Fix #10490: Allow ships to exit depots if another is not moving at the exit point...

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

/*
 * 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 northern most tile on the map defines 0 and
 * everything south of that has a positive number.
 */

#include "stdafx.h"
#include "core/backup_type.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 "vehicle_base.h"
#include "vehicle_gui.h"
#include "blitter/factory.hpp"
#include "strings_func.h"
#include "zoom_func.h"
#include "vehicle_func.h"
#include "company_func.h"
#include "waypoint_func.h"
#include "window_func.h"
#include "tilehighlight_func.h"
#include "window_gui.h"
#include "linkgraph/linkgraph_gui.h"
#include "viewport_kdtree.h"
#include "town_kdtree.h"
#include "viewport_sprite_sorter.h"
#include "bridge_map.h"
#include "company_base.h"
#include "command_func.h"
#include "network/network_func.h"
#include "framerate_type.h"
#include "viewport_cmd.h"

#include <forward_list>
#include <stack>

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

#include "safeguards.h"

Point _tile_fract_coords;


ViewportSignKdtree _viewport_sign_kdtree(&Kdtree_ViewportSignXYFunc);
static int _viewport_sign_maxwidth = 0;


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 {
        std::string string;
        StringID string_id;
        Colours colour;
        int32_t x;
        int32_t y;
        uint16_t width;
};

struct TileSpriteToDraw {
        SpriteID image;
        PaletteID pal;
        const SubSprite *sub;           ///< only draw a rectangular part of the sprite
        int32_t x;                        ///< screen X coordinate of sprite
        int32_t y;                        ///< screen Y coordinate of sprite
};

struct ChildScreenSpriteToDraw {
        SpriteID image;
        PaletteID pal;
        const SubSprite *sub;           ///< only draw a rectangular part of the sprite
        int32_t x;
        int32_t y;
        bool relative;
        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 std::vector<TileSpriteToDraw> TileSpriteToDrawVector;
typedef std::vector<StringSpriteToDraw> StringSpriteToDrawVector;
typedef std::vector<ParentSpriteToDraw> ParentSpriteToDrawVector;
typedef std::vector<ChildScreenSpriteToDraw> ChildScreenSpriteToDrawVector;

/** 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;

        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 bool MarkViewportDirty(const Viewport *vp, int left, int top, int right, int bottom);

static ViewportDrawer _vd;

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;

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)
{
        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 focus Either the tile index or vehicle ID to focus.
 * @param zoom Zoomlevel to display
 */
void InitializeWindowViewport(Window *w, int x, int y,
        int width, int height, std::variant<TileIndex, VehicleID> focus, ZoomLevel zoom)
{
        assert(w->viewport == nullptr);

        ViewportData *vp = new ViewportData();

        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_width = ScaleByZoom(width, zoom);
        vp->virtual_height = ScaleByZoom(height, zoom);

        Point pt;

        if (std::holds_alternative<VehicleID>(focus)) {
                const Vehicle *veh;

                vp->follow_vehicle = std::get<VehicleID>(focus);
                veh = Vehicle::Get(vp->follow_vehicle);
                pt = MapXYZToViewport(vp, veh->x_pos, veh->y_pos, veh->z_pos);
        } else {
                TileIndex tile = std::get<TileIndex>(focus);
                if (tile == INVALID_TILE) {
                        /* No tile? Use center of main viewport. */
                        const Window *mw = GetMainWindow();

                        /* center on same place as main window (zoom is maximum, no adjustment needed) */
                        pt.x = mw->viewport->scrollpos_x + mw->viewport->virtual_width / 2;
                        pt.x -= vp->virtual_width / 2;
                        pt.y = mw->viewport->scrollpos_y + mw->viewport->virtual_height / 2;
                        pt.y -= vp->virtual_height / 2;
                } else {
                        x = TileX(tile) * TILE_SIZE;
                        y = TileY(tile) * TILE_SIZE;
                        pt = MapXYZToViewport(vp, x, y, GetSlopePixelZ(x, y));
                }
                vp->follow_vehicle = INVALID_VEHICLE;
        }

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

        vp->overlay = nullptr;

        w->viewport = vp;
        vp->virtual_left = 0;
        vp->virtual_top = 0;
}

static Point _vp_move_offs;

static void DoSetViewportPosition(Window::IteratorToFront it, int left, int top, int width, int height)
{
        for (; !it.IsEnd(); ++it) {
                const Window *w = *it;
                if (left + width > w->left &&
                                w->left + w->width > left &&
                                top + height > w->top &&
                                w->top + w->height > top) {

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

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

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

                        if (top + height > w->top + w->height) {
                                DoSetViewportPosition(it, left, top, width, (w->top + w->height - top));
                                DoSetViewportPosition(it, 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) {
                        Window::IteratorToFront it(w);
                        ++it;
                        DoSetViewportPosition(it, 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 underlying tile coordinate.
 *
 * Returns exact point of the map that is visible in the given place
 * of the viewport (3D perspective), height of tiles and foundations matter.
 *
 * @param vp  Viewport that contains the (\a x, \a y) screen coordinate
 * @param x   Screen x coordinate, distance in pixels from the left edge of viewport frame
 * @param y   Screen y coordinate, distance in pixels from the top edge of viewport frame
 * @param clamp_to_map Clamp the coordinate outside of the map to the closest, non-void tile within the map
 * @return Tile coordinate or (-1, -1) if given x or y is not within viewport frame
 */
Point TranslateXYToTileCoord(const Viewport *vp, int x, int y, bool clamp_to_map)
{
        if (!IsInsideBS(x, vp->left, vp->width) || !IsInsideBS(y, vp->top, vp->height)) {
                Point pt = { -1, -1 };
                return pt;
        }

        return InverseRemapCoords2(
                        ScaleByZoom(x - vp->left, vp->zoom) + vp->virtual_left,
                        ScaleByZoom(y - vp->top, vp->zoom) + vp->virtual_top, clamp_to_map);
}

/* 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, WidgetID widget_zoom_in, WidgetID 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_t x, int32_t 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.emplace_back();
        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, 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_t x, int32_t 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] = (uint)_vd.parent_sprites_to_draw.size() - 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, SpriteType::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.back();
        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_t 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, SpriteType::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   = std::min(left  , RemapCoords(x + w          , y + bb_offset_y, z + bb_offset_z).x);
                right  = std::max(right , RemapCoords(x + bb_offset_x, y + h          , z + bb_offset_z).x + 1);
                top    = std::min(top   , RemapCoords(x + bb_offset_x, y + bb_offset_y, z + dz         ).y);
                bottom = std::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.emplace_back();
        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 + std::max(bb_offset_x, w) - 1;

        ps.ymin = y + bb_offset_y;
        ps.ymax = y + std::max(bb_offset_y, h) - 1;

        ps.zmin = z + bb_offset_z;
        ps.zmax = z + std::max(bb_offset_z, dz) - 1;

        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 a diagonal rectangle given by _thd.size and _thd.pos
 * @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.
 */
bool IsInsideRotatedRectangle(int x, int 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.
 * @param scale if true, scale offsets to base zoom level.
 * @param relative if true, draw sprite relative to parent sprite offsets.
 */
void AddChildSpriteScreen(SpriteID image, PaletteID pal, int x, int y, bool transparent, const SubSprite *sub, bool scale, bool relative)
{
        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 = (uint)_vd.child_screen_sprites_to_draw.size();

        ChildScreenSpriteToDraw &cs = _vd.child_screen_sprites_to_draw.emplace_back();
        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.relative = relative;
        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, Colours colour, uint16_t width)
{
        assert(width != 0);
        StringSpriteToDraw &ss = _vd.string_sprites_to_draw.emplace_back();
        ss.string = GetString(string);
        ss.string_id = string;
        ss.x = x;
        ss.y = y;
        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.
 * @param extra_offs_x Pixel X offset for the sprite position.
 * @param extra_offs_y Pixel Y offset for the sprite position.
 */
static void DrawSelectionSprite(SpriteID image, PaletteID pal, const TileInfo *ti, int z_offset, FoundationPart foundation_part, int extra_offs_x = 0, int extra_offs_y = 0)
{
        /* 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, nullptr, extra_offs_x, extra_offs_y);
        } else {
                /* draw on top of foundation */
                AddChildSpriteToFoundation(image, pal, nullptr, foundation_part, extra_offs_x, extra_offs_y - 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 bool IsPartOfAutoLine(int px, int py)
{
        px -= _thd.selstart.x;
        py -= _thd.selstart.y;

        if ((_thd.drawstyle & HT_DRAG_MASK) != HT_LINE) return false;

        switch (_thd.drawstyle & HT_DIR_MASK) {
                case HT_DIR_X:  return py == 0; // x direction
                case HT_DIR_Y:  return px == 0; // y direction
                case HT_DIR_HU: return px == -py || px == -py - 16; // horizontal upper
                case HT_DIR_HL: return px == -py || px == -py + 16; // horizontal lower
                case HT_DIR_VL: return px == py || px == py + 16; // vertical left
                case HT_DIR_VR: return px == py || px == py - 16; // vertical right
                default:
                        NOT_REACHED();
        }
}

/* [direction][side] */
static const HighLightStyle _autorail_type[6][2] = {
        { HT_DIR_X,  HT_DIR_X },
        { HT_DIR_Y,  HT_DIR_Y },
        { HT_DIR_HU, HT_DIR_HL },
        { HT_DIR_HL, HT_DIR_HU },
        { HT_DIR_VL, HT_DIR_VR },
        { HT_DIR_VR, HT_DIR_VL }
};

#include "table/autorail.h"

/**
 * Draws autorail highlights.
 *
 * @param *ti TileInfo Tile that is being drawn
 * @param autorail_type Offset into _AutorailTilehSprite[][]
 */
static void DrawAutorailSelection(const TileInfo *ti, uint autorail_type)
{
        SpriteID image;
        PaletteID pal;
        int offset;

        FoundationPart foundation_part = FOUNDATION_PART_NORMAL;
        Slope autorail_tileh = RemoveHalftileSlope(ti->tileh);
        if (IsHalftileSlope(ti->tileh)) {
                static const uint _lower_rail[4] = { 5U, 2U, 4U, 3U };
                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));
                }
        }

        offset = _AutorailTilehSprite[autorail_tileh][autorail_type];
        if (offset >= 0) {
                image = SPR_AUTORAIL_BASE + offset;
                pal = PAL_NONE;
        } else {
                image = SPR_AUTORAIL_BASE - offset;
                pal = PALETTE_SEL_TILE_RED;
        }

        DrawSelectionSprite(image, _thd.make_square_red ? PALETTE_SEL_TILE_RED : pal, ti, 7, foundation_part);
}

enum TileHighlightType {
        THT_NONE,
        THT_WHITE,
        THT_BLUE,
        THT_RED,
};

const Station *_viewport_highlight_station; ///< Currently selected station for coverage area highlight
const Waypoint *_viewport_highlight_waypoint; ///< Currently selected waypoint for coverage area highlight
const Town *_viewport_highlight_town; ///< Currently selected town for coverage area highlight

/**
 * Get tile highlight type of coverage area for a given tile.
 * @param t Tile that is being drawn
 * @return Tile highlight type to draw
 */
static TileHighlightType GetTileHighlightType(TileIndex t)
{
        if (_viewport_highlight_station != nullptr) {
                if (IsTileType(t, MP_STATION) && GetStationIndex(t) == _viewport_highlight_station->index) return THT_WHITE;
                if (_viewport_highlight_station->TileIsInCatchment(t)) return THT_BLUE;
        }
        if (_viewport_highlight_waypoint != nullptr) {
                if (IsTileType(t, MP_STATION) && GetStationIndex(t) == _viewport_highlight_waypoint->index) return THT_BLUE;
        }

        if (_viewport_highlight_town != nullptr) {
                if (IsTileType(t, MP_HOUSE)) {
                        if (GetTownIndex(t) == _viewport_highlight_town->index) {
                                TileHighlightType type = THT_RED;
                                for (const Station *st : _viewport_highlight_town->stations_near) {
                                        if (st->owner != _current_company) continue;
                                        if (st->TileIsInCatchment(t)) return THT_BLUE;
                                }
                                return type;
                        }
                } else if (IsTileType(t, MP_STATION)) {
                        for (const Station *st : _viewport_highlight_town->stations_near) {
                                if (st->owner != _current_company) continue;
                                if (GetStationIndex(t) == st->index) return THT_WHITE;
                        }
                }
        }

        return THT_NONE;
}

/**
 * Draw tile highlight for coverage area highlight.
 * @param *ti TileInfo Tile that is being drawn
 * @param tht Highlight type to draw.
 */
static void DrawTileHighlightType(const TileInfo *ti, TileHighlightType tht)
{
        switch (tht) {
                default:
                case THT_NONE: break;
                case THT_WHITE: DrawTileSelectionRect(ti, PAL_NONE); break;
                case THT_BLUE:  DrawTileSelectionRect(ti, PALETTE_SEL_TILE_BLUE); break;
                case THT_RED:   DrawTileSelectionRect(ti, PALETTE_SEL_TILE_RED); break;
        }
}

/**
 * Highlights tiles insede local authority of selected towns.
 * @param *ti TileInfo Tile that is being drawn
 */
static void HighlightTownLocalAuthorityTiles(const TileInfo *ti)
{
        /* Going through cases in order of computational time. */

        if (_town_local_authority_kdtree.Count() == 0) return;

        /* Tile belongs to town regardless of distance from town. */
        if (GetTileType(ti->tile) == MP_HOUSE) {
                if (!Town::GetByTile(ti->tile)->show_zone) return;

                DrawTileSelectionRect(ti, PALETTE_CRASH);
                return;
        }

        /* If the closest town in the highlighted list is far, we can stop searching. */
        TownID tid = _town_local_authority_kdtree.FindNearest(TileX(ti->tile), TileY(ti->tile));
        Town *closest_highlighted_town = Town::Get(tid);

        if (DistanceManhattan(ti->tile, closest_highlighted_town->xy) >= _settings_game.economy.dist_local_authority) return;

        /* Tile is inside of the local autrhority distance of a highlighted town,
           but it is possible that a non-highlighted town is even closer. */
        Town *closest_town = ClosestTownFromTile(ti->tile, _settings_game.economy.dist_local_authority);

        if (closest_town->show_zone) {
                DrawTileSelectionRect(ti, PALETTE_CRASH);
        }

}

/**
 * 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)
{
        /* Highlight tiles insede local authority of selected towns. */
        HighlightTownLocalAuthorityTiles(ti);

        /* Draw a red error square? */
        bool is_redsq = _thd.redsq == ti->tile;
        if (is_redsq) DrawTileSelectionRect(ti, PALETTE_TILE_RED_PULSATING);

        TileHighlightType tht = GetTileHighlightType(ti->tile);
        DrawTileHighlightType(ti, tht);

        /* No tile selection active? */
        if ((_thd.drawstyle & HT_DRAG_MASK) == HT_NONE) return;

        if (_thd.diagonal) { // We're drawing a 45 degrees rotated (diagonal) rectangle
                if (IsInsideRotatedRectangle((int)ti->x, (int)ti->y)) goto draw_inner;
                return;
        }

        /* Inside the inner area? */
        if (IsInsideBS(ti->x, _thd.pos.x, _thd.size.x) &&
                        IsInsideBS(ti->y, _thd.pos.y, _thd.size.y)) {
draw_inner:
                if (_thd.drawstyle & HT_RECT) {
                        if (!is_redsq) DrawTileSelectionRect(ti, _thd.make_square_red ? PALETTE_SEL_TILE_RED : PAL_NONE);
                } else if (_thd.drawstyle & HT_POINT) {
                        /* 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(SPR_DOT, PAL_NONE, ti, z, foundation_part);
                } else if (_thd.drawstyle & HT_RAIL) {
                        /* autorail highlight piece under cursor */
                        HighLightStyle type = _thd.drawstyle & HT_DIR_MASK;
                        assert(type < HT_DIR_END);
                        DrawAutorailSelection(ti, _autorail_type[type][0]);
                } else if (IsPartOfAutoLine(ti->x, ti->y)) {
                        /* autorail highlighting long line */
                        HighLightStyle dir = _thd.drawstyle & HT_DIR_MASK;
                        uint side;

                        if (dir == HT_DIR_X || dir == HT_DIR_Y) {
                                side = 0;
                        } else {
                                TileIndex start = TileVirtXY(_thd.selstart.x, _thd.selstart.y);
                                side = Delta(Delta(TileX(start), TileX(ti->tile)), Delta(TileY(start), TileY(ti->tile)));
                        }

                        DrawAutorailSelection(ti, _autorail_type[dir][side]);
                }
                return;
        }

        /* Check if it's inside the outer area? */
        if (!is_redsq && (tht == THT_NONE || tht == THT_RED) && _thd.outersize.x > 0 &&
                        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);
                return;
        }
}

/**
 * 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;
                        _cur_ti.x = tilecoord.x * TILE_SIZE;
                        _cur_ti.y = tilecoord.y * TILE_SIZE;

                        if (IsInsideBS(tilecoord.x, 0, Map::SizeX()) && IsInsideBS(tilecoord.y, 0, Map::SizeY())) {
                                /* This includes the south border at Map::MaxX / Map::MaxY. When terraforming we still draw tile selections there. */
                                _cur_ti.tile = TileXY(tilecoord.x, tilecoord.y);
                                tile_type = GetTileType(_cur_ti.tile);
                        } else {
                                _cur_ti.tile = INVALID_TILE;
                                tile_type = MP_VOID;
                        }

                        if (tile_type != MP_VOID) {
                                /* We are inside the map => paint landscape. */
                                _cur_ti.tileh = GetTilePixelSlope(_cur_ti.tile, &_cur_ti.z);
                        } else {
                                /* We are outside the map => paint black. */
                                _cur_ti.tileh = GetTilePixelSlopeOutsideMap(tilecoord.x, tilecoord.y, &_cur_ti.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(_cur_ti.tile)) {
                                        /* Is the bridge visible? */
                                        TileIndex bridge_tile = GetNorthernBridgeEnd(_cur_ti.tile);
                                        int bridge_height = ZOOM_LVL_BASE * (GetBridgePixelHeight(bridge_tile) - TilePixelHeight(_cur_ti.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(&_cur_ti);
                                if (_cur_ti.tile != INVALID_TILE) DrawTileSelection(&_cur_ti);
                        }
                }
        }
}

/**
 * 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, 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(WidgetDimensions::scaled.fullbevel.top + GetCharacterHeight(FS_NORMAL) + WidgetDimensions::scaled.fullbevel.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, 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, INVALID_COLOUR, sign->width_small | 0x8000);
                }
                AddStringToDraw(sign->center - sign_half_width, sign->top - shadow_offset, string_small, colour, sign->width_small | 0x8000);
        }
}

static Rect ExpandRectWithViewportSignMargins(Rect r, ZoomLevel zoom)
{
        /* Pessimistically always use normal font, but also assume small font is never larger in either dimension */
        const int fh = GetCharacterHeight(FS_NORMAL);
        const int max_tw = _viewport_sign_maxwidth / 2 + 1;
        const int expand_y = ScaleByZoom(WidgetDimensions::scaled.fullbevel.top + fh + WidgetDimensions::scaled.fullbevel.bottom, zoom);
        const int expand_x = ScaleByZoom(WidgetDimensions::scaled.fullbevel.left + max_tw + WidgetDimensions::scaled.fullbevel.right, zoom);

        r.left -= expand_x;
        r.right += expand_x;
        r.top -= expand_y;
        r.bottom += expand_y;

        return r;
}

static void ViewportAddKdtreeSigns(DrawPixelInfo *dpi)
{
        Rect search_rect{ dpi->left, dpi->top, dpi->left + dpi->width, dpi->top + dpi->height };
        search_rect = ExpandRectWithViewportSignMargins(search_rect, dpi->zoom);

        bool show_stations = HasBit(_display_opt, DO_SHOW_STATION_NAMES) && _game_mode != GM_MENU;
        bool show_waypoints = HasBit(_display_opt, DO_SHOW_WAYPOINT_NAMES) && _game_mode != GM_MENU;
        bool show_towns = HasBit(_display_opt, DO_SHOW_TOWN_NAMES) && _game_mode != GM_MENU;
        bool show_signs = HasBit(_display_opt, DO_SHOW_SIGNS) && !IsInvisibilitySet(TO_SIGNS);
        bool show_competitors = HasBit(_display_opt, DO_SHOW_COMPETITOR_SIGNS);

        /* Collect all the items first and draw afterwards, to ensure layering */
        std::vector<const BaseStation *> stations;
        std::vector<const Town *> towns;
        std::vector<const Sign *> signs;

        _viewport_sign_kdtree.FindContained(search_rect.left, search_rect.top, search_rect.right, search_rect.bottom, [&](const ViewportSignKdtreeItem & item) {
                switch (item.type) {
                        case ViewportSignKdtreeItem::VKI_STATION: {
                                if (!show_stations) break;
                                const BaseStation *st = BaseStation::Get(item.id.station);

                                /* Don't draw if station is owned by another company and competitor station names are hidden. Stations owned by none are never ignored. */
                                if (!show_competitors && _local_company != st->owner && st->owner != OWNER_NONE) break;

                                stations.push_back(st);
                                break;
                        }

                        case ViewportSignKdtreeItem::VKI_WAYPOINT: {
                                if (!show_waypoints) break;
                                const BaseStation *st = BaseStation::Get(item.id.station);

                                /* Don't draw if station is owned by another company and competitor station names are hidden. Stations owned by none are never ignored. */
                                if (!show_competitors && _local_company != st->owner && st->owner != OWNER_NONE) break;

                                stations.push_back(st);
                                break;
                        }

                        case ViewportSignKdtreeItem::VKI_TOWN:
                                if (!show_towns) break;
                                towns.push_back(Town::Get(item.id.town));
                                break;

                        case ViewportSignKdtreeItem::VKI_SIGN: {
                                if (!show_signs) break;
                                const Sign *si = Sign::Get(item.id.sign);

                                /* 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 (!show_competitors && _local_company != si->owner && si->owner != OWNER_DEITY) break;

                                signs.push_back(si);
                                break;
                        }

                        default:
                                NOT_REACHED();
                }
        });

        /* Layering order (bottom to top): Town names, signs, stations */

        for (const auto *t : towns) {
                SetDParam(0, t->index);
                SetDParam(1, t->cache.population);
                ViewportAddString(dpi, ZOOM_LVL_OUT_16X, &t->cache.sign,
                        _settings_client.gui.population_in_label ? STR_VIEWPORT_TOWN_POP : STR_VIEWPORT_TOWN,
                        STR_VIEWPORT_TOWN_TINY_WHITE, STR_VIEWPORT_TOWN_TINY_BLACK);
        }

        /* Do not draw signs nor station names if they are set invisible */
        if (IsInvisibilitySet(TO_SIGNS)) return;

        for (const auto *si : signs) {
                SetDParam(0, si->index);
                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->owner == OWNER_NONE) ? COLOUR_GREY : (si->owner == OWNER_DEITY ? INVALID_COLOUR : _company_colours[si->owner]));
        }

        for (const auto *st : stations) {
                SetDParam(0, st->index);
                SetDParam(1, st->facilities);
                if (Station::IsExpected(st)) {
                        /* Station */
                        ViewportAddString(dpi, ZOOM_LVL_OUT_16X, &st->sign,
                                STR_VIEWPORT_STATION, STR_VIEWPORT_STATION_TINY, STR_NULL,
                                (st->owner == OWNER_NONE || !st->IsInUse()) ? COLOUR_GREY : _company_colours[st->owner]);
                } else {
                        /* Waypoint */
                        ViewportAddString(dpi, ZOOM_LVL_OUT_16X, &st->sign,
                                STR_VIEWPORT_WAYPOINT, STR_VIEWPORT_WAYPOINT_TINY, STR_NULL,
                                (st->owner == OWNER_NONE || !st->IsInUse()) ? COLOUR_GREY : _company_colours[st->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;

        std::string name = GetString(str);
        this->width_normal = WidgetDimensions::scaled.fullbevel.left + Align(GetStringBoundingBox(name).width, 2) + WidgetDimensions::scaled.fullbevel.right;
        this->center = center;

        /* zoomed out version */
        if (str_small != STR_NULL) {
                name = GetString(str_small);
        }
        this->width_small = WidgetDimensions::scaled.fullbevel.left + Align(GetStringBoundingBox(name, FS_SMALL).width, 2) + WidgetDimensions::scaled.fullbevel.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_END];

        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(WidgetDimensions::scaled.fullbevel.top + GetCharacterHeight(FS_NORMAL) + WidgetDimensions::scaled.fullbevel.bottom + 1, zoom);
        }

        for (const Window *w : Window::Iterate()) {
                Viewport *vp = w->viewport;
                if (vp != nullptr && vp->zoom <= maxzoom) {
                        assert(vp->width != 0);
                        Rect &zl = zoomlevels[vp->zoom];
                        MarkViewportDirty(vp, zl.left, zl.top, zl.right, zl.bottom);
                }
        }
}

static void ViewportDrawTileSprites(const TileSpriteToDrawVector *tstdv)
{
        for (const TileSpriteToDraw &ts : *tstdv) {
                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 replicating the way original sorter did it. */
static void ViewportSortParentSprites(ParentSpriteToSortVector *psdv)
{
        if (psdv->size() < 2) return;

        /* We rely on sprites being, for the most part, already ordered.
         * So we don't need to move many of them and can keep track of their
         * order efficiently by using stack. We always move sprites to the front
         * of the current position, i.e. to the top of the stack.
         * Also use special constants to indicate sorting state without
         * adding extra fields to ParentSpriteToDraw structure.
         */
        const uint32_t ORDER_COMPARED = UINT32_MAX; // Sprite was compared but we still need to compare the ones preceding it
        const uint32_t ORDER_RETURNED = UINT32_MAX - 1; // Makr sorted sprite in case there are other occurrences of it in the stack
        std::stack<ParentSpriteToDraw *> sprite_order;
        uint32_t next_order = 0;

        std::forward_list<std::pair<int64_t, ParentSpriteToDraw *>> sprite_list;  // We store sprites in a list sorted by xmin+ymin

        /* Initialize sprite list and order. */
        for (auto p = psdv->rbegin(); p != psdv->rend(); p++) {
                sprite_list.push_front(std::make_pair((*p)->xmin + (*p)->ymin, *p));
                sprite_order.push(*p);
                (*p)->order = next_order++;
        }

        sprite_list.sort();

        std::vector<ParentSpriteToDraw *> preceding;  // Temporarily stores sprites that precede current and their position in the list
        auto preceding_prev = sprite_list.begin(); // Store iterator in case we need to delete a single preciding sprite
        auto out = psdv->begin();  // Iterator to output sorted sprites

        while (!sprite_order.empty()) {

                auto s = sprite_order.top();
                sprite_order.pop();

                /* Sprite is already sorted, ignore it. */
                if (s->order == ORDER_RETURNED) continue;

                /* Sprite was already compared, just need to output it. */
                if (s->order == ORDER_COMPARED) {
                        *(out++) = s;
                        s->order = ORDER_RETURNED;
                        continue;
                }

                preceding.clear();

                /* We only need sprites with xmin <= s->xmax && ymin <= s->ymax && zmin <= s->zmax
                 * So by iterating sprites with xmin + ymin <= s->xmax + s->ymax
                 * we get all we need and some more that we filter out later.
                 * We don't include zmin into the sum as there are usually more neighbors on x and y than z
                 * so including it will actually increase the amount of false positives.
                 * Also min coordinates can be > max so using max(xmin, xmax) + max(ymin, ymax)
                 * to ensure that we iterate the current sprite as we need to remove it from the list.
                 */
                auto ssum = std::max(s->xmax, s->xmin) + std::max(s->ymax, s->ymin);
                auto prev = sprite_list.before_begin();
                auto x = sprite_list.begin();
                while (x != sprite_list.end() && ((*x).first <= ssum)) {
                        auto p = (*x).second;
                        if (p == s) {
                                /* We found the current sprite, remove it and move on. */
                                x = sprite_list.erase_after(prev);
                                continue;
                        }

                        auto p_prev = prev;
                        prev = x++;

                        if (s->xmax < p->xmin || s->ymax < p->ymin || s->zmax < p->zmin) continue;
                        if (s->xmin <= p->xmax && // overlap in X?
                                        s->ymin <= p->ymax && // overlap in Y?
                                        s->zmin <= p->zmax) { // overlap in Z?
                                if (s->xmin + s->xmax + s->ymin + s->ymax + s->zmin + s->zmax <=
                                                p->xmin + p->xmax + p->ymin + p->ymax + p->zmin + p->zmax) {
                                        continue;
                                }
                        }
                        preceding.push_back(p);
                        preceding_prev = p_prev;
                }

                if (preceding.empty()) {
                        /* No preceding sprites, add current one to the output */
                        *(out++) = s;
                        s->order = ORDER_RETURNED;
                        continue;
                }

                /* Optimization for the case when we only have 1 sprite to move. */
                if (preceding.size() == 1) {
                        auto p = preceding[0];
                        /* We can only output the preceding sprite if there can't be any other sprites preceding it. */
                        if (p->xmax <= s->xmax && p->ymax <= s->ymax && p->zmax <= s->zmax) {
                                p->order = ORDER_RETURNED;
                                s->order = ORDER_RETURNED;
                                sprite_list.erase_after(preceding_prev);
                                *(out++) = p;
                                *(out++) = s;
                                continue;
                        }
                }

                /* Sort all preceding sprites by order and assign new orders in reverse (as original sorter did). */
                std::sort(preceding.begin(), preceding.end(), [](const ParentSpriteToDraw *a, const ParentSpriteToDraw *b) {
                        return a->order > b->order;
                });

                s->order = ORDER_COMPARED;
                sprite_order.push(s);  // Still need to output so push it back for now

                for (auto p: preceding) {
                        p->order = next_order++;
                        sprite_order.push(p);
                }
        }
}


static void ViewportDrawParentSprites(const ParentSpriteToSortVector *psd, const ChildScreenSpriteToDrawVector *csstdv)
{
        for (const ParentSpriteToDraw *ps : *psd) {
                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->data() + child_idx;
                        child_idx = cs->next;
                        if (cs->relative) {
                                DrawSpriteViewport(cs->image, cs->pal, ps->left + cs->x, ps->top + cs->y, cs->sub);
                        } else {
                                DrawSpriteViewport(cs->image, cs->pal, ps->x + cs->x, ps->y + cs->y, cs->sub);
                        }
                }
        }
}

/**
 * Draws the bounding boxes of all ParentSprites
 * @param psd Array of ParentSprites
 */
static void ViewportDrawBoundingBoxes(const ParentSpriteToSortVector *psd)
{
        for (const ParentSpriteToDraw *ps : *psd) {
                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);
        }
}

/**
 * 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_t)colour);
                dst = blitter->MoveTo(dst, 0, 1);
        } while (--bottom > 0);
}

static void ViewportDrawStrings(ZoomLevel zoom, const StringSpriteToDrawVector *sstdv)
{
        for (const StringSpriteToDraw &ss : *sstdv) {
                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 = WidgetDimensions::scaled.fullbevel.top + (small ? GetCharacterHeight(FS_SMALL) : GetCharacterHeight(FS_NORMAL)) + WidgetDimensions::scaled.fullbevel.bottom;

                if (ss.colour != INVALID_COLOUR) {
                        if (IsTransparencySet(TO_SIGNS) && ss.string_id != 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 - 1, y + h - 1, ss.colour,
                                        IsTransparencySet(TO_SIGNS) ? FR_TRANSPARENT : FR_NONE
                                );
                        }
                }

                DrawString(x + WidgetDimensions::scaled.fullbevel.left, x + w - 1 - WidgetDimensions::scaled.fullbevel.right, y + WidgetDimensions::scaled.fullbevel.top, ss.string, colour, SA_HOR_CENTER, false, small ? FS_SMALL : FS_NORMAL);
        }
}

void ViewportDoDraw(const Viewport *vp, int left, int top, int right, int bottom)
{
        _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 = _cur_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(_cur_dpi->dst_ptr, x - _cur_dpi->left, y - _cur_dpi->top);
        AutoRestoreBackup dpi_backup(_cur_dpi, &_vd.dpi);

        ViewportAddLandscape();
        ViewportAddVehicles(&_vd.dpi);

        ViewportAddKdtreeSigns(&_vd.dpi);

        DrawTextEffects(&_vd.dpi);

        if (!_vd.tile_sprites_to_draw.empty()) ViewportDrawTileSprites(&_vd.tile_sprites_to_draw);

        for (auto &psd : _vd.parent_sprites_to_draw) {
                _vd.parent_sprites_to_sort.push_back(&psd);
        }

        _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 (!_vd.string_sprites_to_draw.empty()) {
                /* 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);
        }

        _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();
}

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;

        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
        );
}

/**
 * Draw the viewport of this window.
 */
void Window::DrawViewport() const
{
        PerformanceAccumulator framerate(PFE_DRAWWORLD);

        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;
}

/**
 * Ensure that a given viewport has a valid scroll position.
 *
 * There must be a visible piece of the map in the center of the viewport.
 * If there isn't, the viewport will be scrolled to nearest such location.
 *
 * @param vp The viewport.
 * @param[in,out] scroll_x Viewport X scroll.
 * @param[in,out] scroll_y Viewport Y scroll.
 */
static inline void ClampViewportToMap(const Viewport *vp, int *scroll_x, int *scroll_y)
{
        /* Centre of the viewport is hot spot. */
        Point pt = {
                *scroll_x + vp->virtual_width / 2,
                *scroll_y + vp->virtual_height / 2
        };

        /* Find nearest tile that is within borders of the map. */
        bool clamped;
        pt = InverseRemapCoords2(pt.x, pt.y, true, &clamped);

        if (clamped) {
                /* Convert back to viewport coordinates and remove centering. */
                pt = RemapCoords2(pt.x, pt.y);
                *scroll_x = pt.x - vp->virtual_width / 2;
                *scroll_y = pt.y - vp->virtual_height / 2;
        }
}

/**
 * Clamp the smooth scroll to a maxmimum speed and distance based on time elapsed.
 *
 * Every 30ms, we move 1/4th of the distance, to give a smooth movement experience.
 * But we never go over the max_scroll speed.
 *
 * @param delta_ms Time elapsed since last update.
 * @param delta_hi The distance to move in highest dimension (can't be zero).
 * @param delta_lo The distance to move in lowest dimension.
 * @param[out] delta_hi_clamped The clamped distance to move in highest dimension.
 * @param[out] delta_lo_clamped The clamped distance to move in lowest dimension.
 */
static void ClampSmoothScroll(uint32_t delta_ms, int64_t delta_hi, int64_t delta_lo, int &delta_hi_clamped, int &delta_lo_clamped)
{
        /** A tile is 64 pixels in width at 1x zoom; viewport coordinates are in 4x zoom. */
        constexpr int PIXELS_PER_TILE = TILE_PIXELS * 2 * ZOOM_LVL_BASE;

        assert(delta_hi != 0);

        /* Move at most 75% of the distance every 30ms, for a smooth experience */
        int64_t delta_left = delta_hi * std::pow(0.75, delta_ms / 30.0);
        /* Move never more than 16 tiles per 30ms. */
        int max_scroll = Map::ScaleBySize1D(16 * PIXELS_PER_TILE * delta_ms / 30);

        /* We never go over the max_scroll speed. */
        delta_hi_clamped = Clamp(delta_hi - delta_left, -max_scroll, max_scroll);
        /* The lower delta is in ratio of the higher delta, so we keep going straight at the destination. */
        delta_lo_clamped = delta_lo * delta_hi_clamped / delta_hi;

        /* Ensure we always move (delta_hi can't be zero). */
        if (delta_hi_clamped == 0) {
                delta_hi_clamped = delta_hi > 0 ? 1 : -1;
        }
}

/**
 * Update the viewport position being displayed.
 * @param w %Window owning the viewport.
 */
void UpdateViewportPosition(Window *w, uint32_t delta_ms)
{
        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;

                int current_x = w->viewport->scrollpos_x;
                int current_y = w->viewport->scrollpos_y;

                bool update_overlay = false;
                if (delta_x != 0 || delta_y != 0) {
                        if (_settings_client.gui.smooth_scroll) {
                                int delta_x_clamped;
                                int delta_y_clamped;

                                if (abs(delta_x) > abs(delta_y)) {
                                        ClampSmoothScroll(delta_ms, delta_x, delta_y, delta_x_clamped, delta_y_clamped);
                                } else {
                                        ClampSmoothScroll(delta_ms, delta_y, delta_x, delta_y_clamped, delta_x_clamped);
                                }

                                w->viewport->scrollpos_x += delta_x_clamped;
                                w->viewport->scrollpos_y += delta_y_clamped;
                        } 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);

                /* When moving small amounts around the border we can get stuck, and
                 * not actually move. In those cases, teleport to the destination. */
                if ((delta_x != 0 || delta_y != 0) && current_x == w->viewport->scrollpos_x && current_y == w->viewport->scrollpos_y) {
                        w->viewport->scrollpos_x = w->viewport->dest_scrollpos_x;
                        w->viewport->scrollpos_y = w->viewport->dest_scrollpos_y;
                }

                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
 * @return true if the viewport contains a dirty block
 * @ingroup dirty
 */
static bool MarkViewportDirty(const Viewport *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 false;

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

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

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

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

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

        AddDirtyBlock(
                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
        );

        return true;
}

/**
 * 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)
 * @return true if at least one viewport has a dirty block
 * @ingroup dirty
 */
bool MarkAllViewportsDirty(int left, int top, int right, int bottom)
{
        bool dirty = false;

        for (const Window *w : Window::Iterate()) {
                Viewport *vp = w->viewport;
                if (vp != nullptr) {
                        assert(vp->width != 0);
                        if (MarkViewportDirty(vp, left, top, right, bottom)) dirty = true;
                }
        }

        return dirty;
}

void ConstrainAllViewportsZoom()
{
        for (Window *w : Window::Iterate()) {
                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.)
 * @param tile_height_override Height of the tile (#TileHeight).
 * @ingroup dirty
 */
void MarkTileDirtyByTile(TileIndex tile, int bridge_level_offset, int tile_height_override)
{
        Point pt = RemapCoords(TileX(tile) * TILE_SIZE, TileY(tile) * TILE_SIZE, tile_height_override * TILE_HEIGHT);
        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);
}

/**
 * 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) {
                        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, Map::SizeX() * TILE_SIZE - TILE_SIZE);
                int y_end = Clamp(y_start + y_size, 0, Map::SizeY() * TILE_SIZE - TILE_SIZE);

                x_start = Clamp(x_start, 0, Map::SizeX() * TILE_SIZE - TILE_SIZE);
                y_start = Clamp(y_start, 0, Map::SizeY() * 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 < Map::MaxX() && y < Map::MaxY()) {
                                        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(WidgetDimensions::scaled.fullbevel.top + (small ? GetCharacterHeight(FS_SMALL) : GetCharacterHeight(FS_NORMAL)) + WidgetDimensions::scaled.fullbevel.bottom, vp->zoom);

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


/**
 * Check whether any viewport sign was clicked, and dispatch the click.
 * @param vp the clicked viewport
 * @param x X position of click
 * @param y Y position of click
 * @return true if the sign was hit
 */
static bool CheckClickOnViewportSign(const Viewport *vp, int x, int y)
{
        if (_game_mode == GM_MENU) return false;

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

        Rect search_rect{ x - 1, y - 1, x + 1, y + 1 };
        search_rect = ExpandRectWithViewportSignMargins(search_rect, vp->zoom);

        bool show_stations = HasBit(_display_opt, DO_SHOW_STATION_NAMES) && !IsInvisibilitySet(TO_SIGNS);
        bool show_waypoints = HasBit(_display_opt, DO_SHOW_WAYPOINT_NAMES) && !IsInvisibilitySet(TO_SIGNS);
        bool show_towns = HasBit(_display_opt, DO_SHOW_TOWN_NAMES);
        bool show_signs = HasBit(_display_opt, DO_SHOW_SIGNS) && !IsInvisibilitySet(TO_SIGNS);
        bool show_competitors = HasBit(_display_opt, DO_SHOW_COMPETITOR_SIGNS);

        /* Topmost of each type that was hit */
        BaseStation *st = nullptr, *last_st = nullptr;
        Town *t = nullptr, *last_t = nullptr;
        Sign *si = nullptr, *last_si = nullptr;

        /* See ViewportAddKdtreeSigns() for details on the search logic */
        _viewport_sign_kdtree.FindContained(search_rect.left, search_rect.top, search_rect.right, search_rect.bottom, [&](const ViewportSignKdtreeItem & item) {
                switch (item.type) {
                        case ViewportSignKdtreeItem::VKI_STATION:
                                if (!show_stations) break;
                                st = BaseStation::Get(item.id.station);
                                if (!show_competitors && _local_company != st->owner && st->owner != OWNER_NONE) break;
                                if (CheckClickOnViewportSign(vp, x, y, &st->sign)) last_st = st;
                                break;

                        case ViewportSignKdtreeItem::VKI_WAYPOINT:
                                if (!show_waypoints) break;
                                st = BaseStation::Get(item.id.station);
                                if (!show_competitors && _local_company != st->owner && st->owner != OWNER_NONE) break;
                                if (CheckClickOnViewportSign(vp, x, y, &st->sign)) last_st = st;
                                break;

                        case ViewportSignKdtreeItem::VKI_TOWN:
                                if (!show_towns) break;
                                t = Town::Get(item.id.town);
                                if (CheckClickOnViewportSign(vp, x, y, &t->cache.sign)) last_t = t;
                                break;

                        case ViewportSignKdtreeItem::VKI_SIGN:
                                if (!show_signs) break;
                                si = Sign::Get(item.id.sign);
                                if (!show_competitors && _local_company != si->owner && si->owner != OWNER_DEITY) break;
                                if (CheckClickOnViewportSign(vp, x, y, &si->sign)) last_si = si;
                                break;

                        default:
                                NOT_REACHED();
                }
        });

        /* Select which hit to handle based on priority */
        if (last_st != nullptr) {
                if (Station::IsExpected(last_st)) {
                        ShowStationViewWindow(last_st->index);
                } else {
                        ShowWaypointWindow(Waypoint::From(last_st));
                }
                return true;
        } else if (last_t != nullptr) {
                ShowTownViewWindow(last_t->index);
                return true;
        } else if (last_si != nullptr) {
                HandleClickOnSign(last_si);
                return true;
        } else {
                return false;
        }
}


ViewportSignKdtreeItem ViewportSignKdtreeItem::MakeStation(StationID id)
{
        ViewportSignKdtreeItem item;
        item.type = VKI_STATION;
        item.id.station = id;

        const Station *st = Station::Get(id);
        assert(st->sign.kdtree_valid);
        item.center = st->sign.center;
        item.top = st->sign.top;

        /* Assume the sign can be a candidate for drawing, so measure its width */
        _viewport_sign_maxwidth = std::max<int>(_viewport_sign_maxwidth, st->sign.width_normal);

        return item;
}

ViewportSignKdtreeItem ViewportSignKdtreeItem::MakeWaypoint(StationID id)
{
        ViewportSignKdtreeItem item;
        item.type = VKI_WAYPOINT;
        item.id.station = id;

        const Waypoint *st = Waypoint::Get(id);
        assert(st->sign.kdtree_valid);
        item.center = st->sign.center;
        item.top = st->sign.top;

        /* Assume the sign can be a candidate for drawing, so measure its width */
        _viewport_sign_maxwidth = std::max<int>(_viewport_sign_maxwidth, st->sign.width_normal);

        return item;
}

ViewportSignKdtreeItem ViewportSignKdtreeItem::MakeTown(TownID id)
{
        ViewportSignKdtreeItem item;
        item.type = VKI_TOWN;
        item.id.town = id;

        const Town *town = Town::Get(id);
        assert(town->cache.sign.kdtree_valid);
        item.center = town->cache.sign.center;
        item.top = town->cache.sign.top;

        /* Assume the sign can be a candidate for drawing, so measure its width */
        _viewport_sign_maxwidth = std::max<int>(_viewport_sign_maxwidth, town->cache.sign.width_normal);

        return item;
}

ViewportSignKdtreeItem ViewportSignKdtreeItem::MakeSign(SignID id)
{
        ViewportSignKdtreeItem item;
        item.type = VKI_SIGN;
        item.id.sign = id;

        const Sign *sign = Sign::Get(id);
        assert(sign->sign.kdtree_valid);
        item.center = sign->sign.center;
        item.top = sign->sign.top;

        /* Assume the sign can be a candidate for drawing, so measure its width */
        _viewport_sign_maxwidth = std::max<int>(_viewport_sign_maxwidth, sign->sign.width_normal);

        return item;
}

void RebuildViewportKdtree()
{
        /* Reset biggest size sign seen */
        _viewport_sign_maxwidth = 0;

        std::vector<ViewportSignKdtreeItem> items;
        items.reserve(BaseStation::GetNumItems() + Town::GetNumItems() + Sign::GetNumItems());

        for (const Station *st : Station::Iterate()) {
                if (st->sign.kdtree_valid) items.push_back(ViewportSignKdtreeItem::MakeStation(st->index));
        }

        for (const Waypoint *wp : Waypoint::Iterate()) {
                if (wp->sign.kdtree_valid) items.push_back(ViewportSignKdtreeItem::MakeWaypoint(wp->index));
        }

        for (const Town *town : Town::Iterate()) {
                if (town->cache.sign.kdtree_valid) items.push_back(ViewportSignKdtreeItem::MakeTown(town->index));
        }

        for (const Sign *sign : Sign::Iterate()) {
                if (sign->sign.kdtree_valid) items.push_back(ViewportSignKdtreeItem::MakeSign(sign->index));
        }

        _viewport_sign_kdtree.Build(items.begin(), items.end());
}


static bool CheckClickOnLandscape(const Viewport *vp, int x, int y)
{
        Point pt = TranslateXYToTileCoord(vp, x, y);

        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 HandleViewportClicked(const Viewport *vp, int x, int y)
{
        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) {
                PlaceObject();
                return true;
        }

        if (CheckClickOnViewportSign(vp, x, y)) return true;
        bool result = CheckClickOnLandscape(vp, x, y);

        if (v != nullptr) {
                Debug(misc, 2, "Vehicle {} (index {}) at {}", v->unitnumber, v->index, fmt::ptr(v));
                if (IsCompanyBuildableVehicleType(v)) {
                        v = v->First();
                        if (_ctrl_pressed && v->owner == _local_company) {
                                StartStopVehicle(v, true);
                        } else {
                                ShowVehicleViewWindow(v);
                        }
                }
                return true;
        }
        return result;
}

void RebuildViewportOverlay(Window *w)
{
        if (w->viewport->overlay != nullptr &&
                        w->viewport->overlay->GetCompanyMask() != 0 &&
                        w->viewport->overlay->GetCargoMask() != 0) {
                w->viewport->overlay->SetDirty();
                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)Map::SizeX() * (int)TILE_SIZE - 1
                                && y >= 0 && y <= (int)Map::SizeY() * (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);
                if (old  != INVALID_TILE) MarkTileDirtyByTile(old);
        }
}

/**
 * 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.offs.x = ox * TILE_SIZE;
        _thd.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);
}



/**
 * 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;

        if (_thd.freeze) return;

        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:
                                        /* Draw one highlighted tile in any direction */
                                        new_drawstyle = GetAutorailHT(pt.x, pt.y);
                                        break;
                                case 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;
                                        break;
                                default:
                                        NOT_REACHED();
                        }
                        _thd.new_pos.x = x1 & ~TILE_UNIT_MASK;
                        _thd.new_pos.y = y1 & ~TILE_UNIT_MASK;
                }
        }

        /* 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.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.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 paramcount number of params to deal with
 */
static inline void ShowMeasurementTooltips(StringID str, uint paramcount)
{
        if (!_settings_client.gui.measure_tooltip) return;
        GuiShowTooltips(_thd.GetCallbackWnd(), str, TCC_EXIT_VIEWPORT, paramcount);
}

static void HideMeasurementTooltips()
{
        CloseWindowById(WC_TOOLTIPS, 0);
}

/** 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;
        } else {
                _thd.place_mode = HT_SPECIAL | others;
                _thd.next_drawstyle = HT_POINT | others;
        }
        _special_mouse_mode = WSM_SIZING;
}

/** Drag over the map while holding the left mouse down. */
void VpStartDragging(ViewportDragDropSelectionProcess process)
{
        _thd.select_method = VPM_X_AND_Y;
        _thd.select_proc = process;
        _thd.selstart.x = 0;
        _thd.selstart.y = 0;
        _thd.next_drawstyle = HT_RECT;

        _special_mouse_mode = WSM_DRAGGING;
}

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_t 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, 1);
        } else {
                HideMeasurementTooltips();
        }
}

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 = std::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 = std::max(h1, ht);
                        break;
                }
        }

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

static const StringID measure_strings_length[] = {STR_NULL, STR_MEASURE_LENGTH, STR_MEASURE_LENGTH_HEIGHTDIFF};

/**
 * 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;
}

/** 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, (Map::MaxX() - 1) * TILE_SIZE, 1);
                                        CheckOverflow(y, x, (Map::MaxY() - 1) * TILE_SIZE, 1);
                                        assert(x >= 0 && y >= 0 && x <= (int)(Map::MaxX() * TILE_SIZE) && y <= (int)(Map::MaxY() * 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, (Map::MaxX() - 1) * TILE_SIZE, -1);
                                        CheckOverflow(y, x, (Map::MaxY() - 1) * TILE_SIZE, -1);
                                        assert(x >= 0 && y >= 0 && x <= (int)(Map::MaxX() * TILE_SIZE) && y <= (int)(Map::MaxY() * 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;
                                }
                        }
                }
        }

        if (_settings_client.gui.measure_tooltip) {
                TileIndex t0 = TileVirtXY(_thd.selstart.x, _thd.selstart.y);
                TileIndex t1 = TileVirtXY(x, y);
                uint distance = DistanceManhattan(t0, t1) + 1;
                byte index = 0;

                if (distance != 1) {
                        int heightdiff = CalcHeightdiff(b, distance, t0, t1);
                        /* 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 ((b & HT_DIR_MASK) != HT_DIR_X && (b & HT_DIR_MASK) != HT_DIR_Y) {
                                distance = CeilDiv(distance, 2);
                        }

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

                ShowMeasurementTooltips(measure_strings_length[index], index);
        }

        _thd.selend.x = x;
        _thd.selend.y = y;
        _thd.next_drawstyle = b;
}

/**
 * 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;
        }

        /* 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);
                        }
                        if (_settings_client.gui.measure_tooltip) {
                                TileIndex t0 = TileVirtXY(sx, sy);
                                TileIndex t1 = TileVirtXY(x, y);
                                uint distance = DistanceManhattan(t0, t1) + 1;
                                byte index = 0;

                                if (distance != 1) {
                                        /* 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; */
                                        int heightdiff = CalcHeightdiff(HT_LINE | style, 0, t0, t1);

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

                                ShowMeasurementTooltips(measure_strings_length[index], index);
                        }
                        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], index);
                        }
                        break;

                default: NOT_REACHED();
        }

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

/**
 * Handle the mouse while dragging for placement/resizing.
 * @return State of handling the event.
 */
EventState VpHandlePlaceSizingDrag()
{
        if (_special_mouse_mode != WSM_SIZING && _special_mouse_mode != WSM_DRAGGING) 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() ) */
        if (_left_button_down) {
                if (_special_mouse_mode == WSM_DRAGGING) {
                        /* Only register a drag event when the mouse moved. */
                        if (_thd.new_pos.x == _thd.selstart.x && _thd.new_pos.y == _thd.selstart.y) return ES_HANDLED;
                        _thd.selstart.x = _thd.new_pos.x;
                        _thd.selstart.y = _thd.new_pos.y;
                }

                w->OnPlaceDrag(_thd.select_method, _thd.select_proc, GetTileBelowCursor());
                return ES_HANDLED;
        }

        /* Mouse button released. */
        _special_mouse_mode = WSM_NONE;
        if (_special_mouse_mode == WSM_DRAGGING) return ES_HANDLED;

        /* Keep the selected tool, but reset it to the original mode. */
        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);

        HideMeasurementTooltips();
        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();
                        HideMeasurementTooltips();
                }
        }

        /* 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 ((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);
}

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, Map::SizeX() * TILE_SIZE - 1), Clamp(y, 0, Map::SizeY() * 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;
}

/** 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);
}

/**
 * Scroll players main viewport.
 * @param flags type of operation
 * @param tile tile to center viewport on
 * @param target ViewportScrollTarget of scroll target
 * @param ref company or client id depending on the target
 * @return the cost of this operation or an error
 */
CommandCost CmdScrollViewport(DoCommandFlag flags, TileIndex tile, ViewportScrollTarget target, uint32_t ref)
{
        if (_current_company != OWNER_DEITY) return CMD_ERROR;
        switch (target) {
                case VST_EVERYONE:
                        break;
                case VST_COMPANY:
                        if (_local_company != (CompanyID)ref) return CommandCost();
                        break;
                case VST_CLIENT:
                        if (_network_own_client_id != (ClientID)ref) return CommandCost();
                        break;
                default:
                        return CMD_ERROR;
        }

        if (flags & DC_EXEC) {
                ResetObjectToPlace();
                ScrollMainWindowToTile(tile);
        }
        return CommandCost();
}

void MarkCatchmentTilesDirty()
{
        if (_viewport_highlight_town != nullptr) {
                MarkWholeScreenDirty();
                return;
        }
        if (_viewport_highlight_station != nullptr) {
                if (_viewport_highlight_station->catchment_tiles.tile == INVALID_TILE) {
                        MarkWholeScreenDirty();
                        _viewport_highlight_station = nullptr;
                } else {
                        BitmapTileIterator it(_viewport_highlight_station->catchment_tiles);
                        for (TileIndex tile = it; tile != INVALID_TILE; tile = ++it) {
                                MarkTileDirtyByTile(tile);
                        }
                }
        }
        if (_viewport_highlight_waypoint != nullptr) {
                if (!_viewport_highlight_waypoint->IsInUse()) {
                        _viewport_highlight_waypoint = nullptr;
                }
                MarkWholeScreenDirty();
        }
}

static void SetWindowDirtyForViewportCatchment()
{
        if (_viewport_highlight_station != nullptr) SetWindowDirty(WC_STATION_VIEW, _viewport_highlight_station->index);
        if (_viewport_highlight_waypoint != nullptr) SetWindowDirty(WC_WAYPOINT_VIEW, _viewport_highlight_waypoint->index);
        if (_viewport_highlight_town != nullptr) SetWindowDirty(WC_TOWN_VIEW, _viewport_highlight_town->index);
}

static void ClearViewportCatchment()
{
        MarkCatchmentTilesDirty();
        _viewport_highlight_station = nullptr;
        _viewport_highlight_waypoint = nullptr;
        _viewport_highlight_town = nullptr;
}

/**
 * Select or deselect station for coverage area highlight.
 * Selecting a station will deselect a town.
 * @param *st Station in question
 * @param sel Select or deselect given station
 */
void SetViewportCatchmentStation(const Station *st, bool sel)
{
        SetWindowDirtyForViewportCatchment();
        if (sel && _viewport_highlight_station != st) {
                ClearViewportCatchment();
                _viewport_highlight_station = st;
                MarkCatchmentTilesDirty();
        } else if (!sel && _viewport_highlight_station == st) {
                MarkCatchmentTilesDirty();
                _viewport_highlight_station = nullptr;
        }
        if (_viewport_highlight_station != nullptr) SetWindowDirty(WC_STATION_VIEW, _viewport_highlight_station->index);
}

/**
 * Select or deselect waypoint for coverage area highlight.
 * Selecting a waypoint will deselect a town.
 * @param *wp Waypoint in question
 * @param sel Select or deselect given waypoint
 */
void SetViewportCatchmentWaypoint(const Waypoint *wp, bool sel)
{
        SetWindowDirtyForViewportCatchment();
        if (sel && _viewport_highlight_waypoint != wp) {
                ClearViewportCatchment();
                _viewport_highlight_waypoint = wp;
                MarkCatchmentTilesDirty();
        } else if (!sel && _viewport_highlight_waypoint == wp) {
                MarkCatchmentTilesDirty();
                _viewport_highlight_waypoint = nullptr;
        }
        if (_viewport_highlight_waypoint != nullptr) SetWindowDirty(WC_WAYPOINT_VIEW, _viewport_highlight_waypoint->index);
}

/**
 * Select or deselect town for coverage area highlight.
 * Selecting a town will deselect a station.
 * @param *t Town in question
 * @param sel Select or deselect given town
 */
void SetViewportCatchmentTown(const Town *t, bool sel)
{
        SetWindowDirtyForViewportCatchment();
        if (sel && _viewport_highlight_town != t) {
                ClearViewportCatchment();
                _viewport_highlight_town = t;
                MarkWholeScreenDirty();
        } else if (!sel && _viewport_highlight_town == t) {
                _viewport_highlight_town = nullptr;
                MarkWholeScreenDirty();
        }
        if (_viewport_highlight_town != nullptr) SetWindowDirty(WC_TOWN_VIEW, _viewport_highlight_town->index);
}