset (screen coordinates) relative to parent sprite.
 * @param y sprite y-offset (screen coordinates) relative to parent sprite.
 * @param transparent if true, switch the palette between the provided palette and the transparent palette,
 * @param sub Only draw a part of the sprite.
 */
void AddChildSpriteScreen(SpriteID image, PaletteID pal, int x, int y, bool transparent, const SubSprite *sub, bool scale)
{
        assert((image & SPRITE_MASK) < MAX_SPRITES);

        /* If the ParentSprite was clipped by the viewport bounds, do not draw the ChildSprites either */
        if (_vd.last_child == nullptr) return;

        /* make the sprites transparent with the right palette */
        if (transparent) {
                SetBit(image, PALETTE_MODIFIER_TRANSPARENT);
                pal = PALETTE_TO_TRANSPARENT;
        }

        *_vd.last_child = _vd.child_screen_sprites_to_draw.Length();

        ChildScreenSpriteToDraw *cs = _vd.child_screen_sprites_to_draw.Append();
        cs->image = image;
        cs->pal = pal;
        cs->sub = sub;
        cs->x = scale ? x * ZOOM_LVL_BASE : x;
        cs->y = scale ? y * ZOOM_LVL_BASE : y;
        cs->next = -1;

        /* Append the sprite to the active ChildSprite list.
         * If the active ParentSprite is a foundation, update last_foundation_child as well.
         * Note: ChildSprites of foundations are NOT sequential in the vector, as selection sprites are added at last. */
        if (_vd.last_foundation_child[0] == _vd.last_child) _vd.last_foundation_child[0] = &cs->next;
        if (_vd.last_foundation_child[1] == _vd.last_child) _vd.last_foundation_child[1] = &cs->next;
        _vd.last_child = &cs->next;
}

static void AddStringToDraw(int x, int y, StringID string, uint64 params_1, uint64 params_2, Colours colour, uint16 width)
{
        assert(width != 0);
        StringSpriteToDraw *ss = _vd.string_sprites_to_draw.Append();
        ss->string = string;
        ss->x = x;
        ss->y = y;
        ss->params[0] = params_1;
        ss->params[1] = params_2;
        ss->width = width;
        ss->colour = colour;
}


/**
 * Draws sprites between ground sprite and everything above.
 *
 * The sprite is either drawn as TileSprite or as ChildSprite of the active foundation.
 *
 * @param image the image to draw.
 * @param pal the provided palette.
 * @param ti TileInfo Tile that is being drawn
 * @param z_offset Z offset relative to the groundsprite. Only used for the sprite position, not for sprite sorting.
 * @param foundation_part Foundation part the sprite belongs to.
 */
static void DrawSelectionSprite(SpriteID image, PaletteID pal, const TileInfo *ti, int z_offset, FoundationPart foundation_part)
{
        /* FIXME: This is not totally valid for some autorail highlights that extend over the edges of the tile. */
        if (_vd.foundation[foundation_part] == -1) {
                /* draw on real ground */
                AddTileSpriteToDraw(image, pal, ti->x, ti->y, ti->z + z_offset);
        } else {
                /* draw on top of foundation */
                AddChildSpriteToFoundation(image, pal, nullptr, foundation_part, 0, -z_offset * ZOOM_LVL_BASE);
        }
}

/**
 * Draws a selection rectangle on a tile.
 *
 * @param ti TileInfo Tile that is being drawn
 * @param pal Palette to apply.
 */
static void DrawTileSelectionRect(const TileInfo *ti, PaletteID pal)
{
        if (!IsValidTile(ti->tile)) return;

        SpriteID sel;
        if (IsHalftileSlope(ti->tileh)) {
                Corner halftile_corner = GetHalftileSlopeCorner(ti->tileh);
                SpriteID sel2 = SPR_HALFTILE_SELECTION_FLAT + halftile_corner;
                DrawSelectionSprite(sel2, pal, ti, 7 + TILE_HEIGHT, FOUNDATION_PART_HALFTILE);

                Corner opposite_corner = OppositeCorner(halftile_corner);
                if (IsSteepSlope(ti->tileh)) {
                        sel = SPR_HALFTILE_SELECTION_DOWN;
                } else {
                        sel = ((ti->tileh & SlopeWithOneCornerRaised(opposite_corner)) != 0 ? SPR_HALFTILE_SELECTION_UP : SPR_HALFTILE_SELECTION_FLAT);
                }
                sel += opposite_corner;
        } else {
                sel = SPR_SELECT_TILE + SlopeToSpriteOffset(ti->tileh);
        }
        DrawSelectionSprite(sel, pal, ti, 7, FOUNDATION_PART_NORMAL);
}

static HighLightStyle GetPartOfAutoLine(int px, int py, const Point &selstart, const Point &selend, HighLightStyle dir)
{
        if (!IsInRangeInclusive(selstart.x & ~TILE_UNIT_MASK, selend.x & ~TILE_UNIT_MASK, px)) return HT_DIR_END;
        if (!IsInRangeInclusive(selstart.y & ~TILE_UNIT_MASK, selend.y & ~TILE_UNIT_MASK, py)) return HT_DIR_END;

        px -= selstart.x & ~TILE_UNIT_MASK;
        py -= selstart.y & ~TILE_UNIT_MASK;

        switch (dir) {
                case HT_DIR_X: return (py == 0) ? HT_DIR_X : HT_DIR_END;
                case HT_DIR_Y: return (px == 0) ? HT_DIR_Y : HT_DIR_END;
                case HT_DIR_HU: return (px == -py) ? HT_DIR_HU : (px == -py - (int)TILE_SIZE) ? HT_DIR_HL : HT_DIR_END;
                case HT_DIR_HL: return (px == -py) ? HT_DIR_HL : (px == -py + (int)TILE_SIZE) ? HT_DIR_HU : HT_DIR_END;
                case HT_DIR_VL: return (px ==  py) ? HT_DIR_VL : (px ==  py + (int)TILE_SIZE) ? HT_DIR_VR : HT_DIR_END;
                case HT_DIR_VR: return (px ==  py) ? HT_DIR_VR : (px ==  py - (int)TILE_SIZE) ? HT_DIR_VL : HT_DIR_END;
                default: NOT_REACHED(); break;
        }

        return HT_DIR_END;
}

#include "table/autorail.h"

/**
 * Draws autorail highlights.
 *
 * @param *ti TileInfo Tile that is being drawn
 * @param autorail_type \c HT_DIR_XXX, offset into _AutorailTilehSprite[][]
 * @param pal Palette to use, -1 to autodetect
 */
static void DrawAutorailSelection(const TileInfo *ti, HighLightStyle autorail_type, PaletteID pal = -1)
{
        SpriteID image;
        int offset;

        FoundationPart foundation_part = FOUNDATION_PART_NORMAL;
        Slope autorail_tileh = RemoveHalftileSlope(ti->tileh);
        if (IsHalftileSlope(ti->tileh)) {
                static const HighLightStyle _lower_rail[CORNER_END] = { HT_DIR_VR, HT_DIR_HU, HT_DIR_VL, HT_DIR_HL }; // CORNER_W, CORNER_S, CORNER_E, CORNER_N
                Corner halftile_corner = GetHalftileSlopeCorner(ti->tileh);
                if (autorail_type != _lower_rail[halftile_corner]) {
                        foundation_part = FOUNDATION_PART_HALFTILE;
                        /* Here we draw the highlights of the "three-corners-raised"-slope. That looks ok to me. */
                        autorail_tileh = SlopeWithThreeCornersRaised(OppositeCorner(halftile_corner));
                }
        }

        assert(autorail_type < HT_DIR_END);
        offset = _AutorailTilehSprite[autorail_tileh][autorail_type];
        if (offset >= 0) {
                image = SPR_AUTORAIL_BASE + offset;
                if (pal == (PaletteID)-1) pal = _thd.make_square_red ? PALETTE_SEL_TILE_RED : PAL_NONE;
        } else {
                image = SPR_AUTORAIL_BASE - offset;
                if (pal == (PaletteID)-1) pal = PALETTE_SEL_TILE_RED;
        }

        DrawSelectionSprite(image, pal, ti, 7, foundation_part);
}

/**
 * Checks if the specified tile is selected and if so draws selection using correct selectionstyle.
 * @param *ti TileInfo Tile that is being drawn
 */
static void DrawTileSelection(const TileInfo *ti)
{
        /* Draw a red error square? */
        bool is_redsq = _thd.redsq == ti->tile;
        if (is_redsq) DrawTileSelectionRect(ti, PALETTE_TILE_RED_PULSATING);

        switch (_thd.drawstyle & HT_DRAG_MASK) {
                default: break; // No tile selection active?

                case HT_RECT:
                        if (!is_redsq) {
                                if (IsInsideSelectedRectangle(ti->x, ti->y)) {
                                        DrawTileSelectionRect(ti, _thd.make_square_red ? PALETTE_SEL_TILE_RED : PAL_NONE);
                                } else if (_thd.outersize.x > 0 &&
                                                /* Check if it's inside the outer area? */
                                                IsInsideBS(ti->x, _thd.pos.x + _thd.offs.x, _thd.size.x + _thd.outersize.x) &&
                                                IsInsideBS(ti->y, _thd.pos.y + _thd.offs.y, _thd.size.y + _thd.outersize.y)) {
                                        /* Draw a blue rect. */
                                        DrawTileSelectionRect(ti, PALETTE_SEL_TILE_BLUE);
                                }
                        }
                        break;

                case HT_POINT:
                        if (IsInsideSelectedRectangle(ti->x, ti->y)) {
                                /* Figure out the Z coordinate for the single dot. */
                                int z = 0;
                                FoundationPart foundation_part = FOUNDATION_PART_NORMAL;
                                if (ti->tileh & SLOPE_N) {
                                        z += TILE_HEIGHT;
                                        if (RemoveHalftileSlope(ti->tileh) == SLOPE_STEEP_N) z += TILE_HEIGHT;
                                }
                                if (IsHalftileSlope(ti->tileh)) {
                                        Corner halftile_corner = GetHalftileSlopeCorner(ti->tileh);
                                        if ((halftile_corner == CORNER_W) || (halftile_corner == CORNER_E)) z += TILE_HEIGHT;
                                        if (halftile_corner != CORNER_S) {
                                                foundation_part = FOUNDATION_PART_HALFTILE;
                                                if (IsSteepSlope(ti->tileh)) z -= TILE_HEIGHT;
                                        }
                                }
                                DrawSelectionSprite(_cur_dpi->zoom <= ZOOM_LVL_DETAIL ? SPR_DOT : SPR_DOT_SMALL, PAL_NONE, ti, z, foundation_part);
                        }
                        break;

                case HT_RAIL:
                        if (ti->tile == TileVirtXY(_thd.pos.x, _thd.pos.y)) {
                                assert((_thd.drawstyle & HT_DIR_MASK) < HT_DIR_END);
                                DrawAutorailSelection(ti, _thd.drawstyle & HT_DIR_MASK);
                        }
                        break;

                case HT_LINE: {
                        HighLightStyle type = GetPartOfAutoLine(ti->x, ti->y, _thd.selstart, _thd.selend, _thd.drawstyle & HT_DIR_MASK);
                        if (type < HT_DIR_END) {
                                DrawAutorailSelection(ti, type);
                        } else if (_thd.dir2 < HT_DIR_END) {
                                type = GetPartOfAutoLine(ti->x, ti->y, _thd.selstart2, _thd.selend2, _thd.dir2);
                                if (type < HT_DIR_END) DrawAutorailSelection(ti, type, PALETTE_SEL_TILE_BLUE);
                        }
                        break;
                }
        }
}

/**
 * Returns the y coordinate in the viewport coordinate system where the given
 * tile is painted.
 * @param tile Any tile.
 * @return The viewport y coordinate where the tile is painted.
 */
static int GetViewportY(Point tile)
{
        /* Each increment in X or Y direction moves down by half a tile, i.e. TILE_PIXELS / 2. */
        return (tile.y * (int)(TILE_PIXELS / 2) + tile.x * (int)(TILE_PIXELS / 2) - TilePixelHeightOutsideMap(tile.x, tile.y)) << ZOOM_LVL_SHIFT;
}

/**
 * Add the landscape to the viewport, i.e. all ground tiles and buildings.
 */
static void ViewportAddLandscape()
{
        assert(_vd.dpi.top <= _vd.dpi.top + _vd.dpi.height);
        assert(_vd.dpi.left <= _vd.dpi.left + _vd.dpi.width);

        Point upper_left = InverseRemapCoords(_vd.dpi.left, _vd.dpi.top);
        Point upper_right = InverseRemapCoords(_vd.dpi.left + _vd.dpi.width, _vd.dpi.top);

        /* Transformations between tile coordinates and viewport rows/columns: See vp_column_row
         *   column = y - x
         *   row    = x + y
         *   x      = (row - column) / 2
         *   y      = (row + column) / 2
         * Note: (row, columns) pairs are only valid, if they are both even or both odd.
         */

        /* Columns overlap with neighbouring columns by a half tile.
         *  - Left column is column of upper_left (rounded down) and one column to the left.
         *  - Right column is column of upper_right (rounded up) and one column to the right.
         * Note: Integer-division does not round down for negative numbers, so ensure rounding with another increment/decrement.
         */
        int left_column = (upper_left.y - upper_left.x) / (int)TILE_SIZE - 2;
        int right_column = (upper_right.y - upper_right.x) / (int)TILE_SIZE + 2;

        int potential_bridge_height = ZOOM_LVL_BASE * TILE_HEIGHT * _settings_game.construction.max_bridge_height;

        /* Rows overlap with neighbouring rows by a half tile.
         * The first row that could possibly be visible is the row above upper_left (if it is at height 0).
         * Due to integer-division not rounding down for negative numbers, we need another decrement.
         */
        int row = (upper_left.x + upper_left.y) / (int)TILE_SIZE - 2;
        bool last_row = false;
        for (; !last_row; row++) {
                last_row = true;
                for (int column = left_column; column <= right_column; column++) {
                        /* Valid row/column? */
                        if ((row + column) % 2 != 0) continue;

                        Point tilecoord;
                        tilecoord.x = (row - column) / 2;
                        tilecoord.y = (row + column) / 2;
                        assert(column == tilecoord.y - tilecoord.x);
                        assert(row == tilecoord.y + tilecoord.x);

                        TileType tile_type;
                        TileInfo tile_info;
                        _cur_ti = &tile_info;
                        tile_info.x = tilecoord.x * TILE_SIZE; // FIXME tile_info should use signed integers
                        tile_info.y = tilecoord.y * TILE_SIZE;

                        if (IsInsideBS(tilecoord.x, 0, MapSizeX()) && IsInsideBS(tilecoord.y, 0, MapSizeY())) {
                                /* This includes the south border at MapMaxX / MapMaxY. When terraforming we still draw tile selections there. */
                                tile_info.tile = TileXY(tilecoord.x, tilecoord.y);
                                tile_type = GetTileType(tile_info.tile);
                        } else {
                                tile_info.tile = INVALID_TILE;
                                tile_type = MP_VOID;
                        }

                        if (tile_type != MP_VOID) {
                                /* We are inside the map => paint landscape. */
                                tile_info.tileh = GetTilePixelSlope(tile_info.tile, &tile_info.z);
                        } else {
                                /* We are outside the map => paint black. */
                                tile_info.tileh = GetTilePixelSlopeOutsideMap(tilecoord.x, tilecoord.y, &tile_info.z);
                        }

                        int viewport_y = GetViewportY(tilecoord);

                        if (viewport_y + MAX_TILE_EXTENT_BOTTOM < _vd.dpi.top) {
                                /* The tile in this column is not visible yet.
                                 * Tiles in other columns may be visible, but we need more rows in any case. */
                                last_row = false;
                                continue;
                        }

                        int min_visible_height = viewport_y - (_vd.dpi.top + _vd.dpi.height);
                        bool tile_visible = min_visible_height <= 0;

                        if (tile_type != MP_VOID) {
                                /* Is tile with buildings visible? */
                                if (min_visible_height < MAX_TILE_EXTENT_TOP) tile_visible = true;

                                if (IsBridgeAbove(tile_info.tile)) {
                                        /* Is the bridge visible? */
                                        TileIndex bridge_tile = GetNorthernBridgeEnd(tile_info.tile);
                                        int bridge_height = ZOOM_LVL_BASE * (GetBridgePixelHeight(bridge_tile) - TilePixelHeight(tile_info.tile));
                                        if (min_visible_height < bridge_height + MAX_TILE_EXTENT_TOP) tile_visible = true;
                                }

                                /* Would a higher bridge on a more southern tile be visible?
                                 * If yes, we need to loop over more rows to possibly find one. */
                                if (min_visible_height < potential_bridge_height + MAX_TILE_EXTENT_TOP) last_row = false;
                        } else {
                                /* Outside of map. If we are on the north border of the map, there may still be a bridge visible,
                                 * so we need to loop over more rows to possibly find one. */
                                if ((tilecoord.x <= 0 || tilecoord.y <= 0) && min_visible_height < potential_bridge_height + MAX_TILE_EXTENT_TOP) last_row = false;
                        }

                        if (tile_visible) {
                                last_row = false;
                                _vd.foundation_part = FOUNDATION_PART_NONE;
                                _vd.foundation[0] = -1;
                                _vd.foundation[1] = -1;
                                _vd.last_foundation_child[0] = nullptr;
                                _vd.last_foundation_child[1] = nullptr;

                                _tile_type_procs[tile_type]->draw_tile_proc(&tile_info);
                                if (tile_info.tile != INVALID_TILE) {
                                        DrawTileSelection(&tile_info);
                                        DrawTileZoning(&tile_info);
                                }
                        }
                }
        }
}

/**
 * Add a string to draw in the viewport
 * @param dpi current viewport area
 * @param small_from Zoomlevel from when the small font should be used
 * @param sign sign position and dimension
 * @param string_normal String for normal and 2x zoom level
 * @param string_small String for 4x and 8x zoom level
 * @param string_small_shadow Shadow string for 4x and 8x zoom level; or #STR_NULL if no shadow
 * @param colour colour of the sign background; or INVALID_COLOUR if transparent
 */
void ViewportAddString(const DrawPixelInfo *dpi, ZoomLevel small_from, const ViewportSign *sign, StringID string_normal, StringID string_small, StringID string_small_shadow, uint64 params_1, uint64 params_2, Colours colour)
{
        bool small = dpi->zoom >= small_from;

        int left   = dpi->left;
        int top    = dpi->top;
        int right  = left + dpi->width;
        int bottom = top + dpi->height;

        int sign_height     = ScaleByZoom(VPSM_TOP + FONT_HEIGHT_NORMAL + VPSM_BOTTOM, dpi->zoom);
        int sign_half_width = ScaleByZoom((small ? sign->width_small : sign->width_normal) / 2, dpi->zoom);

        if (bottom < sign->top ||
                        top   > sign->top + sign_height ||
                        right < sign->center - sign_half_width ||
                        left  > sign->center + sign_half_width) {
                return;
        }

        if (!small) {
                AddStringToDraw(sign->center - sign_half_width, sign->top, string_normal, params_1, params_2, colour, sign->width_normal);
        } else {
                int shadow_offset = 0;
                if (string_small_shadow != STR_NULL) {
                        shadow_offset = 4;
                        AddStringToDraw(sign->center - sign_half_width + shadow_offset, sign->top, string_small_shadow, params_1, params_2, INVALID_COLOUR, sign->width_small);
                }
                AddStringToDraw(sign->center - sign_half_width, sign->top - shadow_offset, string_small, params_1, params_2,
                                colour, sign->width_small | 0x8000);
        }
}
 
struct ViewportAddStringApproxBoundsChecker {
        int top;
        int bottom;

        ViewportAddStringApproxBoundsChecker(const DrawPixelInfo *dpi)
        {
                this->top    = dpi->top - ScaleByZoom(VPSM_TOP + FONT_HEIGHT_NORMAL + VPSM_BOTTOM, dpi->zoom);
                this->bottom = dpi->top + dpi->height;
        }

        bool IsSignMaybeOnScreen(const ViewportSign *sign) const
        {
                return !(this->bottom < sign->top || this->top > sign->top);
        }
};

static void ViewportAddTownNames(DrawPixelInfo *dpi)
{
        if (!HasBit(_display_opt, DO_SHOW_TOWN_NAMES) || _game_mode == GM_MENU) return;

        ViewportAddStringApproxBoundsChecker checker(dpi);

        const Town *t;
        FOR_ALL_TOWNS(t) {
                if (!checker.IsSignMaybeOnScreen(&t->cache.sign)) continue;
                ViewportAddString(dpi, ZOOM_LVL_OUT_64X, &t->cache.sign,
                                t->Label(), t->SmallLabel(), STR_VIEWPORT_TOWN_TINY_BLACK,
                                t->index, t->cache.population);
        }
}
 
 
/**
 * Check whether to show a sign above a given station/waypoint.
 * @param st Pointer to the station/waypoint.
 * @return Whether the sign should be shown.
 */
static bool IsStationSignVisible(const BaseStation *st)
{
        /* Don't draw if the display options are disabled */
        return HasBit(_display_opt, Station::IsExpected(st) ? DO_SHOW_STATION_NAMES : DO_SHOW_WAYPOINT_NAMES) &&
                        /* Don't draw if station is owned by another company and competitor station names are hidden. Stations owned by none are never ignored. */
                        (HasBit(_display_opt, DO_SHOW_COMPETITOR_SIGNS) || _local_company == st->owner || st->owner == OWNER_NONE);
}


static void ViewportAddStationNames(DrawPixelInfo *dpi)
{
        if (!(HasBit(_display_opt, DO_SHOW_STATION_NAMES) || HasBit(_display_opt, DO_SHOW_WAYPOINT_NAMES)) || _game_mode == GM_MENU) return;

        ViewportAddStringApproxBoundsChecker checker(dpi);

        const BaseStation *st;
        FOR_ALL_BASE_STATIONS(st) {
                if (!IsStationSignVisible(st)) continue;

                StringID str = Station::IsExpected(st) ? STR_VIEWPORT_STATION : STR_VIEWPORT_WAYPOINT;

                if (!checker.IsSignMaybeOnScreen(&st->sign)) continue;

                ViewportAddString(dpi, ZOOM_LVL_OUT_16X, &st->sign, str, str + 1, STR_NULL, st->index, st->facilities,
                                (st->owner == OWNER_NONE || !st->IsInUse()) ? COLOUR_GREY : _company_colours[st->owner]);
        }
}


static void ViewportAddSigns(DrawPixelInfo *dpi)
{
        /* Signs are turned off or are invisible */
        if (!HasBit(_display_opt, DO_SHOW_SIGNS) || IsInvisibilitySet(TO_SIGNS)) return;

        ViewportAddStringApproxBoundsChecker checker(dpi);

        const Sign *si;
        FOR_ALL_SIGNS(si) {
                /* Don't draw if sign is owned by another company and competitor signs should be hidden.
                 * Note: It is intentional that also signs owned by OWNER_NONE are hidden. Bankrupt
                 * companies can leave OWNER_NONE signs after them. */
                if (!HasBit(_display_opt, DO_SHOW_COMPETITOR_SIGNS) && _local_company != si->owner && si->owner != OWNER_DEITY) continue;

                if (!checker.IsSignMaybeOnScreen(&si->sign)) continue;

                ViewportAddString(dpi, ZOOM_LVL_OUT_16X, &si->sign,
                                STR_WHITE_SIGN,
                                (IsTransparencySet(TO_SIGNS) || si->owner == OWNER_DEITY) ? STR_VIEWPORT_SIGN_SMALL_WHITE : STR_VIEWPORT_SIGN_SMALL_BLACK, STR_NULL,
                                si->index, 0, (si->owner == OWNER_NONE) ? COLOUR_GREY : (si->owner == OWNER_DEITY ? INVALID_COLOUR : _company_colours[si->owner]));
        }
}

/**
 * Update the position of the viewport sign.
 * @param center the (preferred) center of the viewport sign
 * @param top    the new top of the sign
 * @param str    the string to show in the sign
 * @param str_small the string to show when zoomed out. STR_NULL means same as \a str
 */
void ViewportSign::UpdatePosition(int center, int top, StringID str, StringID str_small)
{
        if (this->width_normal != 0) this->MarkDirty();

        this->top = top;

        char buffer[DRAW_STRING_BUFFER];

        GetString(buffer, str, lastof(buffer));
        this->width_normal = VPSM_LEFT + Align(GetStringBoundingBox(buffer).width, 2) + VPSM_RIGHT;
        this->center = center;

        /* zoomed out version */
        if (str_small != STR_NULL) {
                GetString(buffer, str_small, lastof(buffer));
        }
        this->width_small = VPSM_LEFT + Align(GetStringBoundingBox(buffer, FS_SMALL).width, 2) + VPSM_RIGHT;

        this->MarkDirty();
}

/**
 * Mark the sign dirty in all viewports.
 * @param maxzoom Maximum %ZoomLevel at which the text is visible.
 *
 * @ingroup dirty
 */
void ViewportSign::MarkDirty(ZoomLevel maxzoom) const
{
        Rect zoomlevels[ZOOM_LVL_COUNT];

        for (ZoomLevel zoom = ZOOM_LVL_BEGIN; zoom != ZOOM_LVL_END; zoom++) {
                /* FIXME: This doesn't switch to width_small when appropriate. */
                zoomlevels[zoom].left   = this->center - ScaleByZoom(this->width_normal / 2 + 1, zoom);
                zoomlevels[zoom].top    = this->top    - ScaleByZoom(1, zoom);
                zoomlevels[zoom].right  = this->center + ScaleByZoom(this->width_normal / 2 + 1, zoom);
                zoomlevels[zoom].bottom = this->top    + ScaleByZoom(VPSM_TOP + FONT_HEIGHT_NORMAL + VPSM_BOTTOM + 1, zoom);
        }

        for (ViewPort *vp : _viewport_window_cache) {
                if (vp->zoom <= maxzoom) {
                        Rect &zl = zoomlevels[vp->zoom];
                        MarkViewportDirty(vp, zl.left, zl.top, zl.right, zl.bottom);
                }
        }
}

static void ViewportDrawTileSprites(const TileSpriteToDrawVector *tstdv)
{
        const TileSpriteToDraw *tsend = tstdv->End();
        for (const TileSpriteToDraw *ts = tstdv->Begin(); ts != tsend; ++ts) {
                DrawSpriteViewport(ts->image, ts->pal, ts->x, ts->y, ts->sub);
        }
}

/** This fallback sprite checker always exists. */
static bool ViewportSortParentSpritesChecker()
{
        return true;
}

/** Sort parent sprites pointer array */
static void ViewportSortParentSprites(ParentSpriteToSortVector *psdv)
{
        ParentSpriteToDraw **psdvend = psdv->End();
        ParentSpriteToDraw **psd = psdv->Begin();
        while (psd != psdvend) {
                ParentSpriteToDraw *ps = *psd;

                if (ps->comparison_done) {
                        psd++;
                        continue;
                }

                ps->comparison_done = true;

                for (ParentSpriteToDraw **psd2 = psd + 1; psd2 != psdvend; psd2++) {
                        ParentSpriteToDraw *ps2 = *psd2;

                        if (ps2->comparison_done) continue;

                        /* Decide which comparator to use, based on whether the bounding
                         * boxes overlap
                         */
                        if (ps->xmax >= ps2->xmin && ps->xmin <= ps2->xmax && // overlap in X?
                                        ps->ymax >= ps2->ymin && ps->ymin <= ps2->ymax && // overlap in Y?
                                        ps->zmax >= ps2->zmin && ps->zmin <= ps2->zmax) { // overlap in Z?
                                /* Use X+Y+Z as the sorting order, so sprites closer to the bottom of
                                 * the screen and with higher Z elevation, are drawn in front.
                                 * Here X,Y,Z are the coordinates of the "center of mass" of the sprite,
                                 * i.e. X=(left+right)/2, etc.
                                 * However, since we only care about order, don't actually divide / 2
                                 */
                                if (ps->xmin + ps->xmax + ps->ymin + ps->ymax + ps->zmin + ps->zmax <=
                                                ps2->xmin + ps2->xmax + ps2->ymin + ps2->ymax + ps2->zmin + ps2->zmax) {
                                        continue;
                                }
                        } else {
                                /* We only change the order, if it is definite.
                                 * I.e. every single order of X, Y, Z says ps2 is behind ps or they overlap.
                                 * That is: If one partial order says ps behind ps2, do not change the order.
                                 */
                                if (ps->xmax < ps2->xmin ||
                                                ps->ymax < ps2->ymin ||
                                                ps->zmax < ps2->zmin) {
                                        continue;
                                }
                        }

                        /* Move ps2 in front of ps */
                        ParentSpriteToDraw *temp = ps2;
                        for (ParentSpriteToDraw **psd3 = psd2; psd3 > psd; psd3--) {
                                *psd3 = *(psd3 - 1);
                        }
                        *psd = temp;
                }
        }
}

static void ViewportDrawParentSprites(const ParentSpriteToSortVector *psd, const ChildScreenSpriteToDrawVector *csstdv)
{
        const ParentSpriteToDraw * const *psd_end = psd->End();
        for (const ParentSpriteToDraw * const *it = psd->Begin(); it != psd_end; it++) {
                const ParentSpriteToDraw *ps = *it;
                if (ps->image != SPR_EMPTY_BOUNDING_BOX) DrawSpriteViewport(ps->image, ps->pal, ps->x, ps->y, ps->sub);

                int child_idx = ps->first_child;
                while (child_idx >= 0) {
                        const ChildScreenSpriteToDraw *cs = csstdv->Get(child_idx);
                        child_idx = cs->next;
                        DrawSpriteViewport(cs->image, cs->pal, ps->left + cs->x, ps->top + cs->y, cs->sub);
                }
        }
}

/**
 * Draws the bounding boxes of all ParentSprites
 * @param psd Array of ParentSprites
 */
static void ViewportDrawBoundingBoxes(const ParentSpriteToSortVector *psd)
{
        const ParentSpriteToDraw * const *psd_end = psd->End();
        for (const ParentSpriteToDraw * const *it = psd->Begin(); it != psd_end; it++) {
                const ParentSpriteToDraw *ps = *it;
                Point pt1 = RemapCoords(ps->xmax + 1, ps->ymax + 1, ps->zmax + 1); // top front corner
                Point pt2 = RemapCoords(ps->xmin    , ps->ymax + 1, ps->zmax + 1); // top left corner
                Point pt3 = RemapCoords(ps->xmax + 1, ps->ymin    , ps->zmax + 1); // top right corner
                Point pt4 = RemapCoords(ps->xmax + 1, ps->ymax + 1, ps->zmin    ); // bottom front corner

                DrawBox(        pt1.x,         pt1.y,
                        pt2.x - pt1.x, pt2.y - pt1.y,
                        pt3.x - pt1.x, pt3.y - pt1.y,
                        pt4.x - pt1.x, pt4.y - pt1.y);
        }
}

static void ViewportMapStoreBridgeTunnel(const ViewPort * const vp, const TileIndex tile)
{
        extern LegendAndColour _legend_land_owners[NUM_NO_COMPANY_ENTRIES + MAX_COMPANIES + 1];
        extern uint _company_to_list_pos[MAX_COMPANIES];

        /* No need to bother for hidden things */
        const bool tile_is_tunnel = IsTunnel(tile);
        if (tile_is_tunnel) {
                if (!_settings_client.gui.show_tunnels_on_map) return;
        } else {
                if (!_settings_client.gui.show_bridges_on_map) return;
        }

        const Owner o = GetTileOwner(tile);

        if (o < MAX_COMPANIES && !_legend_land_owners[_company_to_list_pos[o]].show_on_map) return;

        /* Check if already stored */
        TunnelBridgeToMapVector * const tbtmv = tile_is_tunnel ? &_vd.tunnel_to_map : &_vd.bridge_to_map;
        TunnelBridgeToMap *tbtm = tbtmv->Begin();
        const TunnelBridgeToMap * const tbtm_end = tbtmv->End();
        while (tbtm != tbtm_end) {
                if (tile == tbtm->from_tile || tile == tbtm->to_tile) return;
                tbtm++;
        }

        /* It's a new one, add it to the list */
        tbtm = tbtmv->Append();
        TileIndex other_end = GetOtherTunnelBridgeEnd(tile);

        /* ensure deterministic ordering, to avoid render flicker */
        if (other_end > tile) {
                tbtm->from_tile = other_end;
                tbtm->to_tile = tile;
        } else {
                tbtm->from_tile = tile;
                tbtm->to_tile = other_end;
        }
}

void ViewportMapClearTunnelCache()
{
        _vd.tunnel_to_map.Clear();
}

void ViewportMapInvalidateTunnelCacheByTile(const TileIndex tile)
{
        TunnelBridgeToMapVector * const tbtmv = &_vd.tunnel_to_map;
        for (TunnelBridgeToMap *tbtm = tbtmv->Begin(); tbtm != tbtmv->End(); tbtm++) {
                if (tbtm->from_tile == tile || tbtm->to_tile == tile) {
                        tbtmv->Erase(tbtm);
                        tbtm--;
                }
        }
}

/**
 * Draw/colour the blocks that have been redrawn.
 */
static void ViewportDrawDirtyBlocks()
{
        Blitter *blitter = BlitterFactory::GetCurrentBlitter();
        const DrawPixelInfo *dpi = _cur_dpi;
        void *dst;
        int right =  UnScaleByZoom(dpi->width,  dpi->zoom);
        int bottom = UnScaleByZoom(dpi->height, dpi->zoom);

        int colour = _string_colourmap[_dirty_block_colour & 0xF];

        dst = dpi->dst_ptr;

        byte bo = UnScaleByZoom(dpi->left + dpi->top, dpi->zoom) & 1;
        do {
                for (int i = (bo ^= 1); i < right; i += 2) blitter->SetPixel(dst, i, 0, (uint8)colour);
                dst = blitter->MoveTo(dst, 0, 1);
        } while (--bottom > 0);
}

static void ViewportDrawStrings(ZoomLevel zoom, const StringSpriteToDrawVector *sstdv)
{
        const StringSpriteToDraw *ssend = sstdv->End();
        for (const StringSpriteToDraw *ss = sstdv->Begin(); ss != ssend; ++ss) {
                TextColour colour = TC_BLACK;
                bool small = HasBit(ss->width, 15);
                int w = GB(ss->width, 0, 15);
                int x = UnScaleByZoom(ss->x, zoom);
                int y = UnScaleByZoom(ss->y, zoom);
                int h = VPSM_TOP + (small ? FONT_HEIGHT_SMALL : FONT_HEIGHT_NORMAL) + VPSM_BOTTOM;

                SetDParam(0, ss->params[0]);
                SetDParam(1, ss->params[1]);

                if (ss->colour != INVALID_COLOUR) {
                        /* Do not draw signs nor station names if they are set invisible */
                        if (IsInvisibilitySet(TO_SIGNS) && ss->string != STR_WHITE_SIGN) continue;

                        if (IsTransparencySet(TO_SIGNS) && ss->string != STR_WHITE_SIGN) {
                                /* Don't draw the rectangle.
                                 * Real colours need the TC_IS_PALETTE_COLOUR flag.
                                 * Otherwise colours from _string_colourmap are assumed. */
                                colour = (TextColour)_colour_gradient[ss->colour][6] | TC_IS_PALETTE_COLOUR;
                        } else {
                                /* Draw the rectangle if 'transparent station signs' is off,
                                 * or if we are drawing a general text sign (STR_WHITE_SIGN). */
                                DrawFrameRect(
                                        x, y, x + w, y + h, ss->colour,
                                        IsTransparencySet(TO_SIGNS) ? FR_TRANSPARENT : FR_NONE
                                );
                        }
                }

                DrawString(x + VPSM_LEFT, x + w - 1 - VPSM_RIGHT, y + VPSM_TOP, ss->string, colour, SA_HOR_CENTER);
        }
}

static inline Vehicle *GetVehicleFromWindow(Window *w)
{
        if (w) {
                WindowClass wc = w->window_class;
                WindowNumber wn = w->window_number;

                if (wc == WC_DROPDOWN_MENU) GetParentWindowInfo(w, wc, wn);

                switch (wc) {
                        case WC_VEHICLE_VIEW:
                        case WC_VEHICLE_ORDERS:
                        case WC_VEHICLE_TIMETABLE:
                        case WC_VEHICLE_DETAILS:
                        case WC_VEHICLE_REFIT:
                        case WC_VEHICLE_CARGO_TYPE_LOAD_ORDERS:
                        case WC_VEHICLE_CARGO_TYPE_UNLOAD_ORDERS:
                                if (wn != INVALID_VEHICLE) return Vehicle::Get(wn);
                                break;
                        default:
                                break;
                }
        }
        return nullptr;
}

static inline TileIndex GetLastValidOrderLocation(const Vehicle *veh)
{
        Order *order;
        TileIndex tmp, result = INVALID_TILE;
        FOR_VEHICLE_ORDERS(veh, order) {
                switch (order->GetType()) {
                        case OT_GOTO_STATION:
                        case OT_GOTO_WAYPOINT:
                        case OT_IMPLICIT:
                        case OT_GOTO_DEPOT:
                                tmp = order->GetLocation(veh, veh->type == VEH_AIRCRAFT);
                                if (tmp != INVALID_TILE) result = tmp;
                                break;
                        default:
                                break;
                }
        }
        return result;
}

static inline Order *GetFinalOrder(const Vehicle *veh, Order *order)
{
        // Use Floyd's cycle-finding algorithm to prevent endless loop
        // due to a cycle formed by confitional orders.
        auto cycle_check = order;

        while (order->IsType(OT_CONDITIONAL)) {
                order = veh->GetOrder(order->GetConditionSkipToOrder());

                if (cycle_check->IsType(OT_CONDITIONAL)) {
                        cycle_check = veh->GetOrder(cycle_check->GetConditionSkipToOrder());

                        if (cycle_check->IsType(OT_CONDITIONAL)) {
                                cycle_check = veh->GetOrder(cycle_check->GetConditionSkipToOrder());
                        }
                }

                bool cycle_detected = (order->IsType(OT_CONDITIONAL) && (order == cycle_check));

                if (cycle_detected) return nullptr;
        }

        return order;
}
 
static bool ViewportMapPrepareVehicleRoute(const Vehicle * const veh)
{
        if (!veh) return false;

        if (_vp_route_paths.size() == 0) {
                TileIndex from_tile = GetLastValidOrderLocation(veh);
                if (from_tile == INVALID_TILE) return false;

                Order *order;
                FOR_VEHICLE_ORDERS(veh, order) {
                        Order *final_order = GetFinalOrder(veh, order);
                        if (final_order == nullptr) continue;
                        const TileIndex to_tile = final_order->GetLocation(veh, veh->type == VEH_AIRCRAFT);
                        if (to_tile == INVALID_TILE) continue;

                        DrawnPathRouteTileLine path = { from_tile, to_tile, (final_order == order) };
                        if (path.from_tile > path.to_tile) std::swap(path.from_tile, path.to_tile);
                        _vp_route_paths.push_back(path);

                        const OrderType ot = order->GetType();
                        if (ot == OT_GOTO_STATION || ot == OT_GOTO_DEPOT || ot == OT_GOTO_WAYPOINT || ot == OT_IMPLICIT) from_tile = to_tile;
                }
                // remove duplicate lines
                std::sort(_vp_route_paths.begin(), _vp_route_paths.end());
                _vp_route_paths.erase(std::unique(_vp_route_paths.begin(), _vp_route_paths.end()), _vp_route_paths.end());
        }
        return true;
}

/** Draw the route of a vehicle. */
static void ViewportMapDrawVehicleRoute(const ViewPort *vp)
{
        const Vehicle *veh = GetVehicleFromWindow(_focused_window);

        if (!veh) {
                if (!_vp_route_paths.empty()) {
                        // make sure we remove any leftover paths
                        MarkRoutePathsDirty(_vp_route_paths);
                        _vp_route_paths.clear();
                        _vp_route_paths_last_mark_dirty.clear();
                        DEBUG(misc, 1, "ViewportMapDrawVehicleRoute: redrawing dirty paths 0");
                }
                return;
        }

        switch (_settings_client.gui.show_vehicle_route) {
                /* case 0: return; // No */
        case 1: { // Simple
                if (!ViewportMapPrepareVehicleRoute(veh)) {
                        if (!_vp_route_paths.empty()) {
                                // make sure we remove any leftover paths
                                MarkRoutePathsDirty(_vp_route_paths);
                                _vp_route_paths.clear();
                                DEBUG(misc, 1, "ViewportMapDrawVehicleRoute: redrawing dirty paths 1");
                        }
                        return;
                }

                DrawPixelInfo *old_dpi = _cur_dpi;
                _cur_dpi = &_dpi_for_text;

                for (const auto &iter : _vp_route_paths) {
                        const Point from_pt = RemapCoords2(TileX(iter.from_tile) * TILE_SIZE + TILE_SIZE / 2, TileY(iter.from_tile) * TILE_SIZE + TILE_SIZE / 2);
                        const int from_x = UnScaleByZoom(from_pt.x, vp->zoom);
                        const int from_y = UnScaleByZoom(from_pt.y, vp->zoom);

                        const Point to_pt = RemapCoords2(TileX(iter.to_tile) * TILE_SIZE + TILE_SIZE / 2, TileY(iter.to_tile) * TILE_SIZE + TILE_SIZE / 2);
                        const int to_x = UnScaleByZoom(to_pt.x, vp->zoom);
                        const int to_y = UnScaleByZoom(to_pt.y, vp->zoom);

                        int line_width = 3;
                        if (_settings_client.gui.dash_level_of_route_lines == 0) {
                                GfxDrawLine(from_x, from_y, to_x, to_y, PC_BLACK, 3, _settings_client.gui.dash_level_of_route_lines);
                                line_width = 1;
                        }
                        GfxDrawLine(from_x, from_y, to_x, to_y, iter.order_match ? PC_WHITE : PC_YELLOW, line_width, _settings_client.gui.dash_level_of_route_lines);
                }

                if (_vp_route_paths_last_mark_dirty != _vp_route_paths) {
                        // make sure we're not drawing a partial path
                        MarkRoutePathsDirty(_vp_route_paths);
                        _vp_route_paths_last_mark_dirty = _vp_route_paths;
                        DEBUG(misc, 1, "ViewportMapDrawVehicleRoute: redrawing dirty paths 2");
                }

                _cur_dpi = old_dpi;
                break;
        }
        }
}

static inline void DrawRouteStep(const ViewPort * const vp, const TileIndex tile, const RankOrderTypeList list)
{
        if (tile == INVALID_TILE) return;
        const uint step_count = list.size() > max_rank_order_type_count ? 1 : (uint)list.size();
        const Point pt = RemapCoords2(TileX(tile) * TILE_SIZE + TILE_SIZE / 2, TileY(tile) * TILE_SIZE + TILE_SIZE / 2);
        const int x = UnScaleByZoomLower(pt.x - _vd.dpi.left, _vd.dpi.zoom) - (_vp_route_step_width / 2);
        const int char_height = GetCharacterHeight(FS_SMALL) + 1;
        const int rsth = _vp_route_step_height_top + (int)step_count * char_height + _vp_route_step_height_bottom;
        const int y = UnScaleByZoomLower(pt.y - _vd.dpi.top, _vd.dpi.zoom) - rsth;

        /* Draw the background. */
        DrawSprite(SPR_ROUTE_STEP_TOP, PAL_NONE, _cur_dpi->left + x, _cur_dpi->top + y);
        uint y2 = y + _vp_route_step_height_top;

        for (uint r = step_count; r != 0; r--, y2 += char_height) {
                DrawSprite(SPR_ROUTE_STEP_MIDDLE, PAL_NONE, _cur_dpi->left + x, _cur_dpi->top + y2, &_vp_route_step_subsprite);
        }

        DrawSprite(SPR_ROUTE_STEP_BOTTOM, PAL_NONE, _cur_dpi->left + x, _cur_dpi->top + y2);
        SpriteID s = SPR_ROUTE_STEP_BOTTOM_SHADOW;
        DrawSprite(SetBit(s, PALETTE_MODIFIER_TRANSPARENT), PALETTE_TO_TRANSPARENT, _cur_dpi->left + x, _cur_dpi->top + y2);

        /* Fill with the data. */
        DrawPixelInfo *old_dpi = _cur_dpi;
        y2 = y + _vp_route_step_height_top;
        _cur_dpi = &_dpi_for_text;

        if (list.size() > max_rank_order_type_count) {
                /* Write order overflow item */
                SetDParam(0, list.size());
                DrawString(_dpi_for_text.left + x, _dpi_for_text.left + x + _vp_route_step_width - 1, _dpi_for_text.top + y2,
                                STR_VIEWPORT_SHOW_VEHICLE_ROUTE_STEP_OVERFLOW, TC_FROMSTRING, SA_CENTER, false, FS_SMALL);
        } else {
                for (RankOrderTypeList::const_iterator cit = list.begin(); cit != list.end(); cit++, y2 += char_height) {
                        bool ok = true;
                        switch (cit->second) {
                                case OT_GOTO_STATION:
                                        SetDParam(1, STR_VIEWPORT_SHOW_VEHICLE_ROUTE_STEP_STATION);
                                        break;
                                case OT_GOTO_DEPOT:
                                        SetDParam(1, STR_VIEWPORT_SHOW_VEHICLE_ROUTE_STEP_DEPOT);
                                        break;
                                case OT_GOTO_WAYPOINT:
                                        SetDParam(1, STR_VIEWPORT_SHOW_VEHICLE_ROUTE_STEP_WAYPOINT);
                                        break;
                                case OT_IMPLICIT:
                                        SetDParam(1, STR_VIEWPORT_SHOW_VEHICLE_ROUTE_STEP_IMPLICIT);
                                        break;
                                default: // OT_NOTHING OT_LOADING OT_LEAVESTATION OT_DUMMY OT_CONDITIONAL
                                        ok = false;
                                        break;
                        }
                        if (ok) {
                        /* Write order's info */
                                SetDParam(0, cit->first);
                                DrawString(_dpi_for_text.left + x, _dpi_for_text.left + x + _vp_route_step_width - 1, _dpi_for_text.top + y2,
                                                STR_VIEWPORT_SHOW_VEHICLE_ROUTE_STEP, TC_FROMSTRING, SA_CENTER, false, FS_SMALL);
                        }
                }
        }
        _cur_dpi = old_dpi;
}

static bool ViewportPrepareVehicleRouteSteps(const Vehicle * const veh)
{
        if (!veh) return false;

        if (_vp_route_steps.size() == 0) {
                /* Prepare data. */
                Order *order;
                int order_rank = 0;
                FOR_VEHICLE_ORDERS(veh, order) {
                        const TileIndex tile = order->GetLocation(veh, veh->type == VEH_AIRCRAFT);
                        order_rank++;
                        if (tile == INVALID_TILE) continue;
                        _vp_route_steps[tile].push_back(std::pair<int, OrderType>(order_rank, order->GetType()));
                }
        }

        return true;
}

/** Draw the route steps of a vehicle. */
static void ViewportDrawVehicleRouteSteps(const ViewPort * const vp)
{
        const Vehicle * const veh = GetVehicleFromWindow(_focused_window);
        if (veh && ViewportPrepareVehicleRouteSteps(veh)) {
                if (_vp_route_steps != _vp_route_steps_last_mark_dirty) {
                        for (RouteStepsMap::const_iterator cit = _vp_route_steps.begin(); cit != _vp_route_steps.end(); cit++) {
                                MarkRouteStepDirty(cit);
                        }
                        _vp_route_steps_last_mark_dirty = _vp_route_steps;
                }

                for (RouteStepsMap::const_iterator cit = _vp_route_steps.begin(); cit != _vp_route_steps.end(); cit++) {
                        DrawRouteStep(vp, cit->first, cit->second);
                }
        }
}

void ViewportDrawPlans(const ViewPort *vp)
{
        DrawPixelInfo *old_dpi = _cur_dpi;
        _cur_dpi = &_dpi_for_text;

        Plan *p;
        FOR_ALL_PLANS(p) {
                if (!p->IsVisible()) continue;
                for (PlanLineVector::iterator it = p->lines.begin(); it != p->lines.end(); it++) {
                        PlanLine *pl = *it;
                        if (!pl->visible) continue;
                        for (uint i = 1; i < pl->tiles.size(); i++) {
                                const TileIndex from_tile = pl->tiles[i - 1];
                                const Point from_pt = RemapCoords2(TileX(from_tile) * TILE_SIZE + TILE_SIZE / 2, TileY(from_tile) * TILE_SIZE + TILE_SIZE / 2);
                                const int from_x = UnScaleByZoom(from_pt.x, vp->zoom);
                                const int from_y = UnScaleByZoom(from_pt.y, vp->zoom);

                                const TileIndex to_tile = pl->tiles[i];
                                const Point to_pt = RemapCoords2(TileX(to_tile) * TILE_SIZE + TILE_SIZE / 2, TileY(to_tile) * TILE_SIZE + TILE_SIZE / 2);
                                const int to_x = UnScaleByZoom(to_pt.x, vp->zoom);
                                const int to_y = UnScaleByZoom(to_pt.y, vp->zoom);

                                GfxDrawLine(from_x, from_y, to_x, to_y, PC_BLACK, 3);
                                if (pl->focused) {
                                        GfxDrawLine(from_x, from_y, to_x, to_y, PC_RED, 1);
                                }
                                else {
                                        GfxDrawLine(from_x, from_y, to_x, to_y, PC_WHITE, 1);
                                }
                        }
                }
        }

        if (_current_plan && _current_plan->temp_line->tiles.size() > 1) {
                for (uint i = 1; i < _current_plan->temp_line->tiles.size(); i++) {
                        const TileIndex from_tile = _current_plan->temp_line->tiles[i - 1];
                        const Point from_pt = RemapCoords2(TileX(from_tile) * TILE_SIZE + TILE_SIZE / 2, TileY(from_tile) * TILE_SIZE + TILE_SIZE / 2);
                        const int from_x = UnScaleByZoom(from_pt.x, vp->zoom);
                        const int from_y = UnScaleByZoom(from_pt.y, vp->zoom);

                        const TileIndex to_tile = _current_plan->temp_line->tiles[i];
                        const Point to_pt = RemapCoords2(TileX(to_tile) * TILE_SIZE + TILE_SIZE / 2, TileY(to_tile) * TILE_SIZE + TILE_SIZE / 2);
                        const int to_x = UnScaleByZoom(to_pt.x, vp->zoom);
                        const int to_y = UnScaleByZoom(to_pt.y, vp->zoom);

                        GfxDrawLine(from_x, from_y, to_x, to_y, PC_WHITE, 3, 1);
                }
        }

        _cur_dpi = old_dpi;
}

#define SLOPIFY_COLOUR(tile, height, vF, vW, vS, vE, vN, action) { \
        if (show_slope) { \
                const Slope slope = GetTileSlope((tile), (height)); \
                switch (slope) { \
                        case SLOPE_FLAT: \
                        case SLOPE_ELEVATED: \
                                action (vF); break; \
                        default: { \
                                switch (slope & SLOPE_EW) { \
                                        case SLOPE_W: action (vW); break; \
                                        case SLOPE_E: action (vE); break; \
                                        default:      action (slope & SLOPE_S) ? (vS) : (vN); break; \
                                } \
                                break; \
                        } \
                } \
                } else { \
                action (vF); \
                } \
}
#define RETURN_SLOPIFIED_COLOUR(tile, height, colour, colour_light, colour_dark) SLOPIFY_COLOUR(tile, height, colour, colour_light, colour_dark, colour_dark, colour_light, return)
#define ASSIGN_SLOPIFIED_COLOUR(tile, height, colour, colour_light, colour_dark, to_var) SLOPIFY_COLOUR(tile, height, colour, colour_light, colour_dark, colour_dark, colour_light, to_var =)
#define GET_SLOPE_INDEX(slope_index) SLOPIFY_COLOUR(tile, nullptr, 0, 1, 2, 3, 4, slope_index =)

#define COL8TO32(x) _cur_palette.palette[x].data
#define COLOUR_FROM_INDEX(x) ((const uint8 *)&(x))[colour_index]
#define IS32(x) (is_32bpp ? COL8TO32(x) : (x))

/* Variables containing Colour if 32bpp or palette index if 8bpp. */
uint32 _vp_map_vegetation_clear_colours[16][6][8]; ///< [Slope][ClearGround][Multi (see LoadClearGroundMainColours())]
uint32 _vp_map_vegetation_tree_colours[5][MAX_TREE_COUNT_BY_LANDSCAPE]; ///< [TreeGround][max of _tree_count_by_landscape]
uint32 _vp_map_water_colour[5]; ///< [Slope]

static inline uint ViewportMapGetColourIndexMulti(const TileIndex tile, const ClearGround cg)
{
        switch (cg) {
        case CLEAR_GRASS:
        case CLEAR_SNOW:
        case CLEAR_DESERT:
                return GetClearDensity(tile);
        case CLEAR_ROUGH:
                return GB(TileX(tile) ^ TileY(tile), 4, 3);
        case CLEAR_ROCKS:
                return TileHash(TileX(tile), TileY(tile)) & 1;
        case CLEAR_FIELDS:
                return GetFieldType(tile) & 7;
        default: NOT_REACHED();
        }
}

static const ClearGround _treeground_to_clearground[5] = {
        CLEAR_GRASS, // TREE_GROUND_GRASS
        CLEAR_ROUGH, // TREE_GROUND_ROUGH
        CLEAR_SNOW,  // TREE_GROUND_SNOW_DESERT, make it +1 if _settings_game.game_creation.landscape == LT_TROPIC
        CLEAR_GRASS, // TREE_GROUND_SHORE
        CLEAR_SNOW,  // TREE_GROUND_ROUGH_SNOW, make it +1 if _settings_game.game_creation.landscape == LT_TROPIC
};

template <bool is_32bpp, bool show_slope>
static inline uint32 ViewportMapGetColourVegetation(const TileIndex tile, TileType t, const uint colour_index)
{
        uint32 colour;
        switch (t) {
        case MP_CLEAR: {
                Slope slope = show_slope ? (Slope)(GetTileSlope(tile, nullptr) & 15) : SLOPE_FLAT;
                uint multi;
                ClearGround cg = GetClearGround(tile);
                if (cg == CLEAR_FIELDS && colour_index & 1) {
                        cg = CLEAR_GRASS;
                        multi = 1;
                }
                else multi = ViewportMapGetColourIndexMulti(tile, cg);
                return _vp_map_vegetation_clear_colours[slope][cg][multi];
        }

        case MP_INDUSTRY:
                colour = IsTileForestIndustry(tile) ? (colour_index & 1 ? PC_GREEN : 0x7B) : GREY_SCALE(3);
                break;

        case MP_TREES: {
                const TreeGround tg = GetTreeGround(tile);
                const uint td = GetTreeDensity(tile);
                if (IsTransparencySet(TO_TREES)) {
                        ClearGround cg = _treeground_to_clearground[tg];
                        if (cg == CLEAR_SNOW && _settings_game.game_creation.landscape == LT_TROPIC) cg = CLEAR_DESERT;
                        Slope slope = show_slope ? (Slope)(GetTileSlope(tile, nullptr) & 15) : SLOPE_FLAT;
                        uint32 ground_colour = _vp_map_vegetation_clear_colours[slope][cg][td];

                        if (IsInvisibilitySet(TO_TREES)) {
                                /* Like ground. */
                                return ground_colour;
                        }

                        /* Take ground and make it darker. */
                        if (is_32bpp) {
                                return Blitter_32bppBase::MakeTransparent(ground_colour, 192, 256).data;
                        }
                        else {
                                /* 8bpp transparent snow trees give blue. Definitely don't want that. Prefer grey. */
                                if (cg == CLEAR_SNOW && td > 1) return GREY_SCALE(13 - GetTreeCount(tile));
                                return _pal2trsp_remap_ptr[ground_colour];
                        }
                }
                else {
                        if (tg == TREE_GROUND_SNOW_DESERT || tg == TREE_GROUND_ROUGH_SNOW) {
                                return _vp_map_vegetation_clear_colours[colour_index][_settings_game.game_creation.landscape == LT_TROPIC ? CLEAR_DESERT : CLEAR_SNOW][td];
                        }
                        else {
                                const uint rnd = min(GetTreeCount(tile) ^ (((tile & 3) ^ (TileY(tile) & 3)) * td), MAX_TREE_COUNT_BY_LANDSCAPE - 1);
                                return _vp_map_vegetation_tree_colours[tg][rnd];
                        }
                }
        }

        case MP_WATER:
                if (is_32bpp) {
                        uint slope_index = 0;
                        if (GetWaterTileType(tile) != WATER_TILE_COAST) GET_SLOPE_INDEX(slope_index);
                        return _vp_map_water_colour[slope_index];
                }
                /* FALL THROUGH */

        default:
                colour = ApplyMask(MKCOLOUR_XXXX(GREY_SCALE(3)), &_smallmap_vehicles_andor[t]);
                colour = COLOUR_FROM_INDEX(colour);
                break;
        }

        if (is_32bpp) {
                return COL8TO32(colour);
        }
        else {
                if (show_slope) ASSIGN_SLOPIFIED_COLOUR(tile, nullptr, colour, _lighten_colour[colour], _darken_colour[colour], colour);
                return colour;
        }
}

template <bool is_32bpp, bool show_slope>
static inline uint32 ViewportMapGetColourIndustries(const TileIndex tile, const TileType t, const uint colour_index)
{
        extern LegendAndColour _legend_from_industries[NUM_INDUSTRYTYPES + 1];
        extern uint _industry_to_list_pos[NUM_INDUSTRYTYPES];
        extern bool _smallmap_show_heightmap;

        TileType t2 = t;
        if (t == MP_INDUSTRY) {
                /* If industry is allowed to be seen, use its colour on the map. */
                const IndustryType it = Industry::GetByTile(tile)->type;
                if (_legend_from_industries[_industry_to_list_pos[it]].show_on_map)
                        return IS32(GetIndustrySpec(it)->map_colour);
                /* Otherwise, return the colour which will make it disappear. */
                t2 = IsTileOnWater(tile) ? MP_WATER : MP_CLEAR;
        }

        if (is_32bpp && t2 == MP_WATER) {
                uint slope_index = 0;
                if (t != MP_INDUSTRY && GetWaterTileType(tile) != WATER_TILE_COAST) GET_SLOPE_INDEX(slope_index); ///< Ignore industry on water not shown on map.
                return _vp_map_water_colour[slope_index];
        }

        const int h = TileHeight(tile);
        const SmallMapColourScheme * const cs = &_heightmap_schemes[_settings_client.gui.smallmap_land_colour];
        const uint32 colours = ApplyMask(_smallmap_show_heightmap ? cs->height_colours[h] : cs->default_colour, &_smallmap_vehicles_andor[t2]);
        uint32 colour = COLOUR_FROM_INDEX(colours);

        if (show_slope) ASSIGN_SLOPIFIED_COLOUR(tile, nullptr, colour, _lighten_colour[colour], _darken_colour[colour], colour);

        return IS32(colour);
}

template <bool is_32bpp, bool show_slope>
static inline uint32 ViewportMapGetColourOwner(const TileIndex tile, TileType t, const uint colour_index)
{
        extern LegendAndColour _legend_land_owners[NUM_NO_COMPANY_ENTRIES + MAX_COMPANIES + 1];
        extern uint _company_to_list_pos[MAX_COMPANIES];

        switch (t) {
        case MP_INDUSTRY: return IS32(PC_DARK_GREY);
        case MP_HOUSE:    return IS32(colour_index & 1 ? PC_DARK_RED : GREY_SCALE(3));
        default:          break;
        }

        const Owner o = GetTileOwner(tile);
        if ((o < MAX_COMPANIES && !_legend_land_owners[_company_to_list_pos[o]].show_on_map) || o == OWNER_NONE || o == OWNER_WATER) {
                if (t == MP_WATER) {
                        if (is_32bpp) {
                                uint slope_index = 0;
                                if (GetWaterTileType(tile) != WATER_TILE_COAST) GET_SLOPE_INDEX(slope_index);
                                return _vp_map_water_colour[slope_index];
                        }
                        else {
                                return PC_WATER;
                        }
                }

                const int h = TileHeight(tile);
                uint32 colour = COLOUR_FROM_INDEX(_heightmap_schemes[_settings_client.gui.smallmap_land_colour].height_colours[h]);
                if (show_slope) ASSIGN_SLOPIFIED_COLOUR(tile, nullptr, colour, _lighten_colour[colour], _darken_colour[colour], colour);
                return IS32(colour);

        }
        else if (o == OWNER_TOWN) {
                return IS32(t == MP_ROAD ? (colour_index & 1 ? PC_BLACK : GREY_SCALE(3)) : PC_DARK_RED);
        }

        /* Train stations are sometimes hard to spot.
        * So we give the player a hint by mixing his colour with black. */
        uint32 colour = _legend_land_owners[_company_to_list_pos[o]].colour;
        if (t != MP_STATION) {
                if (show_slope) ASSIGN_SLOPIFIED_COLOUR(tile, nullptr, colour, _lighten_colour[colour], _darken_colour[colour], colour);
        }
        else {
                if (GetStationType(tile) == STATION_RAIL) colour = colour_index & 1 ? colour : PC_BLACK;
        }
        if (is_32bpp) return COL8TO32(colour);
        return colour;
}

static inline void ViewportMapStoreBridgeAboveTile(const ViewPort * const vp, const TileIndex tile)
{
        /* No need to bother for hidden things */
        if (!_settings_client.gui.show_bridges_on_map) return;

        /* Check existing stored bridges */
        TunnelBridgeToMap *tbtm = _vd.bridge_to_map.Begin();
        TunnelBridgeToMap *tbtm_end = _vd.bridge_to_map.End();
        for (; tbtm != tbtm_end; ++tbtm) {
                if (!IsBridge(tbtm->from_tile)) continue;

                TileIndex from = tbtm->from_tile;
                TileIndex to = tbtm->to_tile;
                if (TileX(from) == TileX(to) && TileX(from) == TileX(tile)) {
                        if (TileY(from) > TileY(to)) std::swap(from, to);
                        if (TileY(from) <= TileY(tile) && TileY(tile) <= TileY(to)) return; /* already covered */
                }
                else if (TileY(from) == TileY(to) && TileY(from) == TileY(tile)) {
                        if (TileX(from) > TileX(to)) std::swap(from, to);
                        if (TileX(from) <= TileX(tile) && TileX(tile) <= TileX(to)) return; /* already covered */
                }
        }

        ViewportMapStoreBridgeTunnel(vp, GetSouthernBridgeEnd(tile));
}

static inline TileIndex ViewportMapGetMostSignificantTileType(const ViewPort * const vp, const TileIndex from_tile, TileType * const tile_type)
{
        if (vp->zoom <= ZOOM_LVL_OUT_128X || !_settings_client.gui.viewport_map_scan_surroundings) {
                const TileType ttype = GetTileType(from_tile);
                /* Store bridges and tunnels. */
                if (ttype != MP_TUNNELBRIDGE) {
                        *tile_type = ttype;
                        if (IsBridgeAbove(from_tile)) ViewportMapStoreBridgeAboveTile(vp, from_tile);
                }
                else {
                        ViewportMapStoreBridgeTunnel(vp, from_tile);
                        switch (GetTunnelBridgeTransportType(from_tile)) {
                        case TRANSPORT_RAIL: *tile_type = MP_RAILWAY; break;
                        case TRANSPORT_ROAD: *tile_type = MP_ROAD;    break;
                        default:             *tile_type = MP_WATER;   break;
                        }
                }
                return from_tile;
        }

        const uint8 length = (vp->zoom - ZOOM_LVL_OUT_128X) * 2;
        TileArea tile_area = TileArea(from_tile, length, length);
        tile_area.ClampToMap();

        /* Find the most important tile of the area. */
        TileIndex result = from_tile;
        uint importance = 0;
        TILE_AREA_LOOP_WITH_PREFETCH(tile, tile_area) {
                const TileType ttype = GetTileType(tile);
                const uint tile_importance = _tiletype_importance[ttype];
                if (tile_importance > importance) {
                        importance = tile_importance;
                        result = tile;
                }
                if (ttype != MP_TUNNELBRIDGE && IsBridgeAbove(tile)) {
                        ViewportMapStoreBridgeAboveTile(vp, tile);
                }
        }

        /* Store bridges and tunnels. */
        *tile_type = GetTileType(result);
        if (*tile_type == MP_TUNNELBRIDGE) {
                ViewportMapStoreBridgeTunnel(vp, result);
                switch (GetTunnelBridgeTransportType(result)) {
                case TRANSPORT_RAIL: *tile_type = MP_RAILWAY; break;
                case TRANSPORT_ROAD: *tile_type = MP_ROAD;    break;
                default:             *tile_type = MP_WATER;   break;
                }
        }

        return result;
}

/** Get the colour of a tile, can be 32bpp RGB or 8bpp palette index. */
template <bool is_32bpp, bool show_slope>
uint32 ViewportMapGetColour(const ViewPort * const vp, uint x, uint y, const uint colour_index)
{
        if (!(IsInsideMM(x, TILE_SIZE, MapMaxX() * TILE_SIZE - 1) &&
                IsInsideMM(y, TILE_SIZE, MapMaxY() * TILE_SIZE - 1)))
                return 0;

        /* Very approximative but fast way to get the tile when taking Z into account. */
        const TileIndex tile_tmp = TileVirtXY(x, y);
        const uint z = TileHeight(tile_tmp) * 4;
        TileIndex tile = TileVirtXY(x + z, y + z);
        if (tile >= MapSize()) return 0;
        if (_settings_game.construction.freeform_edges) {
                /* tile_tmp and tile must be from the same side,
                * otherwise it's an approximation erroneous case
                * that leads to a graphic glitch below south west border.
                */
                if (TileX(tile_tmp) > (MapSizeX() - (MapSizeX() / 8)))
                        if ((TileX(tile_tmp) < (MapSizeX() / 2)) != (TileX(tile) < (MapSizeX() / 2)))
                                return 0;
        }
        TileType tile_type = MP_VOID;
        tile = ViewportMapGetMostSignificantTileType(vp, tile, &tile_type);
        if (tile_type == MP_VOID) return 0;

        /* Return the colours. */
        switch (vp->map_type) {
        default:              return ViewportMapGetColourOwner<is_32bpp, show_slope>(tile, tile_type, colour_index);
        case VPMT_INDUSTRY:   return ViewportMapGetColourIndustries<is_32bpp, show_slope>(tile, tile_type, colour_index);
        case VPMT_VEGETATION: return ViewportMapGetColourVegetation<is_32bpp, show_slope>(tile, tile_type, colour_index);
        }
}

/* Taken from http://stereopsis.com/doubleblend.html, PixelBlend() is faster than ComposeColourRGBANoCheck() */
static inline void PixelBlend(uint32 * const d, const uint32 s)
{
        const uint32 a = (s >> 24) + 1;
        const uint32 dstrb = *d & 0xFF00FF;
        const uint32 dstg = *d & 0xFF00;
        const uint32 srcrb = s & 0xFF00FF;
        const uint32 srcg = s & 0xFF00;
        uint32 drb = srcrb - dstrb;
        uint32 dg = srcg - dstg;
        drb *= a;
        dg *= a;
        drb >>= 8;
        dg >>= 8;
        uint32 rb = (drb + dstrb) & 0xFF00FF;
        uint32 g = (dg + dstg) & 0xFF00;
        *d = rb | g;
}

/** Draw the bounding boxes of the scrolling viewport (right-clicked and dragged) */
static void ViewportMapDrawScrollingViewportBox(const ViewPort * const vp)
{
        if (_scrolling_viewport && _scrolling_viewport->viewport) {
                const ViewPort * const vp_scrolling = _scrolling_viewport->viewport;
                if (vp_scrolling->zoom < ZOOM_LVL_DRAW_MAP) {
                        /* Check intersection of dpi and vp_scrolling */
                        const int mask = ScaleByZoom(-1, vp->zoom);
                        const int vp_scrolling_virtual_top_mask = vp_scrolling->virtual_top & mask;
                        const int vp_scrolling_virtual_bottom_mask = (vp_scrolling->virtual_top + vp_scrolling->virtual_height) & mask;
                        const int t_inter = max(vp_scrolling_virtual_top_mask, _vd.dpi.top);
                        const int b_inter = min(vp_scrolling_virtual_bottom_mask, _vd.dpi.top + _vd.dpi.height);
                        if (t_inter < b_inter) {
                                const int vp_scrolling_virtual_left_mask = vp_scrolling->virtual_left & mask;
                                const int vp_scrolling_virtual_right_mask = (vp_scrolling->virtual_left + vp_scrolling->virtual_width) & mask;
                                const int l_inter = max(vp_scrolling_virtual_left_mask, _vd.dpi.left);
                                const int r_inter = min(vp_scrolling_virtual_right_mask, _vd.dpi.left + _vd.dpi.width);
                                if (l_inter < r_inter) {
                                        /* OK, so we can draw something that tells where the scrolling viewport is */
                                        Blitter * const blitter = BlitterFactory::GetCurrentBlitter();
                                        const int w_inter = UnScaleByZoom(r_inter - l_inter, vp->zoom);
                                        const int h_inter = UnScaleByZoom(b_inter - t_inter, vp->zoom);
                                        const int x = UnScaleByZoom(l_inter - _vd.dpi.left, vp->zoom);
                                        const int y = UnScaleByZoom(t_inter - _vd.dpi.top, vp->zoom);

                                        /* If asked, with 32bpp we can do some blending */
                                        if (_settings_client.gui.show_scrolling_viewport_on_map >= 2 && blitter->GetScreenDepth() == 32)
                                                for (int j = y; j < y + h_inter; j++)
                                                        for (int i = x; i < x + w_inter; i++)
                                                                PixelBlend((uint32*)blitter->MoveTo(_vd.dpi.dst_ptr, i, j), 0x40FCFCFC);

                                        /* Draw area contour */
                                        if (_settings_client.gui.show_scrolling_viewport_on_map != 2) {
                                                if (t_inter == vp_scrolling_virtual_top_mask)
                                                        for (int i = x; i < x + w_inter; i += 2)
                                                                blitter->SetPixel(_vd.dpi.dst_ptr, i, y, PC_WHITE);
                                                if (b_inter == vp_scrolling_virtual_bottom_mask)
                                                        for (int i = x; i < x + w_inter; i += 2)
                                                                blitter->SetPixel(_vd.dpi.dst_ptr, i, y + h_inter, PC_WHITE);
                                                if (l_inter == vp_scrolling_virtual_left_mask)
                                                        for (int j = y; j < y + h_inter; j += 2)
                                                                blitter->SetPixel(_vd.dpi.dst_ptr, x, j, PC_WHITE);
                                                if (r_inter == vp_scrolling_virtual_right_mask)
                                                        for (int j = y; j < y + h_inter; j += 2)
                                                                blitter->SetPixel(_vd.dpi.dst_ptr, x + w_inter, j, PC_WHITE);
                                        }
                                }
                        }
                }
        }
}

uint32 *_vp_map_line; ///< Buffer for drawing the map of a viewport.
 
static void ViewportMapDrawBridgeTunnel(const ViewPort * const vp, const TunnelBridgeToMap * const tbtm, const int z,
        const bool is_tunnel, const int w, const int h, Blitter * const blitter)
{
        extern LegendAndColour _legend_land_owners[NUM_NO_COMPANY_ENTRIES + MAX_COMPANIES + 1];
        extern uint _company_to_list_pos[MAX_COMPANIES];

        TileIndex tile = tbtm->from_tile;
        const Owner o = GetTileOwner(tile);
        if (o < MAX_COMPANIES && !_legend_land_owners[_company_to_list_pos[o]].show_on_map) return;

        uint8 colour;
        if (vp->map_type == VPMT_OWNER && _settings_client.gui.use_owner_colour_for_tunnelbridge && o < MAX_COMPANIES) {
                colour = _legend_land_owners[_company_to_list_pos[o]].colour;
                colour = is_tunnel ? _darken_colour[colour] : _lighten_colour[colour];
        }
        else {
                colour = is_tunnel ? PC_BLACK : PC_VERY_LIGHT_YELLOW;
        }

        TileIndexDiff delta = TileOffsByDiagDir(GetTunnelBridgeDirection(tile));
        for (; tile != tbtm->to_tile; tile += delta) { // For each tile
                const Point pt = RemapCoords(TileX(tile) * TILE_SIZE, TileY(tile) * TILE_SIZE, z);
                const int x = UnScaleByZoomLower(pt.x - _vd.dpi.left, _vd.dpi.zoom);
                if (IsInsideMM(x, 0, w)) {
                        const int y = UnScaleByZoomLower(pt.y - _vd.dpi.top, _vd.dpi.zoom);
                        if (IsInsideMM(y, 0, h)) blitter->SetPixel(_vd.dpi.dst_ptr, x, y, colour);
                }
        }
}

/** Draw the map on a viewport. */
template <bool is_32bpp, bool show_slope>
void ViewportMapDraw(const ViewPort * const vp)
{
        assert(vp != nullptr);
        Blitter * const blitter = BlitterFactory::GetCurrentBlitter();

        SmallMapWindow::RebuildColourIndexIfNecessary();

        /* Index of colour: _green_map_heights[] contains blocks of 4 colours, say ABCD
        * For a XXXY colour block to render nicely, follow the model:
        *   line 1: ABCDABCDABCD
        *   line 2: CDABCDABCDAB
        *   line 3: ABCDABCDABCD
        * => colour_index_base's second bit is changed every new line.
        */
        const  int sx = UnScaleByZoomLower(_vd.dpi.left, _vd.dpi.zoom);
        const  int sy = UnScaleByZoomLower(_vd.dpi.top, _vd.dpi.zoom);
        const uint line_padding = 2 * (sy & 1);
        uint       colour_index_base = (sx + line_padding) & 3;

        const  int incr_a = (1 << (vp->zoom - 2)) / ZOOM_LVL_BASE;
        const  int incr_b = (1 << (vp->zoom - 1)) / ZOOM_LVL_BASE;
        const  int a = (_vd.dpi.left >> 2) / ZOOM_LVL_BASE;
        int        b = (_vd.dpi.top >> 1) / ZOOM_LVL_BASE;
        const  int w = UnScaleByZoom(_vd.dpi.width, vp->zoom);
        const  int h = UnScaleByZoom(_vd.dpi.height, vp->zoom);
        int        j = 0;

        /* Render base map. */
        do { // For each line
                int i = w;
                uint colour_index = colour_index_base;
                colour_index_base ^= 2;
                uint32 *vp_map_line_ptr32 = _vp_map_line;
                uint8 *vp_map_line_ptr8 = (uint8*)_vp_map_line;
                int c = b - a;
                int d = b + a;
                do { // For each pixel of a line
                        if (is_32bpp) {
                                *vp_map_line_ptr32 = ViewportMapGetColour<is_32bpp, show_slope>(vp, c, d, colour_index);
                                vp_map_line_ptr32++;
                        }
                        else {
                                *vp_map_line_ptr8 = (uint8)ViewportMapGetColour<is_32bpp, show_slope>(vp, c, d, colour_index);
                                vp_map_line_ptr8++;
                        }
                        colour_index = ++colour_index & 3;
                        c -= incr_a;
                        d += incr_a;
                } while (--i);
                if (is_32bpp) {
                        blitter->SetLine32(_vd.dpi.dst_ptr, 0, j, _vp_map_line, w);
                }
                else {
                        blitter->SetLine(_vd.dpi.dst_ptr, 0, j, (uint8*)_vp_map_line, w);
                }
                b += incr_b;
        } while (++j < h);

        /* Render tunnels */
        if (_settings_client.gui.show_tunnels_on_map && _vd.tunnel_to_map.Length() != 0) {
                const TunnelBridgeToMap * const tbtm_end = _vd.tunnel_to_map.End();
                for (const TunnelBridgeToMap *tbtm = _vd.tunnel_to_map.Begin(); tbtm != tbtm_end; tbtm++) { // For each tunnel
                        const int tunnel_z = GetTileZ(tbtm->from_tile) * TILE_HEIGHT;
                        const Point pt_from = RemapCoords(TileX(tbtm->from_tile) * TILE_SIZE, TileY(tbtm->from_tile) * TILE_SIZE, tunnel_z);
                        const Point pt_to = RemapCoords(TileX(tbtm->to_tile) * TILE_SIZE, TileY(tbtm->to_tile) * TILE_SIZE, tunnel_z);

                        /* check if tunnel is wholly outside redrawing area */
                        const int x_from = UnScaleByZoomLower(pt_from.x - _vd.dpi.left, _vd.dpi.zoom);
                        const int x_to = UnScaleByZoomLower(pt_to.x - _vd.dpi.left, _vd.dpi.zoom);
                        if ((x_from < 0 && x_to < 0) || (x_from > w && x_to > w)) continue;
                        const int y_from = UnScaleByZoomLower(pt_from.y - _vd.dpi.top, _vd.dpi.zoom);
                        const int y_to = UnScaleByZoomLower(pt_to.y - _vd.dpi.top, _vd.dpi.zoom);
                        if ((y_from < 0 && y_to < 0) || (y_from > h && y_to > h)) continue;

                        ViewportMapDrawBridgeTunnel(vp, tbtm, tunnel_z, true, w, h, blitter);
                }
        }

        /* Render bridges */
        if (_settings_client.gui.show_bridges_on_map && _vd.bridge_to_map.Length() != 0) {
                const TunnelBridgeToMap * const tbtm_end = _vd.bridge_to_map.End();
                for (const TunnelBridgeToMap *tbtm = _vd.bridge_to_map.Begin(); tbtm != tbtm_end; tbtm++) { // For each bridge
                        ViewportMapDrawBridgeTunnel(vp, tbtm, (GetBridgeHeight(tbtm->from_tile) - 1) * TILE_HEIGHT, false, w, h, blitter);
                }
        }
}

void ViewportDoDraw(const ViewPort *vp, int left, int top, int right, int bottom)
{
        DrawPixelInfo *old_dpi = _cur_dpi;
        _cur_dpi = &_vd.dpi;

        _vd.dpi.zoom = vp->zoom;
        int mask = ScaleByZoom(-1, vp->zoom);

        _vd.combine_sprites = SPRITE_COMBINE_NONE;

        _vd.dpi.width = (right - left) & mask;
        _vd.dpi.height = (bottom - top) & mask;
        _vd.dpi.left = left & mask;
        _vd.dpi.top = top & mask;
        _vd.dpi.pitch = old_dpi->pitch;
        _vd.last_child = nullptr;

        int x = UnScaleByZoom(_vd.dpi.left - (vp->virtual_left & mask), vp->zoom) + vp->left;
        int y = UnScaleByZoom(_vd.dpi.top - (vp->virtual_top & mask), vp->zoom) + vp->top;

        _vd.dpi.dst_ptr = BlitterFactory::GetCurrentBlitter()->MoveTo(old_dpi->dst_ptr, x - old_dpi->left, y - old_dpi->top);

        _dpi_for_text = _vd.dpi;
        _dpi_for_text.left = UnScaleByZoom(_dpi_for_text.left, _dpi_for_text.zoom);
        _dpi_for_text.top = UnScaleByZoom(_dpi_for_text.top, _dpi_for_text.zoom);
        _dpi_for_text.width = UnScaleByZoom(_dpi_for_text.width, _dpi_for_text.zoom);
        _dpi_for_text.height = UnScaleByZoom(_dpi_for_text.height, _dpi_for_text.zoom);
        _dpi_for_text.zoom = ZOOM_LVL_NORMAL;

        if (vp->zoom >= ZOOM_LVL_DRAW_MAP) {
                /* Here the rendering is like smallmap. */
                if (BlitterFactory::GetCurrentBlitter()->GetScreenDepth() == 32) {
                        if (_settings_client.gui.show_slopes_on_viewport_map) ViewportMapDraw<true, true>(vp);
                        else ViewportMapDraw<true, false>(vp);
                }
                else {
                        _pal2trsp_remap_ptr = IsTransparencySet(TO_TREES) ? GetNonSprite(GB(PALETTE_TO_TRANSPARENT, 0, PALETTE_WIDTH), ST_RECOLOUR) + 1 : nullptr;
                        if (_settings_client.gui.show_slopes_on_viewport_map) ViewportMapDraw<false, true>(vp);
                        else ViewportMapDraw<false, false>(vp);
                }
                ViewportMapDrawVehicles(&_vd.dpi);
                if (_scrolling_viewport && _settings_client.gui.show_scrolling_viewport_on_map) ViewportMapDrawScrollingViewportBox(vp);
                if (vp->zoom < ZOOM_LVL_OUT_256X) ViewportAddTownNames(&_vd.dpi);
        }
        else {
                /* Classic rendering. */
                ViewportAddLandscape();
                ViewportAddVehicles(&_vd.dpi);

                ViewportAddTownNames(&_vd.dpi);
                ViewportAddStationNames(&_vd.dpi);
                ViewportAddSigns(&_vd.dpi);

                DrawTextEffects(&_vd.dpi);

                if (_vd.tile_sprites_to_draw.Length() != 0) ViewportDrawTileSprites(&_vd.tile_sprites_to_draw);

                ParentSpriteToDraw *psd_end = _vd.parent_sprites_to_draw.End();
                for (ParentSpriteToDraw *it = _vd.parent_sprites_to_draw.Begin(); it != psd_end; it++) {
                        *_vd.parent_sprites_to_sort.Append() = it;
                }

                _vp_sprite_sorter(&_vd.parent_sprites_to_sort);
                ViewportDrawParentSprites(&_vd.parent_sprites_to_sort, &_vd.child_screen_sprites_to_draw);

                if (_draw_bounding_boxes) ViewportDrawBoundingBoxes(&_vd.parent_sprites_to_sort);
        }
        if (_draw_dirty_blocks) ViewportDrawDirtyBlocks();

        DrawPixelInfo dp = _vd.dpi;
        ZoomLevel zoom = _vd.dpi.zoom;
        dp.zoom = ZOOM_LVL_NORMAL;
        dp.width = UnScaleByZoom(dp.width, zoom);
        dp.height = UnScaleByZoom(dp.height, zoom);
        _cur_dpi = &dp;

        if (vp->overlay != nullptr && vp->overlay->GetCargoMask() != 0 && vp->overlay->GetCompanyMask() != 0) {
                /* translate to window coordinates */
                dp.left = x;
                dp.top = y;
                vp->overlay->Draw(&dp);
        }

        if (_settings_client.gui.show_vehicle_route) ViewportMapDrawVehicleRoute(vp);
        if (_vd.string_sprites_to_draw.Length() != 0) {
                /* translate to world coordinates */
                dp.left = UnScaleByZoom(_vd.dpi.left, zoom);
                dp.top = UnScaleByZoom(_vd.dpi.top, zoom);
                ViewportDrawStrings(zoom, &_vd.string_sprites_to_draw);
        }
        if (_settings_client.gui.show_vehicle_route_steps) ViewportDrawVehicleRouteSteps(vp);
        ViewportDrawPlans(vp);

        _cur_dpi = old_dpi;

        _vd.bridge_to_map.Clear();
        _vd.string_sprites_to_draw.Clear();
        _vd.tile_sprites_to_draw.Clear();
        _vd.parent_sprites_to_draw.Clear();
        _vd.parent_sprites_to_sort.Clear();
        _vd.child_screen_sprites_to_draw.Clear();
}

/**
 * Make sure we don't draw a too big area at a time.
 * If we do, the sprite sorter will run into major performance problems and the sprite memory may overflow.
 */
static void ViewportDrawChk(const ViewPort *vp, int left, int top, int right, int bottom)
{
        if ((vp->zoom < ZOOM_LVL_DRAW_MAP) && (ScaleByZoom(bottom - top, vp->zoom) * ScaleByZoom(right - left, vp->zoom) > 180000 * ZOOM_LVL_BASE * ZOOM_LVL_BASE)) {
                if ((bottom - top) > (right - left)) {
                        int t = (top + bottom) >> 1;
                        ViewportDrawChk(vp, left, top, right, t);
                        ViewportDrawChk(vp, left, t, right, bottom);
                } else {
                        int t = (left + right) >> 1;
                        ViewportDrawChk(vp, left, top, t, bottom);
                        ViewportDrawChk(vp, t, top, right, bottom);
                }
        } else {
                ViewportDoDraw(vp,
                        ScaleByZoom(left - vp->left, vp->zoom) + vp->virtual_left,
                        ScaleByZoom(top - vp->top, vp->zoom) + vp->virtual_top,
                        ScaleByZoom(right - vp->left, vp->zoom) + vp->virtual_left,
                        ScaleByZoom(bottom - vp->top, vp->zoom) + vp->virtual_top
                );
        }
}

static inline void ViewportDraw(const ViewPort *vp, int left, int top, int right, int bottom)
{
        if (right <= vp->left || bottom <= vp->top) return;

        if (left >= vp->left + vp->width) return;

        if (left < vp->left) left = vp->left;
        if (right > vp->left + vp->width) right = vp->left + vp->width;

        if (top >= vp->top + vp->height) return;

        if (top < vp->top) top = vp->top;
        if (bottom > vp->top + vp->height) bottom = vp->top + vp->height;

        ViewportDrawChk(vp, left, top, right, bottom);
}

/**
 * Draw the viewport of this window.
 */
void Window::DrawViewport() const
{
        DrawPixelInfo *dpi = _cur_dpi;

        dpi->left += this->left;
        dpi->top += this->top;

        ViewportDraw(this->viewport, dpi->left, dpi->top, dpi->left + dpi->width, dpi->top + dpi->height);

        dpi->left -= this->left;
        dpi->top -= this->top;
}

/**
 * Continue criteria for the SearchMapEdge function.
 * @param iter       Value to check.
 * @param iter_limit Maximum value for the iter
 * @param sy         Screen y coordinate calculated for the tile at hand
 * @param sy_limit   Limit to the screen y coordinate
 * @return True when we should continue searching.
 */
typedef bool ContinueMapEdgeSearch(int iter, int iter_limit, int sy, int sy_limit);

/** Continue criteria for searching a no-longer-visible tile in negative direction, starting at some tile. */
static inline bool ContinueLowerMapEdgeSearch(int iter, int iter_limit, int sy, int sy_limit) { return iter > 0          && sy > sy_limit; }
/** Continue criteria for searching a no-longer-visible tile in positive direction, starting at some tile. */
static inline bool ContinueUpperMapEdgeSearch(int iter, int iter_limit, int sy, int sy_limit) { return iter < iter_limit && sy < sy_limit; }

/**
 * Searches, starting at the given tile, by applying the given offset to iter, for a no longer visible tile.
 * The whole sense of this function is keeping the to-be-written code small, thus it is a little bit abstracted
 * so the same function can be used for both the X and Y locations. As such a reference to one of the elements
 * in curr_tile was needed.
 * @param curr_tile  A tile
 * @param iter       Reference to either the X or Y of curr_tile.
 * @param iter_limit Upper search limit for the iter value.
 * @param offset     Search in steps of this size
 * @param sy_limit   Search limit to be passed to the criteria
 * @param continue_criteria Search as long as this criteria is true
 * @return The final value of iter.
 */
static int SearchMapEdge(Point &curr_tile, int &iter, int iter_limit, int offset, int sy_limit, ContinueMapEdgeSearch continue_criteria)
{
        int sy;
        do {
                iter = Clamp(iter + offset, 0, iter_limit);
                sy = GetViewportY(curr_tile);
        } while (continue_criteria(iter, iter_limit, sy, sy_limit));

        return iter;
}

/**
 * Determine the clamping of either the X or Y coordinate to the map.
 * @param curr_tile   A tile
 * @param iter        Reference to either the X or Y of curr_tile.
 * @param iter_limit  Upper search limit for the iter value.
 * @param start       Start value for the iteration.
 * @param other_ref   Reference to the opposite axis in curr_tile than of iter.
 * @param other_value Start value for of the opposite axis
 * @param vp_value    Value of the viewport location in the opposite axis as for iter.
 * @param other_limit Limit for the other value, so if iter is X, then other_limit is for Y.
 * @param vp_top      Top of the viewport.
 * @param vp_bottom   Bottom of the viewport.
 * @return Clamped version of vp_value.
 */
static inline int ClampXYToMap(Point &curr_tile, int &iter, int iter_limit, int start, int &other_ref, int other_value, int vp_value, int other_limit, int vp_top, int vp_bottom)
{
        bool upper_edge = other_value < _settings_game.construction.max_heightlevel / 4;

        /*
         * First get an estimate of the tiles relevant for us at that edge.  Relevant in the sense
         * "at least close to the visible area". Thus, we don't look at exactly each tile, inspecting
         * e.g. every tenth should be enough. After all, the desired screen limit is set such that
         * the bordermost tiles are painted in the middle of the screen when one hits the limit,
         * i.e. it is no harm if there is some small error in that calculation
         */

        other_ref = upper_edge ? 0 : other_limit;
        iter = start;
        int min_iter = SearchMapEdge(curr_tile, iter, iter_limit, upper_edge ? -10 : +10, vp_top,    upper_edge ? ContinueLowerMapEdgeSearch : ContinueUpperMapEdgeSearch);
        iter = start;
        int max_iter = SearchMapEdge(curr_tile, iter, iter_limit, upper_edge ? +10 : -10, vp_bottom, upper_edge ? ContinueUpperMapEdgeSearch : ContinueLowerMapEdgeSearch);

        max_iter = min(max_iter + _settings_game.construction.max_heightlevel / 4, iter_limit);
        min_iter = min(min_iter, max_iter);

        /* Now, calculate the highest heightlevel of these tiles. Again just as an estimate. */
        int max_heightlevel_at_edge = 0;
        for (iter = min_iter; iter <= max_iter; iter += 10) {
                max_heightlevel_at_edge = max(max_heightlevel_at_edge, (int)TileHeight(TileXY(curr_tile.x, curr_tile.y)));
        }

        /* Based on that heightlevel, calculate the limit. For the upper edge a tile with height zero would
         * get a limit of zero, on the other side it depends on the number of tiles along the axis. */
        return upper_edge ?
                        max(vp_value, -max_heightlevel_at_edge * (int)(TILE_HEIGHT * 2 * ZOOM_LVL_BASE)) :
                        min(vp_value, (other_limit * TILE_SIZE * 4 - max_heightlevel_at_edge * TILE_HEIGHT * 2) * ZOOM_LVL_BASE);
}

static inline void ClampViewportToMap(const ViewPort *vp, int &x, int &y)
{
        int original_y = y;

        /* Centre of the viewport is hot spot */
        x += vp->virtual_width / 2;
        y += vp->virtual_height / 2;

        /* Convert viewport coordinates to map coordinates
         * Calculation is scaled by 4 to avoid rounding errors */
        int vx = -x + y * 2;
        int vy =  x + y * 2;

        /* Find out which tile corresponds to (vx,vy) if one assumes height zero.  The cast is necessary to prevent C++ from
         * converting the result to an uint, which gives an overflow instead of a negative result... */
        int tx = vx / (int)(TILE_SIZE * 4 * ZOOM_LVL_BASE);
        int ty = vy / (int)(TILE_SIZE * 4 * ZOOM_LVL_BASE);

        Point curr_tile;
        vx = ClampXYToMap(curr_tile, curr_tile.y, MapMaxY(), ty, curr_tile.x, tx, vx, MapMaxX(), original_y, original_y + vp->virtual_height);
        vy = ClampXYToMap(curr_tile, curr_tile.x, MapMaxX(), tx, curr_tile.y, ty, vy, MapMaxY(), original_y, original_y + vp->virtual_height);

        /* Convert map coordinates to viewport coordinates */
        x = (-vx + vy) / 2;
        y = ( vx + vy) / 4;

        /* Remove centering */
        x -= vp->virtual_width / 2;
        y -= vp->virtual_height / 2;
}

/**
 * Update the viewport position being displayed.
 * @param w %Window owning the viewport.
 */
void UpdateViewportPosition(Window *w)
{
        const ViewPort *vp = w->viewport;

        if (w->viewport->follow_vehicle != INVALID_VEHICLE) {
                const Vehicle *veh = Vehicle::Get(w->viewport->follow_vehicle);
                Point pt = MapXYZToViewport(vp, veh->x_pos, veh->y_pos, veh->z_pos);

                w->viewport->scrollpos_x = pt.x;
                w->viewport->scrollpos_y = pt.y;
                SetViewportPosition(w, pt.x, pt.y);
        } else {
                /* Ensure the destination location is within the map */
                ClampViewportToMap(vp, w->viewport->dest_scrollpos_x, w->viewport->dest_scrollpos_y);

                int delta_x = w->viewport->dest_scrollpos_x - w->viewport->scrollpos_x;
                int delta_y = w->viewport->dest_scrollpos_y - w->viewport->scrollpos_y;

                bool update_overlay = false;
                if (delta_x != 0 || delta_y != 0) {
                        if (_settings_client.gui.smooth_scroll) {
                                int max_scroll = ScaleByMapSize1D(512 * ZOOM_LVL_BASE);
                                /* Not at our desired position yet... */
                                w->viewport->scrollpos_x += Clamp(delta_x / 4, -max_scroll, max_scroll);
                                w->viewport->scrollpos_y += Clamp(delta_y / 4, -max_scroll, max_scroll);
                        } else {
                                w->viewport->scrollpos_x = w->viewport->dest_scrollpos_x;
                                w->viewport->scrollpos_y = w->viewport->dest_scrollpos_y;
                        }
                        update_overlay = (w->viewport->scrollpos_x == w->viewport->dest_scrollpos_x &&
                                                                w->viewport->scrollpos_y == w->viewport->dest_scrollpos_y);
                }

                ClampViewportToMap(vp, w->viewport->scrollpos_x, w->viewport->scrollpos_y);

                if (_scrolling_viewport == w && _settings_client.gui.show_scrolling_viewport_on_map) {
                        const int gap = ScaleByZoom(1, ZOOM_LVL_MAX);

                        int lr_low = vp->virtual_left;
                        int lr_hi = w->viewport->scrollpos_x;
                        if (lr_low > lr_hi) Swap(lr_low, lr_hi);
                        int right = lr_hi + vp->virtual_width + gap;

                        int tb_low = vp->virtual_top;
                        int tb_hi = w->viewport->scrollpos_y;
                        if (tb_low > tb_hi) Swap(tb_low, tb_hi);
                        int bottom = tb_hi + vp->virtual_height + gap;

                        MarkAllViewportMapsDirty(lr_low, tb_low, right, bottom);
                }

                SetViewportPosition(w, w->viewport->scrollpos_x, w->viewport->scrollpos_y);
                if (update_overlay) RebuildViewportOverlay(w);
        }
}

/**
 * Marks a viewport as dirty for repaint if it displays (a part of) the area the needs to be repainted.
 * @param vp     The viewport to mark as dirty
 * @param left   Left edge of area to repaint
 * @param top    Top edge of area to repaint
 * @param right  Right edge of area to repaint
 * @param bottom Bottom edge of area to repaint
 * @ingroup dirty
 */
static void MarkViewportDirty(const ViewPort * const vp, int left, int top, int right, int bottom)
{
        /* Rounding wrt. zoom-out level */
        right  += (1 << vp->zoom) - 1;
        bottom += (1 << vp->zoom) - 1;

        right -= vp->virtual_left;
        if (right <= 0) return;

        bottom -= vp->virtual_top;
        if (bottom <= 0) return;

        left = max(0, left - vp->virtual_left);

        if (left >= vp->virtual_width) return;

        top = max(0, top - vp->virtual_top);

        if (top >= vp->virtual_height) return;

        SetDirtyBlocks(
                UnScaleByZoomLower(left, vp->zoom) + vp->left,
                UnScaleByZoomLower(top, vp->zoom) + vp->top,
                UnScaleByZoom(right, vp->zoom) + vp->left + 1,
                UnScaleByZoom(bottom, vp->zoom) + vp->top + 1
        );
}

/**
 * Mark all viewports that display an area as dirty (in need of repaint).
 * @param left   Left   edge of area to repaint. (viewport coordinates, that is wrt. #ZOOM_LVL_NORMAL)
 * @param top    Top    edge of area to repaint. (viewport coordinates, that is wrt. #ZOOM_LVL_NORMAL)
 * @param right  Right  edge of area to repaint. (viewport coordinates, that is wrt. #ZOOM_LVL_NORMAL)
 * @param bottom Bottom edge of area to repaint. (viewport coordinates, that is wrt. #ZOOM_LVL_NORMAL)
 * @param mark_dirty_if_zoomlevel_is_below To tell if an update is relevant or not (for example, animations in map mode are not)
 * @ingroup dirty
 */
void MarkAllViewportsDirty(int left, int top, int right, int bottom, const ZoomLevel mark_dirty_if_zoomlevel_is_below)
{
        for (const ViewPort * const vp : _viewport_window_cache) {
                if (vp->zoom >= mark_dirty_if_zoomlevel_is_below) continue;
                MarkViewportDirty(vp, left, top, right, bottom);
        }
}
 
static void MarkRouteStepDirty(RouteStepsMap::const_iterator cit)
{
        const uint size = cit->second.size() > max_rank_order_type_count ? 1 : (uint)cit->second.size();
        MarkRouteStepDirty(cit->first, size);
}

static void MarkRouteStepDirty(const TileIndex tile, uint order_nr)
{
        assert(tile != INVALID_TILE);
        const Point pt = RemapCoords2(TileX(tile) * TILE_SIZE + TILE_SIZE / 2, TileY(tile) * TILE_SIZE + TILE_SIZE / 2);
        const int char_height = GetCharacterHeight(FS_SMALL) + 1;
        for (const ViewPort * const vp : _viewport_window_cache) {
                const int half_width = ScaleByZoom((_vp_route_step_width / 2) + 1, vp->zoom);
                const int height = ScaleByZoom(_vp_route_step_height_top + char_height * order_nr + _vp_route_step_height_bottom, vp->zoom);
                MarkViewportDirty(vp, pt.x - half_width, pt.y - height, pt.x + half_width, pt.y);
        }
}

void MarkAllRouteStepsDirty(const Vehicle *veh)
{
        ViewportPrepareVehicleRouteSteps(veh);
        for (RouteStepsMap::const_iterator cit = _vp_route_steps.begin(); cit != _vp_route_steps.end(); cit++) {
                MarkRouteStepDirty(cit);
        }
        _vp_route_steps_last_mark_dirty.swap(_vp_route_steps);
        _vp_route_steps.clear();
}

/**
 * Mark all viewports in map mode that display an area as dirty (in need of repaint).
 * @param left   Left edge of area to repaint
 * @param top    Top edge of area to repaint
 * @param right  Right edge of area to repaint
 * @param bottom Bottom edge of area to repaint
 * @ingroup dirty
 */
void MarkAllViewportMapsDirty(int left, int top, int right, int bottom)
{
        Window *w;
        FOR_ALL_WINDOWS_FROM_BACK(w) {
                const ViewPort *vp = w->viewport;
                if (vp != nullptr && vp->zoom >= ZOOM_LVL_DRAW_MAP) {
                        assert(vp->width != 0);
                        MarkViewportDirty(vp, left, top, right, bottom);
                }
        }
}

void ConstrainAllViewportsZoom()
{
        Window *w;
        FOR_ALL_WINDOWS_FROM_FRONT(w) {
                if (w->viewport == nullptr) continue;

                ZoomLevel zoom = static_cast<ZoomLevel>(Clamp(w->viewport->zoom, _settings_client.gui.zoom_min, _settings_client.gui.zoom_max));
                if (zoom != w->viewport->zoom) {
                        while (w->viewport->zoom < zoom) DoZoomInOutWindow(ZOOM_OUT, w);
                        while (w->viewport->zoom > zoom) DoZoomInOutWindow(ZOOM_IN, w);
                }
        }
}

/**
 * Mark a tile given by its index dirty for repaint.
 * @param tile The tile to mark dirty.
 * @param bridge_level_offset Height of bridge on tile to also mark dirty. (Height level relative to north corner.)
 * @ingroup dirty
 */
void MarkTileDirtyByTile(const TileIndex tile, const ZoomLevel mark_dirty_if_zoomlevel_is_below, int bridge_level_offset)
{
        Point pt = RemapCoords(TileX(tile) * TILE_SIZE, TileY(tile) * TILE_SIZE, TilePixelHeight(tile));
        MarkAllViewportsDirty(
                pt.x - MAX_TILE_EXTENT_LEFT,
                pt.y - MAX_TILE_EXTENT_TOP - ZOOM_LVL_BASE * TILE_HEIGHT * bridge_level_offset,
                pt.x + MAX_TILE_EXTENT_RIGHT,
                pt.y + MAX_TILE_EXTENT_BOTTOM,
                mark_dirty_if_zoomlevel_is_below);
}

/**
 * Mark a (virtual) tile outside the map dirty for repaint.
 * @param x Tile X position.
 * @param y Tile Y position.
 * @ingroup dirty
 */
void MarkTileDirtyByTileOutsideMap(int x, int y)
{
        Point pt = RemapCoords(x * TILE_SIZE, y * TILE_SIZE, TilePixelHeightOutsideMap(x, y));
        MarkAllViewportsDirty(
                        pt.x - MAX_TILE_EXTENT_LEFT,
                        pt.y, // no buildings outside of map
                        pt.x + MAX_TILE_EXTENT_RIGHT,
                        pt.y + MAX_TILE_EXTENT_BOTTOM);
}

void MarkTileLineDirty(const TileIndex from_tile, const TileIndex to_tile)
{
        assert(from_tile != INVALID_TILE);
        assert(to_tile != INVALID_TILE);

        const Point from_pt = RemapCoords2(TileX(from_tile) * TILE_SIZE + TILE_SIZE / 2, TileY(from_tile) * TILE_SIZE + TILE_SIZE / 2);
        const Point to_pt = RemapCoords2(TileX(to_tile) * TILE_SIZE + TILE_SIZE / 2, TileY(to_tile) * TILE_SIZE + TILE_SIZE / 2);

        const int block_radius = 20;

        int x1 = from_pt.x / block_radius;
        int y1 = from_pt.y / block_radius;
        const int x2 = to_pt.x / block_radius;
        const int y2 = to_pt.y / block_radius;

        /* http://en.wikipedia.org/wiki/Bresenham%27s_line_algorithm#Simplification */
        const int dx = abs(x2 - x1);
        const int dy = abs(y2 - y1);
        const int sx = (x1 < x2) ? 1 : -1;
        const int sy = (y1 < y2) ? 1 : -1;
        int err = dx - dy;
        for (;;) {
                MarkAllViewportsDirty(
                                (x1 - 1) * block_radius,
                                (y1 - 1) * block_radius,
                                (x1 + 1) * block_radius,
                                (y1 + 1) * block_radius,
                                ZOOM_LVL_END
                );
                if (x1 == x2 && y1 == y2) break;
                const int e2 = 2 * err;
                if (e2 > -dy) {
                        err -= dy;
                        x1 += sx;
                }
                if (e2 < dx) {
                        err += dx;
                        y1 += sy;
                }
        }
}

static void MarkRoutePathsDirty(const std::vector<DrawnPathRouteTileLine> &lines)
{
        for (std::vector<DrawnPathRouteTileLine>::const_iterator it = lines.begin(); it != lines.end(); ++it) {
                MarkTileLineDirty(it->from_tile, it->to_tile);
        }
}

void MarkAllRoutePathsDirty(const Vehicle *veh)
{
        switch (_settings_client.gui.show_vehicle_route) {
        case 0: // No
                return;

        case 1: // Simple
                ViewportMapPrepareVehicleRoute(veh);
                break;
        }

        for (const auto &iter : _vp_route_paths) {
                MarkTileLineDirty(iter.from_tile, iter.to_tile);
        }
        
        _vp_route_paths_last_mark_dirty.swap(_vp_route_paths);
        _vp_route_paths.clear();
}

/**
 * Mark all tiles in a given bridge by their index dirty for repaint.
 * @param tile The start tile of the bridge to mark dirty.
 * @param tile The end tile of the bridge to mark dirty.
 * @ingroup dirty
 */
void MarkBridgeTilesDirtyByTile(TileIndex tile_start, TileIndex tile_end)
{
        MarkTileDirtyByTile(tile_start);
        MarkTileDirtyByTile(tile_end);

        Axis direction;
        if (TileX(tile_start) == TileX(tile_end)) {
                direction = AXIS_Y;
        } else if (TileY(tile_start) == TileY(tile_end)) {
                direction = AXIS_X;
        }

        if (tile_end < tile_start) Swap(tile_start, tile_end);

        TileIndexDiff delta = (direction == AXIS_X ? TileDiffXY(1, 0) : TileDiffXY(0, 1));
        for (TileIndex tile = tile_start; tile <= tile_end; tile += delta) {
                MarkTileDirtyByTile(tile);
        }
}
 
void CheckMarkDirtyFocusedRoutePaths(const Vehicle *veh)
{
        const Vehicle *focused_veh = GetVehicleFromWindow(_focused_window);
        if (focused_veh && veh == focused_veh) {
                MarkAllRoutePathsDirty(veh);
                MarkAllRouteStepsDirty(veh);
        }
}

/**
 * Marks the selected tiles as dirty.
 *
 * This function marks the selected tiles as dirty for repaint
 *
 * @ingroup dirty
 */
static void SetSelectionTilesDirty()
{
        int x_size = _thd.size.x;
        int y_size = _thd.size.y;

        if (!_thd.diagonal) { // Selecting in a straight rectangle (or a single square)
                int x_start = _thd.pos.x;
                int y_start = _thd.pos.y;

                if (_thd.outersize.x != 0 || _thd.outersize.y != 0) {
                        x_size  += _thd.outersize.x;
                        x_start += _thd.offs.x;
                        y_size  += _thd.outersize.y;
                        y_start += _thd.offs.y;
                }

                x_size -= TILE_SIZE;
                y_size -= TILE_SIZE;

                assert(x_size >= 0);
                assert(y_size >= 0);

                int x_end = Clamp(x_start + x_size, 0, MapSizeX() * TILE_SIZE - TILE_SIZE);
                int y_end = Clamp(y_start + y_size, 0, MapSizeY() * TILE_SIZE - TILE_SIZE);

                x_start = Clamp(x_start, 0, MapSizeX() * TILE_SIZE - TILE_SIZE);
                y_start = Clamp(y_start, 0, MapSizeY() * TILE_SIZE - TILE_SIZE);

                /* make sure everything is multiple of TILE_SIZE */
                assert((x_end | y_end | x_start | y_start) % TILE_SIZE == 0);

                /* How it works:
                 * Suppose we have to mark dirty rectangle of 3x4 tiles:
                 *   x
                 *  xxx
                 * xxxxx
                 *  xxxxx
                 *   xxx
                 *    x
                 * This algorithm marks dirty columns of tiles, so it is done in 3+4-1 steps:
                 * 1)  x     2)  x
                 *    xxx       Oxx
                 *   Oxxxx     xOxxx
                 *    xxxxx     Oxxxx
                 *     xxx       xxx
                 *      x         x
                 * And so forth...
                 */

                int top_x = x_end; // coordinates of top dirty tile
                int top_y = y_start;
                int bot_x = top_x; // coordinates of bottom dirty tile
                int bot_y = top_y;

                do {
                        /* topmost dirty point */
                        TileIndex top_tile = TileVirtXY(top_x, top_y);
                        Point top = RemapCoords(top_x, top_y, GetTileMaxPixelZ(top_tile));

                        /* bottommost point */
                        TileIndex bottom_tile = TileVirtXY(bot_x, bot_y);
                        Point bot = RemapCoords(bot_x + TILE_SIZE, bot_y + TILE_SIZE, GetTilePixelZ(bottom_tile)); // bottommost point

                        /* the 'x' coordinate of 'top' and 'bot' is the same (and always in the same distance from tile middle),
                         * tile height/slope affects only the 'y' on-screen coordinate! */

                        int l = top.x - TILE_PIXELS * ZOOM_LVL_BASE; // 'x' coordinate of left   side of the dirty rectangle
                        int t = top.y;                               // 'y' coordinate of top    side of the dirty rectangle
                        int r = top.x + TILE_PIXELS * ZOOM_LVL_BASE; // 'x' coordinate of right  side of the dirty rectangle
                        int b = bot.y;                               // 'y' coordinate of bottom side of the dirty rectangle

                        static const int OVERLAY_WIDTH = 4 * ZOOM_LVL_BASE; // part of selection sprites is drawn outside the selected area (in particular: terraforming)

                        /* For halftile foundations on SLOPE_STEEP_S the sprite extents some more towards the top */
                        MarkAllViewportsDirty(l - OVERLAY_WIDTH, t - OVERLAY_WIDTH - TILE_HEIGHT * ZOOM_LVL_BASE, r + OVERLAY_WIDTH, b + OVERLAY_WIDTH);

                        /* haven't we reached the topmost tile yet? */
                        if (top_x != x_start) {
                                top_x -= TILE_SIZE;
                        } else {
                                top_y += TILE_SIZE;
                        }

                        /* the way the bottom tile changes is different when we reach the bottommost tile */
                        if (bot_y != y_end) {
                                bot_y += TILE_SIZE;
                        } else {
                                bot_x -= TILE_SIZE;
                        }
                } while (bot_x >= top_x);
        } else { // Selecting in a 45 degrees rotated (diagonal) rectangle.
                /* a_size, b_size describe a rectangle with rotated coordinates */
                int a_size = x_size + y_size, b_size = x_size - y_size;

                int interval_a = a_size < 0 ? -(int)TILE_SIZE : (int)TILE_SIZE;
                int interval_b = b_size < 0 ? -(int)TILE_SIZE : (int)TILE_SIZE;

                for (int a = -interval_a; a != a_size + interval_a; a += interval_a) {
                        for (int b = -interval_b; b != b_size + interval_b; b += interval_b) {
                                uint x = (_thd.pos.x + (a + b) / 2) / TILE_SIZE;
                                uint y = (_thd.pos.y + (a - b) / 2) / TILE_SIZE;

                                if (x < MapMaxX() && y < MapMaxY()) {
                                        MarkTileDirtyByTile(TileXY(x, y));
                                }
                        }
                }
        }
}


void SetSelectionRed(bool b)
{
        _thd.make_square_red = b;
        SetSelectionTilesDirty();
}

/**
 * Test whether a sign is below the mouse
 * @param vp the clicked viewport
 * @param x X position of click
 * @param y Y position of click
 * @param sign the sign to check
 * @return true if the sign was hit
 */
static bool CheckClickOnViewportSign(const ViewPort *vp, int x, int y, const ViewportSign *sign)
{
        bool small = (vp->zoom >= ZOOM_LVL_OUT_16X);
        int sign_half_width = ScaleByZoom((small ? sign->width_small : sign->width_normal) / 2, vp->zoom);
        int sign_height = ScaleByZoom(VPSM_TOP + (small ? FONT_HEIGHT_SMALL : FONT_HEIGHT_NORMAL) + VPSM_BOTTOM, vp->zoom);

        x = ScaleByZoom(x - vp->left, vp->zoom) + vp->virtual_left;
        y = ScaleByZoom(y - vp->top, vp->zoom) + vp->virtual_top;

        return y >= sign->top && y < sign->top + sign_height &&
                        x >= sign->center - sign_half_width && x < sign->center + sign_half_width;
}

static bool CheckClickOnTown(const ViewPort *vp, int x, int y)
{
        if (!HasBit(_display_opt, DO_SHOW_TOWN_NAMES)) return false;

        const Town *t;
        FOR_ALL_TOWNS(t) {
                if (CheckClickOnViewportSign(vp, x, y, &t->cache.sign)) {
                        ShowTownViewWindow(t->index);
                        return true;
                }
        }

        return false;
}

static bool CheckClickOnStation(const ViewPort *vp, int x, int y)
{
        if (!(HasBit(_display_opt, DO_SHOW_STATION_NAMES) || HasBit(_display_opt, DO_SHOW_WAYPOINT_NAMES)) || IsInvisibilitySet(TO_SIGNS)) return false;

        const BaseStation *st;
        FOR_ALL_BASE_STATIONS(st) {
                if (!IsStationSignVisible(st)) continue;

                if (CheckClickOnViewportSign(vp, x, y, &st->sign)) {
                        if (Station::IsExpected(st)) {
                                ShowStationViewWindow(st->index);
                        } else {
                                ShowWaypointWindow(Waypoint::From(st));
                        }
                        return true;
                }
        }

        return false;
}


static bool CheckClickOnSign(const ViewPort *vp, int x, int y)
{
        /* Signs are turned off, or they are transparent and invisibility is ON, or company is a spectator */
        if (!HasBit(_display_opt, DO_SHOW_SIGNS) || IsInvisibilitySet(TO_SIGNS) || _local_company == COMPANY_SPECTATOR) return false;

        const Sign *si;
        FOR_ALL_SIGNS(si) {
                /* If competitor signs are hidden, don't check signs that aren't owned by local company */
                if (!HasBit(_display_opt, DO_SHOW_COMPETITOR_SIGNS) && _local_company != si->owner && si->owner != OWNER_DEITY) continue;
                if (si->owner == OWNER_DEITY && _game_mode != GM_EDITOR) continue;

                if (CheckClickOnViewportSign(vp, x, y, &si->sign)) {
                        HandleClickOnSign(si);
                        return true;
                }
        }

        return false;
}


static bool CheckClickOnLandscape(const ViewPort *vp, int x, int y)
{
        Point pt = TranslateXYToTileCoord(vp, x, y);
 
        _tile_fract_coords.x = pt.x & TILE_UNIT_MASK;
        _tile_fract_coords.y = pt.y & TILE_UNIT_MASK;

        if (pt.x != -1) return ClickTile(TileVirtXY(pt.x, pt.y));
        return true;
}

static void PlaceObject()
{
        Point pt;
        Window *w;

        pt = GetTileBelowCursor();
        if (pt.x == -1) return;

        if ((_thd.place_mode & HT_DRAG_MASK) == HT_POINT) {
                pt.x += TILE_SIZE / 2;
                pt.y += TILE_SIZE / 2;
        }

        _tile_fract_coords.x = pt.x & TILE_UNIT_MASK;
        _tile_fract_coords.y = pt.y & TILE_UNIT_MASK;

        w = _thd.GetCallbackWnd();
        if (w != nullptr) w->OnPlaceObject(pt, TileVirtXY(pt.x, pt.y));
}

bool HandleViewportDoubleClicked(Window *w, int x, int y)
{
        ViewPort *vp = w->viewport;
        if (vp->zoom < ZOOM_LVL_DRAW_MAP) return false;

        switch (_settings_client.gui.action_when_viewport_map_is_dblclicked) {
        case 0: // Do nothing
                return false;
        case 1: // Zoom in main viewport
                while (vp->zoom != ZOOM_LVL_VIEWPORT)
                        ZoomInOrOutToCursorWindow(true, w);
                return true;
        case 2: // Open an extra viewport
                ShowExtraViewPortWindowForTileUnderCursor();
                return true;
        default:
                return false;
        }
}

bool HandleViewportClicked(const ViewPort *vp, int x, int y, bool double_click)
{
        /* No click in smallmap mode except for plan making. */
        if (vp->zoom >= ZOOM_LVL_DRAW_MAP && !(_thd.place_mode == HT_POINT && _thd.select_proc == DDSP_DRAW_PLANLINE)) return true;

        const Vehicle *v = CheckClickOnVehicle(vp, x, y);

        if (_thd.place_mode & HT_VEHICLE) {
                if (v != nullptr && VehicleClicked(v)) return true;
        }

        /* Vehicle placement mode already handled above. */
        if ((_thd.place_mode & HT_DRAG_MASK) != HT_NONE) {
                if (_thd.place_mode & HT_POLY) {
                        /* In polyline mode double-clicking on a single white line, finishes current polyline.
                         * If however the user double-clicks on a line that has a white and a blue section,
                         * both lines (white and blue) will be constructed consecutively. */
                        static bool stop_snap_on_double_click = false;
                        if (double_click && stop_snap_on_double_click) {
                                SetRailSnapMode(RSM_NO_SNAP);
                                return true;
                        }
                        stop_snap_on_double_click = !(_thd.drawstyle & HT_LINE) || (_thd.dir2 == HT_DIR_END);
                }

                PlaceObject();
                return true;
        }

        if (CheckClickOnTown(vp, x, y)) return true;
        if (CheckClickOnStation(vp, x, y)) return true;
        if (CheckClickOnSign(vp, x, y)) return true;
        bool result = CheckClickOnLandscape(vp, x, y);

        if (v != nullptr) {
                DEBUG(misc, 2, "Vehicle %d (index %d) at %p", v->unitnumber, v->index, v);
                if (IsCompanyBuildableVehicleType(v)) {
                        v = v->First();
                        WindowClass wc = _thd.GetCallbackWnd()->window_class;
                        if (_ctrl_pressed && v->owner == _local_company) {
                                StartStopVehicle(v, true);
                        } else if ( wc != WC_CREATE_TEMPLATE && wc != WC_TEMPLATEGUI_MAIN) {
                                ShowVehicleViewWindow(v);
                        }
                }
                return true;
        }
        return result;
}
 
void HandleViewportToolTip(Window *w, int x, int y)
{
        const ViewportData *vp = w->viewport;
        if (vp == nullptr || _game_mode == GM_MENU || HasModalProgress()) return;

        TooltipCloseCondition close_cond = (_settings_client.gui.hover_delay_ms == 0) ? TCC_RIGHT_CLICK : TCC_HOVER;

        const BaseStation *st;
        FOR_ALL_BASE_STATIONS(st) {
                if (IsStationSignVisible(st) && CheckClickOnViewportSign(vp, x, y, &st->sign)) {
                        char tip[DRAW_STRING_BUFFER] = "";
                        GetTileTooltipsForStation(st->index, tip, lastof(tip));
                        GuiShowTooltips(w, tip, close_cond);
                        return;
                }
        }

        Point tile = TranslateXYToTileCoord(vp, x, y, false);
        if (IsInsideMM(tile.x, 0, MapMaxX() * TILE_SIZE) && IsInsideMM(tile.y, 0, MapMaxY() * TILE_SIZE)) {
                GuiShowTooltipsForTile(w, TileVirtXY(tile.x, tile.y), close_cond);
                return;
        }

        DeleteWindowById(WC_TOOLTIPS, 0); // close old tooltips window as now hovering this viewport
}

void RebuildViewportOverlay(Window *w)
{
        if (w->viewport->overlay != nullptr &&
                        w->viewport->overlay->GetCompanyMask() != 0 &&
                        w->viewport->overlay->GetCargoMask() != 0) {
                w->viewport->overlay->RebuildCache();
                w->SetDirty();
        }
}

/**
 * Scrolls the viewport in a window to a given location.
 * @param x       Desired x location of the map to scroll to (world coordinate).
 * @param y       Desired y location of the map to scroll to (world coordinate).
 * @param z       Desired z location of the map to scroll to (world coordinate). Use \c -1 to scroll to the height of the map at the \a x, \a y location.
 * @param w       %Window containing the viewport.
 * @param instant Jump to the location instead of slowly moving to it.
 * @return Destination of the viewport was changed (to activate other actions when the viewport is already at the desired position).
 */
bool ScrollWindowTo(int x, int y, int z, Window *w, bool instant)
{
        /* The slope cannot be acquired outside of the map, so make sure we are always within the map. */
        if (z == -1) {
                if ( x >= 0 && x <= (int)MapSizeX() * (int)TILE_SIZE - 1
                                && y >= 0 && y <= (int)MapSizeY() * (int)TILE_SIZE - 1) {
                        z = GetSlopePixelZ(x, y);
                } else {
                        z = TileHeightOutsideMap(x / (int)TILE_SIZE, y / (int)TILE_SIZE);
                }
        }

        Point pt = MapXYZToViewport(w->viewport, x, y, z);
        w->viewport->follow_vehicle = INVALID_VEHICLE;

        if (w->viewport->dest_scrollpos_x == pt.x && w->viewport->dest_scrollpos_y == pt.y) return false;

        if (instant) {
                w->viewport->scrollpos_x = pt.x;
                w->viewport->scrollpos_y = pt.y;
                RebuildViewportOverlay(w);
        }

        w->viewport->dest_scrollpos_x = pt.x;
        w->viewport->dest_scrollpos_y = pt.y;
        return true;
}

/**
 * Scrolls the viewport in a window to a given location.
 * @param tile    Desired tile to center on.
 * @param w       %Window containing the viewport.
 * @param instant Jump to the location instead of slowly moving to it.
 * @return Destination of the viewport was changed (to activate other actions when the viewport is already at the desired position).
 */
bool ScrollWindowToTile(TileIndex tile, Window *w, bool instant)
{
        return ScrollWindowTo(TileX(tile) * TILE_SIZE, TileY(tile) * TILE_SIZE, -1, w, instant);
}

/**
 * Scrolls the viewport of the main window to a given location.
 * @param tile    Desired tile to center on.
 * @param instant Jump to the location instead of slowly moving to it.
 * @return Destination of the viewport was changed (to activate other actions when the viewport is already at the desired position).
 */
bool ScrollMainWindowToTile(TileIndex tile, bool instant)
{
        return ScrollMainWindowTo(TileX(tile) * TILE_SIZE + TILE_SIZE / 2, TileY(tile) * TILE_SIZE + TILE_SIZE / 2, -1, instant);
}

/**
 * Set a tile to display a red error square.
 * @param tile Tile that should show the red error square.
 */
void SetRedErrorSquare(TileIndex tile)
{
        TileIndex old;

        old = _thd.redsq;
        _thd.redsq = tile;

        if (tile != old) {
                if (tile != INVALID_TILE) MarkTileDirtyByTile(tile, ZOOM_LVL_DRAW_MAP);
                if (old  != INVALID_TILE) MarkTileDirtyByTile(old, ZOOM_LVL_DRAW_MAP);
        }
}

/**
 * Highlight \a w by \a h tiles at the cursor.
 * @param w Width of the highlighted tiles rectangle.
 * @param h Height of the highlighted tiles rectangle.
 */
void SetTileSelectSize(int w, int h)
{
        _thd.new_size.x = w * TILE_SIZE;
        _thd.new_size.y = h * TILE_SIZE;
        _thd.new_outersize.x = 0;
        _thd.new_outersize.y = 0;
}

void SetTileSelectBigSize(int ox, int oy, int sx, int sy)
{
        _thd.new_offs.x = ox * TILE_SIZE;
        _thd.new_offs.y = oy * TILE_SIZE;
        _thd.new_outersize.x = sx * TILE_SIZE;
        _thd.new_outersize.y = sy * TILE_SIZE;
}

/** returns the best autorail highlight type from map coordinates */
static HighLightStyle GetAutorailHT(int x, int y)
{
        return HT_RAIL | _autorail_piece[x & TILE_UNIT_MASK][y & TILE_UNIT_MASK];
}

/**
 * Reset tile highlighting.
 */
void TileHighlightData::Reset()
{
        this->pos.x = 0;
        this->pos.y = 0;
        this->new_pos.x = 0;
        this->new_pos.y = 0;
}

/**
 * Is the user dragging a 'diagonal rectangle'?
 * @return User is dragging a rotated rectangle.
 */
bool TileHighlightData::IsDraggingDiagonal()
{
        return (this->place_mode & HT_DIAGONAL) != 0 && _ctrl_pressed && _left_button_down;
}

/**
 * Get the window that started the current highlighting.
 * @return The window that requested the current tile highlighting, or \c nullptr if not available.
 */
Window *TileHighlightData::GetCallbackWnd()
{
        return FindWindowById(this->window_class, this->window_number);
}

static HighLightStyle CalcPolyrailDrawstyle(Point pt, bool dragging);

static inline void CalcNewPolylineOutersize()
{
        /* use the 'outersize' to mark the second (blue) part of a polyline selection */
        if (_thd.dir2 < HT_DIR_END) {
                /* get bounds of the second part */
                int outer_x1 = _thd.selstart2.x & ~TILE_UNIT_MASK;
                int outer_y1 = _thd.selstart2.y & ~TILE_UNIT_MASK;
                int outer_x2 = _thd.selend2.x & ~TILE_UNIT_MASK;
                int outer_y2 = _thd.selend2.y & ~TILE_UNIT_MASK;
                if (outer_x1 > outer_x2) Swap(outer_x1, outer_x2);
                if (outer_y1 > outer_y2) Swap(outer_y1, outer_y2);
                /* include the first part */
                outer_x1 = min<int>(outer_x1, _thd.new_pos.x);
                outer_y1 = min<int>(outer_y1, _thd.new_pos.y);
                outer_x2 = max<int>(outer_x2, _thd.new_pos.x + _thd.new_size.x - TILE_SIZE);
                outer_y2 = max<int>(outer_y2, _thd.new_pos.y + _thd.new_size.y - TILE_SIZE);
                /* write new values */
                _thd.new_offs.x = outer_x1 - _thd.new_pos.x;
                _thd.new_offs.y = outer_y1 - _thd.new_pos.y;
                _thd.new_outersize.x = outer_x2 - outer_x1 + TILE_SIZE - _thd.new_size.x;
                _thd.new_outersize.y = outer_y2 - outer_y1 + TILE_SIZE - _thd.new_size.y;
        } else {
                _thd.new_offs.x = 0;
                _thd.new_offs.y = 0;
                _thd.new_outersize.x = 0;
                _thd.new_outersize.y = 0;
        }
}

/**
 * Updates tile highlighting for all cases.
 * Uses _thd.selstart and _thd.selend and _thd.place_mode (set elsewhere) to determine _thd.pos and _thd.size
 * Also drawstyle is determined. Uses _thd.new.* as a buffer and calls SetSelectionTilesDirty() twice,
 * Once for the old and once for the new selection.
 * _thd is TileHighlightData, found in viewport.h
 */
void UpdateTileSelection()
{
        int x1;
        int y1;

        HighLightStyle new_drawstyle = HT_NONE;
        bool new_diagonal = false;

        if ((_thd.place_mode & HT_DRAG_MASK) == HT_SPECIAL) {
                x1 = _thd.selend.x;
                y1 = _thd.selend.y;
                if (x1 != -1) {
                        int x2 = _thd.selstart.x & ~TILE_UNIT_MASK;
                        int y2 = _thd.selstart.y & ~TILE_UNIT_MASK;
                        x1 &= ~TILE_UNIT_MASK;
                        y1 &= ~TILE_UNIT_MASK;

                        if (_thd.IsDraggingDiagonal()) {
                                new_diagonal = true;
                        } else {
                                if (x1 >= x2) Swap(x1, x2);
                                if (y1 >= y2) Swap(y1, y2);
                        }
                        _thd.new_pos.x = x1;
                        _thd.new_pos.y = y1;
                        _thd.new_size.x = x2 - x1;
                        _thd.new_size.y = y2 - y1;
                        if (!new_diagonal) {
                                _thd.new_size.x += TILE_SIZE;
                                _thd.new_size.y += TILE_SIZE;
                        }
                        new_drawstyle = _thd.next_drawstyle;
                }
        } else if ((_thd.place_mode & HT_DRAG_MASK) != HT_NONE) {
                Point pt = GetTileBelowCursor();
                x1 = pt.x;
                y1 = pt.y;
                if (x1 != -1) {
                        switch (_thd.place_mode & HT_DRAG_MASK) {
                                case HT_RECT:
                                        new_drawstyle = HT_RECT;
                                        break;
                                case HT_POINT:
                                        new_drawstyle = HT_POINT;
                                        x1 += TILE_SIZE / 2;
                                        y1 += TILE_SIZE / 2;
                                        break;
                                case HT_RAIL:
                                case HT_LINE:
                                        /* HT_POLY */
                                        if (_thd.place_mode & HT_POLY) {
                                                RailSnapMode snap_mode = GetRailSnapMode();
                                                if (snap_mode == RSM_NO_SNAP ||
                                                                (snap_mode == RSM_SNAP_TO_TILE && GetRailSnapTile() == TileVirtXY(pt.x, pt.y))) {
                                                        new_drawstyle = GetAutorailHT(pt.x, pt.y);
                                                        _thd.new_offs.x = 0;
                                                        _thd.new_offs.y = 0;
                                                        _thd.new_outersize.x = 0;
                                                        _thd.new_outersize.y = 0;
                                                        _thd.dir2 = HT_DIR_END;
                                                } else {
                                                        new_drawstyle = CalcPolyrailDrawstyle(pt, false);
                                                        if (new_drawstyle != HT_NONE) {
                                                                x1 = _thd.selstart.x & ~TILE_UNIT_MASK;
                                                                y1 = _thd.selstart.y & ~TILE_UNIT_MASK;
                                                                int x2 = _thd.selend.x & ~TILE_UNIT_MASK;
                                                                int y2 = _thd.selend.y & ~TILE_UNIT_MASK;
                                                                if (x1 > x2) Swap(x1, x2);
                                                                if (y1 > y2) Swap(y1, y2);
                                                                _thd.new_pos.x = x1;
                                                                _thd.new_pos.y = y1;
                                                                _thd.new_size.x = x2 - x1 + TILE_SIZE;
                                                                _thd.new_size.y = y2 - y1 + TILE_SIZE;
                                                        }
                                                }
                                                break;
                                        }
                                        /* HT_RAIL */
                                        if (_thd.place_mode & HT_RAIL) {
                                                /* Draw one highlighted tile in any direction */
                                                new_drawstyle = GetAutorailHT(pt.x, pt.y);
                                                break;
                                        }
                                        /* HT_LINE */
                                        switch (_thd.place_mode & HT_DIR_MASK) {
                                                case HT_DIR_X: new_drawstyle = HT_LINE | HT_DIR_X; break;
                                                case HT_DIR_Y: new_drawstyle = HT_LINE | HT_DIR_Y; break;

                                                case HT_DIR_HU:
                                                case HT_DIR_HL:
                                                        new_drawstyle = (pt.x & TILE_UNIT_MASK) + (pt.y & TILE_UNIT_MASK) <= TILE_SIZE ? HT_LINE | HT_DIR_HU : HT_LINE | HT_DIR_HL;
                                                        break;

                                                case HT_DIR_VL:
                                                case HT_DIR_VR:
                                                        new_drawstyle = (pt.x & TILE_UNIT_MASK) > (pt.y & TILE_UNIT_MASK) ? HT_LINE | HT_DIR_VL : HT_LINE | HT_DIR_VR;
                                                        break;

                                                default: NOT_REACHED();
                                        }
                                        _thd.selstart.x = x1 & ~TILE_UNIT_MASK;
                                        _thd.selstart.y = y1 & ~TILE_UNIT_MASK;
                                        _thd.selend.x = x1;
                                        _thd.selend.y = y1;
                                        break;
                                default:
                                        NOT_REACHED();
                                        break;
                        }
                        _thd.new_pos.x = x1 & ~TILE_UNIT_MASK;
                        _thd.new_pos.y = y1 & ~TILE_UNIT_MASK;
                }
        }

        if (new_drawstyle & HT_LINE) CalcNewPolylineOutersize();

        /* redraw selection */
        if (_thd.drawstyle != new_drawstyle ||
                        _thd.pos.x != _thd.new_pos.x || _thd.pos.y != _thd.new_pos.y ||
                        _thd.size.x != _thd.new_size.x || _thd.size.y != _thd.new_size.y ||
                        _thd.offs.x != _thd.new_offs.x || _thd.offs.y != _thd.new_offs.y ||
                        _thd.outersize.x != _thd.new_outersize.x ||
                        _thd.outersize.y != _thd.new_outersize.y ||
                        _thd.diagonal    != new_diagonal) {
                /* Clear the old tile selection? */
                if ((_thd.drawstyle & HT_DRAG_MASK) != HT_NONE) SetSelectionTilesDirty();

                _thd.drawstyle = new_drawstyle;
                _thd.pos = _thd.new_pos;
                _thd.size = _thd.new_size;
                _thd.offs = _thd.new_offs;
                _thd.outersize = _thd.new_outersize;
                _thd.diagonal = new_diagonal;
                _thd.dirty = 0xff;

                /* Draw the new tile selection? */
                if ((new_drawstyle & HT_DRAG_MASK) != HT_NONE) SetSelectionTilesDirty();
        }
}

/**
 * Displays the measurement tooltips when selecting multiple tiles
 * @param str String to be displayed
 * @param close_cond Condition for closing this tooltip.
 */
static inline void ShowMeasurementTooltips(StringID str, TooltipCloseCondition close_cond = TCC_LEFT_CLICK)
{
        if (!_settings_client.gui.measure_tooltip) return;
        GuiShowTooltips(_thd.GetCallbackWnd(), str, close_cond);
}

/** highlighting tiles while only going over them with the mouse */
void VpStartPlaceSizing(TileIndex tile, ViewportPlaceMethod method, ViewportDragDropSelectionProcess process)
{
        _thd.select_method = method;
        _thd.select_proc   = process;
        _thd.selend.x = TileX(tile) * TILE_SIZE;
        _thd.selstart.x = TileX(tile) * TILE_SIZE;
        _thd.selend.y = TileY(tile) * TILE_SIZE;
        _thd.selstart.y = TileY(tile) * TILE_SIZE;

        /* Needed so several things (road, autoroad, bridges, ...) are placed correctly.
         * In effect, placement starts from the centre of a tile
         */
        if (method == VPM_X_OR_Y || method == VPM_FIX_X || method == VPM_FIX_Y) {
                _thd.selend.x += TILE_SIZE / 2;
                _thd.selend.y += TILE_SIZE / 2;
                _thd.selstart.x += TILE_SIZE / 2;
                _thd.selstart.y += TILE_SIZE / 2;
        }

        HighLightStyle others = _thd.place_mode & ~(HT_DRAG_MASK | HT_DIR_MASK);
        if ((_thd.place_mode & HT_DRAG_MASK) == HT_RECT) {
                _thd.place_mode = HT_SPECIAL | others;
                _thd.next_drawstyle = HT_RECT | others;
        } else if (_thd.place_mode & (HT_RAIL | HT_LINE)) {
                _thd.place_mode = HT_SPECIAL | others;
                _thd.next_drawstyle = _thd.drawstyle | others;
                _current_snap_lock.x = -1;
                if ((_thd.place_mode & HT_POLY) != 0 && GetRailSnapMode() == RSM_NO_SNAP) {
                        SetRailSnapMode(RSM_SNAP_TO_TILE);
                        SetRailSnapTile(tile);
                }
        } else {
                _thd.place_mode = HT_SPECIAL | others;
                _thd.next_drawstyle = HT_POINT | others;
        }
        _special_mouse_mode = WSM_SIZING;
}

void VpSetPlaceSizingLimit(int limit)
{
        _thd.sizelimit = limit;
}

/**
 * Highlights all tiles between a set of two tiles. Used in dock and tunnel placement
 * @param from TileIndex of the first tile to highlight
 * @param to TileIndex of the last tile to highlight
 */
void VpSetPresizeRange(TileIndex from, TileIndex to)
{
        uint64 distance = DistanceManhattan(from, to) + 1;

        _thd.selend.x = TileX(to) * TILE_SIZE;
        _thd.selend.y = TileY(to) * TILE_SIZE;
        _thd.selstart.x = TileX(from) * TILE_SIZE;
        _thd.selstart.y = TileY(from) * TILE_SIZE;
        _thd.next_drawstyle = HT_RECT;

        /* show measurement only if there is any length to speak of */
        if (distance > 1) {
                SetDParam(0, distance);
                ShowMeasurementTooltips(STR_MEASURE_LENGTH, TCC_HOVER);
        }
}

static void VpStartPreSizing()
{
        _thd.selend.x = -1;
        _special_mouse_mode = WSM_PRESIZE;
}

/**
 * returns information about the 2x1 piece to be build.
 * The lower bits (0-3) are the track type.
 */
static HighLightStyle Check2x1AutoRail(int mode)
{
        int fxpy = _tile_fract_coords.x + _tile_fract_coords.y;
        int sxpy = (_thd.selend.x & TILE_UNIT_MASK) + (_thd.selend.y & TILE_UNIT_MASK);
        int fxmy = _tile_fract_coords.x - _tile_fract_coords.y;
        int sxmy = (_thd.selend.x & TILE_UNIT_MASK) - (_thd.selend.y & TILE_UNIT_MASK);

        switch (mode) {
                default: NOT_REACHED();
                case 0: // end piece is lower right
                        if (fxpy >= 20 && sxpy <= 12) return HT_DIR_HL;
                        if (fxmy < -3 && sxmy > 3) return HT_DIR_VR;
                        return HT_DIR_Y;

                case 1:
                        if (fxmy > 3 && sxmy < -3) return HT_DIR_VL;
                        if (fxpy <= 12 && sxpy >= 20) return HT_DIR_HU;
                        return HT_DIR_Y;

                case 2:
                        if (fxmy > 3 && sxmy < -3) return HT_DIR_VL;
                        if (fxpy >= 20 && sxpy <= 12) return HT_DIR_HL;
                        return HT_DIR_X;

                case 3:
                        if (fxmy < -3 && sxmy > 3) return HT_DIR_VR;
                        if (fxpy <= 12 && sxpy >= 20) return HT_DIR_HU;
                        return HT_DIR_X;
        }
}

/**
 * Check if the direction of start and end tile should be swapped based on
 * the dragging-style. Default directions are:
 * in the case of a line (HT_RAIL, HT_LINE):  DIR_NE, DIR_NW, DIR_N, DIR_E
 * in the case of a rect (HT_RECT, HT_POINT): DIR_S, DIR_E
 * For example dragging a rectangle area from south to north should be swapped to
 * north-south (DIR_S) to obtain the same results with less code. This is what
 * the return value signifies.
 * @param style HighLightStyle dragging style
 * @param start_tile start tile of drag
 * @param end_tile end tile of drag
 * @return boolean value which when true means start/end should be swapped
 */
static bool SwapDirection(HighLightStyle style, TileIndex start_tile, TileIndex end_tile)
{
        uint start_x = TileX(start_tile);
        uint start_y = TileY(start_tile);
        uint end_x = TileX(end_tile);
        uint end_y = TileY(end_tile);

        switch (style & HT_DRAG_MASK) {
                case HT_RAIL:
                case HT_LINE: return (end_x > start_x || (end_x == start_x && end_y > start_y));

                case HT_RECT:
                case HT_POINT: return (end_x != start_x && end_y < start_y);
                default: NOT_REACHED();
        }

        return false;
}

/**
 * Calculates height difference between one tile and another.
 * Multiplies the result to suit the standard given by #TILE_HEIGHT_STEP.
 *
 * To correctly get the height difference we need the direction we are dragging
 * in, as well as with what kind of tool we are dragging. For example a horizontal
 * autorail tool that starts in bottom and ends at the top of a tile will need the
 * maximum of SW, S and SE, N corners respectively. This is handled by the lookup table below
 * See #_tileoffs_by_dir in map.cpp for the direction enums if you can't figure out the values yourself.
 * @param style      Highlighting style of the drag. This includes direction and style (autorail, rect, etc.)
 * @param distance   Number of tiles dragged, important for horizontal/vertical drags, ignored for others.
 * @param start_tile Start tile of the drag operation.
 * @param end_tile   End tile of the drag operation.
 * @return Height difference between two tiles. The tile measurement tool utilizes this value in its tooltip.
 */
static int CalcHeightdiff(HighLightStyle style, uint distance, TileIndex start_tile, TileIndex end_tile)
{
        bool swap = SwapDirection(style, start_tile, end_tile);
        uint h0, h1; // Start height and end height.

        if (start_tile == end_tile) return 0;
        if (swap) Swap(start_tile, end_tile);

        switch (style & HT_DRAG_MASK) {
                case HT_RECT: {
                        static const TileIndexDiffC heightdiff_area_by_dir[] = {
                                /* Start */ {1, 0}, /* Dragging east */ {0, 0}, // Dragging south
                                /* End   */ {0, 1}, /* Dragging east */ {1, 1}  // Dragging south
                        };

                        /* In the case of an area we can determine whether we were dragging south or
                         * east by checking the X-coordinates of the tiles */
                        byte style_t = (byte)(TileX(end_tile) > TileX(start_tile));
                        start_tile = TILE_ADD(start_tile, ToTileIndexDiff(heightdiff_area_by_dir[style_t]));
                        end_tile   = TILE_ADD(end_tile, ToTileIndexDiff(heightdiff_area_by_dir[2 + style_t]));
                }
                FALLTHROUGH;

                case HT_POINT:
                        h0 = TileHeight(start_tile);
                        h1 = TileHeight(end_tile);
                        break;
                default: { // All other types, this is mostly only line/autorail
                        static const HighLightStyle flip_style_direction[] = {
                                HT_DIR_X, HT_DIR_Y, HT_DIR_HL, HT_DIR_HU, HT_DIR_VR, HT_DIR_VL
                        };
                        static const TileIndexDiffC heightdiff_line_by_dir[] = {
                                /* Start */ {1, 0}, {1, 1}, /* HT_DIR_X  */ {0, 1}, {1, 1}, // HT_DIR_Y
                                /* Start */ {1, 0}, {0, 0}, /* HT_DIR_HU */ {1, 0}, {1, 1}, // HT_DIR_HL
                                /* Start */ {1, 0}, {1, 1}, /* HT_DIR_VL */ {0, 1}, {1, 1}, // HT_DIR_VR

                                /* Start */ {0, 1}, {0, 0}, /* HT_DIR_X  */ {1, 0}, {0, 0}, // HT_DIR_Y
                                /* End   */ {0, 1}, {0, 0}, /* HT_DIR_HU */ {1, 1}, {0, 1}, // HT_DIR_HL
                                /* End   */ {1, 0}, {0, 0}, /* HT_DIR_VL */ {0, 0}, {0, 1}, // HT_DIR_VR
                        };

                        distance %= 2; // we're only interested if the distance is even or uneven
                        style &= HT_DIR_MASK;

                        /* To handle autorail, we do some magic to be able to use a lookup table.
                         * Firstly if we drag the other way around, we switch start&end, and if needed
                         * also flip the drag-position. Eg if it was on the left, and the distance is even
                         * that means the end, which is now the start is on the right */
                        if (swap && distance == 0) style = flip_style_direction[style];

                        /* Use lookup table for start-tile based on HighLightStyle direction */
                        byte style_t = style * 2;
                        assert(style_t < lengthof(heightdiff_line_by_dir) - 13);
                        h0 = TileHeight(TILE_ADD(start_tile, ToTileIndexDiff(heightdiff_line_by_dir[style_t])));
                        uint ht = TileHeight(TILE_ADD(start_tile, ToTileIndexDiff(heightdiff_line_by_dir[style_t + 1])));
                        h0 = max(h0, ht);

                        /* Use lookup table for end-tile based on HighLightStyle direction
                         * flip around side (lower/upper, left/right) based on distance */
                        if (distance == 0) style_t = flip_style_direction[style] * 2;
                        assert(style_t < lengthof(heightdiff_line_by_dir) - 13);
                        h1 = TileHeight(TILE_ADD(end_tile, ToTileIndexDiff(heightdiff_line_by_dir[12 + style_t])));
                        ht = TileHeight(TILE_ADD(end_tile, ToTileIndexDiff(heightdiff_line_by_dir[12 + style_t + 1])));
                        h1 = max(h1, ht);
                        break;
                }
        }

        if (swap) Swap(h0, h1);
        return (int)(h1 - h0) * TILE_HEIGHT_STEP;
}

static void ShowLengthMeasurement(HighLightStyle style, TileIndex start_tile, TileIndex end_tile, TooltipCloseCondition close_cond = TCC_LEFT_CLICK, bool show_single_tile_length = false)
{
        static const StringID measure_strings_length[] = {STR_NULL, STR_MEASURE_LENGTH, STR_MEASURE_LENGTH_HEIGHTDIFF};

        if (_settings_client.gui.measure_tooltip) {
                uint distance = DistanceManhattan(start_tile, end_tile) + 1;
                byte index = 0;

                if (show_single_tile_length || distance != 1) {
                        int heightdiff = CalcHeightdiff(style, distance, start_tile, end_tile);
                        /* If we are showing a tooltip for horizontal or vertical drags,
                         * 2 tiles have a length of 1. To bias towards the ceiling we add
                         * one before division. It feels more natural to count 3 lengths as 2 */
                        if ((style & HT_DIR_MASK) != HT_DIR_X && (style & HT_DIR_MASK) != HT_DIR_Y) {
                                distance = CeilDiv(distance, 2);
                        }

                        SetDParam(index++, distance);
                        if (heightdiff != 0) SetDParam(index++, heightdiff);
                }

                ShowMeasurementTooltips(measure_strings_length[index]);
        }
}

/**
 * Check for underflowing the map.
 * @param test  the variable to test for underflowing
 * @param other the other variable to update to keep the line
 * @param mult  the constant to multiply the difference by for \c other
 */
static void CheckUnderflow(int &test, int &other, int mult)
{
        if (test >= 0) return;

        other += mult * test;
        test = 0;
}

/**
 * Check for overflowing the map.
 * @param test  the variable to test for overflowing
 * @param other the other variable to update to keep the line
 * @param max   the maximum value for the \c test variable
 * @param mult  the constant to multiply the difference by for \c other
 */
static void CheckOverflow(int &test, int &other, int max, int mult)
{
        if (test <= max) return;

        other += mult * (test - max);
        test = max;
}

static const uint X_DIRS = (1 << DIR_NE) | (1 << DIR_SW);
static const uint Y_DIRS = (1 << DIR_SE) | (1 << DIR_NW);
static const uint HORZ_DIRS = (1 << DIR_W) | (1 << DIR_E);
static const uint VERT_DIRS = (1 << DIR_N) | (1 << DIR_S);

Trackdir PointDirToTrackdir(const Point &pt, Direction dir)
{
        Trackdir ret;

        if (IsDiagonalDirection(dir)) {
                ret = DiagDirToDiagTrackdir(DirToDiagDir(dir));
        } else {
                int x = pt.x & TILE_UNIT_MASK;
                int y = pt.y & TILE_UNIT_MASK;
                int ns = x + y;
                int we = y - x;
                if (HasBit(HORZ_DIRS, dir)) {
                        ret = TrackDirectionToTrackdir(ns < (int)TILE_SIZE ? TRACK_UPPER : TRACK_LOWER, dir);
                } else {
                        ret = TrackDirectionToTrackdir(we < 0 ? TRACK_LEFT : TRACK_RIGHT, dir);
                }
        }

        return ret;
}

static bool FindPolyline(const Point &pt, const LineSnapPoint &start, Polyline *ret)
{
        /* relative coordinats of the mouse point (offset against the snap point) */
        int x = pt.x - start.x;
        int y = pt.y - start.y;
        int we = y - x;
        int ns = x + y;

        /* in-tile alignment of the snap point (there are two variants: [0, 8] or [8, 0]) */
        uint align_x = start.x & TILE_UNIT_MASK;
        uint align_y = start.y & TILE_UNIT_MASK;
        assert((align_x == TILE_SIZE / 2 && align_y == 0 && !(start.dirs & X_DIRS)) || (align_x == 0 && align_y == TILE_SIZE / 2 && !(start.dirs & Y_DIRS)));

        /* absolute distance between points (in tiles) */
        uint d_x = abs(RoundDivSU(x < 0 ? x - align_y : x + align_y, TILE_SIZE));
        uint d_y = abs(RoundDivSU(y < 0 ? y - align_x : y + align_x, TILE_SIZE));
        uint d_ns = abs(RoundDivSU(ns, TILE_SIZE));
        uint d_we = abs(RoundDivSU(we, TILE_SIZE));

        /* Find on which quadrant is the mouse point (reltively to the snap point).
         * Numeration (clockwise like in Direction):
         * ortho            diag
         *   \   2   /       2 | 3
         *     \   /         --+---> [we]
         *  1    X    3      1 | 0
         *     /   \           v
         *  [x]  0  [y]       [ns]          */
        uint ortho_quadrant = 2 * (x < 0) + ((x < 0) != (y < 0)); // implicit cast: false/true --> 0/1
        uint diag_quadrant = 2 * (ns < 0) + ((ns < 0) != (we < 0));

        /* direction from the snap point to the mouse point */
        Direction ortho_line_dir = ChangeDir(DIR_S, (DirDiff)(2 * ortho_quadrant)); // DIR_S is the middle of the ortho quadrant no. 0
        Direction diag_line_dir = ChangeDir(DIR_SE, (DirDiff)(2 * diag_quadrant));  // DIR_SE is the middle of the diag quadrant no. 0
        if (!HasBit(start.dirs, ortho_line_dir) && !HasBit(start.dirs, diag_line_dir)) return false;

        /* length of booth segments of auto line (choosing orthogonal direction first) */
        uint ortho_len = 0, ortho_len2 = 0;
        if (HasBit(start.dirs, ortho_line_dir)) {
                bool is_len_even = (align_x != 0) ? d_x >= d_y : d_x <= d_y;
                ortho_len = 2 * min(d_x, d_y) - (int)is_len_even;
                assert((int)ortho_len >= 0);
                if (d_ns == 0 || d_we == 0) { // just single segment?
                        ortho_len++;
                } else {
                        ortho_len2 = abs((int)d_x - (int)d_y) + (int)is_len_even;
                }
        }

        /* length of booth segments of auto line (choosing diagonal direction first) */
        uint diag_len = 0, diag_len2 = 0;
        if (HasBit(start.dirs, diag_line_dir)) {
                if (d_x == 0 || d_y == 0) { // just single segment?
                        diag_len = d_x + d_y;
                } else {
                        diag_len = min(d_ns, d_we);
                        diag_len2 = d_x + d_y - diag_len;
                }
        }

        /* choose the best variant */
        if (ortho_len != 0 && diag_len != 0) {
                /* in the first place, choose this line whose first segment ends up closer
                 * to the mouse point (thus the second segment is shorter) */
                int cmp = ortho_len2 - diag_len2;
                /* if equeal, choose the shorter line */
                if (cmp == 0) cmp = ortho_len - diag_len;
                /* finally look at small "units" and choose the line which is closer to the mouse point */
                if (cmp == 0) cmp = min(abs(we), abs(ns)) - min(abs(x), abs(y));
                /* based on comparison, disable one of variants */
                if (cmp > 0) {
                        ortho_len = 0;
                } else {
                        diag_len = 0;
                }
        }

        /* store results */
        if (ortho_len != 0) {
                ret->first_dir = ortho_line_dir;
                ret->first_len = ortho_len;
                ret->second_dir = (ortho_len2 != 0) ? diag_line_dir : INVALID_DIR;
                ret->second_len = ortho_len2;
        } else if (diag_len != 0) {
                ret->first_dir = diag_line_dir;
                ret->first_len = diag_len;
                ret->second_dir = (diag_len2 != 0) ? ortho_line_dir : INVALID_DIR;
                ret->second_len = diag_len2;
        } else {
                return false;
        }

        ret->start = start;
        return true;
}

/**
 * Calculate squared euclidean distance between two points.
 * @param a the first point
 * @param b the second point
 * @return |b - a| ^ 2
 */
static inline uint SqrDist(const Point &a, const Point &b)
{
        return (b.x - a.x) * (b.x - a.x) + (b.y - a.y) * (b.y - a.y);
}

static LineSnapPoint *FindBestPolyline(const Point &pt, LineSnapPoint *snap_points, uint num_points, Polyline *ret)
{
        /* Find the best polyline (a pair of two lines - the white one and the blue
         * one) led from any of saved snap points to the mouse cursor. */

        LineSnapPoint *best_snap_point = nullptr; // the best polyline we found so far is led from this snap point

        for (int i = 0; i < (int)num_points; i++) {
                /* try to fit a polyline */
                Polyline polyline;
                if (!FindPolyline(pt, snap_points[i], &polyline)) continue; // skip non-matching snap points
                /* check whether we've found a better polyline */
                if (best_snap_point != nullptr) {
                        /* firstly choose shorter polyline (the one with smaller amount of
                         * track pieces composing booth the white and the blue line) */
                        uint cur_len = polyline.first_len + polyline.second_len;
                        uint best_len = ret->first_len + ret->second_len;
                        if (cur_len > best_len) continue;
                        /* secondly choose that polyline which has longer first (white) line */
                        if (cur_len == best_len && polyline.first_len < ret->first_len) continue;
                        /* finally check euclidean distance to snap points and choose the
                         * one which is closer */
                        if (cur_len == best_len && polyline.first_len == ret->first_len && SqrDist(pt, snap_points[i]) >= SqrDist(pt, *best_snap_point)) continue;
                }
                /* save the found polyline */
                *ret = polyline;
                best_snap_point = &snap_points[i];
        }

        return best_snap_point;
}

/** while dragging */
static void CalcRaildirsDrawstyle(int x, int y, int method)
{
        HighLightStyle b;

        int dx = _thd.selstart.x - (_thd.selend.x & ~TILE_UNIT_MASK);
        int dy = _thd.selstart.y - (_thd.selend.y & ~TILE_UNIT_MASK);
        uint w = abs(dx) + TILE_SIZE;
        uint h = abs(dy) + TILE_SIZE;

        if (method & ~(VPM_RAILDIRS | VPM_SIGNALDIRS)) {
                /* We 'force' a selection direction; first four rail buttons. */
                method &= ~(VPM_RAILDIRS | VPM_SIGNALDIRS);
                int raw_dx = _thd.selstart.x - _thd.selend.x;
                int raw_dy = _thd.selstart.y - _thd.selend.y;
                switch (method) {
                        case VPM_FIX_X:
                                b = HT_LINE | HT_DIR_Y;
                                x = _thd.selstart.x;
                                break;

                        case VPM_FIX_Y:
                                b = HT_LINE | HT_DIR_X;
                                y = _thd.selstart.y;
                                break;

                        case VPM_FIX_HORIZONTAL:
                                if (dx == -dy) {
                                        /* We are on a straight horizontal line. Determine the 'rail'
                                         * to build based the sub tile location. */
                                        b = (x & TILE_UNIT_MASK) + (y & TILE_UNIT_MASK) >= TILE_SIZE ? HT_LINE | HT_DIR_HL : HT_LINE | HT_DIR_HU;
                                } else {
                                        /* We are not on a straight line. Determine the rail to build
                                         * based on whether we are above or below it. */
                                        b = dx + dy >= (int)TILE_SIZE ? HT_LINE | HT_DIR_HU : HT_LINE | HT_DIR_HL;

                                        /* Calculate where a horizontal line through the start point and
                                         * a vertical line from the selected end point intersect and
                                         * use that point as the end point. */
                                        int offset = (raw_dx - raw_dy) / 2;
                                        x = _thd.selstart.x - (offset & ~TILE_UNIT_MASK);
                                        y = _thd.selstart.y + (offset & ~TILE_UNIT_MASK);

                                        /* 'Build' the last half rail tile if needed */
                                        if ((offset & TILE_UNIT_MASK) > (TILE_SIZE / 2)) {
                                                if (dx + dy >= (int)TILE_SIZE) {
                                                        x += (dx + dy < 0) ? (int)TILE_SIZE : -(int)TILE_SIZE;
                                                } else {
                                                        y += (dx + dy < 0) ? (int)TILE_SIZE : -(int)TILE_SIZE;
                                                }
                                        }

                                        /* Make sure we do not overflow the map! */
                                        CheckUnderflow(x, y, 1);
                                        CheckUnderflow(y, x, 1);
                                        CheckOverflow(x, y, (MapMaxX() - 1) * TILE_SIZE, 1);
                                        CheckOverflow(y, x, (MapMaxY() - 1) * TILE_SIZE, 1);
                                        assert(x >= 0 && y >= 0 && x <= (int)(MapMaxX() * TILE_SIZE) && y <= (int)(MapMaxY() * TILE_SIZE));
                                }
                                break;

                        case VPM_FIX_VERTICAL:
                                if (dx == dy) {
                                        /* We are on a straight vertical line. Determine the 'rail'
                                         * to build based the sub tile location. */
                                        b = (x & TILE_UNIT_MASK) > (y & TILE_UNIT_MASK) ? HT_LINE | HT_DIR_VL : HT_LINE | HT_DIR_VR;
                                } else {
                                        /* We are not on a straight line. Determine the rail to build
                                         * based on whether we are left or right from it. */
                                        b = dx < dy ? HT_LINE | HT_DIR_VL : HT_LINE | HT_DIR_VR;

                                        /* Calculate where a vertical line through the start point and
                                         * a horizontal line from the selected end point intersect and
                                         * use that point as the end point. */
                                        int offset = (raw_dx + raw_dy + (int)TILE_SIZE) / 2;
                                        x = _thd.selstart.x - (offset & ~TILE_UNIT_MASK);
                                        y = _thd.selstart.y - (offset & ~TILE_UNIT_MASK);

                                        /* 'Build' the last half rail tile if needed */
                                        if ((offset & TILE_UNIT_MASK) > (TILE_SIZE / 2)) {
                                                if (dx - dy < 0) {
                                                        y += (dx > dy) ? (int)TILE_SIZE : -(int)TILE_SIZE;
                                                } else {
                                                        x += (dx < dy) ? (int)TILE_SIZE : -(int)TILE_SIZE;
                                                }
                                        }

                                        /* Make sure we do not overflow the map! */
                                        CheckUnderflow(x, y, -1);
                                        CheckUnderflow(y, x, -1);
                                        CheckOverflow(x, y, (MapMaxX() - 1) * TILE_SIZE, -1);
                                        CheckOverflow(y, x, (MapMaxY() - 1) * TILE_SIZE, -1);
                                        assert(x >= 0 && y >= 0 && x <= (int)(MapMaxX() * TILE_SIZE) && y <= (int)(MapMaxY() * TILE_SIZE));
                                }
                                break;

                        default:
                                NOT_REACHED();
                }
        } else if (TileVirtXY(_thd.selstart.x, _thd.selstart.y) == TileVirtXY(x, y)) { // check if we're only within one tile
                if (method & VPM_RAILDIRS) {
                        b = GetAutorailHT(x, y);
                } else { // rect for autosignals on one tile
                        b = HT_RECT;
                }
        } else if (h == TILE_SIZE) { // Is this in X direction?
                if (dx == (int)TILE_SIZE) { // 2x1 special handling
                        b = (Check2x1AutoRail(3)) | HT_LINE;
                } else if (dx == -(int)TILE_SIZE) {
                        b = (Check2x1AutoRail(2)) | HT_LINE;
                } else {
                        b = HT_LINE | HT_DIR_X;
                }
                y = _thd.selstart.y;
        } else if (w == TILE_SIZE) { // Or Y direction?
                if (dy == (int)TILE_SIZE) { // 2x1 special handling
                        b = (Check2x1AutoRail(1)) | HT_LINE;
                } else if (dy == -(int)TILE_SIZE) { // 2x1 other direction
                        b = (Check2x1AutoRail(0)) | HT_LINE;
                } else {
                        b = HT_LINE | HT_DIR_Y;
                }
                x = _thd.selstart.x;
        } else if (w > h * 2) { // still count as x dir?
                b = HT_LINE | HT_DIR_X;
                y = _thd.selstart.y;
        } else if (h > w * 2) { // still count as y dir?
                b = HT_LINE | HT_DIR_Y;
                x = _thd.selstart.x;
        } else { // complicated direction
                int d = w - h;
                _thd.selend.x = _thd.selend.x & ~TILE_UNIT_MASK;
                _thd.selend.y = _thd.selend.y & ~TILE_UNIT_MASK;

                /* four cases. */
                if (x > _thd.selstart.x) {
                        if (y > _thd.selstart.y) {
                                /* south */
                                if (d == 0) {
                                        b = (x & TILE_UNIT_MASK) > (y & TILE_UNIT_MASK) ? HT_LINE | HT_DIR_VL : HT_LINE | HT_DIR_VR;
                                } else if (d >= 0) {
                                        x = _thd.selstart.x + h;
                                        b = HT_LINE | HT_DIR_VL;
                                } else {
                                        y = _thd.selstart.y + w;
                                        b = HT_LINE | HT_DIR_VR;
                                }
                        } else {
                                /* west */
                                if (d == 0) {
                                        b = (x & TILE_UNIT_MASK) + (y & TILE_UNIT_MASK) >= TILE_SIZE ? HT_LINE | HT_DIR_HL : HT_LINE | HT_DIR_HU;
                                } else if (d >= 0) {
                                        x = _thd.selstart.x + h;
                                        b = HT_LINE | HT_DIR_HL;
                                } else {
                                        y = _thd.selstart.y - w;
                                        b = HT_LINE | HT_DIR_HU;
                                }
                        }
                } else {
                        if (y > _thd.selstart.y) {
                                /* east */
                                if (d == 0) {
                                        b = (x & TILE_UNIT_MASK) + (y & TILE_UNIT_MASK) >= TILE_SIZE ? HT_LINE | HT_DIR_HL : HT_LINE | HT_DIR_HU;
                                } else if (d >= 0) {
                                        x = _thd.selstart.x - h;
                                        b = HT_LINE | HT_DIR_HU;
                                } else {
                                        y = _thd.selstart.y + w;
                                        b = HT_LINE | HT_DIR_HL;
                                }
                        } else {
                                /* north */
                                if (d == 0) {
                                        b = (x & TILE_UNIT_MASK) > (y & TILE_UNIT_MASK) ? HT_LINE | HT_DIR_VL : HT_LINE | HT_DIR_VR;
                                } else if (d >= 0) {
                                        x = _thd.selstart.x - h;
                                        b = HT_LINE | HT_DIR_VR;
                                } else {
                                        y = _thd.selstart.y - w;
                                        b = HT_LINE | HT_DIR_VL;
                                }
                        }
                }
        }

        _thd.selend.x = x;
        _thd.selend.y = y;
        _thd.dir2 = HT_DIR_END;
        _thd.next_drawstyle = b;

        ShowLengthMeasurement(b, TileVirtXY(_thd.selstart.x, _thd.selstart.y), TileVirtXY(_thd.selend.x, _thd.selend.y));
}

static HighLightStyle CalcPolyrailDrawstyle(Point pt, bool dragging)
{
        RailSnapMode snap_mode = GetRailSnapMode();

        /* are we only within one tile? */
        if (snap_mode == RSM_SNAP_TO_TILE && GetRailSnapTile() == TileVirtXY(pt.x, pt.y)) {
                _thd.selend.x = pt.x;
                _thd.selend.y = pt.y;
                return GetAutorailHT(pt.x, pt.y);
        }

        /* find the best track */
        Polyline line;

        bool lock_snapping = dragging && snap_mode == RSM_SNAP_TO_RAIL;
        if (!lock_snapping) _current_snap_lock.x = -1;

        const LineSnapPoint *snap_point;
        if (_current_snap_lock.x != -1) {
                snap_point = FindBestPolyline(pt, &_current_snap_lock, 1, &line);
        } else if (snap_mode == RSM_SNAP_TO_TILE) {
                snap_point = FindBestPolyline(pt, _tile_snap_points.Begin(), _tile_snap_points.Length(), &line);
        } else {
                assert(snap_mode == RSM_SNAP_TO_RAIL);
                snap_point = FindBestPolyline(pt, _rail_snap_points.Begin(), _rail_snap_points.Length(), &line);
        }

        if (snap_point == nullptr) return HT_NONE; // no match

        if (lock_snapping && _current_snap_lock.x == -1) {
                /* lock down the snap point */
                _current_snap_lock = *snap_point;
                _current_snap_lock.dirs &= (1 << line.first_dir) | (1 << ReverseDir(line.first_dir));
        }

        TileIndexDiffC first_dir = TileIndexDiffCByDir(line.first_dir);
        _thd.selstart.x  = line.start.x;
        _thd.selstart.y  = line.start.y;
        _thd.selend.x    = _thd.selstart.x + line.first_len * first_dir.x * (IsDiagonalDirection(line.first_dir) ? TILE_SIZE : TILE_SIZE / 2);
        _thd.selend.y    = _thd.selstart.y + line.first_len * first_dir.y * (IsDiagonalDirection(line.first_dir) ? TILE_SIZE : TILE_SIZE / 2);
        _thd.selstart2.x = _thd.selend.x;
        _thd.selstart2.y = _thd.selend.y;
        _thd.selstart.x  += first_dir.x;
        _thd.selstart.y  += first_dir.y;
        _thd.selend.x    -= first_dir.x;
        _thd.selend.y    -= first_dir.y;
        Trackdir seldir = PointDirToTrackdir(_thd.selstart, line.first_dir);
        _thd.selstart.x  &= ~TILE_UNIT_MASK;
        _thd.selstart.y  &= ~TILE_UNIT_MASK;

        if (line.second_len != 0) {
                TileIndexDiffC second_dir = TileIndexDiffCByDir(line.second_dir);
                _thd.selend2.x   = _thd.selstart2.x + line.second_len * second_dir.x * (IsDiagonalDirection(line.second_dir) ? TILE_SIZE : TILE_SIZE / 2);
                _thd.selend2.y   = _thd.selstart2.y + line.second_len * second_dir.y * (IsDiagonalDirection(line.second_dir) ? TILE_SIZE : TILE_SIZE / 2);
                _thd.selstart2.x += second_dir.x;
                _thd.selstart2.y += second_dir.y;
                _thd.selend2.x   -= second_dir.x;
                _thd.selend2.y   -= second_dir.y;
                Trackdir seldir2 = PointDirToTrackdir(_thd.selstart2, line.second_dir);
                _thd.selstart2.x &= ~TILE_UNIT_MASK;
                _thd.selstart2.y &= ~TILE_UNIT_MASK;
                _thd.dir2 = (HighLightStyle)TrackdirToTrack(seldir2);
        } else {
                _thd.dir2 = HT_DIR_END;
        }

        HighLightStyle ret = HT_LINE | (HighLightStyle)TrackdirToTrack(seldir);
        ShowLengthMeasurement(ret, TileVirtXY(_thd.selstart.x, _thd.selstart.y), TileVirtXY(_thd.selend.x, _thd.selend.y), TCC_HOVER, true);
        return ret;
}

/**
 * Selects tiles while dragging
 * @param x X coordinate of end of selection
 * @param y Y coordinate of end of selection
 * @param method modifies the way tiles are selected. Possible
 * methods are VPM_* in viewport.h
 */
void VpSelectTilesWithMethod(int x, int y, ViewportPlaceMethod method)
{
        int sx, sy;
        HighLightStyle style;

        if (x == -1) {
                _thd.selend.x = -1;
                return;
        }

        if ((_thd.place_mode & HT_POLY) && GetRailSnapMode() != RSM_NO_SNAP) {
                Point pt = { x, y };
                _thd.next_drawstyle = CalcPolyrailDrawstyle(pt, true);
                return;
        }

        /* Special handling of drag in any (8-way) direction */
        if (method & (VPM_RAILDIRS | VPM_SIGNALDIRS)) {
                _thd.selend.x = x;
                _thd.selend.y = y;
                CalcRaildirsDrawstyle(x, y, method);
                return;
        }

        /* Needed so level-land is placed correctly */
        if ((_thd.next_drawstyle & HT_DRAG_MASK) == HT_POINT) {
                x += TILE_SIZE / 2;
                y += TILE_SIZE / 2;
        }

        sx = _thd.selstart.x;
        sy = _thd.selstart.y;

        int limit = 0;

        switch (method) {
                case VPM_X_OR_Y: // drag in X or Y direction
                        if (abs(sy - y) < abs(sx - x)) {
                                y = sy;
                                style = HT_DIR_X;
                        } else {
                                x = sx;
                                style = HT_DIR_Y;
                        }
                        goto calc_heightdiff_single_direction;

                case VPM_X_LIMITED: // Drag in X direction (limited size).
                        limit = (_thd.sizelimit - 1) * TILE_SIZE;
                        FALLTHROUGH;

                case VPM_FIX_X: // drag in Y direction
                        x = sx;
                        style = HT_DIR_Y;
                        goto calc_heightdiff_single_direction;

                case VPM_Y_LIMITED: // Drag in Y direction (limited size).
                        limit = (_thd.sizelimit - 1) * TILE_SIZE;
                        FALLTHROUGH;

                case VPM_FIX_Y: // drag in X direction
                        y = sy;
                        style = HT_DIR_X;

calc_heightdiff_single_direction:;
                        if (limit > 0) {
                                x = sx + Clamp(x - sx, -limit, limit);
                                y = sy + Clamp(y - sy, -limit, limit);
                        }
                        /* With current code passing a HT_LINE style to calculate the height
                         * difference is enough. However if/when a point-tool is created
                         * with this method, function should be called with new_style (below)
                         * instead of HT_LINE | style case HT_POINT is handled specially
                         * new_style := (_thd.next_drawstyle & HT_RECT) ? HT_LINE | style : _thd.next_drawstyle; */
                        ShowLengthMeasurement(HT_LINE | style, TileVirtXY(sx, sy), TileVirtXY(x, y));
                        break;

                case VPM_A_B_LINE: { // drag an A to B line
                        TileIndex t0 = TileVirtXY(sx, sy);
                        TileIndex t1 = TileVirtXY(x, y);
                        uint dx = Delta(TileX(t0), TileX(t1)) + 1;
                        uint dy = Delta(TileY(t0), TileY(t1)) + 1;
                        byte index = 0;

                        /* If dragging an area (eg dynamite tool) and it is actually a single
                         * row/column, change the type to 'line' to get proper calculation for height */
                        style = (HighLightStyle)_thd.next_drawstyle;
                        if (style & HT_RECT) {
                                if (dx == 1) {
                                        style = HT_LINE | HT_DIR_Y;
                                } else if (dy == 1) {
                                        style = HT_LINE | HT_DIR_X;
                                }
                        }

                        int heightdiff = 0;

                        if (dx != 1 || dy != 1) {
                                heightdiff = CalcHeightdiff(style, 0, t0, t1);
                                SetDParam(index++, DistanceManhattan(t0, t1));
                                SetDParam(index++, sqrtl(dx * dx + dy * dy)); //DistanceSquare does not like big numbers
                                
                        } else {
                                index += 2;
                        }
                        
                        SetDParam(index++, DistanceFromEdge(t1));
                        SetDParam(index++, GetTileMaxZ(t1) * TILE_HEIGHT_STEP);
                        SetDParam(index++, heightdiff);
                        //Show always the measurement tooltip
                        GuiShowTooltips(_thd.GetCallbackWnd(),STR_MEASURE_DIST_HEIGHTDIFF);
                        break;
                }
                
                case VPM_X_AND_Y_LIMITED: // Drag an X by Y constrained rect area.
                        limit = (_thd.sizelimit - 1) * TILE_SIZE;
                        x = sx + Clamp(x - sx, -limit, limit);
                        y = sy + Clamp(y - sy, -limit, limit);
                        FALLTHROUGH;

                case VPM_X_AND_Y: // drag an X by Y area
                        if (_settings_client.gui.measure_tooltip) {
                                static const StringID measure_strings_area[] = {
                                        STR_NULL, STR_NULL, STR_MEASURE_AREA, STR_MEASURE_AREA_HEIGHTDIFF
                                };

                                TileIndex t0 = TileVirtXY(sx, sy);
                                TileIndex t1 = TileVirtXY(x, y);
                                uint dx = Delta(TileX(t0), TileX(t1)) + 1;
                                uint dy = Delta(TileY(t0), TileY(t1)) + 1;
                                byte index = 0;

                                /* If dragging an area (eg dynamite tool) and it is actually a single
                                 * row/column, change the type to 'line' to get proper calculation for height */
                                style = (HighLightStyle)_thd.next_drawstyle;
                                if (_thd.IsDraggingDiagonal()) {
                                        /* Determine the "area" of the diagonal dragged selection.
                                         * We assume the area is the number of tiles along the X
                                         * edge and the number of tiles along the Y edge. However,
                                         * multiplying these two numbers does not give the exact
                                         * number of tiles; basically we are counting the black
                                         * squares on a chess board and ignore the white ones to
                                         * make the tile counts at the edges match up. There is no
                                         * other way to make a proper count though.
                                         *
                                         * First convert to the rotated coordinate system. */
                                        int dist_x = TileX(t0) - TileX(t1);
                                        int dist_y = TileY(t0) - TileY(t1);
                                        int a_max = dist_x + dist_y;
                                        int b_max = dist_y - dist_x;

                                        /* Now determine the size along the edge, but due to the
                                         * chess board principle this counts double. */
                                        a_max = abs(a_max + (a_max > 0 ? 2 : -2)) / 2;
                                        b_max = abs(b_max + (b_max > 0 ? 2 : -2)) / 2;

                                        /* We get a 1x1 on normal 2x1 rectangles, due to it being
                                         * a seen as two sides. As the result for actual building
                                         * will be the same as non-diagonal dragging revert to that
                                         * behaviour to give it a more normally looking size. */
                                        if (a_max != 1 || b_max != 1) {
                                                dx = a_max;
                                                dy = b_max;
                                        }
                                } else if (style & HT_RECT) {
                                        if (dx == 1) {
                                                style = HT_LINE | HT_DIR_Y;
                                        } else if (dy == 1) {
                                                style = HT_LINE | HT_DIR_X;
                                        }
                                }

                                if (dx != 1 || dy != 1) {
                                        int heightdiff = CalcHeightdiff(style, 0, t0, t1);

                                        SetDParam(index++, dx - (style & HT_POINT ? 1 : 0));
                                        SetDParam(index++, dy - (style & HT_POINT ? 1 : 0));
                                        if (heightdiff != 0) SetDParam(index++, heightdiff);
                                }

                                ShowMeasurementTooltips(measure_strings_area[index]);
                        }
                        break;

                default: NOT_REACHED();
        }

        _thd.selend.x = x;
        _thd.selend.y = y;
        _thd.dir2 = HT_DIR_END;
}

/**
 * Handle the mouse while dragging for placement/resizing.
 * @return State of handling the event.
 */
EventState VpHandlePlaceSizingDrag()
{
        if (_special_mouse_mode != WSM_SIZING) return ES_NOT_HANDLED;

        /* stop drag mode if the window has been closed */
        Window *w = _thd.GetCallbackWnd();
        if (w == nullptr) {
                ResetObjectToPlace();
                return ES_HANDLED;
        }

        /* While dragging execute the drag procedure of the corresponding window (mostly VpSelectTilesWithMethod() ).
         * Do it even if the button is no longer pressed to make sure that OnPlaceDrag was called at least once. */
        w->OnPlaceDrag(_thd.select_method, _thd.select_proc, GetTileBelowCursor());
        if (_left_button_down) return ES_HANDLED;

        /* mouse button released..
         * keep the selected tool, but reset it to the original mode. */
        _special_mouse_mode = WSM_NONE;
        HighLightStyle others = _thd.place_mode & ~(HT_DRAG_MASK | HT_DIR_MASK);
        if ((_thd.next_drawstyle & HT_DRAG_MASK) == HT_RECT) {
                _thd.place_mode = HT_RECT | others;
        } else if (_thd.select_method & VPM_SIGNALDIRS) {
                _thd.place_mode = HT_RECT | others;
        } else if (_thd.select_method & VPM_RAILDIRS) {
                _thd.place_mode = (_thd.select_method & ~VPM_RAILDIRS ? _thd.next_drawstyle : HT_RAIL) | others;
        } else {
                _thd.place_mode = HT_POINT | others;
        }
        SetTileSelectSize(1, 1);

        if (_thd.place_mode & HT_POLY) {
                if (GetRailSnapMode() == RSM_SNAP_TO_TILE) SetRailSnapMode(RSM_NO_SNAP);
                if (_thd.drawstyle == HT_NONE) return ES_HANDLED;
        }

        w->OnPlaceMouseUp(_thd.select_method, _thd.select_proc, _thd.selend, TileVirtXY(_thd.selstart.x, _thd.selstart.y), TileVirtXY(_thd.selend.x, _thd.selend.y));
        return ES_HANDLED;
}

/**
 * Change the cursor and mouse click/drag handling to a mode for performing special operations like tile area selection, object placement, etc.
 * @param icon New shape of the mouse cursor.
 * @param pal Palette to use.
 * @param mode Mode to perform.
 * @param w %Window requesting the mode change.
 */
void SetObjectToPlaceWnd(CursorID icon, PaletteID pal, HighLightStyle mode, Window *w)
{
        SetObjectToPlace(icon, pal, mode, w->window_class, w->window_number);
}

#include "table/animcursors.h"

/**
 * Change the cursor and mouse click/drag handling to a mode for performing special operations like tile area selection, object placement, etc.
 * @param icon New shape of the mouse cursor.
 * @param pal Palette to use.
 * @param mode Mode to perform.
 * @param window_class %Window class of the window requesting the mode change.
 * @param window_num Number of the window in its class requesting the mode change.
 */
void SetObjectToPlace(CursorID icon, PaletteID pal, HighLightStyle mode, WindowClass window_class, WindowNumber window_num)
{
        if (_thd.window_class != WC_INVALID) {
                /* Undo clicking on button and drag & drop */
                Window *w = _thd.GetCallbackWnd();
                /* Call the abort function, but set the window class to something
                 * that will never be used to avoid infinite loops. Setting it to
                 * the 'next' window class must not be done because recursion into
                 * this function might in some cases reset the newly set object to
                 * place or not properly reset the original selection. */
                _thd.window_class = WC_INVALID;
                if (w != nullptr) w->OnPlaceObjectAbort();
        }

        /* Mark the old selection dirty, in case the selection shape or colour changes */
        if ((_thd.drawstyle & HT_DRAG_MASK) != HT_NONE) SetSelectionTilesDirty();

        SetTileSelectSize(1, 1);

        _thd.make_square_red = false;

        if (mode == HT_DRAG) { // HT_DRAG is for dragdropping trains in the depot window
                mode = HT_NONE;
                _special_mouse_mode = WSM_DRAGDROP;
        } else {
                _special_mouse_mode = WSM_NONE;
        }

        _thd.place_mode = mode;
        _thd.window_class = window_class;
        _thd.window_number = window_num;

        if ((mode & HT_DRAG_MASK) == HT_SPECIAL) { // special tools, like tunnels or docks start with presizing mode
                VpStartPreSizing();
        }

        if (mode & HT_POLY) {
                SetRailSnapMode((mode & HT_NEW_POLY) == HT_NEW_POLY ? RSM_NO_SNAP : RSM_SNAP_TO_RAIL);
        }

        if ((icon & ANIMCURSOR_FLAG) != 0) {
                SetAnimatedMouseCursor(_animcursors[icon & ~ANIMCURSOR_FLAG]);
        } else {
                SetMouseCursor(icon, pal);
        }

}

/** Reset the cursor and mouse mode handling back to default (normal cursor, only clicking in windows). */
void ResetObjectToPlace()
{
        SetObjectToPlace(SPR_CURSOR_MOUSE, PAL_NONE, HT_NONE, WC_MAIN_WINDOW, 0);
}

ViewportMapType ChangeRenderMode(const ViewPort *vp, bool down) {
        ViewportMapType map_type = vp->map_type;
        if (vp->zoom < ZOOM_LVL_DRAW_MAP) return map_type;
        if (down) {
                return (map_type == VPMT_MIN) ? VPMT_MAX : (ViewportMapType) (map_type - 1);
        } else {
                return (map_type == VPMT_MAX) ? VPMT_MIN : (ViewportMapType) (map_type + 1);
        }
}

Point GetViewportStationMiddle(const ViewPort *vp, const Station *st)
{
        int x = TileX(st->xy) * TILE_SIZE;
        int y = TileY(st->xy) * TILE_SIZE;
        int z = GetSlopePixelZ(Clamp(x, 0, MapSizeX() * TILE_SIZE - 1), Clamp(y, 0, MapSizeY() * TILE_SIZE - 1));

        Point p = RemapCoords(x, y, z);
        p.x = UnScaleByZoom(p.x - vp->virtual_left, vp->zoom) + vp->left;
        p.y = UnScaleByZoom(p.y - vp->virtual_top, vp->zoom) + vp->top;
        return p;
}

void DrawOverlay(const TileInfo *ti, TileType tt) 
{
        if (Overlays::Instance()->IsTileLogicSignalInput(ti)) {
                DrawTileSelectionRect(ti, PALETTE_SEL_TILE_RED);
        } else if (Overlays::Instance()->IsTileLogicSignalOutput(ti)) {
                DrawTileSelectionRect(ti, PALETTE_SEL_TILE_BLUE);
        } else if (Overlays::Instance()->IsTileInCatchmentArea(ti, PRODUCTION)) { 
                DrawTileSelectionRect(ti, PALETTE_SEL_TILE_BLUE);
        } else if (Overlays::Instance()->IsTileInCatchmentArea(ti, ACCEPTANCE)) { 
                DrawTileSelectionRect(ti, PAL_NONE);
        }
}

/** Helper class for getting the best sprite sorter. */
struct ViewportSSCSS {
        VpSorterChecker fct_checker; ///< The check function.
        VpSpriteSorter fct_sorter;   ///< The sorting function.
};

/** List of sorters ordered from best to worst. */
static ViewportSSCSS _vp_sprite_sorters[] = {
#ifdef WITH_SSE
        { &ViewportSortParentSpritesSSE41Checker, &ViewportSortParentSpritesSSE41 },
#endif
        { &ViewportSortParentSpritesChecker, &ViewportSortParentSprites }
};

/** Choose the "best" sprite sorter and set _vp_sprite_sorter. */
void InitializeSpriteSorter()
{
        for (uint i = 0; i < lengthof(_vp_sprite_sorters); i++) {
                if (_vp_sprite_sorters[i].fct_checker()) {
                        _vp_sprite_sorter = _vp_sprite_sorters[i].fct_sorter;
                        break;
                }
        }
        assert(_vp_sprite_sorter != nullptr);
}

static LineSnapPoint LineSnapPointAtRailTrackEndpoint(TileIndex tile, DiagDirection exit_dir, bool bidirectional)
{
        LineSnapPoint ret;
        ret.x = (TILE_SIZE / 2) * (uint)(2 * TileX(tile) + TileIndexDiffCByDiagDir(exit_dir).x + 1);
        ret.y = (TILE_SIZE / 2) * (uint)(2 * TileY(tile) + TileIndexDiffCByDiagDir(exit_dir).y + 1);

        ret.dirs = 0;
        SetBit(ret.dirs, DiagDirToDir(exit_dir));
        SetBit(ret.dirs, ChangeDir(DiagDirToDir(exit_dir), DIRDIFF_45LEFT));
        SetBit(ret.dirs, ChangeDir(DiagDirToDir(exit_dir), DIRDIFF_45RIGHT));
        if (bidirectional) ret.dirs |= ROR<uint8>(ret.dirs, DIRDIFF_REVERSE);

        return ret;
}

/**
 * Store the position of lastly built rail track; for highlighting purposes.
 *
 * In "polyline" highlighting mode, the stored end point will be used as a snapping point for new
 * tracks allowing to place multi-segment polylines.
 *
 * @param start_tile         tile where the track starts
 * @param end_tile           tile where the track ends
 * @param start_track        track piece on the start_tile
 * @param bidirectional_exit whether to allow to highlight next track in any direction; otherwise new track will have to fallow the stored one (usefull when placing tunnels and bridges)
 */
void StoreRailPlacementEndpoints(TileIndex start_tile, TileIndex end_tile, Track start_track, bool bidirectional_exit)
{
        if (start_tile != INVALID_TILE && end_tile != INVALID_TILE) {
                /* calculate trackdirs at booth ends of the track */
                Trackdir exit_trackdir_at_start = TrackToTrackdir(start_track);
                Trackdir exit_trackdir_at_end = ReverseTrackdir(TrackToTrackdir(start_track));
                if (start_tile != end_tile) { // multi-tile case
                        /* determine proper direction (pointing outside of the track) */
                        uint distance = DistanceManhattan(start_tile, end_tile);
                        if (distance > DistanceManhattan(TileAddByDiagDir(start_tile, TrackdirToExitdir(exit_trackdir_at_start)), end_tile)) {
                                Swap(exit_trackdir_at_start, exit_trackdir_at_end);
                        }
                        /* determine proper track on the end tile - switch between upper/lower or left/right based on the length */
                        if (distance % 2 != 0) exit_trackdir_at_end = NextTrackdir(exit_trackdir_at_end);
                }

                LineSnapPoint snap_start = LineSnapPointAtRailTrackEndpoint(start_tile, TrackdirToExitdir(exit_trackdir_at_start), bidirectional_exit);
                LineSnapPoint snap_end = LineSnapPointAtRailTrackEndpoint(end_tile, TrackdirToExitdir(exit_trackdir_at_end), bidirectional_exit);
                /* Find if we already had these coordinates before. */
                LineSnapPoint *snap;
                bool had_start = false;
                bool had_end = false;
                for (snap = _rail_snap_points.Begin(); snap != _rail_snap_points.End(); snap++) {
                        had_start |= (snap->x == snap_start.x && snap->y == snap_start.y);
                        had_end |= (snap->x == snap_end.x && snap->y == snap_end.y);
                }
                /* Create new snap point set. */
                if (had_start && had_end) {
                        /* just stop snaping, don't forget snap points */
                        SetRailSnapMode(RSM_NO_SNAP);
                } else {
                        /* include only new points */
                        _rail_snap_points.Clear();
                        if (!had_start) *_rail_snap_points.Append() = snap_start;
                        if (!had_end) *_rail_snap_points.Append() = snap_end;
                        SetRailSnapMode(RSM_SNAP_TO_RAIL);
                }
        }
}

bool CurrentlySnappingRailPlacement()
{
        return (_thd.place_mode & HT_POLY) && GetRailSnapMode() == RSM_SNAP_TO_RAIL;
}

static RailSnapMode GetRailSnapMode()
{
        if (_rail_snap_mode == RSM_SNAP_TO_TILE && _tile_snap_points.Length() == 0) return RSM_NO_SNAP;
        if (_rail_snap_mode == RSM_SNAP_TO_RAIL && _rail_snap_points.Length() == 0) return RSM_NO_SNAP;
        return _rail_snap_mode;
}

static void SetRailSnapMode(RailSnapMode mode)
{
        _rail_snap_mode = mode;

        if ((_thd.place_mode & HT_POLY) && (GetRailSnapMode() == RSM_NO_SNAP)) {
                SetTileSelectSize(1, 1);
        }
}

static TileIndex GetRailSnapTile()
{
        if (_tile_snap_points.Length() == 0) return INVALID_TILE;
        return TileVirtXY(_tile_snap_points[DIAGDIR_NE].x, _tile_snap_points[DIAGDIR_NE].y);
}

static void SetRailSnapTile(TileIndex tile)
{
        _tile_snap_points.Clear();
        if (tile == INVALID_TILE) return;

        for (DiagDirection dir = DIAGDIR_BEGIN; dir < DIAGDIR_END; dir++) {
                LineSnapPoint *point = _tile_snap_points.Append();
                *point = LineSnapPointAtRailTrackEndpoint(tile, dir, false);
                point->dirs = ROR<uint8>(point->dirs, DIRDIFF_REVERSE);
        }
}

void ResetRailPlacementSnapping()
{
        _rail_snap_mode = RSM_NO_SNAP;
        _tile_snap_points.Clear();
        _rail_snap_points.Clear();
        _current_snap_lock.x = -1;
}