Merge branch 'development' into feature/no_multiplayer_grf_limit

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

/* $Id$ */

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

/** @file rail_cmd.cpp Handling of rail tiles. */

#include "stdafx.h"
#include "cmd_helper.h"
#include "viewport_func.h"
#include "command_func.h"
#include "depot_base.h"
#include "pathfinder/yapf/yapf_cache.h"
#include "newgrf_debug.h"
#include "newgrf_railtype.h"
#include "train.h"
#include "autoslope.h"
#include "water.h"
#include "tunnelbridge_map.h"
#include "bridge_signal_map.h"
#include "vehicle_func.h"
#include "sound_func.h"
#include "tunnelbridge.h"
#include "elrail_func.h"
#include "town.h"
#include "pbs.h"
#include "company_base.h"
#include "core/backup_type.hpp"
#include "date_func.h"
#include "strings_func.h"
#include "company_gui.h"
#include "object_map.h"
#include "tracerestrict.h"
#include "logic_signals.h"
#include "core/container_func.hpp"

#include "table/strings.h"
#include "table/railtypes.h"
#include "table/track_land.h"

#include "safeguards.h"

/** Helper type for lists/vectors of trains */
typedef SmallVector<Train *, 16> TrainList;

RailtypeInfo _railtypes[RAILTYPE_END];
TileIndex _rail_track_endtile; ///< The end of a rail track; as hidden return from the rail build/remove command for GUI purposes.
RailType _sorted_railtypes[RAILTYPE_END];
uint8 _sorted_railtypes_size;

/** Enum holding the signal offset in the sprite sheet according to the side it is representing. */
enum SignalOffsets {
        SIGNAL_TO_SOUTHWEST,
        SIGNAL_TO_NORTHEAST,
        SIGNAL_TO_SOUTHEAST,
        SIGNAL_TO_NORTHWEST,
        SIGNAL_TO_EAST,
        SIGNAL_TO_WEST,
        SIGNAL_TO_SOUTH,
        SIGNAL_TO_NORTH,
};

/**
 * Reset all rail type information to its default values.
 */
void ResetRailTypes()
{
        assert_compile(lengthof(_original_railtypes) <= lengthof(_railtypes));

        uint i = 0;
        for (; i < lengthof(_original_railtypes); i++) _railtypes[i] = _original_railtypes[i];

        static const RailtypeInfo empty_railtype = {
                {0,0,0,0,0,0,0,0,0,0,0,0},
                {0,0,0,0,0,0,0,0,{}},
                {0,0,0,0,0,0,0,0},
                {0,0,0,0,0,0},
                0, RAILTYPES_NONE, RAILTYPES_NONE, 0, 0, 0, RTFB_NONE, 0, 0, 0, 0, 0,
                RailTypeLabelList(), 0, 0, RAILTYPES_NONE, RAILTYPES_NONE, 0,
                {}, {} };
        for (; i < lengthof(_railtypes);          i++) _railtypes[i] = empty_railtype;
}

void ResolveRailTypeGUISprites(RailtypeInfo *rti)
{
        SpriteID cursors_base = GetCustomRailSprite(rti, INVALID_TILE, RTSG_CURSORS);
        if (cursors_base != 0) {
                rti->gui_sprites.build_ns_rail = cursors_base +  0;
                rti->gui_sprites.build_x_rail  = cursors_base +  1;
                rti->gui_sprites.build_ew_rail = cursors_base +  2;
                rti->gui_sprites.build_y_rail  = cursors_base +  3;
                rti->gui_sprites.auto_rail     = cursors_base +  4;
                rti->gui_sprites.build_depot   = cursors_base +  5;
                rti->gui_sprites.build_tunnel  = cursors_base +  6;
                rti->gui_sprites.convert_rail  = cursors_base +  7;
                rti->cursor.rail_ns   = cursors_base +  8;
                rti->cursor.rail_swne = cursors_base +  9;
                rti->cursor.rail_ew   = cursors_base + 10;
                rti->cursor.rail_nwse = cursors_base + 11;
                rti->cursor.autorail  = cursors_base + 12;
                rti->cursor.depot     = cursors_base + 13;
                rti->cursor.tunnel    = cursors_base + 14;
                rti->cursor.convert   = cursors_base + 15;
        }

        /* Array of default GUI signal sprite numbers. */
        /* Logic signals don't have their own sprites yet, lets use one-way pbs sprites for now */
        const SpriteID _signal_lookup[2][SIGTYPE_END] = {
                {SPR_IMG_SIGNAL_ELECTRIC_NORM,  SPR_IMG_SIGNAL_ELECTRIC_ENTRY, SPR_IMG_SIGNAL_ELECTRIC_EXIT,
                 SPR_IMG_SIGNAL_ELECTRIC_COMBO, SPR_IMG_SIGNAL_ELECTRIC_PBS,   SPR_IMG_SIGNAL_ELECTRIC_PBS_OWAY,
                 SPR_IMG_SIGNAL_ELECTRIC_LOGIC},

                {SPR_IMG_SIGNAL_SEMAPHORE_NORM,  SPR_IMG_SIGNAL_SEMAPHORE_ENTRY, SPR_IMG_SIGNAL_SEMAPHORE_EXIT,
                 SPR_IMG_SIGNAL_SEMAPHORE_COMBO, SPR_IMG_SIGNAL_SEMAPHORE_PBS,   SPR_IMG_SIGNAL_SEMAPHORE_PBS_OWAY,
                 SPR_IMG_SIGNAL_SEMAPHORE_LOGIC},
        };

        for (SignalType type = SIGTYPE_NORMAL; type < SIGTYPE_END; type = (SignalType)(type + 1)) {
                for (SignalVariant var = SIG_ELECTRIC; var <= SIG_SEMAPHORE; var = (SignalVariant)(var + 1)) {
                        SpriteID red   = GetCustomSignalSprite(rti, INVALID_TILE, type, var, SIGNAL_STATE_RED, true);
                        SpriteID green = GetCustomSignalSprite(rti, INVALID_TILE, type, var, SIGNAL_STATE_GREEN, true);
                        rti->gui_sprites.signals[type][var][0] = (red != 0)   ? red + SIGNAL_TO_SOUTH   : _signal_lookup[var][type];
                        rti->gui_sprites.signals[type][var][1] = (green != 0) ? green + SIGNAL_TO_SOUTH : _signal_lookup[var][type] + 1;
                }
        }
}

/**
 * Compare railtypes based on their sorting order.
 * @param first  The railtype to compare to.
 * @param second The railtype to compare.
 * @return True iff the first should be sorted before the second.
 */
static int CDECL CompareRailTypes(const RailType *first, const RailType *second)
{
        return GetRailTypeInfo(*first)->sorting_order - GetRailTypeInfo(*second)->sorting_order;
}

/**
 * Resolve sprites of custom rail types
 */
void InitRailTypes()
{
        for (RailType rt = RAILTYPE_BEGIN; rt != RAILTYPE_END; rt++) {
                RailtypeInfo *rti = &_railtypes[rt];
                ResolveRailTypeGUISprites(rti);
        }

        _sorted_railtypes_size = 0;
        for (RailType rt = RAILTYPE_BEGIN; rt != RAILTYPE_END; rt++) {
                if (_railtypes[rt].label != 0) {
                        _sorted_railtypes[_sorted_railtypes_size++] = rt;
                }
        }
        QSortT(_sorted_railtypes, _sorted_railtypes_size, CompareRailTypes);
}

/**
 * Allocate a new rail type label
 */
RailType AllocateRailType(RailTypeLabel label)
{
        for (RailType rt = RAILTYPE_BEGIN; rt != RAILTYPE_END; rt++) {
                RailtypeInfo *rti = &_railtypes[rt];

                if (rti->label == 0) {
                        /* Set up new rail type */
                        *rti = _original_railtypes[RAILTYPE_RAIL];
                        rti->label = label;
                        rti->alternate_labels.Clear();

                        /* Make us compatible with ourself. */
                        rti->powered_railtypes    = (RailTypes)(1 << rt);
                        rti->compatible_railtypes = (RailTypes)(1 << rt);

                        /* We also introduce ourself. */
                        rti->introduces_railtypes = (RailTypes)(1 << rt);

                        /* Default sort order; order of allocation, but with some
                         * offsets so it's easier for NewGRF to pick a spot without
                         * changing the order of other (original) rail types.
                         * The << is so you can place other railtypes in between the
                         * other railtypes, the 7 is to be able to place something
                         * before the first (default) rail type. */
                        rti->sorting_order = rt << 4 | 7;
                        return rt;
                }
        }

        return INVALID_RAILTYPE;
}

static const byte _track_sloped_sprites[14] = {
        14, 15, 22, 13,
         0, 21, 17, 12,
        23,  0, 18, 20,
        19, 16
};


/*         4
 *     ---------
 *    |\       /|
 *    | \    1/ |
 *    |  \   /  |
 *    |   \ /   |
 *  16|    \    |32
 *    |   / \2  |
 *    |  /   \  |
 *    | /     \ |
 *    |/       \|
 *     ---------
 *         8
 */



/* MAP2 byte:    abcd???? => Signal On? Same coding as map3lo
 * MAP3LO byte:  abcd???? => Signal Exists?
 *               a and b are for diagonals, upper and left,
 *               one for each direction. (ie a == NE->SW, b ==
 *               SW->NE, or v.v., I don't know. b and c are
 *               similar for lower and right.
 * MAP2 byte:    ????abcd => Type of ground.
 * MAP3LO byte:  ????abcd => Type of rail.
 * MAP5:         00abcdef => rail
 *               01abcdef => rail w/ signals
 *               10uuuuuu => unused
 *               11uuuudd => rail depot
 */

/**
 * Tests if a vehicle interacts with the specified track.
 * All track bits interact except parallel #TRACK_BIT_HORZ or #TRACK_BIT_VERT.
 *
 * @param tile The tile.
 * @param track The track.
 * @return Succeeded command (no train found), or a failed command (a train was found).
 */
static CommandCost EnsureNoTrainOnTrack(TileIndex tile, Track track)
{
        TrackBits rail_bits = TrackToTrackBits(track);
        return EnsureNoTrainOnTrackBits(tile, rail_bits);
}

/**
 * Check that the new track bits may be built.
 * @param tile %Tile to build on.
 * @param to_build New track bits.
 * @param flags    Flags of the operation.
 * @return Succeeded or failed command.
 */
static CommandCost CheckTrackCombination(TileIndex tile, TrackBits to_build, uint flags)
{
        if (!IsPlainRail(tile)) return_cmd_error(STR_ERROR_IMPOSSIBLE_TRACK_COMBINATION);

        /* So, we have a tile with tracks on it (and possibly signals). Let's see
         * what tracks first */
        TrackBits current = GetTrackBits(tile); // The current track layout.
        TrackBits future = current | to_build;  // The track layout we want to build.

        /* Are we really building something new? */
        if (current == future) {
                /* Nothing new is being built */
                return_cmd_error(STR_ERROR_ALREADY_BUILT);
        }

        /* Let's see if we may build this */
        if ((flags & DC_NO_RAIL_OVERLAP) || HasSignals(tile)) {
                /* If we are not allowed to overlap (flag is on for ai companies or we have
                 * signals on the tile), check that */
                if (future != TRACK_BIT_HORZ && future != TRACK_BIT_VERT) {
                        return_cmd_error((flags & DC_NO_RAIL_OVERLAP) ? STR_ERROR_IMPOSSIBLE_TRACK_COMBINATION : STR_ERROR_MUST_REMOVE_SIGNALS_FIRST);
                }
        }
        /* Normally, we may overlap and any combination is valid */
        return CommandCost();
}


/** Valid TrackBits on a specific (non-steep)-slope without foundation */
static const TrackBits _valid_tracks_without_foundation[15] = {
        TRACK_BIT_ALL,
        TRACK_BIT_RIGHT,
        TRACK_BIT_UPPER,
        TRACK_BIT_X,

        TRACK_BIT_LEFT,
        TRACK_BIT_NONE,
        TRACK_BIT_Y,
        TRACK_BIT_LOWER,

        TRACK_BIT_LOWER,
        TRACK_BIT_Y,
        TRACK_BIT_NONE,
        TRACK_BIT_LEFT,

        TRACK_BIT_X,
        TRACK_BIT_UPPER,
        TRACK_BIT_RIGHT,
};

/** Valid TrackBits on a specific (non-steep)-slope with leveled foundation */
static const TrackBits _valid_tracks_on_leveled_foundation[15] = {
        TRACK_BIT_NONE,
        TRACK_BIT_LEFT,
        TRACK_BIT_LOWER,
        TRACK_BIT_Y | TRACK_BIT_LOWER | TRACK_BIT_LEFT,

        TRACK_BIT_RIGHT,
        TRACK_BIT_ALL,
        TRACK_BIT_X | TRACK_BIT_LOWER | TRACK_BIT_RIGHT,
        TRACK_BIT_ALL,

        TRACK_BIT_UPPER,
        TRACK_BIT_X | TRACK_BIT_UPPER | TRACK_BIT_LEFT,
        TRACK_BIT_ALL,
        TRACK_BIT_ALL,

        TRACK_BIT_Y | TRACK_BIT_UPPER | TRACK_BIT_RIGHT,
        TRACK_BIT_ALL,
        TRACK_BIT_ALL
};

/**
 * Checks if a track combination is valid on a specific slope and returns the needed foundation.
 *
 * @param tileh Tile slope.
 * @param bits  Trackbits.
 * @return Needed foundation or FOUNDATION_INVALID if track/slope combination is not allowed.
 */
Foundation GetRailFoundation(Slope tileh, TrackBits bits)
{
        if (bits == TRACK_BIT_NONE) return FOUNDATION_NONE;

        if (IsSteepSlope(tileh)) {
                /* Test for inclined foundations */
                if (bits == TRACK_BIT_X) return FOUNDATION_INCLINED_X;
                if (bits == TRACK_BIT_Y) return FOUNDATION_INCLINED_Y;

                /* Get higher track */
                Corner highest_corner = GetHighestSlopeCorner(tileh);
                TrackBits higher_track = CornerToTrackBits(highest_corner);

                /* Only higher track? */
                if (bits == higher_track) return HalftileFoundation(highest_corner);

                /* Overlap with higher track? */
                if (TracksOverlap(bits | higher_track)) return FOUNDATION_INVALID;

                /* either lower track or both higher and lower track */
                return ((bits & higher_track) != 0 ? FOUNDATION_STEEP_BOTH : FOUNDATION_STEEP_LOWER);
        } else {
                if ((~_valid_tracks_without_foundation[tileh] & bits) == 0) return FOUNDATION_NONE;

                bool valid_on_leveled = ((~_valid_tracks_on_leveled_foundation[tileh] & bits) == 0);

                Corner track_corner;
                switch (bits) {
                        case TRACK_BIT_LEFT:  track_corner = CORNER_W; break;
                        case TRACK_BIT_LOWER: track_corner = CORNER_S; break;
                        case TRACK_BIT_RIGHT: track_corner = CORNER_E; break;
                        case TRACK_BIT_UPPER: track_corner = CORNER_N; break;

                        case TRACK_BIT_HORZ:
                                if (tileh == SLOPE_N) return HalftileFoundation(CORNER_N);
                                if (tileh == SLOPE_S) return HalftileFoundation(CORNER_S);
                                return (valid_on_leveled ? FOUNDATION_LEVELED : FOUNDATION_INVALID);

                        case TRACK_BIT_VERT:
                                if (tileh == SLOPE_W) return HalftileFoundation(CORNER_W);
                                if (tileh == SLOPE_E) return HalftileFoundation(CORNER_E);
                                return (valid_on_leveled ? FOUNDATION_LEVELED : FOUNDATION_INVALID);

                        case TRACK_BIT_X:
                                if (IsSlopeWithOneCornerRaised(tileh)) return FOUNDATION_INCLINED_X;
                                return (valid_on_leveled ? FOUNDATION_LEVELED : FOUNDATION_INVALID);

                        case TRACK_BIT_Y:
                                if (IsSlopeWithOneCornerRaised(tileh)) return FOUNDATION_INCLINED_Y;
                                return (valid_on_leveled ? FOUNDATION_LEVELED : FOUNDATION_INVALID);

                        default:
                                return (valid_on_leveled ? FOUNDATION_LEVELED : FOUNDATION_INVALID);
                }
                /* Single diagonal track */

                /* Track must be at least valid on leveled foundation */
                if (!valid_on_leveled) return FOUNDATION_INVALID;

                /* If slope has three raised corners, build leveled foundation */
                if (IsSlopeWithThreeCornersRaised(tileh)) return FOUNDATION_LEVELED;

                /* If neighboured corners of track_corner are lowered, build halftile foundation */
                if ((tileh & SlopeWithThreeCornersRaised(OppositeCorner(track_corner))) == SlopeWithOneCornerRaised(track_corner)) return HalftileFoundation(track_corner);

                /* else special anti-zig-zag foundation */
                return SpecialRailFoundation(track_corner);
        }
}


/**
 * Tests if a track can be build on a tile.
 *
 * @param tileh Tile slope.
 * @param rail_bits Tracks to build.
 * @param existing Tracks already built.
 * @param tile Tile (used for water test)
 * @return Error message or cost for foundation building.
 */
static CommandCost CheckRailSlope(Slope tileh, TrackBits rail_bits, TrackBits existing, TileIndex tile)
{
        /* don't allow building on the lower side of a coast */
        if (GetFloodingBehaviour(tile) != FLOOD_NONE) {
                if (!IsSteepSlope(tileh) && ((~_valid_tracks_on_leveled_foundation[tileh] & (rail_bits | existing)) != 0)) return_cmd_error(STR_ERROR_CAN_T_BUILD_ON_WATER);
        }

        Foundation f_new = GetRailFoundation(tileh, rail_bits | existing);

        /* check track/slope combination */
        if ((f_new == FOUNDATION_INVALID) ||
                        ((f_new != FOUNDATION_NONE) && (!_settings_game.construction.build_on_slopes))) {
                return_cmd_error(STR_ERROR_LAND_SLOPED_IN_WRONG_DIRECTION);
        }

        Foundation f_old = GetRailFoundation(tileh, existing);
        return CommandCost(EXPENSES_CONSTRUCTION, f_new != f_old ? _price[PR_BUILD_FOUNDATION] : (Money)0);
}

/* Validate functions for rail building */
static inline bool ValParamTrackOrientation(Track track)
{
        return IsValidTrack(track);
}

/**
 * Build a single piece of rail
 * @param tile tile  to build on
 * @param flags operation to perform
 * @param p1 railtype of being built piece (normal, mono, maglev)
 * @param p2 rail track to build
 * @param text unused
 * @return the cost of this operation or an error
 */
CommandCost CmdBuildSingleRail(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32 p2, const char *text)
{
        RailType railtype = Extract<RailType, 0, 5>(p1);
        Track track = Extract<Track, 0, 3>(p2);
        CommandCost cost(EXPENSES_CONSTRUCTION);

        _rail_track_endtile = INVALID_TILE;

        if (!ValParamRailtype(railtype) || !ValParamTrackOrientation(track)) return CMD_ERROR;

        Slope tileh = GetTileSlope(tile);
        TrackBits trackbit = TrackToTrackBits(track);

        switch (GetTileType(tile)) {
                case MP_RAILWAY: {
                        CommandCost ret = CheckTileOwnership(tile);
                        if (ret.Failed()) return ret;

                        if (!IsPlainRail(tile)) return DoCommand(tile, 0, 0, flags, CMD_LANDSCAPE_CLEAR); // just get appropriate error message

                        if (!IsCompatibleRail(GetRailType(tile), railtype)) return_cmd_error(STR_ERROR_IMPOSSIBLE_TRACK_COMBINATION);

                        ret = CheckTrackCombination(tile, trackbit, flags);
                        if (ret.Succeeded()) ret = EnsureNoTrainOnTrack(tile, track);
                        if (ret.Failed()) {
                                if (ret.GetErrorMessage() == STR_ERROR_ALREADY_BUILT) _rail_track_endtile = tile;
                                return ret;
                        }

                        ret = CheckRailSlope(tileh, trackbit, GetTrackBits(tile), tile);
                        if (ret.Failed()) return ret;
                        cost.AddCost(ret);

                        /* If the rail types don't match, try to convert only if engines of
                         * the new rail type are not powered on the present rail type and engines of
                         * the present rail type are powered on the new rail type. */
                        if (GetRailType(tile) != railtype && !HasPowerOnRail(railtype, GetRailType(tile))) {
                                if (HasPowerOnRail(GetRailType(tile), railtype)) {
                                        ret = DoCommand(tile, tile, railtype, flags, CMD_CONVERT_RAIL);
                                        if (ret.Failed()) return ret;
                                        cost.AddCost(ret);
                                } else {
                                        return CMD_ERROR;
                                }
                        }

                        if (flags & DC_EXEC) {
                                SetRailGroundType(tile, RAIL_GROUND_BARREN);
                                TrackBits bits = GetTrackBits(tile);
                                SetTrackBits(tile, bits | trackbit);
                                ResetRailAge(tile);
                                /* Subtract old infrastructure count. */
                                uint pieces = CountBits(bits);
                                if (TracksOverlap(bits)) pieces *= pieces;
                                Company::Get(GetTileOwner(tile))->infrastructure.rail[GetRailType(tile)] -= pieces;
                                /* Add new infrastructure count. */
                                pieces = CountBits(bits | trackbit);
                                if (TracksOverlap(bits | trackbit)) pieces *= pieces;
                                Company::Get(GetTileOwner(tile))->infrastructure.rail[GetRailType(tile)] += pieces;
                                DirtyCompanyInfrastructureWindows(GetTileOwner(tile));
                        }
                        break;
                }

                case MP_ROAD: {
                        /* Level crossings may only be built on these slopes */
                        if (!HasBit(VALID_LEVEL_CROSSING_SLOPES, tileh)) return_cmd_error(STR_ERROR_LAND_SLOPED_IN_WRONG_DIRECTION);

                        CommandCost ret = EnsureNoVehicleOnGround(tile);
                        if (ret.Failed()) return ret;

                        if (IsNormalRoad(tile)) {
                                if (HasRoadWorks(tile)) return_cmd_error(STR_ERROR_ROAD_WORKS_IN_PROGRESS);

                                if (GetDisallowedRoadDirections(tile) != DRD_NONE) return_cmd_error(STR_ERROR_CROSSING_ON_ONEWAY_ROAD);

                                if (RailNoLevelCrossings(railtype)) return_cmd_error(STR_ERROR_CROSSING_DISALLOWED);

                                RoadTypes roadtypes = GetRoadTypes(tile);
                                RoadBits road = GetRoadBits(tile, ROADTYPE_ROAD);
                                RoadBits tram = GetRoadBits(tile, ROADTYPE_TRAM);
                                if ((track == TRACK_X && ((road | tram) & ROAD_X) == 0) ||
                                                (track == TRACK_Y && ((road | tram) & ROAD_Y) == 0)) {
                                        Owner road_owner = GetRoadOwner(tile, ROADTYPE_ROAD);
                                        Owner tram_owner = GetRoadOwner(tile, ROADTYPE_TRAM);
                                        /* Disallow breaking end-of-line of someone else
                                         * so trams can still reverse on this tile. */
                                        if (Company::IsValidID(tram_owner) && HasExactlyOneBit(tram)) {
                                                CommandCost ret = CheckOwnership(tram_owner);
                                                if (ret.Failed()) return ret;
                                        }
                                        /* Crossings must always have a road... */
                                        uint num_new_road_pieces = 2 - CountBits(road);
                                        if (road == ROAD_NONE) road_owner = _current_company;
                                        roadtypes |= ROADTYPES_ROAD;
                                        /* ...but tram is not required. */
                                        uint num_new_tram_pieces = (tram != ROAD_NONE) ? 2 - CountBits(tram) : 0;

                                        cost.AddCost((num_new_road_pieces + num_new_tram_pieces) * _price[PR_BUILD_ROAD]);

                                        if (flags & DC_EXEC) {
                                                MakeRoadCrossing(tile, road_owner, tram_owner, _current_company, (track == TRACK_X ? AXIS_Y : AXIS_X), railtype, roadtypes, GetTownIndex(tile));
                                                UpdateLevelCrossing(tile, false);
                                                Company::Get(_current_company)->infrastructure.rail[railtype] += LEVELCROSSING_TRACKBIT_FACTOR;
                                                DirtyCompanyInfrastructureWindows(_current_company);
                                                if (num_new_road_pieces > 0 && Company::IsValidID(road_owner)) {
                                                        Company::Get(road_owner)->infrastructure.road[ROADTYPE_ROAD] += num_new_road_pieces;
                                                        DirtyCompanyInfrastructureWindows(road_owner);
                                                }
                                                if (num_new_tram_pieces > 0 && Company::IsValidID(tram_owner)) {
                                                        Company::Get(tram_owner)->infrastructure.road[ROADTYPE_TRAM] += num_new_tram_pieces;
                                                        DirtyCompanyInfrastructureWindows(tram_owner);
                                                }
                                        }
                                        break;
                                }
                        }

                        if (IsLevelCrossing(tile) && GetCrossingRailBits(tile) == trackbit) {
                                _rail_track_endtile = tile;
                                return_cmd_error(STR_ERROR_ALREADY_BUILT);
                        }
                }
                FALLTHROUGH;

                default: {
                        /* Will there be flat water on the lower halftile? */
                        bool water_ground = IsTileType(tile, MP_WATER) && IsSlopeWithOneCornerRaised(tileh);

                        CommandCost ret = CheckRailSlope(tileh, trackbit, TRACK_BIT_NONE, tile);
                        if (ret.Failed()) return ret;
                        cost.AddCost(ret);

                        ret = DoCommand(tile, 0, 0, flags, CMD_LANDSCAPE_CLEAR);
                        if (ret.Failed()) return ret;
                        cost.AddCost(ret);

                        if (water_ground) {
                                cost.AddCost(-_price[PR_CLEAR_WATER]);
                                cost.AddCost(_price[PR_CLEAR_ROUGH]);
                        }

                        if (flags & DC_EXEC) {
                                MakeRailNormal(tile, _current_company, trackbit, railtype);
                                if (water_ground) SetRailGroundType(tile, RAIL_GROUND_WATER);
                                Company::Get(_current_company)->infrastructure.rail[railtype]++;
                                DirtyCompanyInfrastructureWindows(_current_company);
                        }
                        break;
                }
        }

        if (flags & DC_EXEC) {
                MarkTileDirtyByTile(tile);
                AddTrackToSignalBuffer(tile, track, _current_company);
                YapfNotifyTrackLayoutChange(tile, track);
        }

        cost.AddCost(RailBuildCost(railtype));
        _rail_track_endtile = tile;
        return cost;
}

/**
 * Remove a single piece of track
 * @param tile tile to remove track from
 * @param flags operation to perform
 * @param p1 unused
 * @param p2 rail orientation
 * @param text unused
 * @return the cost of this operation or an error
 */
CommandCost CmdRemoveSingleRail(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32 p2, const char *text)
{
        Track track = Extract<Track, 0, 3>(p2);
        CommandCost cost(EXPENSES_CONSTRUCTION);
        bool crossing = false;

        _rail_track_endtile = INVALID_TILE;

        if (!ValParamTrackOrientation(track)) return CMD_ERROR;
        TrackBits trackbit = TrackToTrackBits(track);

        /* Need to read tile owner now because it may change when the rail is removed
         * Also, in case of floods, _current_company != owner
         * There may be invalid tiletype even in exec run (when removing long track),
         * so do not call GetTileOwner(tile) in any case here */
        Owner owner = INVALID_OWNER;

        Train *v = NULL;

        switch (GetTileType(tile)) {
                case MP_ROAD: {
                        if (!IsLevelCrossing(tile) || GetCrossingRailBits(tile) != trackbit) return_cmd_error(STR_ERROR_THERE_IS_NO_RAILROAD_TRACK);

                        if (_current_company != OWNER_WATER) {
                                CommandCost ret = CheckTileOwnership(tile);
                                if (ret.Failed()) return ret;
                        }

                        if (!(flags & DC_BANKRUPT)) {
                                CommandCost ret = EnsureNoVehicleOnGround(tile);
                                if (ret.Failed()) return ret;
                        }

                        cost.AddCost(RailClearCost(GetRailType(tile)));

                        if (flags & DC_EXEC) {
                                if (HasReservedTracks(tile, trackbit)) {
                                        v = GetTrainForReservation(tile, track);
                                        if (v != NULL) FreeTrainTrackReservation(v);
                                }
                                owner = GetTileOwner(tile);
                                Company::Get(owner)->infrastructure.rail[GetRailType(tile)] -= LEVELCROSSING_TRACKBIT_FACTOR;
                                DirtyCompanyInfrastructureWindows(owner);
                                MakeRoadNormal(tile, GetCrossingRoadBits(tile), GetRoadTypes(tile), GetTownIndex(tile), GetRoadOwner(tile, ROADTYPE_ROAD), GetRoadOwner(tile, ROADTYPE_TRAM));
                                DeleteNewGRFInspectWindow(GSF_RAILTYPES, tile);
                        }
                        break;
                }

                case MP_RAILWAY: {
                        TrackBits present;
                        /* There are no rails present at depots. */
                        if (!IsPlainRail(tile)) return_cmd_error(STR_ERROR_THERE_IS_NO_RAILROAD_TRACK);

                        if (_current_company != OWNER_WATER) {
                                CommandCost ret = CheckTileOwnership(tile);
                                if (ret.Failed()) return ret;
                        }

                        CommandCost ret = EnsureNoTrainOnTrack(tile, track);
                        if (ret.Failed()) return ret;

                        present = GetTrackBits(tile);
                        if ((present & trackbit) == 0) return_cmd_error(STR_ERROR_THERE_IS_NO_RAILROAD_TRACK);
                        if (present == (TRACK_BIT_X | TRACK_BIT_Y)) crossing = true;

                        cost.AddCost(RailClearCost(GetRailType(tile)));

                        /* Charge extra to remove signals on the track, if they are there */
                        if (HasSignalOnTrack(tile, track)) {
                                cost.AddCost(DoCommand(tile, track, 0, flags, CMD_REMOVE_SIGNALS));
                        }

                        if (flags & DC_EXEC) {
                                if (HasReservedTracks(tile, trackbit)) {
                                        v = GetTrainForReservation(tile, track);
                                        if (v != NULL) FreeTrainTrackReservation(v);
                                }

                                owner = GetTileOwner(tile);

                                /* Subtract old infrastructure count. */
                                uint pieces = CountBits(present);
                                if (TracksOverlap(present)) pieces *= pieces;
                                Company::Get(owner)->infrastructure.rail[GetRailType(tile)] -= pieces;
                                /* Add new infrastructure count. */
                                present ^= trackbit;
                                pieces = CountBits(present);
                                if (TracksOverlap(present)) pieces *= pieces;
                                Company::Get(owner)->infrastructure.rail[GetRailType(tile)] += pieces;
                                DirtyCompanyInfrastructureWindows(owner);

                                if (present == 0) {
                                        Slope tileh = GetTileSlope(tile);
                                        /* If there is flat water on the lower halftile, convert the tile to shore so the water remains */
                                        if (GetRailGroundType(tile) == RAIL_GROUND_WATER && IsSlopeWithOneCornerRaised(tileh)) {
                                                MakeShore(tile);
                                        } else {
                                                DoClearSquare(tile);
                                        }
                                        DeleteNewGRFInspectWindow(GSF_RAILTYPES, tile);
                                } else {
                                        SetTrackBits(tile, present);
                                        SetTrackReservation(tile, GetRailReservationTrackBits(tile) & present);
                                }
                        }
                        break;
                }

                default: return_cmd_error(STR_ERROR_THERE_IS_NO_RAILROAD_TRACK);
        }

        if (flags & DC_EXEC) {
                /* if we got that far, 'owner' variable is set correctly */
                assert(Company::IsValidID(owner));

                MarkTileDirtyByTile(tile);
                if (crossing) {
                        /* crossing is set when only TRACK_BIT_X and TRACK_BIT_Y are set. As we
                         * are removing one of these pieces, we'll need to update signals for
                         * both directions explicitly, as after the track is removed it won't
                         * 'connect' with the other piece. */
                        AddTrackToSignalBuffer(tile, TRACK_X, owner);
                        AddTrackToSignalBuffer(tile, TRACK_Y, owner);
                        YapfNotifyTrackLayoutChange(tile, TRACK_X);
                        YapfNotifyTrackLayoutChange(tile, TRACK_Y);
                } else {
                        AddTrackToSignalBuffer(tile, track, owner);
                        YapfNotifyTrackLayoutChange(tile, track);
                }

                if (v != NULL) TryPathReserve(v, true);
        }

        _rail_track_endtile = tile;
        return cost;
}


/**
 * Called from water_cmd if a non-flat rail-tile gets flooded and should be converted to shore.
 * The function floods the lower halftile, if the tile has a halftile foundation.
 *
 * @param t The tile to flood.
 * @return true if something was flooded.
 */
bool FloodHalftile(TileIndex t)
{
        assert(IsPlainRailTile(t));

        bool flooded = false;
        if (GetRailGroundType(t) == RAIL_GROUND_WATER) return flooded;

        Slope tileh = GetTileSlope(t);
        TrackBits rail_bits = GetTrackBits(t);

        if (IsSlopeWithOneCornerRaised(tileh)) {
                TrackBits lower_track = CornerToTrackBits(OppositeCorner(GetHighestSlopeCorner(tileh)));

                TrackBits to_remove = lower_track & rail_bits;
                if (to_remove != 0) {
                        Backup<CompanyByte> cur_company(_current_company, OWNER_WATER, FILE_LINE);
                        flooded = DoCommand(t, 0, FIND_FIRST_BIT(to_remove), DC_EXEC, CMD_REMOVE_SINGLE_RAIL).Succeeded();
                        cur_company.Restore();
                        if (!flooded) return flooded; // not yet floodable
                        rail_bits = rail_bits & ~to_remove;
                        if (rail_bits == 0) {
                                MakeShore(t);
                                MarkTileDirtyByTile(t);
                                return flooded;
                        }
                }

                if (IsNonContinuousFoundation(GetRailFoundation(tileh, rail_bits))) {
                        flooded = true;
                        SetRailGroundType(t, RAIL_GROUND_WATER);
                        MarkTileDirtyByTile(t);
                }
        } else {
                /* Make shore on steep slopes and 'three-corners-raised'-slopes. */
                if (ApplyFoundationToSlope(GetRailFoundation(tileh, rail_bits), &tileh) == 0) {
                        if (IsSteepSlope(tileh) || IsSlopeWithThreeCornersRaised(tileh)) {
                                flooded = true;
                                SetRailGroundType(t, RAIL_GROUND_WATER);
                                MarkTileDirtyByTile(t);
                        }
                }
        }
        return flooded;
}

static const TileIndexDiffC _trackdelta[] = {
        { -1,  0 }, {  0,  1 }, { -1,  0 }, {  0,  1 }, {  1,  0 }, {  0,  1 },
        {  0,  0 },
        {  0,  0 },
        {  1,  0 }, {  0, -1 }, {  0, -1 }, {  1,  0 }, {  0, -1 }, { -1,  0 },
        {  0,  0 },
        {  0,  0 }
};


static CommandCost ValidateAutoDrag(Trackdir *trackdir, TileIndex start, TileIndex end)
{
        int x = TileX(start);
        int y = TileY(start);
        int ex = TileX(end);
        int ey = TileY(end);

        if (!ValParamTrackOrientation(TrackdirToTrack(*trackdir))) return CMD_ERROR;

        /* calculate delta x,y from start to end tile */
        int dx = ex - x;
        int dy = ey - y;

        /* calculate delta x,y for the first direction */
        int trdx = _trackdelta[*trackdir].x;
        int trdy = _trackdelta[*trackdir].y;

        if (!IsDiagonalTrackdir(*trackdir)) {
                trdx += _trackdelta[*trackdir ^ 1].x;
                trdy += _trackdelta[*trackdir ^ 1].y;
        }

        /* validate the direction */
        while ((trdx <= 0 && dx > 0) ||
                        (trdx >= 0 && dx < 0) ||
                        (trdy <= 0 && dy > 0) ||
                        (trdy >= 0 && dy < 0)) {
                if (!HasBit(*trackdir, 3)) { // first direction is invalid, try the other
                        SetBit(*trackdir, 3); // reverse the direction
                        trdx = -trdx;
                        trdy = -trdy;
                } else { // other direction is invalid too, invalid drag
                        return CMD_ERROR;
                }
        }

        /* (for diagonal tracks, this is already made sure of by above test), but:
         * for non-diagonal tracks, check if the start and end tile are on 1 line */
        if (!IsDiagonalTrackdir(*trackdir)) {
                trdx = _trackdelta[*trackdir].x;
                trdy = _trackdelta[*trackdir].y;
                if (abs(dx) != abs(dy) && abs(dx) + abs(trdy) != abs(dy) + abs(trdx)) return CMD_ERROR;
        }

        return CommandCost();
}

/**
 * Build or remove a stretch of railroad tracks.
 * @param tile start tile of drag
 * @param flags operation to perform
 * @param p1 end tile of drag
 * @param p2 various bitstuffed elements
 * - p2 = (bit 0-4) - railroad type normal/maglev (0 = normal, 1 = mono, 2 = maglev), only used for building
 * - p2 = (bit 5-7) - track-orientation, valid values: 0-5 (Track enum)
 * - p2 = (bit 8)   - 0 = build, 1 = remove tracks
 * - p2 = (bit 9)   - 0 = build up to an obstacle, 1 = fail if an obstacle is found (used for AIs).
 * @param text unused
 * @return the cost of this operation or an error
 */
static CommandCost CmdRailTrackHelper(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32 p2, const char *text)
{
        CommandCost total_cost(EXPENSES_CONSTRUCTION);
        RailType railtype = Extract<RailType, 0, 5>(p2);
        Track track = Extract<Track, 5, 3>(p2);
        bool remove = HasBit(p2, 8);
        bool fail_if_obstacle = HasBit(p2, 9);

        _rail_track_endtile = INVALID_TILE;

        if ((!remove && !ValParamRailtype(railtype)) || !ValParamTrackOrientation(track)) return CMD_ERROR;
        if (p1 >= MapSize()) return CMD_ERROR;
        TileIndex end_tile = p1;
        Trackdir trackdir = TrackToTrackdir(track);

        CommandCost ret = ValidateAutoDrag(&trackdir, tile, end_tile);
        if (ret.Failed()) return ret;

        bool had_success = false;
        CommandCost last_error = CMD_ERROR;
        for (;;) {
                TileIndex last_endtile = _rail_track_endtile;
                CommandCost ret = DoCommand(tile, remove ? 0 : railtype, TrackdirToTrack(trackdir), flags, remove ? CMD_REMOVE_SINGLE_RAIL : CMD_BUILD_SINGLE_RAIL);

                if (ret.Failed()) {
                        last_error = ret;
                        if (_rail_track_endtile == INVALID_TILE) _rail_track_endtile = last_endtile;
                        if (last_error.GetErrorMessage() != STR_ERROR_ALREADY_BUILT && !remove) {
                                if (fail_if_obstacle) return last_error;
                                break;
                        }

                        /* Ownership errors are more important. */
                        if (last_error.GetErrorMessage() == STR_ERROR_OWNED_BY && remove) break;
                } else {
                        had_success = true;
                        total_cost.AddCost(ret);
                }

                if (tile == end_tile) break;

                tile += ToTileIndexDiff(_trackdelta[trackdir]);

                /* toggle railbit for the non-diagonal tracks */
                if (!IsDiagonalTrackdir(trackdir)) ToggleBit(trackdir, 0);
        }

        if (had_success) return total_cost;
        return last_error;
}

/**
 * Build rail on a stretch of track.
 * Stub for the unified rail builder/remover
 * @param tile start tile of drag
 * @param flags operation to perform
 * @param p1 end tile of drag
 * @param p2 various bitstuffed elements
 * - p2 = (bit 0-4) - railroad type normal/maglev (0 = normal, 1 = mono, 2 = maglev)
 * - p2 = (bit 5-7) - track-orientation, valid values: 0-5 (Track enum)
 * - p2 = (bit 8)   - 0 = build, 1 = remove tracks
 * @param text unused
 * @return the cost of this operation or an error
 * @see CmdRailTrackHelper
 */
CommandCost CmdBuildRailroadTrack(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32 p2, const char *text)
{
        return CmdRailTrackHelper(tile, flags, p1, ClrBit(p2, 8), text);
}

/**
 * Build rail on a stretch of track.
 * Stub for the unified rail builder/remover
 * @param tile start tile of drag
 * @param flags operation to perform
 * @param p1 end tile of drag
 * @param p2 various bitstuffed elements
 * - p2 = (bit 0-4) - railroad type normal/maglev (0 = normal, 1 = mono, 2 = maglev), only used for building
 * - p2 = (bit 5-7) - track-orientation, valid values: 0-5 (Track enum)
 * - p2 = (bit 8)   - 0 = build, 1 = remove tracks
 * @param text unused
 * @return the cost of this operation or an error
 * @see CmdRailTrackHelper
 */
CommandCost CmdRemoveRailroadTrack(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32 p2, const char *text)
{
        return CmdRailTrackHelper(tile, flags, p1, SetBit(p2, 8), text);
}

/**
 * Build a train depot
 * @param tile position of the train depot
 * @param flags operation to perform
 * @param p1 rail type
 * @param p2 bit 0..1 entrance direction (DiagDirection)
 * @param text unused
 * @return the cost of this operation or an error
 *
 * @todo When checking for the tile slope,
 * distinguish between "Flat land required" and "land sloped in wrong direction"
 */
CommandCost CmdBuildTrainDepot(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32 p2, const char *text)
{
        /* check railtype and valid direction for depot (0 through 3), 4 in total */
        RailType railtype = Extract<RailType, 0, 5>(p1);
        if (!ValParamRailtype(railtype)) return CMD_ERROR;

        Slope tileh = GetTileSlope(tile);

        DiagDirection dir = Extract<DiagDirection, 0, 2>(p2);

        /* Prohibit construction if
         * The tile is non-flat AND
         * 1) build-on-slopes is disabled
         * 2) the tile is steep i.e. spans two height levels
         * 3) the exit points in the wrong direction
         */

        if (tileh != SLOPE_FLAT && (
                                !_settings_game.construction.build_on_slopes ||
                                !CanBuildDepotByTileh(dir, tileh)
                        )) {
                return_cmd_error(STR_ERROR_FLAT_LAND_REQUIRED);
        }

        CommandCost cost = DoCommand(tile, 0, 0, flags, CMD_LANDSCAPE_CLEAR);
        if (cost.Failed()) return cost;

        if (IsBridgeAbove(tile)) return_cmd_error(STR_ERROR_MUST_DEMOLISH_BRIDGE_FIRST);

        if (!Depot::CanAllocateItem()) return CMD_ERROR;

        if (flags & DC_EXEC) {
                Depot *d = new Depot(tile);
                d->build_date = _date;

                MakeRailDepot(tile, _current_company, d->index, dir, railtype);
                MarkTileDirtyByTile(tile);
                MakeDefaultName(d);

                Company::Get(_current_company)->infrastructure.rail[railtype]++;
                DirtyCompanyInfrastructureWindows(_current_company);

                AddSideToSignalBuffer(tile, INVALID_DIAGDIR, _current_company);
                YapfNotifyTrackLayoutChange(tile, DiagDirToDiagTrack(dir));
        }

        cost.AddCost(_price[PR_BUILD_DEPOT_TRAIN]);
        cost.AddCost(RailBuildCost(railtype));
        return cost;
}

static void ClearBridgeTunnelSignalSimulation(TileIndex entrance, TileIndex exit)
{
        if (IsBridge(entrance)) ClearBridgeEntranceSimulatedSignals(entrance);
        ClrTunnelBridgeSignalSimulationEntrance(entrance);
        ClrTunnelBridgeSignalSimulationExit(exit);
}

static void SetupBridgeTunnelSignalSimulation(TileIndex entrance, TileIndex exit)
{
        SetTunnelBridgeSignalSimulationEntrance(entrance);
        SetTunnelBridgeSignalState(entrance, SIGNAL_STATE_GREEN);
        SetTunnelBridgeSignalSimulationExit(exit);
}

/**
 * Build signals, alternate between double/single, signal/semaphore,
 * pre/exit/combo-signals, and what-else not. If the rail piece does not
 * have any signals, bit 4 (cycle signal-type) is ignored
 * @param tile tile where to build the signals
 * @param flags operation to perform
 * @param p1 various bitstuffed elements
 * - p1 = (bit 0-2) - track-orientation, valid values: 0-5 (Track enum)
 * - p1 = (bit 3)   - 1 = override signal/semaphore, or pre/exit/combo signal or (for bit 7) toggle variant (CTRL-toggle)
 * - p1 = (bit 4)   - 0 = signals, 1 = semaphores
 * - p1 = (bit 5-7) - type of the signal, for valid values see enum SignalType in rail_map.h
 * - p1 = (bit 8)   - convert the present signal type and variant
 * - p1 = (bit 9-11)- start cycle from this signal type
 * - p1 = (bit 12-14)-wrap around after this signal type
 * - p1 = (bit 15-16)-cycle the signal direction this many times
 * - p1 = (bit 17)  - 1 = don't modify an existing signal but don't fail either, 0 = always set new signal type
 * @param p2 used for CmdBuildManySignals() to copy direction of first signal
 * @param text unused
 * @return the cost of this operation or an error
 * @todo p2 should be replaced by two bits for "along" and "against" the track.
 */
CommandCost CmdBuildSingleSignal(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32 p2, const char *text)
{
        Track track = Extract<Track, 0, 3>(p1);
        bool ctrl_pressed = HasBit(p1, 3); // was the CTRL button pressed
        SignalVariant sigvar = (ctrl_pressed ^ HasBit(p1, 4)) ? SIG_SEMAPHORE : SIG_ELECTRIC; // the signal variant of the new signal
        SignalType sigtype = Extract<SignalType, 5, 3>(p1); // the signal type of the new signal
        bool convert_signal = HasBit(p1, 8); // convert button pressed
        SignalType cycle_start = Extract<SignalType, 9, 3>(p1);
        SignalType cycle_stop = Extract<SignalType, 12, 3>(p1);
        uint num_dir_cycle = GB(p1, 15, 2);

        if (sigtype > SIGTYPE_LAST) return CMD_ERROR;
        if (cycle_start > cycle_stop || cycle_stop > SIGTYPE_LAST) return CMD_ERROR;

        /* You can only build signals on plain rail tiles or tunnel/bridges, and the selected track must exist */
        if (IsTileType(tile, MP_TUNNELBRIDGE)) {
                if (GetTunnelBridgeTransportType(tile) != TRANSPORT_RAIL) return CMD_ERROR;
                CommandCost ret = EnsureNoTrainOnTrack(GetOtherTunnelBridgeEnd(tile), track);
                if (ret.Failed()) return ret;
                ret = EnsureNoTrainOnTrack(tile, track);
                if (ret.Failed()) return ret;
        } else if (!ValParamTrackOrientation(track) || !IsPlainRailTile(tile) || !HasTrack(tile, track)) {
                return_cmd_error(STR_ERROR_THERE_IS_NO_RAILROAD_TRACK);
        }
        /* Protect against invalid signal copying */
        if (p2 != 0 && (p2 & SignalOnTrack(track)) == 0) return CMD_ERROR;

        CommandCost ret = CheckTileOwnership(tile);
        if (ret.Failed()) return ret;

        CommandCost cost;
        /* handle signals simulation on tunnel/bridge. */
        if (IsTileType(tile, MP_TUNNELBRIDGE)) {
                TileIndex tile_exit = GetOtherTunnelBridgeEnd(tile);
                cost = CommandCost();
                bool flip_variant = false;
                bool is_pbs = (sigtype == SIGTYPE_PBS) || (sigtype == SIGTYPE_PBS_ONEWAY);
                if (!IsTunnelBridgeWithSignalSimulation(tile)) { // toggle signal zero costs.
                        if (convert_signal) return_cmd_error(STR_ERROR_THERE_ARE_NO_SIGNALS);
                        if (p2 != 12) cost = CommandCost(EXPENSES_CONSTRUCTION, _price[PR_BUILD_SIGNALS] * ((GetTunnelBridgeLength(tile, tile_exit) + 4) >> 2)); // minimal 1
                } else {
                        if (HasBit(p1, 17)) return CommandCost();
                        if ((p2 != 0 && (sigvar == SIG_SEMAPHORE) != IsTunnelBridgeSemaphore(tile)) ||
                                        (convert_signal && (ctrl_pressed || (sigvar == SIG_SEMAPHORE) != IsTunnelBridgeSemaphore(tile)))) {
                                flip_variant = true;
                                cost = CommandCost(EXPENSES_CONSTRUCTION, (_price[PR_BUILD_SIGNALS] + _price[PR_CLEAR_SIGNALS]) *
                                                ((GetTunnelBridgeLength(tile, tile_exit) + 4) >> 2)); // minimal 1
                        }
                }
                if (flags & DC_EXEC) {
                        Company * const c = Company::Get(GetTileOwner(tile));
                        if (IsTunnelBridgeWithSignalSimulation(tile)) c->infrastructure.signal -= GetTunnelBridgeSignalSimulationSignalCount(tile, tile_exit);
                        if (p2 == 0 && IsTunnelBridgeWithSignalSimulation(tile)) { // Toggle signal if already signals present.
                                if (convert_signal) {
                                        if (flip_variant) {
                                                SetTunnelBridgeSemaphore(tile, !IsTunnelBridgeSemaphore(tile));
                                                SetTunnelBridgeSemaphore(tile_exit, IsTunnelBridgeSemaphore(tile));
                                        }
                                        if (!ctrl_pressed) {
                                                SetTunnelBridgePBS(tile, is_pbs);
                                                SetTunnelBridgePBS(tile_exit, is_pbs);
                                        }
                                } else if (ctrl_pressed) {
                                        SetTunnelBridgePBS(tile, !IsTunnelBridgePBS(tile));
                                        SetTunnelBridgePBS(tile_exit, IsTunnelBridgePBS(tile));
                                } else {
                                        if (IsTunnelBridgeSignalSimulationEntrance(tile)) {
                                                ClearBridgeTunnelSignalSimulation(tile, tile_exit);
                                                SetupBridgeTunnelSignalSimulation(tile_exit, tile);
                                        } else {
                                                ClearBridgeTunnelSignalSimulation(tile_exit, tile);
                                                SetupBridgeTunnelSignalSimulation(tile, tile_exit);
                                        }
                                }                       
                        } else {
                                /* Create one direction tunnel/bridge if required. */
                                if (p2 == 0) {
                                        SetupBridgeTunnelSignalSimulation(tile, tile_exit);
                                } else if (p2 == 4 || p2 == 8) {
                                        DiagDirection tbdir = GetTunnelBridgeDirection(tile);
                                        /* If signal only on one side build accordingly one-way tunnel/bridge. */
                                        if ((p2 == 8 && (tbdir == DIAGDIR_NE || tbdir == DIAGDIR_SE)) ||
                                                (p2 == 4 && (tbdir == DIAGDIR_SW || tbdir == DIAGDIR_NW))) {
                                                ClearBridgeTunnelSignalSimulation(tile_exit, tile);
                                                SetupBridgeTunnelSignalSimulation(tile, tile_exit);
                                        } else {
                                                ClearBridgeTunnelSignalSimulation(tile, tile_exit);
                                                SetupBridgeTunnelSignalSimulation(tile_exit, tile);
                                        }
                                }

                                if (p2 == 0 || p2 == 4 || p2 == 8) {
                                        SetTunnelBridgeSemaphore(tile, sigvar == SIG_SEMAPHORE);
                                        SetTunnelBridgeSemaphore(tile_exit, sigvar == SIG_SEMAPHORE);
                                        SetTunnelBridgePBS(tile, is_pbs);
                                        SetTunnelBridgePBS(tile_exit, is_pbs);
                                }
                        }
                        
                        if (IsTunnelBridgeSignalSimulationExit(tile) && IsTunnelBridgePBS(tile) && !HasTunnelBridgeReservation(tile)) SetTunnelBridgeSignalState(tile, SIGNAL_STATE_RED);
                        if (IsTunnelBridgeSignalSimulationExit(tile_exit) && IsTunnelBridgePBS(tile_exit) && !HasTunnelBridgeReservation(tile_exit)) SetTunnelBridgeSignalState(tile_exit, SIGNAL_STATE_RED);
                        
                        MarkBridgeOrTunnelDirty(tile);
                        AddSideToSignalBuffer(tile, INVALID_DIAGDIR, GetTileOwner(tile));
                        AddSideToSignalBuffer(tile_exit, INVALID_DIAGDIR, GetTileOwner(tile));
                        YapfNotifyTrackLayoutChange(tile, track);
                        YapfNotifyTrackLayoutChange(tile_exit, track);
                        if (IsTunnelBridgeWithSignalSimulation(tile)) c->infrastructure.signal += GetTunnelBridgeSignalSimulationSignalCount(tile, tile_exit);
                        DirtyCompanyInfrastructureWindows(GetTileOwner(tile));
                }
                return cost;
        }

        /* See if this is a valid track combination for signals (no overlap) */
        if (TracksOverlap(GetTrackBits(tile))) return_cmd_error(STR_ERROR_NO_SUITABLE_RAILROAD_TRACK);

        /* In case we don't want to change an existing signal, return without error. */
        if (HasBit(p1, 17) && HasSignalOnTrack(tile, track)) return CommandCost();

        /* you can not convert a signal if no signal is on track */
        if (convert_signal && !HasSignalOnTrack(tile, track)) return_cmd_error(STR_ERROR_THERE_ARE_NO_SIGNALS);

        if (!HasSignalOnTrack(tile, track)) {
                /* build new signals */
                cost = CommandCost(EXPENSES_CONSTRUCTION, _price[PR_BUILD_SIGNALS]);
        } else {
                if (p2 != 0 && sigvar != GetSignalVariant(tile, track)) {
                        /* convert signals <-> semaphores */
                        cost = CommandCost(EXPENSES_CONSTRUCTION, _price[PR_BUILD_SIGNALS] + _price[PR_CLEAR_SIGNALS]);

                } else if (convert_signal) {
                        /* convert button pressed */
                        if (ctrl_pressed || GetSignalVariant(tile, track) != sigvar) {
                                /* convert electric <-> semaphore */
                                cost = CommandCost(EXPENSES_CONSTRUCTION, _price[PR_BUILD_SIGNALS] + _price[PR_CLEAR_SIGNALS]);
                        } else {
                                /* it is free to change signal type: normal-pre-exit-combo */
                                cost = CommandCost();
                        }

                } else {
                        /* it is free to change orientation/pre-exit-combo signals */
                        cost = CommandCost();
                }
        }

        if (flags & DC_EXEC) {
                Train *v = NULL;
                /* The new/changed signal could block our path. As this can lead to
                 * stale reservations, we clear the path reservation here and try
                 * to redo it later on. */
                if (HasReservedTracks(tile, TrackToTrackBits(track))) {
                        v = GetTrainForReservation(tile, track);
                        if (v != NULL) FreeTrainTrackReservation(v);
                }

                if (!HasSignals(tile)) {
                        /* there are no signals at all on this tile yet */
                        SetHasSignals(tile, true);
                        SetSignalStates(tile, 0xF); // all signals are on
                        SetPresentSignals(tile, 0); // no signals built by default
                        SetSignalType(tile, track, sigtype);
                        SetSignalVariant(tile, track, sigvar);
                }

                /* Subtract old signal infrastructure count. */
                Company::Get(GetTileOwner(tile))->infrastructure.signal -= CountBits(GetPresentSignals(tile));

                if (p2 == 0) {
                        if (!HasSignalOnTrack(tile, track)) {
                                /* build new signals */
                                SetPresentSignals(tile, GetPresentSignals(tile) | (IsPbsOrLogicSignal(sigtype) ? KillFirstBit(SignalOnTrack(track)) : SignalOnTrack(track)));
                                SetSignalType(tile, track, sigtype);
                                SetSignalVariant(tile, track, sigvar);

                                /* logic signals: create a new signal program */
                                if (sigtype == SIGTYPE_LOGIC) {
                                        CreateSignalProgram(tile, track);
                                }

                                while (num_dir_cycle-- > 0) CycleSignalSide(tile, track);
                        } else {
                                if (convert_signal) {
                                        /* convert signal button pressed */
                                        if (ctrl_pressed) {
                                                /* toggle the present signal variant: SIG_ELECTRIC <-> SIG_SEMAPHORE */
                                                SetSignalVariant(tile, track, (GetSignalVariant(tile, track) == SIG_ELECTRIC) ? SIG_SEMAPHORE : SIG_ELECTRIC);
                                                /* Query current signal type so the check for PBS signals below works. */
                                                sigtype = GetSignalType(tile, track);
                                        } else {
                                                /* convert the present signal to the chosen type and variant */

                                                /* logic signals: create or delete signal program as necessary */
                                                SignalTypeChanged(tile, track, GetSignalType(tile, track), sigtype);

                                                SetSignalType(tile, track, sigtype);
                                                SetSignalVariant(tile, track, sigvar);
                                                if (IsPbsOrLogicSignal(sigtype) && (GetPresentSignals(tile) & SignalOnTrack(track)) == SignalOnTrack(track)) {
                                                        SetPresentSignals(tile, (GetPresentSignals(tile) & ~SignalOnTrack(track)) | KillFirstBit(SignalOnTrack(track)));
                                                }
                                        }

                                } else if (ctrl_pressed) {
                                        /* cycle between cycle_start and cycle_end */
                                        sigtype = (SignalType)(GetSignalType(tile, track) + 1);
                                        if (sigtype < cycle_start || sigtype > cycle_stop) sigtype = cycle_start;

                                        /* logic signals: create or delete signal program as necessary */
                                        SignalTypeChanged(tile, track, GetSignalType(tile, track), sigtype);

                                        SetSignalType(tile, track, sigtype);
                                        if (IsPbsOrLogicSignal(sigtype) && (GetPresentSignals(tile) & SignalOnTrack(track)) == SignalOnTrack(track)) {
                                                SetPresentSignals(tile, (GetPresentSignals(tile) & ~SignalOnTrack(track)) | KillFirstBit(SignalOnTrack(track)));
                                        }
                                } else {
                                        /* cycle the signal side: both -> left -> right -> both -> ... */
                                        CycleSignalSide(tile, track);
                                        /* Query current signal type so the check for PBS signals below works. */
                                        sigtype = GetSignalType(tile, track);
                                }
                        }
                } else {
                        /* If CmdBuildManySignals is called with copying signals, just copy the
                         * direction of the first signal given as parameter by CmdBuildManySignals */
                        SetPresentSignals(tile, (GetPresentSignals(tile) & ~SignalOnTrack(track)) | (p2 & SignalOnTrack(track)));
                        SetSignalVariant(tile, track, sigvar);
                        SetSignalType(tile, track, sigtype);

                        /* logic signals: create a new signal program */
                        if (sigtype == SIGTYPE_LOGIC) {
                                CreateSignalProgram(tile, track);
                        }
                }

                /* Add new signal infrastructure count. */
                Company::Get(GetTileOwner(tile))->infrastructure.signal += CountBits(GetPresentSignals(tile));
                DirtyCompanyInfrastructureWindows(GetTileOwner(tile));

                if (IsPbsSignal(sigtype)) {
                        /* PBS signals should show red unless they are on reserved tiles without a train. */
                        uint mask = GetPresentSignals(tile) & SignalOnTrack(track);
                        SetSignalStates(tile, (GetSignalStates(tile) & ~mask) | ((HasBit(GetRailReservationTrackBits(tile), track) && EnsureNoVehicleOnGround(tile).Succeeded() ? UINT_MAX : 0) & mask));
                }
                MarkTileDirtyByTile(tile, ZOOM_LVL_DRAW_MAP);
                AddTrackToSignalBuffer(tile, track, _current_company);
                YapfNotifyTrackLayoutChange(tile, track);
                if (v != NULL) {
                        /* Extend the train's path if it's not stopped or loading, or not at a safe position. */
                        if (!(((v->vehstatus & VS_STOPPED) && v->cur_speed == 0) || v->current_order.IsType(OT_LOADING)) ||
                                        !IsSafeWaitingPosition(v, v->tile, v->GetVehicleTrackdir(), true, _settings_game.pf.forbid_90_deg)) {
                                TryPathReserve(v, true);
                        }
                }
        }

        return cost;
}

static bool CheckSignalAutoFill(TileIndex &tile, Trackdir &trackdir, int &signal_ctr, bool remove)
{
        tile = AddTileIndexDiffCWrap(tile, _trackdelta[trackdir]);
        if (tile == INVALID_TILE) return false;

        /* Check for track bits on the new tile */
        TrackdirBits trackdirbits = TrackStatusToTrackdirBits(GetTileTrackStatus(tile, TRANSPORT_RAIL, 0));

        if (TracksOverlap(TrackdirBitsToTrackBits(trackdirbits))) return false;
        trackdirbits &= TrackdirReachesTrackdirs(trackdir);

        /* No track bits, must stop */
        if (trackdirbits == TRACKDIR_BIT_NONE) return false;

        /* Get the first track dir */
        trackdir = RemoveFirstTrackdir(&trackdirbits);

        /* Any left? It's a junction so we stop */
        if (trackdirbits != TRACKDIR_BIT_NONE) return false;

        switch (GetTileType(tile)) {
                case MP_RAILWAY:
                        if (IsRailDepot(tile)) return false;
                        if (!remove && HasSignalOnTrack(tile, TrackdirToTrack(trackdir))) return false;
                        signal_ctr++;
                        if (IsDiagonalTrackdir(trackdir)) {
                                signal_ctr++;
                                /* Ensure signal_ctr even so X and Y pieces get signals */
                                ClrBit(signal_ctr, 0);
                        }
                        return true;

                case MP_ROAD:
                        if (!IsLevelCrossing(tile)) return false;
                        signal_ctr += 2;
                        return true;

                case MP_TUNNELBRIDGE: {
                        if (!remove && IsTunnelBridgeWithSignalSimulation(tile)) return false;
                        TileIndex orig_tile = tile; // backup old value

                        if (GetTunnelBridgeTransportType(tile) != TRANSPORT_RAIL) return false;
                        if (GetTunnelBridgeDirection(tile) != TrackdirToExitdir(trackdir)) return false;

                        /* Skip to end of tunnel or bridge
                         * note that tile is a parameter by reference, so it must be updated */
                        tile = GetOtherTunnelBridgeEnd(tile);

                        signal_ctr += (GetTunnelBridgeLength(orig_tile, tile) + 2) * 2;
                        return true;
                }

                default: return false;
        }
}

/**
 * Build many signals by dragging; AutoSignals
 * @param tile start tile of drag
 * @param flags operation to perform
 * @param p1  end tile of drag
 * @param p2 various bitstuffed elements
 * - p2 = (bit  0- 2) - track-orientation, valid values: 0-5 (Track enum)
 * - p2 = (bit  3)    - 1 = override signal/semaphore, or pre/exit/combo signal (CTRL-toggle)
 * - p2 = (bit  4)    - 0 = signals, 1 = semaphores
 * - p2 = (bit  5)    - 0 = build, 1 = remove signals
 * - p2 = (bit  6)    - 0 = selected stretch, 1 = auto fill
 * - p2 = (bit  7- 9) - default signal type
 * - p2 = (bit 10)    - 0 = keep fixed distance, 1 = minimise gaps between signals
 * - p2 = (bit 24-31) - user defined signals_density
 * @param text unused
 * @return the cost of this operation or an error
 */
static CommandCost CmdSignalTrackHelper(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32 p2, const char *text)
{
        CommandCost total_cost(EXPENSES_CONSTRUCTION);
        TileIndex start_tile = tile;

        Track track = Extract<Track, 0, 3>(p2);
        bool mode = HasBit(p2, 3);
        bool semaphores = HasBit(p2, 4);
        bool remove = HasBit(p2, 5);
        bool autofill = HasBit(p2, 6);
        bool minimise_gaps = HasBit(p2, 10);
        byte signal_density = GB(p2, 24, 8);

        if (p1 >= MapSize() || !ValParamTrackOrientation(track)) return CMD_ERROR;
        TileIndex end_tile = p1;
        if (signal_density == 0 || signal_density > 20) return CMD_ERROR;

        if (!IsPlainRailTile(tile)) return_cmd_error(STR_ERROR_THERE_IS_NO_RAILROAD_TRACK);

        /* for vertical/horizontal tracks, double the given signals density
         * since the original amount will be too dense (shorter tracks) */
        signal_density *= 2;

        Trackdir trackdir = TrackToTrackdir(track);
        CommandCost ret = ValidateAutoDrag(&trackdir, tile, end_tile);
        if (ret.Failed()) return ret;

        track = TrackdirToTrack(trackdir); // trackdir might have changed, keep track in sync
        Trackdir start_trackdir = trackdir;

        /* Must start on a valid track to be able to avoid loops */
        if (!HasTrack(tile, track)) return CMD_ERROR;

        SignalType sigtype = (SignalType)GB(p2, 7, 3);
        if (sigtype > SIGTYPE_LAST) return CMD_ERROR;

        byte signals;
        /* copy the signal-style of the first rail-piece if existing */
        if (HasSignalOnTrack(tile, track)) {
                signals = GetPresentSignals(tile) & SignalOnTrack(track);
                assert(signals != 0);

                /* copy signal/semaphores style (independent of CTRL) */
                semaphores = GetSignalVariant(tile, track) != SIG_ELECTRIC;

                sigtype = GetSignalType(tile, track);
                /* Don't but copy entry or exit-signal type */
                if (sigtype == SIGTYPE_ENTRY || sigtype == SIGTYPE_EXIT) sigtype = SIGTYPE_NORMAL;
        } else { // no signals exist, drag a two-way signal stretch
                signals = IsPbsSignal(sigtype) ? SignalAlongTrackdir(trackdir) : SignalOnTrack(track);
        }

        byte signal_dir = 0;
        if (signals & SignalAlongTrackdir(trackdir))   SetBit(signal_dir, 0);
        if (signals & SignalAgainstTrackdir(trackdir)) SetBit(signal_dir, 1);

        /* signal_ctr         - amount of tiles already processed
         * last_used_ctr      - amount of tiles before previously placed signal
         * signals_density    - setting to put signal on every Nth tile (double space on |, -- tracks)
         * last_suitable_ctr  - amount of tiles before last possible signal place
         * last_suitable_tile - last tile where it is possible to place a signal
         * last_suitable_trackdir - trackdir of the last tile
         **********
         * trackdir   - trackdir to build with autorail
         * semaphores - semaphores or signals
         * signals    - is there a signal/semaphore on the first tile, copy its style (two-way/single-way)
         *              and convert all others to semaphore/signal
         * remove     - 1 remove signals, 0 build signals */
        int signal_ctr = 0;
        int last_used_ctr = INT_MIN; // initially INT_MIN to force building/removing at the first tile
        int last_suitable_ctr = 0;
        TileIndex last_suitable_tile = INVALID_TILE;
        Trackdir last_suitable_trackdir = INVALID_TRACKDIR;
        CommandCost last_error = CMD_ERROR;
        bool had_success = false;
        std::vector<TileIndex> tunnel_bridge_blacklist;
        for (;;) {
                bool tile_ok = true;
                if (IsTileType(tile, MP_TUNNELBRIDGE)) {
                        if (container_unordered_remove(tunnel_bridge_blacklist, tile) > 0) {
                                /* This tile is blacklisted, skip tile and remove from blacklist.
                                 * Mark last used counter as current tile.
                                 */
                                tile_ok = false;
                                last_used_ctr = signal_ctr;
                                last_suitable_tile = INVALID_TILE;
                        }
                }

                /* only build/remove signals with the specified density */
                if (tile_ok && (remove || minimise_gaps || signal_ctr % signal_density == 0 || IsTileType(tile, MP_TUNNELBRIDGE))) {
                        uint32 p1 = GB(TrackdirToTrack(trackdir), 0, 3);
                        SB(p1, 3, 1, mode);
                        SB(p1, 4, 1, semaphores);
                        SB(p1, 5, 3, sigtype);
                        if (!remove && signal_ctr == 0) SetBit(p1, 17);

                        /* Pick the correct orientation for the track direction */
                        signals = 0;
                        if (HasBit(signal_dir, 0)) signals |= SignalAlongTrackdir(trackdir);
                        if (HasBit(signal_dir, 1)) signals |= SignalAgainstTrackdir(trackdir);

                        /* Test tiles in between for suitability as well if minimising gaps. */
                        bool test_only = !remove && minimise_gaps && signal_ctr < (last_used_ctr + signal_density);
                        CommandCost ret = DoCommand(tile, p1, signals, test_only ? flags & ~DC_EXEC : flags, remove ? CMD_REMOVE_SIGNALS : CMD_BUILD_SIGNALS);

                        if (!test_only && ret.Succeeded() && IsTileType(tile, MP_TUNNELBRIDGE) && GetTunnelBridgeDirection(tile) == TrackdirToExitdir(trackdir)) {
                                /* Blacklist far end of tunnel if we just actioned the near end */
                                tunnel_bridge_blacklist.push_back(GetOtherTunnelBridgeEnd(tile));
                        }

                        if (ret.Succeeded()) {
                                /* Remember last track piece where we can place a signal. */
                                last_suitable_ctr = signal_ctr;
                                last_suitable_tile = tile;
                                last_suitable_trackdir = trackdir;
                        } else if (!test_only && last_suitable_tile != INVALID_TILE) {
                                /* If a signal can't be placed, place it at the last possible position. */
                                SB(p1, 0, 3, TrackdirToTrack(last_suitable_trackdir));
                                ClrBit(p1, 17);

                                /* Pick the correct orientation for the track direction. */
                                signals = 0;
                                if (HasBit(signal_dir, 0)) signals |= SignalAlongTrackdir(last_suitable_trackdir);
                                if (HasBit(signal_dir, 1)) signals |= SignalAgainstTrackdir(last_suitable_trackdir);

                                ret = DoCommand(last_suitable_tile, p1, signals, flags, remove ? CMD_REMOVE_SIGNALS : CMD_BUILD_SIGNALS);

                                if (ret.Succeeded() && IsTileType(last_suitable_tile, MP_TUNNELBRIDGE) && GetTunnelBridgeDirection(last_suitable_tile) == TrackdirToExitdir(last_suitable_trackdir)) {
                                        /* Blacklist far end of tunnel if we just actioned the near end */
                                        tunnel_bridge_blacklist.push_back(GetOtherTunnelBridgeEnd(last_suitable_tile));
                                }
                        }

                        /* Collect cost. */
                        if (!test_only) {
                        /* Be user-friendly and try placing signals as much as possible */
                        if (ret.Succeeded()) {
                                had_success = true;
                                total_cost.AddCost(ret);
                                last_used_ctr = last_suitable_ctr;
                                last_suitable_tile = INVALID_TILE;
                        } else {
                                        /* The "No railway" error is the least important one. */
                                        if (ret.GetErrorMessage() != STR_ERROR_THERE_IS_NO_RAILROAD_TRACK ||
                                                        last_error.GetErrorMessage() == INVALID_STRING_ID) {
                                                last_error = ret;
                                        }
                                }
                        }
                }

                if (autofill) {
                        if (!CheckSignalAutoFill(tile, trackdir, signal_ctr, remove)) break;

                        /* Prevent possible loops */
                        if (tile == start_tile && trackdir == start_trackdir) break;
                } else {
                        if (tile == end_tile) break;

                        tile += ToTileIndexDiff(_trackdelta[trackdir]);
                        signal_ctr++;

                        /* toggle railbit for the non-diagonal tracks (|, -- tracks) */
                        if (IsDiagonalTrackdir(trackdir)) {
                                signal_ctr++;
                        } else {
                                ToggleBit(trackdir, 0);
                        }
                }
        }

        return had_success ? total_cost : last_error;
}

/**
 * Build signals on a stretch of track.
 * Stub for the unified signal builder/remover
 * @param tile start tile of drag
 * @param flags operation to perform
 * @param p1  end tile of drag
 * @param p2 various bitstuffed elements
 * - p2 = (bit  0- 2) - track-orientation, valid values: 0-5 (Track enum)
 * - p2 = (bit  3)    - 1 = override signal/semaphore, or pre/exit/combo signal (CTRL-toggle)
 * - p2 = (bit  4)    - 0 = signals, 1 = semaphores
 * - p2 = (bit  5)    - 0 = build, 1 = remove signals
 * - p2 = (bit  6)    - 0 = selected stretch, 1 = auto fill
 * - p2 = (bit  7- 9) - default signal type
 * - p2 = (bit 24-31) - user defined signals_density
 * @param text unused
 * @return the cost of this operation or an error
 * @see CmdSignalTrackHelper
 */
CommandCost CmdBuildSignalTrack(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32 p2, const char *text)
{
        return CmdSignalTrackHelper(tile, flags, p1, p2, text);
}

/**
 * Remove signals
 * @param tile coordinates where signal is being deleted from
 * @param flags operation to perform
 * @param p1 various bitstuffed elements, only track information is used
 *           - (bit  0- 2) - track-orientation, valid values: 0-5 (Track enum)
 *           - (bit  3)    - override signal/semaphore, or pre/exit/combo signal (CTRL-toggle)
 *           - (bit  4)    - 0 = signals, 1 = semaphores
 * @param p2 unused
 * @param text unused
 * @return the cost of this operation or an error
 */
CommandCost CmdRemoveSingleSignal(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32 p2, const char *text)
{
        Track track = Extract<Track, 0, 3>(p1);
        Money cost = _price[PR_CLEAR_SIGNALS];

        if (IsTileType(tile, MP_TUNNELBRIDGE)) {
                TileIndex end = GetOtherTunnelBridgeEnd(tile);
                if (GetTunnelBridgeTransportType(tile) != TRANSPORT_RAIL) return_cmd_error(STR_ERROR_THERE_IS_NO_RAILROAD_TRACK);
                if (!IsTunnelBridgeWithSignalSimulation(tile)) return_cmd_error(STR_ERROR_THERE_ARE_NO_SIGNALS);

                cost *= ((GetTunnelBridgeLength(tile, end) + 4) >> 2);

                CommandCost ret = EnsureNoTrainOnTrack(GetOtherTunnelBridgeEnd(tile), track);
                if (ret.Failed()) return ret;
                ret = EnsureNoTrainOnTrack(tile, track);
                if (ret.Failed()) return ret;
        } else {
                if (!ValParamTrackOrientation(track) || !IsPlainRailTile(tile) || !HasTrack(tile, track)) {
                        return_cmd_error(STR_ERROR_THERE_IS_NO_RAILROAD_TRACK);
                }
                if (!HasSignalOnTrack(tile, track)) {
                        return_cmd_error(STR_ERROR_THERE_ARE_NO_SIGNALS);
                }
                CommandCost ret = EnsureNoTrainOnTrack(tile, track);
                if (ret.Failed()) return ret;
        }

        /* Only water can remove signals from anyone */
        if (_current_company != OWNER_WATER) {
        }

        /* Do it? */
        if (flags & DC_EXEC) {

                if (IsTunnelBridgeWithSignalSimulation(tile)) { // handle tunnel/bridge signals.
                        TileIndex end = GetOtherTunnelBridgeEnd(tile);
                        Company::Get(GetTileOwner(tile))->infrastructure.signal -= GetTunnelBridgeSignalSimulationSignalCount(tile, end);
                        ClearBridgeTunnelSignalSimulation(end, tile);
                        ClearBridgeTunnelSignalSimulation(tile, end);
                        MarkBridgeOrTunnelDirty(tile);
                        AddSideToSignalBuffer(tile, INVALID_DIAGDIR, GetTileOwner(tile));
                        AddSideToSignalBuffer(end, INVALID_DIAGDIR, GetTileOwner(tile));
                        YapfNotifyTrackLayoutChange(tile, track);
                        YapfNotifyTrackLayoutChange(end, track);
                        DirtyCompanyInfrastructureWindows(GetTileOwner(tile));
                        return CommandCost(EXPENSES_CONSTRUCTION, cost);
                }

                Train *v = NULL;
                if (HasReservedTracks(tile, TrackToTrackBits(track))) {
                        v = GetTrainForReservation(tile, track);
                } else if (IsPbsSignal(GetSignalType(tile, track))) {
                        /* PBS signal, might be the end of a path reservation. */
                        Trackdir td = TrackToTrackdir(track);
                        for (int i = 0; v == NULL && i < 2; i++, td = ReverseTrackdir(td)) {
                                /* Only test the active signal side. */
                                if (!HasSignalOnTrackdir(tile, ReverseTrackdir(td))) continue;
                                TileIndex next = TileAddByDiagDir(tile, TrackdirToExitdir(td));
                                TrackBits tracks = TrackdirBitsToTrackBits(TrackdirReachesTrackdirs(td));
                                if (HasReservedTracks(next, tracks)) {
                                        v = GetTrainForReservation(next, TrackBitsToTrack(GetReservedTrackbits(next) & tracks));
                                }
                        }
                }

                /* Remove any links this signal had */
                RemoveSignalLink(tile, track);
                /* Logic signal: remove signal program */
                if (IsLogicSignal(tile, track)) {
                        DeleteSignalProgram(tile, track);
                }

                Company::Get(GetTileOwner(tile))->infrastructure.signal -= CountBits(GetPresentSignals(tile));
                SetPresentSignals(tile, GetPresentSignals(tile) & ~SignalOnTrack(track));
                Company::Get(GetTileOwner(tile))->infrastructure.signal += CountBits(GetPresentSignals(tile));
                DirtyCompanyInfrastructureWindows(GetTileOwner(tile));
                TraceRestrictNotifySignalRemoval(tile, track);

                /* removed last signal from tile? */
                if (GetPresentSignals(tile) == 0) {
                        SetSignalStates(tile, 0);
                        SetHasSignals(tile, false);
                        SetSignalVariant(tile, INVALID_TRACK, SIG_ELECTRIC); // remove any possible semaphores
                }

                AddTrackToSignalBuffer(tile, track, GetTileOwner(tile));
                YapfNotifyTrackLayoutChange(tile, track);
                if (v != NULL) TryPathReserve(v, false);

                MarkTileDirtyByTile(tile, ZOOM_LVL_DRAW_MAP);
        }

        return CommandCost(EXPENSES_CONSTRUCTION, cost);
}

/**
 * Remove signals on a stretch of track.
 * Stub for the unified signal builder/remover
 * @param tile start tile of drag
 * @param flags operation to perform
 * @param p1  end tile of drag
 * @param p2 various bitstuffed elements
 * - p2 = (bit  0- 2) - track-orientation, valid values: 0-5 (Track enum)
 * - p2 = (bit  3)    - 1 = override signal/semaphore, or pre/exit/combo signal (CTRL-toggle)
 * - p2 = (bit  4)    - 0 = signals, 1 = semaphores
 * - p2 = (bit  5)    - 0 = build, 1 = remove signals
 * - p2 = (bit  6)    - 0 = selected stretch, 1 = auto fill
 * - p2 = (bit  7- 9) - default signal type
 * - p2 = (bit 24-31) - user defined signals_density
 * @param text unused
 * @return the cost of this operation or an error
 * @see CmdSignalTrackHelper
 */
CommandCost CmdRemoveSignalTrack(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32 p2, const char *text)
{
        return CmdSignalTrackHelper(tile, flags, p1, SetBit(p2, 5), text); // bit 5 is remove bit
}

/** Update power of train under which is the railtype being converted */
static Vehicle *UpdateTrainPowerProc(Vehicle *v, void *data)
{
        if (v->type != VEH_TRAIN) return NULL;

        TrainList *affected_trains = static_cast<TrainList*>(data);
        affected_trains->Include(Train::From(v)->First());

        return NULL;
}

/**
 * Convert one rail type to the other. You can convert normal rail to
 * monorail/maglev easily or vice-versa.
 * @param tile end tile of rail conversion drag
 * @param flags operation to perform
 * @param p1 start tile of drag
 * @param p2 various bitstuffed elements:
 * - p2 = (bit  0 - 4) new railtype to convert to.
 * - p2 = (bit  5)     build diagonally or not.
 * @param text unused
 * @return the cost of this operation or an error
 */
CommandCost CmdConvertRail(TileIndex tile, DoCommandFlag flags, uint32 p1, uint32 p2, const char *text)
{
        RailType totype = Extract<RailType, 0, 5>(p2);
        TileIndex area_start = p1;
        TileIndex area_end = tile;
        bool diagonal = HasBit(p2, 5);

        if (!ValParamRailtype(totype)) return CMD_ERROR;
        if (area_start >= MapSize()) return CMD_ERROR;

        TrainList affected_trains;

        CommandCost cost(EXPENSES_CONSTRUCTION);
        CommandCost error = CommandCost(STR_ERROR_NO_SUITABLE_RAILROAD_TRACK); // by default, there is no track to convert.

        TileIterator *iter = diagonal ? (TileIterator *)new DiagonalTileIterator(area_start, area_end) : new OrthogonalTileIterator(area_start, area_end);
        for (; (tile = *iter) != INVALID_TILE; ++(*iter)) {
                TileType tt = GetTileType(tile);

                /* Check if there is any track on tile */
                switch (tt) {
                        case MP_RAILWAY:
                                break;
                        case MP_STATION:
                                if (!HasStationRail(tile)) continue;
                                break;
                        case MP_ROAD:
                                if (!IsLevelCrossing(tile)) continue;
                                if (RailNoLevelCrossings(totype)) {
                                        error.MakeError(STR_ERROR_CROSSING_DISALLOWED);
                                        continue;
                                }
                                break;
                        case MP_TUNNELBRIDGE:
                                if (GetTunnelBridgeTransportType(tile) != TRANSPORT_RAIL) continue;
                                break;
                        default: continue;
                }

                /* Original railtype we are converting from */
                RailType type = GetRailType(tile);

                /* Converting to the same type or converting 'hidden' elrail -> rail */
                if (type == totype || (_settings_game.vehicle.disable_elrails && totype == RAILTYPE_RAIL && type == RAILTYPE_ELECTRIC)) continue;

                /* Trying to convert other's rail */
                CommandCost ret = CheckTileOwnership(tile);
                if (ret.Failed()) {
                        error = ret;
                        continue;
                }

                SmallVector<Train *, 2> vehicles_affected;

                /* Vehicle on the tile when not converting Rail <-> ElRail
                 * Tunnels and bridges have special check later */
                if (tt != MP_TUNNELBRIDGE) {
                        if (!IsCompatibleRail(type, totype)) {
                                CommandCost ret = IsPlainRailTile(tile) ? EnsureNoTrainOnTrackBits(tile, GetTrackBits(tile)) : EnsureNoVehicleOnGround(tile);
                                if (ret.Failed()) {
                                        error = ret;
                                        continue;
                                }
                        }
                        if (flags & DC_EXEC) { // we can safely convert, too
                                TrackBits reserved = GetReservedTrackbits(tile);
                                Track     track;
                                while ((track = RemoveFirstTrack(&reserved)) != INVALID_TRACK) {
                                        Train *v = GetTrainForReservation(tile, track);
                                        if (v != NULL && !HasPowerOnRail(v->railtype, totype)) {
                                                /* No power on new rail type, reroute. */
                                                FreeTrainTrackReservation(v);
                                                *vehicles_affected.Append() = v;
                                        }
                                }

                                /* Update the company infrastructure counters. */
                                if (!IsRailStationTile(tile) || !IsStationTileBlocked(tile)) {
                                        Company *c = Company::Get(GetTileOwner(tile));
                                        uint num_pieces = IsLevelCrossingTile(tile) ? LEVELCROSSING_TRACKBIT_FACTOR : 1;
                                        if (IsPlainRailTile(tile)) {
                                                TrackBits bits = GetTrackBits(tile);
                                                num_pieces = CountBits(bits);
                                                if (TracksOverlap(bits)) num_pieces *= num_pieces;
                                        }
                                        c->infrastructure.rail[type] -= num_pieces;
                                        c->infrastructure.rail[totype] += num_pieces;
                                        DirtyCompanyInfrastructureWindows(c->index);
                                }

                                SetRailType(tile, totype);
                                MarkTileDirtyByTile(tile, ZOOM_LVL_DRAW_MAP);
                                /* update power of train on this tile */
                                FindVehicleOnPos(tile, &affected_trains, &UpdateTrainPowerProc);
                        }
                }

                switch (tt) {
                        case MP_RAILWAY:
                                switch (GetRailTileType(tile)) {
                                        case RAIL_TILE_DEPOT:
                                                if (flags & DC_EXEC) {
                                                        /* notify YAPF about the track layout change */
                                                        YapfNotifyTrackLayoutChange(tile, GetRailDepotTrack(tile));

                                                        /* Update build vehicle window related to this depot */
                                                        InvalidateWindowData(WC_VEHICLE_DEPOT, tile);
                                                        InvalidateWindowData(WC_BUILD_VEHICLE, tile);
                                                }
                                                cost.AddCost(RailConvertCost(type, totype));
                                                break;

                                        default: // RAIL_TILE_NORMAL, RAIL_TILE_SIGNALS
                                                if (flags & DC_EXEC) {
                                                        /* notify YAPF about the track layout change */
                                                        TrackBits tracks = GetTrackBits(tile);
                                                        while (tracks != TRACK_BIT_NONE) {
                                                                YapfNotifyTrackLayoutChange(tile, RemoveFirstTrack(&tracks));
                                                        }
                                                }
                                                cost.AddCost(RailConvertCost(type, totype) * CountBits(GetTrackBits(tile)));
                                                break;
                                }
                                break;

                        case MP_TUNNELBRIDGE: {
                                TileIndex endtile = GetOtherTunnelBridgeEnd(tile);

                                /* If both ends of tunnel/bridge are in the range, do not try to convert twice -
                                 * it would cause assert because of different test and exec runs */
                                if (endtile < tile) {
                                        if (diagonal) {
                                                if (DiagonalTileArea(area_start, area_end).Contains(endtile)) continue;
                                        } else {
                                                if (OrthogonalTileArea(area_start, area_end).Contains(endtile)) continue;
                                        }
                                }

                                /* When not converting rail <-> el. rail, any vehicle cannot be in tunnel/bridge */
                                if (!IsCompatibleRail(GetRailType(tile), totype)) {
                                        CommandCost ret = TunnelBridgeIsFree(tile, endtile);
                                        if (ret.Failed()) {
                                                error = ret;
                                                continue;
                                        }
                                }

                                if (flags & DC_EXEC) {
                                        Track track = DiagDirToDiagTrack(GetTunnelBridgeDirection(tile));
                                        if (HasTunnelBridgeReservation(tile)) {
                                                Train *v = GetTrainForReservation(tile, track);
                                                if (v != NULL && !HasPowerOnRail(v->railtype, totype)) {
                                                        /* No power on new rail type, reroute. */
                                                        FreeTrainTrackReservation(v);
                                                        *vehicles_affected.Append() = v;
                                                }
                                        }

                                        /* Update the company infrastructure counters. */
                                        uint num_pieces = (GetTunnelBridgeLength(tile, endtile) + 2) * TUNNELBRIDGE_TRACKBIT_FACTOR;
                                        Company *c = Company::Get(GetTileOwner(tile));
                                        c->infrastructure.rail[GetRailType(tile)] -= num_pieces;
                                        c->infrastructure.rail[totype] += num_pieces;
                                        DirtyCompanyInfrastructureWindows(c->index);

                                        SetRailType(tile, totype);
                                        SetRailType(endtile, totype);

                                        FindVehicleOnPos(tile, &affected_trains, &UpdateTrainPowerProc);
                                        FindVehicleOnPos(endtile, &affected_trains, &UpdateTrainPowerProc);

                                        YapfNotifyTrackLayoutChange(tile, track);
                                        YapfNotifyTrackLayoutChange(endtile, track);

                                        if (IsBridge(tile)) {
                                                MarkBridgeDirty(tile);
                                        } else {
                                                MarkTileDirtyByTile(tile, ZOOM_LVL_DRAW_MAP);
                                                MarkTileDirtyByTile(endtile, ZOOM_LVL_DRAW_MAP);
                                        }
                                }

                                cost.AddCost((GetTunnelBridgeLength(tile, endtile) + 2) * RailConvertCost(type, totype));
                                break;
                        }

                        default: // MP_STATION, MP_ROAD
                                if (flags & DC_EXEC) {
                                        Track track = ((tt == MP_STATION) ? GetRailStationTrack(tile) : GetCrossingRailTrack(tile));
                                        YapfNotifyTrackLayoutChange(tile, track);
                                }

                                cost.AddCost(RailConvertCost(type, totype));
                                break;
                }

                for (uint i = 0; i < vehicles_affected.Length(); ++i) {
                        TryPathReserve(vehicles_affected[i], true);
                }
        }

        if (flags & DC_EXEC) {
                /* Railtype changed, update trains as when entering different track */
                for (Train **v = affected_trains.Begin(); v != affected_trains.End(); v++) {
                        (*v)->ConsistChanged(CCF_TRACK);
                }
        }

        delete iter;
        return (cost.GetCost() == 0) ? error : cost;
}

static CommandCost RemoveTrainDepot(TileIndex tile, DoCommandFlag flags)
{
        if (_current_company != OWNER_WATER) {
                CommandCost ret = CheckTileOwnership(tile);
                if (ret.Failed()) return ret;
        }

        CommandCost ret = EnsureNoVehicleOnGround(tile);
        if (ret.Failed()) return ret;

        if (flags & DC_EXEC) {
                /* read variables before the depot is removed */
                DiagDirection dir = GetRailDepotDirection(tile);
                Owner owner = GetTileOwner(tile);
                Train *v = NULL;

                if (HasDepotReservation(tile)) {
                        v = GetTrainForReservation(tile, DiagDirToDiagTrack(dir));
                        if (v != NULL) FreeTrainTrackReservation(v);
                }

                Company::Get(owner)->infrastructure.rail[GetRailType(tile)]--;
                DirtyCompanyInfrastructureWindows(owner);

                delete Depot::GetByTile(tile);
                DoClearSquare(tile);
                AddSideToSignalBuffer(tile, dir, owner);
                YapfNotifyTrackLayoutChange(tile, DiagDirToDiagTrack(dir));
                if (v != NULL) TryPathReserve(v, true);
        }

        return CommandCost(EXPENSES_CONSTRUCTION, _price[PR_CLEAR_DEPOT_TRAIN]);
}

static CommandCost ClearTile_Track(TileIndex tile, DoCommandFlag flags)
{
        CommandCost cost(EXPENSES_CONSTRUCTION);

        if (flags & DC_AUTO) {
                if (!IsTileOwner(tile, _current_company)) {
                        return_cmd_error(STR_ERROR_AREA_IS_OWNED_BY_ANOTHER);
                }

                if (IsPlainRail(tile)) {
                        return_cmd_error(STR_ERROR_MUST_REMOVE_RAILROAD_TRACK);
                } else {
                        return_cmd_error(STR_ERROR_BUILDING_MUST_BE_DEMOLISHED);
                }
        }

        switch (GetRailTileType(tile)) {
                case RAIL_TILE_SIGNALS:
                case RAIL_TILE_NORMAL: {
                        Slope tileh = GetTileSlope(tile);
                        /* Is there flat water on the lower halftile that gets cleared expensively? */
                        bool water_ground = (GetRailGroundType(tile) == RAIL_GROUND_WATER && IsSlopeWithOneCornerRaised(tileh));

                        TrackBits tracks = GetTrackBits(tile);
                        while (tracks != TRACK_BIT_NONE) {
                                Track track = RemoveFirstTrack(&tracks);
                                CommandCost ret = DoCommand(tile, 0, track, flags, CMD_REMOVE_SINGLE_RAIL);
                                if (ret.Failed()) return ret;
                                cost.AddCost(ret);
                        }

                        /* When bankrupting, don't make water dirty, there could be a ship on lower halftile.
                         * Same holds for non-companies clearing the tile, e.g. disasters. */
                        if (water_ground && !(flags & DC_BANKRUPT) && Company::IsValidID(_current_company)) {
                                CommandCost ret = EnsureNoVehicleOnGround(tile);
                                if (ret.Failed()) return ret;

                                /* The track was removed, and left a coast tile. Now also clear the water. */
                                if (flags & DC_EXEC) DoClearSquare(tile);
                                cost.AddCost(_price[PR_CLEAR_WATER]);
                        }

                        return cost;
                }

                case RAIL_TILE_DEPOT:
                        return RemoveTrainDepot(tile, flags);

                default:
                        return CMD_ERROR;
        }
}

/**
 * Get surface height in point (x,y)
 * On tiles with halftile foundations move (x,y) to a safe point wrt. track
 */
static uint GetSaveSlopeZ(uint x, uint y, Track track)
{
        switch (track) {
                case TRACK_UPPER: x &= ~0xF; y &= ~0xF; break;
                case TRACK_LOWER: x |=  0xF; y |=  0xF; break;
                case TRACK_LEFT:  x |=  0xF; y &= ~0xF; break;
                case TRACK_RIGHT: x &= ~0xF; y |=  0xF; break;
                default: break;
        }
        return GetSlopePixelZ(x, y);
}

static void DrawSingleSignal(TileIndex tile, const RailtypeInfo *rti, Track track, SignalState condition, SignalOffsets image, uint pos)
{
        bool side;
        switch (_settings_game.construction.train_signal_side) {
                case 0:  side = false;                                 break; // left
                case 2:  side = true;                                  break; // right
                default: side = _settings_game.vehicle.road_side != 0; break; // driving side
        }
        static const Point SignalPositions[2][12] = {
                { // Signals on the left side
                /*  LEFT      LEFT      RIGHT     RIGHT     UPPER     UPPER */
                        { 8,  5}, {14,  1}, { 1, 14}, { 9, 11}, { 1,  0}, { 3, 10},
                /*  LOWER     LOWER     X         X         Y         Y     */
                        {11,  4}, {14, 14}, {11,  3}, { 4, 13}, { 3,  4}, {11, 13}
                }, { // Signals on the right side
                /*  LEFT      LEFT      RIGHT     RIGHT     UPPER     UPPER */
                        {14,  1}, {12, 10}, { 4,  6}, { 1, 14}, {10,  4}, { 0,  1},
                /*  LOWER     LOWER     X         X         Y         Y     */
                        {14, 14}, { 5, 12}, {11, 13}, { 4,  3}, {13,  4}, { 3, 11}
                }
        };

        uint x = TileX(tile) * TILE_SIZE + SignalPositions[side][pos].x;
        uint y = TileY(tile) * TILE_SIZE + SignalPositions[side][pos].y;

        SignalType type       = GetSignalType(tile, track);
        SignalVariant variant = GetSignalVariant(tile, track);

        SpriteID sprite = GetCustomSignalSprite(rti, tile, type, variant, condition);
        bool is_custom_sprite = (sprite != 0);
        if (sprite != 0) {
                sprite += image;
        } else {
                /* Normal electric signals are stored in a different sprite block than all other signals. */
                sprite = (type == SIGTYPE_NORMAL && variant == SIG_ELECTRIC) ? SPR_ORIGINAL_SIGNALS_BASE : SPR_SIGNALS_BASE - 16;
                sprite += type * 16 + variant * 64 + image * 2 + condition + (type > SIGTYPE_LAST_NOPBS ? 64 : 0);
        }

        AddSortableSpriteToDraw(sprite, PAL_NONE, x, y, 1, 1, BB_HEIGHT_UNDER_BRIDGE, GetSaveSlopeZ(x, y, track));
}

static uint32 _drawtile_track_palette;



/** Offsets for drawing fences */
struct FenceOffset {
        Corner height_ref;  //!< Corner to use height offset from.
        int x_offs;         //!< Bounding box X offset.
        int y_offs;         //!< Bounding box Y offset.
        int x_size;         //!< Bounding box X size.
        int y_size;         //!< Bounding box Y size.
};

/** Offsets for drawing fences */
static FenceOffset _fence_offsets[] = {
        { CORNER_INVALID,  0,  1, 16,  1 }, // RFO_FLAT_X_NW
        { CORNER_INVALID,  1,  0,  1, 16 }, // RFO_FLAT_Y_NE
        { CORNER_W,        8,  8,  1,  1 }, // RFO_FLAT_LEFT
        { CORNER_N,        8,  8,  1,  1 }, // RFO_FLAT_UPPER
        { CORNER_INVALID,  0,  1, 16,  1 }, // RFO_SLOPE_SW_NW
        { CORNER_INVALID,  1,  0,  1, 16 }, // RFO_SLOPE_SE_NE
        { CORNER_INVALID,  0,  1, 16,  1 }, // RFO_SLOPE_NE_NW
        { CORNER_INVALID,  1,  0,  1, 16 }, // RFO_SLOPE_NW_NE
        { CORNER_INVALID,  0, 15, 16,  1 }, // RFO_FLAT_X_SE
        { CORNER_INVALID, 15,  0,  1, 16 }, // RFO_FLAT_Y_SW
        { CORNER_E,        8,  8,  1,  1 }, // RFO_FLAT_RIGHT
        { CORNER_S,        8,  8,  1,  1 }, // RFO_FLAT_LOWER
        { CORNER_INVALID,  0, 15, 16,  1 }, // RFO_SLOPE_SW_SE
        { CORNER_INVALID, 15,  0,  1, 16 }, // RFO_SLOPE_SE_SW
        { CORNER_INVALID,  0, 15, 16,  1 }, // RFO_SLOPE_NE_SE
        { CORNER_INVALID, 15,  0,  1, 16 }, // RFO_SLOPE_NW_SW
};

/**
 * Draw a track fence.
 * @param ti Tile drawing information.
 * @param base_image First fence sprite.
 * @param num_sprites Number of fence sprites.
 * @param rfo Fence to draw.
 */
static void DrawTrackFence(const TileInfo *ti, SpriteID base_image, uint num_sprites, RailFenceOffset rfo)
{
        int z = ti->z;
        if (_fence_offsets[rfo].height_ref != CORNER_INVALID) {
                z += GetSlopePixelZInCorner(RemoveHalftileSlope(ti->tileh), _fence_offsets[rfo].height_ref);
        }
        AddSortableSpriteToDraw(base_image + (rfo % num_sprites), _drawtile_track_palette,
                ti->x + _fence_offsets[rfo].x_offs,
                ti->y + _fence_offsets[rfo].y_offs,
                _fence_offsets[rfo].x_size,
                _fence_offsets[rfo].y_size,
                4, z);
}

/**
 * Draw fence at NW border matching the tile slope.
 */
static void DrawTrackFence_NW(const TileInfo *ti, SpriteID base_image, uint num_sprites)
{
        RailFenceOffset rfo = RFO_FLAT_X_NW;
        if (ti->tileh & SLOPE_NW) rfo = (ti->tileh & SLOPE_W) ? RFO_SLOPE_SW_NW : RFO_SLOPE_NE_NW;
        DrawTrackFence(ti, base_image, num_sprites, rfo);
}

/**
 * Draw fence at SE border matching the tile slope.
 */
static void DrawTrackFence_SE(const TileInfo *ti, SpriteID base_image, uint num_sprites)
{
        RailFenceOffset rfo = RFO_FLAT_X_SE;
        if (ti->tileh & SLOPE_SE) rfo = (ti->tileh & SLOPE_S) ? RFO_SLOPE_SW_SE : RFO_SLOPE_NE_SE;
        DrawTrackFence(ti, base_image, num_sprites, rfo);
}

/**
 * Draw fence at NE border matching the tile slope.
 */
static void DrawTrackFence_NE(const TileInfo *ti, SpriteID base_image, uint num_sprites)
{
        RailFenceOffset rfo = RFO_FLAT_Y_NE;
        if (ti->tileh & SLOPE_NE) rfo = (ti->tileh & SLOPE_E) ? RFO_SLOPE_SE_NE : RFO_SLOPE_NW_NE;
        DrawTrackFence(ti, base_image, num_sprites, rfo);
}


static byte GetTrackGrowthPhase(TileIndex ti, TrackBits trackbits)
{
        if (!IsTileType(ti, MP_RAILWAY))
                return 0;

        if (!IsPlainRailTile(ti))
                return 0;

        if ((GetTrackBits(ti) & trackbits) == 0)
                return 0;

        return GetTrackGrowthPhase(ti);
}

/**
* GetTrackGrowthPhaseEx returns a calculated growth factor
* for a specific track on a tile - by also looking at its
* neighbours
*/
byte GetTrackGrowthPhaseEx(TileIndex ti, Track track)
{
        byte phase = GetTrackGrowthPhase(ti);
        if (phase == 3) return 3;

        /* If this track piece is connected to a neighbour tile///
        * and that neighbour is used less often - we can't
        * be the track piece that is used so often on this tile
        */
        Trackdir td1 = TrackToTrackdir(track);
        DiagDirection dd1 = TrackdirToExitdir(td1);
        TrackBits tb1 = DiagdirReachesTracks(dd1);
        TileIndex ti1 = ti + TileOffsByDiagDir(dd1);
        byte phase1 = GetTrackGrowthPhase(ti1, tb1);
        if (phase1 == 3) return 3;

        /* Same check for the other neighbour */
        Trackdir td2 = ReverseTrackdir(td1);
        DiagDirection dd2 = TrackdirToExitdir(td2);
        TrackBits tb2 = DiagdirReachesTracks(dd2);
        TileIndex ti2 = ti + TileOffsByDiagDir(dd2);
        byte phase2 = GetTrackGrowthPhase(ti2, tb2);
        if (phase2 == 3) return 3;

        /* Return the highest growth factor */
        return max(phase, max(phase1, phase2));
}

static bool GetTrackGrowthSpriteBase(TileIndex tile, Track track, SpriteID& base)
{
        byte phase = GetTrackGrowthPhaseEx(tile, track);
        if (phase == 0)
                return false;

        assert(phase <= 3);

        base = SPR_OLDTRACKS_BASE + 10 * (phase - 1);
        return true;
}

static bool GetTrackGrowthPalette(TileIndex tile, SpriteID& pal)
{
        pal = PAL_NONE;

        /**
        * In arctic, use the 'BARE' palette always, looks better on that terrain
        * obsolete when it will get its own overlays (for snow, also)
        */
        switch (_settings_game.game_creation.landscape) {
        case LT_ARCTIC: pal = PALETTE_TO_BARE_LAND; break;
        default: break;
        }

        /**
        * Use 'BARE' palette for desert in tropical and snow in arctic since it
        * looks better than green. But use other overlays in future!!
        */
        switch (GetRailGroundType(tile)) {
        case RAIL_GROUND_ICE_DESERT: /* fallthrough */
        case RAIL_GROUND_BARREN:     pal = PALETTE_TO_BARE_LAND; break;
        default: break;
        }

        /* Both base and pal set; we can return true */
        return true;
}

void DrawTrackGrowth(TileInfo* ti, TrackBits track)
{
        SpriteID pal, base;
        TileIndex tile = ti->tile;
        RailTypeLabel railTypeLabel = GetRailTypeInfo(GetTileRailType(ti->tile))->label;

        if (railTypeLabel == _planning_tracks_label ||
                railTypeLabel == _pipeline_tracks_label ||
                railTypeLabel == _wires_tracks_label) {
                // Never age these specialized tracks.
                return;
        }

        if (!GetTrackGrowthPalette(tile, pal)) return;

        /* future support for tunnels */
        Slope tileh = ti->tileh;
        if (IsTunnelTile(ti->tile)) tileh = SLOPE_FLAT;

        switch (tileh) {
        case SLOPE_NW:
                assert(track == TRACK_BIT_Y);
                if (GetTrackGrowthSpriteBase(tile, TRACK_Y, base))
                        DrawGroundSprite(base + 9, pal);
                break;
        case SLOPE_SW:
                assert(track == TRACK_BIT_X);
                if (GetTrackGrowthSpriteBase(tile, TRACK_X, base))
                        DrawGroundSprite(base + 8, pal);
                break;
        case SLOPE_SE:
                assert(track == TRACK_BIT_Y);
                if (GetTrackGrowthSpriteBase(tile, TRACK_Y, base))
                        DrawGroundSprite(base + 7, pal);
                break;
        case SLOPE_NE:
                assert(track == TRACK_BIT_X);
                if (GetTrackGrowthSpriteBase(tile, TRACK_X, base))
                        DrawGroundSprite(base + 6, pal);
                break;
        default:
                /* any track bits on any other slope are drawn normally */
                if ((track & TRACK_BIT_Y) != 0 && GetTrackGrowthSpriteBase(tile, TRACK_Y, base))         DrawGroundSprite(base + 0, pal);
                if ((track & TRACK_BIT_X) != 0 && GetTrackGrowthSpriteBase(tile, TRACK_X, base))         DrawGroundSprite(base + 1, pal);
                if ((track & TRACK_BIT_UPPER) != 0 && GetTrackGrowthSpriteBase(tile, TRACK_UPPER, base)) DrawGroundSprite(base + 2, pal);
                if ((track & TRACK_BIT_LOWER) != 0 && GetTrackGrowthSpriteBase(tile, TRACK_LOWER, base)) DrawGroundSprite(base + 3, pal);
                if ((track & TRACK_BIT_RIGHT) != 0 && GetTrackGrowthSpriteBase(tile, TRACK_RIGHT, base)) DrawGroundSprite(base + 4, pal);
                if ((track & TRACK_BIT_LEFT) != 0 && GetTrackGrowthSpriteBase(tile, TRACK_LEFT, base))   DrawGroundSprite(base + 5, pal);
                break;
        }
}

/**
 * Draw fence at SW border matching the tile slope.
 */
static void DrawTrackFence_SW(const TileInfo *ti, SpriteID base_image, uint num_sprites)
{
        RailFenceOffset rfo = RFO_FLAT_Y_SW;
        if (ti->tileh & SLOPE_SW) rfo = (ti->tileh & SLOPE_S) ? RFO_SLOPE_SE_SW : RFO_SLOPE_NW_SW;
        DrawTrackFence(ti, base_image, num_sprites, rfo);
}

/**
 * Draw track fences.
 * @param ti Tile drawing information.
 * @param rti Rail type information.
 */
static void DrawTrackDetails(const TileInfo *ti, const RailtypeInfo *rti)
{
        /* Base sprite for track fences.
         * Note: Halftile slopes only have fences on the upper part. */
        uint num_sprites = 0;
        SpriteID base_image = GetCustomRailSprite(rti, ti->tile, RTSG_FENCES, IsHalftileSlope(ti->tileh) ? TCX_UPPER_HALFTILE : TCX_NORMAL, &num_sprites);
        if (base_image == 0) {
                base_image = SPR_TRACK_FENCE_FLAT_X;
                num_sprites = 8;
        }

        assert(num_sprites > 0);

        switch (GetRailGroundType(ti->tile)) {
                case RAIL_GROUND_FENCE_NW:     DrawTrackFence_NW(ti, base_image, num_sprites); break;
                case RAIL_GROUND_FENCE_SE:     DrawTrackFence_SE(ti, base_image, num_sprites); break;
                case RAIL_GROUND_FENCE_SENW:   DrawTrackFence_NW(ti, base_image, num_sprites);
                                               DrawTrackFence_SE(ti, base_image, num_sprites); break;
                case RAIL_GROUND_FENCE_NE:     DrawTrackFence_NE(ti, base_image, num_sprites); break;
                case RAIL_GROUND_FENCE_SW:     DrawTrackFence_SW(ti, base_image, num_sprites); break;
                case RAIL_GROUND_FENCE_NESW:   DrawTrackFence_NE(ti, base_image, num_sprites);
                                               DrawTrackFence_SW(ti, base_image, num_sprites); break;
                case RAIL_GROUND_FENCE_VERT1:  DrawTrackFence(ti, base_image, num_sprites, RFO_FLAT_LEFT);  break;
                case RAIL_GROUND_FENCE_VERT2:  DrawTrackFence(ti, base_image, num_sprites, RFO_FLAT_RIGHT); break;
                case RAIL_GROUND_FENCE_HORIZ1: DrawTrackFence(ti, base_image, num_sprites, RFO_FLAT_UPPER); break;
                case RAIL_GROUND_FENCE_HORIZ2: DrawTrackFence(ti, base_image, num_sprites, RFO_FLAT_LOWER); break;
                case RAIL_GROUND_WATER: {
                        Corner track_corner;
                        if (IsHalftileSlope(ti->tileh)) {
                                /* Steep slope or one-corner-raised slope with halftile foundation */
                                track_corner = GetHalftileSlopeCorner(ti->tileh);
                        } else {
                                /* Three-corner-raised slope */
                                track_corner = OppositeCorner(GetHighestSlopeCorner(ComplementSlope(ti->tileh)));
                        }
                        switch (track_corner) {
                                case CORNER_W: DrawTrackFence(ti, base_image, num_sprites, RFO_FLAT_LEFT);  break;
                                case CORNER_S: DrawTrackFence(ti, base_image, num_sprites, RFO_FLAT_LOWER); break;
                                case CORNER_E: DrawTrackFence(ti, base_image, num_sprites, RFO_FLAT_RIGHT); break;
                                case CORNER_N: DrawTrackFence(ti, base_image, num_sprites, RFO_FLAT_UPPER); break;
                                default: NOT_REACHED();
                        }
                        break;
                }
                default: break;
        }
}

/* SubSprite for drawing the track halftile of 'three-corners-raised'-sloped rail sprites. */
static const int INF = 1000; // big number compared to tilesprite size
static const SubSprite _halftile_sub_sprite[4] = {
        { -INF    , -INF  , 32 - 33, INF     }, // CORNER_W, clip 33 pixels from right
        { -INF    ,  0 + 7, INF    , INF     }, // CORNER_S, clip 7 pixels from top
        { -31 + 33, -INF  , INF    , INF     }, // CORNER_E, clip 33 pixels from left
        { -INF    , -INF  , INF    , 30 - 23 }  // CORNER_N, clip 23 pixels from bottom
};

static inline void DrawTrackSprite(SpriteID sprite, PaletteID pal, const TileInfo *ti, Slope s)
{
        DrawGroundSprite(sprite, pal, NULL, 0, (ti->tileh & s) ? -8 : 0);
}

static void DrawTrackBitsOverlay(TileInfo *ti, TrackBits track, const RailtypeInfo *rti)
{
        RailGroundType rgt = GetRailGroundType(ti->tile);
        Foundation f = GetRailFoundation(ti->tileh, track);
        Corner halftile_corner = CORNER_INVALID;

        if (IsNonContinuousFoundation(f)) {
                /* Save halftile corner */
                halftile_corner = (f == FOUNDATION_STEEP_BOTH ? GetHighestSlopeCorner(ti->tileh) : GetHalftileFoundationCorner(f));
                /* Draw lower part first */
                track &= ~CornerToTrackBits(halftile_corner);
                f = (f == FOUNDATION_STEEP_BOTH ? FOUNDATION_STEEP_LOWER : FOUNDATION_NONE);
        }

        DrawFoundation(ti, f);
        /* DrawFoundation modifies ti */

        /* Draw ground */
        if (rgt == RAIL_GROUND_WATER) {
                if (track != TRACK_BIT_NONE || IsSteepSlope(ti->tileh)) {
                        /* three-corner-raised slope or steep slope with track on upper part */
                        DrawShoreTile(ti->tileh);
                } else {
                        /* single-corner-raised slope with track on upper part */
                        DrawGroundSprite(SPR_FLAT_WATER_TILE, PAL_NONE);
                }
        } else {
                SpriteID image;

                switch (rgt) {
                        case RAIL_GROUND_BARREN:     image = SPR_FLAT_BARE_LAND;  break;
                        case RAIL_GROUND_ICE_DESERT: image = SPR_FLAT_SNOW_DESERT_TILE; break;
                        default:                     image = SPR_FLAT_GRASS_TILE; break;
                }

                image += SlopeToSpriteOffset(ti->tileh);

                DrawGroundSprite(image, PAL_NONE);
        }

        SpriteID overlay = GetCustomRailSprite(rti, ti->tile, RTSG_OVERLAY);
        SpriteID ground = GetCustomRailSprite(rti, ti->tile, RTSG_GROUND);
        TrackBits pbs = _settings_client.gui.show_track_reservation ? GetRailReservationTrackBits(ti->tile) : TRACK_BIT_NONE;

        if (track == TRACK_BIT_NONE) {
                /* Half-tile foundation, no track here? */
        } else if (ti->tileh == SLOPE_NW && track == TRACK_BIT_Y) {
                DrawGroundSprite(ground + RTO_SLOPE_NW, PAL_NONE);
                if (pbs != TRACK_BIT_NONE) DrawGroundSprite(overlay + RTO_SLOPE_NW, PALETTE_CRASH);
        } else if (ti->tileh == SLOPE_NE && track == TRACK_BIT_X) {
                DrawGroundSprite(ground + RTO_SLOPE_NE, PAL_NONE);
                if (pbs != TRACK_BIT_NONE) DrawGroundSprite(overlay + RTO_SLOPE_NE, PALETTE_CRASH);
        } else if (ti->tileh == SLOPE_SE && track == TRACK_BIT_Y) {
                DrawGroundSprite(ground + RTO_SLOPE_SE, PAL_NONE);
                if (pbs != TRACK_BIT_NONE) DrawGroundSprite(overlay + RTO_SLOPE_SE, PALETTE_CRASH);
        } else if (ti->tileh == SLOPE_SW && track == TRACK_BIT_X) {
                DrawGroundSprite(ground + RTO_SLOPE_SW, PAL_NONE);
                if (pbs != TRACK_BIT_NONE) DrawGroundSprite(overlay + RTO_SLOPE_SW, PALETTE_CRASH);
        } else {
                switch (track) {
                        /* Draw single ground sprite when not overlapping. No track overlay
                         * is necessary for these sprites. */
                        case TRACK_BIT_X:     DrawGroundSprite(ground + RTO_X, PAL_NONE); break;
                        case TRACK_BIT_Y:     DrawGroundSprite(ground + RTO_Y, PAL_NONE); break;
                        case TRACK_BIT_UPPER: DrawTrackSprite(ground + RTO_N, PAL_NONE, ti, SLOPE_N); break;
                        case TRACK_BIT_LOWER: DrawTrackSprite(ground + RTO_S, PAL_NONE, ti, SLOPE_S); break;
                        case TRACK_BIT_RIGHT: DrawTrackSprite(ground + RTO_E, PAL_NONE, ti, SLOPE_E); break;
                        case TRACK_BIT_LEFT:  DrawTrackSprite(ground + RTO_W, PAL_NONE, ti, SLOPE_W); break;
                        case TRACK_BIT_CROSS: DrawGroundSprite(ground + RTO_CROSSING_XY, PAL_NONE); break;
                        case TRACK_BIT_HORZ:  DrawTrackSprite(ground + RTO_N, PAL_NONE, ti, SLOPE_N);
                                              DrawTrackSprite(ground + RTO_S, PAL_NONE, ti, SLOPE_S); break;
                        case TRACK_BIT_VERT:  DrawTrackSprite(ground + RTO_E, PAL_NONE, ti, SLOPE_E);
                                              DrawTrackSprite(ground + RTO_W, PAL_NONE, ti, SLOPE_W); break;

                        default:
                                /* We're drawing a junction tile */
                                if ((track & TRACK_BIT_3WAY_NE) == 0) {
                                        DrawGroundSprite(ground + RTO_JUNCTION_SW, PAL_NONE);
                                } else if ((track & TRACK_BIT_3WAY_SW) == 0) {
                                        DrawGroundSprite(ground + RTO_JUNCTION_NE, PAL_NONE);
                                } else if ((track & TRACK_BIT_3WAY_NW) == 0) {
                                        DrawGroundSprite(ground + RTO_JUNCTION_SE, PAL_NONE);
                                } else if ((track & TRACK_BIT_3WAY_SE) == 0) {
                                        DrawGroundSprite(ground + RTO_JUNCTION_NW, PAL_NONE);
                                } else {
                                        DrawGroundSprite(ground + RTO_JUNCTION_NSEW, PAL_NONE);
                                }

                                /* Mask out PBS bits as we shall draw them afterwards anyway. */
                                track &= ~pbs;

                                /* Draw regular track bits */
                                if (track & TRACK_BIT_X)     DrawGroundSprite(overlay + RTO_X, PAL_NONE);
                                if (track & TRACK_BIT_Y)     DrawGroundSprite(overlay + RTO_Y, PAL_NONE);
                                if (track & TRACK_BIT_UPPER) DrawGroundSprite(overlay + RTO_N, PAL_NONE);
                                if (track & TRACK_BIT_LOWER) DrawGroundSprite(overlay + RTO_S, PAL_NONE);
                                if (track & TRACK_BIT_RIGHT) DrawGroundSprite(overlay + RTO_E, PAL_NONE);
                                if (track & TRACK_BIT_LEFT)  DrawGroundSprite(overlay + RTO_W, PAL_NONE);
                }

                /* Draw reserved track bits */
                if (pbs & TRACK_BIT_X)     DrawGroundSprite(overlay + RTO_X, PALETTE_CRASH);
                if (pbs & TRACK_BIT_Y)     DrawGroundSprite(overlay + RTO_Y, PALETTE_CRASH);
                if (pbs & TRACK_BIT_UPPER) DrawTrackSprite(overlay + RTO_N, PALETTE_CRASH, ti, SLOPE_N);
                if (pbs & TRACK_BIT_LOWER) DrawTrackSprite(overlay + RTO_S, PALETTE_CRASH, ti, SLOPE_S);
                if (pbs & TRACK_BIT_RIGHT) DrawTrackSprite(overlay + RTO_E, PALETTE_CRASH, ti, SLOPE_E);
                if (pbs & TRACK_BIT_LEFT)  DrawTrackSprite(overlay + RTO_W, PALETTE_CRASH, ti, SLOPE_W);
        }

        if (IsValidCorner(halftile_corner)) {
                DrawFoundation(ti, HalftileFoundation(halftile_corner));
                overlay = GetCustomRailSprite(rti, ti->tile, RTSG_OVERLAY, TCX_UPPER_HALFTILE);
                ground = GetCustomRailSprite(rti, ti->tile, RTSG_GROUND, TCX_UPPER_HALFTILE);

                /* Draw higher halftile-overlay: Use the sloped sprites with three corners raised. They probably best fit the lightning. */
                Slope fake_slope = SlopeWithThreeCornersRaised(OppositeCorner(halftile_corner));

                SpriteID image;
                switch (rgt) {
                        case RAIL_GROUND_BARREN:     image = SPR_FLAT_BARE_LAND;  break;
                        case RAIL_GROUND_ICE_DESERT:
                        case RAIL_GROUND_HALF_SNOW:  image = SPR_FLAT_SNOW_DESERT_TILE; break;
                        default:                     image = SPR_FLAT_GRASS_TILE; break;
                }

                image += SlopeToSpriteOffset(fake_slope);

                DrawGroundSprite(image, PAL_NONE, &(_halftile_sub_sprite[halftile_corner]));

                track = CornerToTrackBits(halftile_corner);

                int offset;
                switch (track) {
                        default: NOT_REACHED();
                        case TRACK_BIT_UPPER: offset = RTO_N; break;
                        case TRACK_BIT_LOWER: offset = RTO_S; break;
                        case TRACK_BIT_RIGHT: offset = RTO_E; break;
                        case TRACK_BIT_LEFT:  offset = RTO_W; break;
                }

                DrawTrackSprite(ground + offset, PAL_NONE, ti, fake_slope);
                if (_settings_client.gui.show_track_reservation && HasReservedTracks(ti->tile, track)) {
                        DrawTrackSprite(overlay + offset, PALETTE_CRASH, ti, fake_slope);
                }
        }
}

/**
 * Draw ground sprite and track bits
 * @param ti TileInfo
 * @param track TrackBits to draw
 */
static void DrawTrackBits(TileInfo *ti, TrackBits track)
{
        const RailtypeInfo *rti = GetRailTypeInfo(GetRailType(ti->tile));

        if (rti->UsesOverlay()) {
                DrawTrackBitsOverlay(ti, track, rti);
                if (_settings_client.gui.show_track_overgrowth) DrawTrackGrowth(ti, track);
                return;
        }

        RailGroundType rgt = GetRailGroundType(ti->tile);
        Foundation f = GetRailFoundation(ti->tileh, track);
        Corner halftile_corner = CORNER_INVALID;

        if (IsNonContinuousFoundation(f)) {
                /* Save halftile corner */
                halftile_corner = (f == FOUNDATION_STEEP_BOTH ? GetHighestSlopeCorner(ti->tileh) : GetHalftileFoundationCorner(f));
                /* Draw lower part first */
                track &= ~CornerToTrackBits(halftile_corner);
                f = (f == FOUNDATION_STEEP_BOTH ? FOUNDATION_STEEP_LOWER : FOUNDATION_NONE);
        }

        DrawFoundation(ti, f);
        /* DrawFoundation modifies ti */

        SpriteID image;
        PaletteID pal = PAL_NONE;
        const SubSprite *sub = NULL;
        bool junction = false;

        /* Select the sprite to use. */
        if (track == 0) {
                /* Clear ground (only track on halftile foundation) */
                if (rgt == RAIL_GROUND_WATER) {
                        if (IsSteepSlope(ti->tileh)) {
                                DrawShoreTile(ti->tileh);
                                image = 0;
                        } else {
                                image = SPR_FLAT_WATER_TILE;
                        }
                } else {
                        switch (rgt) {
                                case RAIL_GROUND_BARREN:     image = SPR_FLAT_BARE_LAND;  break;
                                case RAIL_GROUND_ICE_DESERT: image = SPR_FLAT_SNOW_DESERT_TILE; break;
                                default:                     image = SPR_FLAT_GRASS_TILE; break;
                        }
                        image += SlopeToSpriteOffset(ti->tileh);
                }
        } else {
                if (ti->tileh != SLOPE_FLAT) {
                        /* track on non-flat ground */
                        image = _track_sloped_sprites[ti->tileh - 1] + rti->base_sprites.track_y;
                } else {
                        /* track on flat ground */
                        (image = rti->base_sprites.track_y, track == TRACK_BIT_Y) ||
                        (image++,                           track == TRACK_BIT_X) ||
                        (image++,                           track == TRACK_BIT_UPPER) ||
                        (image++,                           track == TRACK_BIT_LOWER) ||
                        (image++,                           track == TRACK_BIT_RIGHT) ||
                        (image++,                           track == TRACK_BIT_LEFT) ||
                        (image++,                           track == TRACK_BIT_CROSS) ||

                        (image = rti->base_sprites.track_ns, track == TRACK_BIT_HORZ) ||
                        (image++,                            track == TRACK_BIT_VERT) ||

                        (junction = true, false) ||
                        (image = rti->base_sprites.ground, (track & TRACK_BIT_3WAY_NE) == 0) ||
                        (image++,                          (track & TRACK_BIT_3WAY_SW) == 0) ||
                        (image++,                          (track & TRACK_BIT_3WAY_NW) == 0) ||
                        (image++,                          (track & TRACK_BIT_3WAY_SE) == 0) ||
                        (image++, true);
                }

                switch (rgt) {
                        case RAIL_GROUND_BARREN:     pal = PALETTE_TO_BARE_LAND; break;
                        case RAIL_GROUND_ICE_DESERT: image += rti->snow_offset;  break;
                        case RAIL_GROUND_WATER: {
                                /* three-corner-raised slope */
                                DrawShoreTile(ti->tileh);
                                Corner track_corner = OppositeCorner(GetHighestSlopeCorner(ComplementSlope(ti->tileh)));
                                sub = &(_halftile_sub_sprite[track_corner]);
                                break;
                        }
                        default: break;
                }
        }

        if (image != 0) DrawGroundSprite(image, pal, sub);

        /* Draw track pieces individually for junction tiles */
        if (junction) {
                if (track & TRACK_BIT_X)     DrawGroundSprite(rti->base_sprites.single_x, PAL_NONE);
                if (track & TRACK_BIT_Y)     DrawGroundSprite(rti->base_sprites.single_y, PAL_NONE);
                if (track & TRACK_BIT_UPPER) DrawGroundSprite(rti->base_sprites.single_n, PAL_NONE);
                if (track & TRACK_BIT_LOWER) DrawGroundSprite(rti->base_sprites.single_s, PAL_NONE);
                if (track & TRACK_BIT_LEFT)  DrawGroundSprite(rti->base_sprites.single_w, PAL_NONE);
                if (track & TRACK_BIT_RIGHT) DrawGroundSprite(rti->base_sprites.single_e, PAL_NONE);
        }

        /* PBS debugging, draw reserved tracks darker */
        if (_game_mode != GM_MENU && _settings_client.gui.show_track_reservation) {
                /* Get reservation, but mask track on halftile slope */
                TrackBits pbs = GetRailReservationTrackBits(ti->tile) & track;
                if (pbs & TRACK_BIT_X) {
                        if (ti->tileh == SLOPE_FLAT || ti->tileh == SLOPE_ELEVATED) {
                                DrawGroundSprite(rti->base_sprites.single_x, PALETTE_CRASH);
                        } else {
                                DrawGroundSprite(_track_sloped_sprites[ti->tileh - 1] + rti->base_sprites.single_sloped - 20, PALETTE_CRASH);
                        }
                }
                if (pbs & TRACK_BIT_Y) {
                        if (ti->tileh == SLOPE_FLAT || ti->tileh == SLOPE_ELEVATED) {
                                DrawGroundSprite(rti->base_sprites.single_y, PALETTE_CRASH);
                        } else {
                                DrawGroundSprite(_track_sloped_sprites[ti->tileh - 1] + rti->base_sprites.single_sloped - 20, PALETTE_CRASH);
                        }
                }
                if (pbs & TRACK_BIT_UPPER) DrawGroundSprite(rti->base_sprites.single_n, PALETTE_CRASH, NULL, 0, ti->tileh & SLOPE_N ? -(int)TILE_HEIGHT : 0);
                if (pbs & TRACK_BIT_LOWER) DrawGroundSprite(rti->base_sprites.single_s, PALETTE_CRASH, NULL, 0, ti->tileh & SLOPE_S ? -(int)TILE_HEIGHT : 0);
                if (pbs & TRACK_BIT_LEFT)  DrawGroundSprite(rti->base_sprites.single_w, PALETTE_CRASH, NULL, 0, ti->tileh & SLOPE_W ? -(int)TILE_HEIGHT : 0);
                if (pbs & TRACK_BIT_RIGHT) DrawGroundSprite(rti->base_sprites.single_e, PALETTE_CRASH, NULL, 0, ti->tileh & SLOPE_E ? -(int)TILE_HEIGHT : 0);
        }

        if (IsValidCorner(halftile_corner)) {
                DrawFoundation(ti, HalftileFoundation(halftile_corner));

                /* Draw higher halftile-overlay: Use the sloped sprites with three corners raised. They probably best fit the lightning. */
                Slope fake_slope = SlopeWithThreeCornersRaised(OppositeCorner(halftile_corner));
                image = _track_sloped_sprites[fake_slope - 1] + rti->base_sprites.track_y;
                pal = PAL_NONE;
                switch (rgt) {
                        case RAIL_GROUND_BARREN:     pal = PALETTE_TO_BARE_LAND; break;
                        case RAIL_GROUND_ICE_DESERT:
                        case RAIL_GROUND_HALF_SNOW:  image += rti->snow_offset;  break; // higher part has snow in this case too
                        default: break;
                }
                DrawGroundSprite(image, pal, &(_halftile_sub_sprite[halftile_corner]));

                if (_game_mode != GM_MENU && _settings_client.gui.show_track_reservation && HasReservedTracks(ti->tile, CornerToTrackBits(halftile_corner))) {
                        static const byte _corner_to_track_sprite[] = {3, 1, 2, 0};
                        DrawGroundSprite(_corner_to_track_sprite[halftile_corner] + rti->base_sprites.single_n, PALETTE_CRASH, NULL, 0, -(int)TILE_HEIGHT);
                }
        }
        
        /* Draw track overgrowth */
        if (_settings_client.gui.show_track_overgrowth) DrawTrackGrowth(ti, track);
}

static void DrawSignals(TileIndex tile, TrackBits rails, const RailtypeInfo *rti)
{
#define MAYBE_DRAW_SIGNAL(x, y, z, t) if (IsSignalPresent(tile, x)) DrawSingleSignal(tile, rti, t, GetSingleSignalState(tile, x), y, z)

        if (!(rails & TRACK_BIT_Y)) {
                if (!(rails & TRACK_BIT_X)) {
                        if (rails & TRACK_BIT_LEFT) {
                                MAYBE_DRAW_SIGNAL(2, SIGNAL_TO_NORTH, 0, TRACK_LEFT);
                                MAYBE_DRAW_SIGNAL(3, SIGNAL_TO_SOUTH, 1, TRACK_LEFT);
                        }
                        if (rails & TRACK_BIT_RIGHT) {
                                MAYBE_DRAW_SIGNAL(0, SIGNAL_TO_NORTH, 2, TRACK_RIGHT);
                                MAYBE_DRAW_SIGNAL(1, SIGNAL_TO_SOUTH, 3, TRACK_RIGHT);
                        }
                        if (rails & TRACK_BIT_UPPER) {
                                MAYBE_DRAW_SIGNAL(3, SIGNAL_TO_WEST, 4, TRACK_UPPER);
                                MAYBE_DRAW_SIGNAL(2, SIGNAL_TO_EAST, 5, TRACK_UPPER);
                        }
                        if (rails & TRACK_BIT_LOWER) {
                                MAYBE_DRAW_SIGNAL(1, SIGNAL_TO_WEST, 6, TRACK_LOWER);
                                MAYBE_DRAW_SIGNAL(0, SIGNAL_TO_EAST, 7, TRACK_LOWER);
                        }
                } else {
                        MAYBE_DRAW_SIGNAL(3, SIGNAL_TO_SOUTHWEST, 8, TRACK_X);
                        MAYBE_DRAW_SIGNAL(2, SIGNAL_TO_NORTHEAST, 9, TRACK_X);
                }
        } else {
                MAYBE_DRAW_SIGNAL(3, SIGNAL_TO_SOUTHEAST, 10, TRACK_Y);
                MAYBE_DRAW_SIGNAL(2, SIGNAL_TO_NORTHWEST, 11, TRACK_Y);
        }
}

static void DrawTile_Track(TileInfo *ti)
{
        const RailtypeInfo *rti = GetRailTypeInfo(GetRailType(ti->tile));

        _drawtile_track_palette = COMPANY_SPRITE_COLOUR(GetTileOwner(ti->tile));

        if (IsPlainRail(ti->tile)) {
                TrackBits rails = GetTrackBits(ti->tile);

                DrawTrackBits(ti, rails);

                if (HasBit(_display_opt, DO_RAIL_FENCES)) DrawTrackDetails(ti, rti);

                DrawOverlay(ti, MP_RAILWAY);

                if (HasRailCatenaryDrawn(GetRailType(ti->tile))) DrawRailCatenary(ti);


                if (HasSignals(ti->tile)) DrawSignals(ti->tile, rails, rti);
        } else {
                /* draw depot */
                const DrawTileSprites *dts;
                PaletteID pal = PAL_NONE;
                SpriteID relocation;

                if (ti->tileh != SLOPE_FLAT) DrawFoundation(ti, FOUNDATION_LEVELED);

                if (IsInvisibilitySet(TO_BUILDINGS)) {
                        /* Draw rail instead of depot */
                        dts = &_depot_invisible_gfx_table[GetRailDepotDirection(ti->tile)];
                } else {
                        dts = &_depot_gfx_table[GetRailDepotDirection(ti->tile)];
                }

                SpriteID image;
                if (rti->UsesOverlay()) {
                        image = SPR_FLAT_GRASS_TILE;
                } else {
                        image = dts->ground.sprite;
                        if (image != SPR_FLAT_GRASS_TILE) image += rti->GetRailtypeSpriteOffset();
                }

                /* adjust ground tile for desert
                 * don't adjust for snow, because snow in depots looks weird */
                if (IsSnowRailGround(ti->tile) && _settings_game.game_creation.landscape == LT_TROPIC) {
                        if (image != SPR_FLAT_GRASS_TILE) {
                                image += rti->snow_offset; // tile with tracks
                        } else {
                                image = SPR_FLAT_SNOW_DESERT_TILE; // flat ground
                        }
                }

                DrawGroundSprite(image, GroundSpritePaletteTransform(image, pal, _drawtile_track_palette));

                if (rti->UsesOverlay()) {
                        SpriteID ground = GetCustomRailSprite(rti, ti->tile, RTSG_GROUND);

                        switch (GetRailDepotDirection(ti->tile)) {
                                case DIAGDIR_NE:
                                        if (!IsInvisibilitySet(TO_BUILDINGS)) break;
                                        FALLTHROUGH;
                                case DIAGDIR_SW:
                                        DrawGroundSprite(ground + RTO_X, PAL_NONE);
                                        break;
                                case DIAGDIR_NW:
                                        if (!IsInvisibilitySet(TO_BUILDINGS)) break;
                                        FALLTHROUGH;
                                case DIAGDIR_SE:
                                        DrawGroundSprite(ground + RTO_Y, PAL_NONE);
                                        break;
                                default:
                                        break;
                        }

                        if (_settings_client.gui.show_track_reservation && HasDepotReservation(ti->tile)) {
                                SpriteID overlay = GetCustomRailSprite(rti, ti->tile, RTSG_OVERLAY);

                                switch (GetRailDepotDirection(ti->tile)) {
                                        case DIAGDIR_NE:
                                                if (!IsInvisibilitySet(TO_BUILDINGS)) break;
                                                FALLTHROUGH;
                                        case DIAGDIR_SW:
                                                DrawGroundSprite(overlay + RTO_X, PALETTE_CRASH);
                                                break;
                                        case DIAGDIR_NW:
                                                if (!IsInvisibilitySet(TO_BUILDINGS)) break;
                                                FALLTHROUGH;
                                        case DIAGDIR_SE:
                                                DrawGroundSprite(overlay + RTO_Y, PALETTE_CRASH);
                                                break;
                                        default:
                                                break;
                                }
                        }
                } else {
                        /* PBS debugging, draw reserved tracks darker */
                        if (_game_mode != GM_MENU && _settings_client.gui.show_track_reservation && HasDepotReservation(ti->tile)) {
                                switch (GetRailDepotDirection(ti->tile)) {
                                        case DIAGDIR_NE:
                                                if (!IsInvisibilitySet(TO_BUILDINGS)) break;
                                                FALLTHROUGH;
                                        case DIAGDIR_SW:
                                                DrawGroundSprite(rti->base_sprites.single_x, PALETTE_CRASH);
                                                break;
                                        case DIAGDIR_NW:
                                                if (!IsInvisibilitySet(TO_BUILDINGS)) break;
                                                FALLTHROUGH;
                                        case DIAGDIR_SE:
                                                DrawGroundSprite(rti->base_sprites.single_y, PALETTE_CRASH);
                                                break;
                                        default:
                                                break;
                                }
                        }
                }
                int depot_sprite = GetCustomRailSprite(rti, ti->tile, RTSG_DEPOT);
                relocation = depot_sprite != 0 ? depot_sprite - SPR_RAIL_DEPOT_SE_1 : rti->GetRailtypeSpriteOffset();

                DrawOverlay(ti, MP_RAILWAY);

                if (HasRailCatenaryDrawn(GetRailType(ti->tile))) DrawRailCatenary(ti);

                DrawRailTileSeq(ti, dts, TO_BUILDINGS, relocation, 0, _drawtile_track_palette);
        }
        DrawBridgeMiddle(ti);
}

void DrawTrainDepotSprite(int x, int y, int dir, RailType railtype)
{
        const DrawTileSprites *dts = &_depot_gfx_table[dir];
        const RailtypeInfo *rti = GetRailTypeInfo(railtype);
        SpriteID image = rti->UsesOverlay() ? SPR_FLAT_GRASS_TILE : dts->ground.sprite;
        uint32 offset = rti->GetRailtypeSpriteOffset();

        if (image != SPR_FLAT_GRASS_TILE) image += offset;
        PaletteID palette = COMPANY_SPRITE_COLOUR(_local_company);

        DrawSprite(image, PAL_NONE, x, y);

        if (rti->UsesOverlay()) {
                SpriteID ground = GetCustomRailSprite(rti, INVALID_TILE, RTSG_GROUND);

                switch (dir) {
                        case DIAGDIR_SW: DrawSprite(ground + RTO_X, PAL_NONE, x, y); break;
                        case DIAGDIR_SE: DrawSprite(ground + RTO_Y, PAL_NONE, x, y); break;
                        default: break;
                }
        }
        int depot_sprite = GetCustomRailSprite(rti, INVALID_TILE, RTSG_DEPOT);
        if (depot_sprite != 0) offset = depot_sprite - SPR_RAIL_DEPOT_SE_1;

        DrawRailTileSeqInGUI(x, y, dts, offset, 0, palette);
}

static int GetSlopePixelZ_Track(TileIndex tile, uint x, uint y)
{
        if (IsPlainRail(tile)) {
                int z;
                Slope tileh = GetTilePixelSlope(tile, &z);
                if (tileh == SLOPE_FLAT) return z;

                z += ApplyPixelFoundationToSlope(GetRailFoundation(tileh, GetTrackBits(tile)), &tileh);
                return z + GetPartialPixelZ(x & 0xF, y & 0xF, tileh);
        } else {
                return GetTileMaxPixelZ(tile);
        }
}

static Foundation GetFoundation_Track(TileIndex tile, Slope tileh)
{
        return IsPlainRail(tile) ? GetRailFoundation(tileh, GetTrackBits(tile)) : FlatteningFoundation(tileh);
}

void AgeTrack(TileIndex ti)
{
        assert(IsPlainRailTile(ti));

        byte age = GetRailAge(ti);

        const byte maxi = 255;
        if (age == maxi)
                return;

        byte inv = maxi - age;

        static byte shift = 7;
        byte delta = max(1, inv >> shift);
        inv -= delta;

        age = maxi - inv;

        byte old_growth = GetTrackGrowthPhase(ti);

        SetRailAge(ti, age);

        /* If rounded growth amount changes, redraw */
        if (GetTrackGrowthPhase(ti) != old_growth)
                MarkTileDirtyByTile(ti);
}

static void TileLoop_Track(TileIndex tile)
{
        if (IsPlainRailTile(tile)) AgeTrack(tile);

        RailGroundType old_ground = GetRailGroundType(tile);
        RailGroundType new_ground;

        if (old_ground == RAIL_GROUND_WATER) {
                TileLoop_Water(tile);
                return;
        }

        switch (_settings_game.game_creation.landscape) {
                case LT_ARCTIC: {
                        int z;
                        Slope slope = GetTileSlope(tile, &z);
                        bool half = false;

                        /* for non-flat track, use lower part of track
                         * in other cases, use the highest part with track */
                        if (IsPlainRail(tile)) {
                                TrackBits track = GetTrackBits(tile);
                                Foundation f = GetRailFoundation(slope, track);

                                switch (f) {
                                        case FOUNDATION_NONE:
                                                /* no foundation - is the track on the upper side of three corners raised tile? */
                                                if (slope != SLOPE_FLAT) z++;
                                                break;

                                        case FOUNDATION_INCLINED_X:
                                        case FOUNDATION_INCLINED_Y:
                                                /* sloped track - is it on a steep slope? */
                                                if (IsSteepSlope(slope)) z++;
                                                break;

                                        case FOUNDATION_STEEP_LOWER:
                                                /* only lower part of steep slope */
                                                z++;
                                                break;

                                        default:
                                                /* if it is a steep slope, then there is a track on higher part */
                                                if (IsSteepSlope(slope)) z++;
                                                z++;
                                                break;
                                }

                                half = IsInsideMM(f, FOUNDATION_STEEP_BOTH, FOUNDATION_HALFTILE_N + 1);
                        } else {
                                /* is the depot on a non-flat tile? */
                                if (slope != SLOPE_FLAT) z++;
                        }

                        /* 'z' is now the lowest part of the highest track bit -
                         * for sloped track, it is 'z' of lower part
                         * for two track bits, it is 'z' of higher track bit
                         * For non-continuous foundations (and STEEP_BOTH), 'half' is set */
                        if (z > GetSnowLine()) {
                                if (half && z - GetSnowLine() == 1) {
                                        /* track on non-continuous foundation, lower part is not under snow */
                                        new_ground = RAIL_GROUND_HALF_SNOW;
                                } else {
                                        new_ground = RAIL_GROUND_ICE_DESERT;
                                }
                                goto set_ground;
                        }
                        break;
                        }

                case LT_TROPIC:
                        if (GetTropicZone(tile) == TROPICZONE_DESERT) {
                                new_ground = RAIL_GROUND_ICE_DESERT;
                                goto set_ground;
                        }
                        break;
        }

        new_ground = RAIL_GROUND_GRASS;

        if (IsPlainRail(tile) && old_ground != RAIL_GROUND_BARREN) { // wait until bottom is green
                /* determine direction of fence */
                TrackBits rail = GetTrackBits(tile);

                Owner owner = GetTileOwner(tile);
                byte fences = 0;

                for (DiagDirection d = DIAGDIR_BEGIN; d < DIAGDIR_END; d++) {
                        static const TrackBits dir_to_trackbits[DIAGDIR_END] = {TRACK_BIT_3WAY_NE, TRACK_BIT_3WAY_SE, TRACK_BIT_3WAY_SW, TRACK_BIT_3WAY_NW};

                        /* Track bit on this edge => no fence. */
                        if ((rail & dir_to_trackbits[d]) != TRACK_BIT_NONE) continue;

                        TileIndex tile2 = tile + TileOffsByDiagDir(d);

                        /* Show fences if it's a house, industry, object, road, tunnelbridge or not owned by us. */
                        if (!IsValidTile(tile2) || IsTileType(tile2, MP_HOUSE) || IsTileType(tile2, MP_INDUSTRY) ||
                                        IsTileType(tile2, MP_ROAD) || (IsTileType(tile2, MP_OBJECT) && !IsObjectType(tile2, OBJECT_OWNED_LAND)) || IsTileType(tile2, MP_TUNNELBRIDGE) || !IsTileOwner(tile2, owner)) {
                                fences |= 1 << d;
                        }
                }

                switch (fences) {
                        case 0: break;
                        case (1 << DIAGDIR_NE): new_ground = RAIL_GROUND_FENCE_NE; break;
                        case (1 << DIAGDIR_SE): new_ground = RAIL_GROUND_FENCE_SE; break;
                        case (1 << DIAGDIR_SW): new_ground = RAIL_GROUND_FENCE_SW; break;
                        case (1 << DIAGDIR_NW): new_ground = RAIL_GROUND_FENCE_NW; break;
                        case (1 << DIAGDIR_NE) | (1 << DIAGDIR_SW): new_ground = RAIL_GROUND_FENCE_NESW; break;
                        case (1 << DIAGDIR_SE) | (1 << DIAGDIR_NW): new_ground = RAIL_GROUND_FENCE_SENW; break;
                        case (1 << DIAGDIR_NE) | (1 << DIAGDIR_SE): new_ground = RAIL_GROUND_FENCE_VERT1; break;
                        case (1 << DIAGDIR_NE) | (1 << DIAGDIR_NW): new_ground = RAIL_GROUND_FENCE_HORIZ2; break;
                        case (1 << DIAGDIR_SE) | (1 << DIAGDIR_SW): new_ground = RAIL_GROUND_FENCE_HORIZ1; break;
                        case (1 << DIAGDIR_SW) | (1 << DIAGDIR_NW): new_ground = RAIL_GROUND_FENCE_VERT2; break;
                        default: NOT_REACHED();
                }
        }

set_ground:
        if (old_ground != new_ground) {
                SetRailGroundType(tile, new_ground);
                MarkTileDirtyByTile(tile);
        }
}


static TrackStatus GetTileTrackStatus_Track(TileIndex tile, TransportType mode, uint sub_mode, DiagDirection side)
{
        /* Case of half tile slope with water. */
        if (mode == TRANSPORT_WATER && IsPlainRail(tile) && GetRailGroundType(tile) == RAIL_GROUND_WATER && IsSlopeWithOneCornerRaised(GetTileSlope(tile))) {
                TrackBits tb = GetTrackBits(tile);
                switch (tb) {
                        default: NOT_REACHED();
                        case TRACK_BIT_UPPER: tb = TRACK_BIT_LOWER; break;
                        case TRACK_BIT_LOWER: tb = TRACK_BIT_UPPER; break;
                        case TRACK_BIT_LEFT:  tb = TRACK_BIT_RIGHT; break;
                        case TRACK_BIT_RIGHT: tb = TRACK_BIT_LEFT;  break;
                }
                return CombineTrackStatus(TrackBitsToTrackdirBits(tb), TRACKDIR_BIT_NONE);
        }

        if (mode != TRANSPORT_RAIL) return 0;

        TrackBits trackbits = TRACK_BIT_NONE;
        TrackdirBits red_signals = TRACKDIR_BIT_NONE;

        switch (GetRailTileType(tile)) {
                default: NOT_REACHED();
                case RAIL_TILE_NORMAL:
                        trackbits = GetTrackBits(tile);
                        break;

                case RAIL_TILE_SIGNALS: {
                        trackbits = GetTrackBits(tile);
                        byte a = GetPresentSignals(tile);
                        uint b = GetSignalStates(tile);

                        b &= a;

                        /* When signals are not present (in neither direction),
                         * we pretend them to be green. Otherwise, it depends on
                         * the signal type. For signals that are only active from
                         * one side, we set the missing signals explicitly to
                         * `green'. Otherwise, they implicitly become `red'. */
                        if (!IsOnewaySignal(tile, TRACK_UPPER) || (a & SignalOnTrack(TRACK_UPPER)) == 0) b |= ~a & SignalOnTrack(TRACK_UPPER);
                        if (!IsOnewaySignal(tile, TRACK_LOWER) || (a & SignalOnTrack(TRACK_LOWER)) == 0) b |= ~a & SignalOnTrack(TRACK_LOWER);

                        if ((b & 0x8) == 0) red_signals |= (TRACKDIR_BIT_LEFT_N | TRACKDIR_BIT_X_NE | TRACKDIR_BIT_Y_SE | TRACKDIR_BIT_UPPER_E);
                        if ((b & 0x4) == 0) red_signals |= (TRACKDIR_BIT_LEFT_S | TRACKDIR_BIT_X_SW | TRACKDIR_BIT_Y_NW | TRACKDIR_BIT_UPPER_W);
                        if ((b & 0x2) == 0) red_signals |= (TRACKDIR_BIT_RIGHT_N | TRACKDIR_BIT_LOWER_E);
                        if ((b & 0x1) == 0) red_signals |= (TRACKDIR_BIT_RIGHT_S | TRACKDIR_BIT_LOWER_W);

                        break;
                }

                case RAIL_TILE_DEPOT: {
                        DiagDirection dir = GetRailDepotDirection(tile);

                        if (side != INVALID_DIAGDIR && side != dir) break;

                        trackbits = DiagDirToDiagTrackBits(dir);
                        break;
                }
        }

        return CombineTrackStatus(TrackBitsToTrackdirBits(trackbits), red_signals);
}

static bool ClickTile_Track(TileIndex tile)
{
        if (_ctrl_pressed && IsPlainRailTile(tile)) {
                TrackBits trackbits = TrackStatusToTrackBits(GetTileTrackStatus(tile, TRANSPORT_RAIL, 0));

                if (trackbits & TRACK_BIT_VERT) { // N-S direction
                        trackbits = (_tile_fract_coords.x <= _tile_fract_coords.y) ? TRACK_BIT_RIGHT : TRACK_BIT_LEFT;
                }

                if (trackbits & TRACK_BIT_HORZ) { // E-W direction
                        trackbits = (_tile_fract_coords.x + _tile_fract_coords.y <= 15) ? TRACK_BIT_UPPER : TRACK_BIT_LOWER;
                }

                Track track = FindFirstTrack(trackbits);
                if (HasTrack(tile, track) && HasSignalOnTrack(tile, track)) {
                        if (GetSignalType(tile, track) == SIGTYPE_LOGIC) {
                                SignalProgram* program = FindSignalProgram(tile, track);
                                if (program != nullptr) {
                                        ShowSignalProgramWindow(program);
                                }
                        } else  {
                                ShowTraceRestrictProgramWindow(tile, track);
                        }
                        return true;
                }
        }

        if (!IsRailDepot(tile)) return false;

        ShowDepotWindow(tile, VEH_TRAIN);
        return true;
}

static void GetTileDesc_Track(TileIndex tile, TileDesc *td)
{
        const RailtypeInfo *rti = GetRailTypeInfo(GetRailType(tile));
        td->rail_speed = rti->max_speed;
        td->railtype = rti->strings.name;
        td->owner[0] = GetTileOwner(tile);
        switch (GetRailTileType(tile)) {
                case RAIL_TILE_NORMAL:
                        td->str = STR_LAI_RAIL_DESCRIPTION_TRACK;
                        break;

                case RAIL_TILE_SIGNALS: {
                        static const StringID signal_type[SIGTYPE_END][SIGTYPE_END] = {
                                {
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_NORMAL_SIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_NORMAL_PRESIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_NORMAL_EXITSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_NORMAL_COMBOSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_NORMAL_PBSSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_NORMAL_NOENTRYSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_NORMAL_LOGICSIGNALS
                                },
                                {
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_NORMAL_PRESIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_PRESIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_PRE_EXITSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_PRE_COMBOSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_PRE_PBSSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_PRE_NOENTRYSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_PRE_LOGICSIGNALS
                                },
                                {
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_NORMAL_EXITSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_PRE_EXITSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_EXITSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_EXIT_COMBOSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_EXIT_PBSSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_EXIT_NOENTRYSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_EXIT_LOGICSIGNALS
                                },
                                {
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_NORMAL_COMBOSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_PRE_COMBOSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_EXIT_COMBOSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_COMBOSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_COMBO_PBSSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_COMBO_NOENTRYSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_COMBO_LOGICSIGNALS
                                },
                                {
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_NORMAL_PBSSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_PRE_PBSSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_EXIT_PBSSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_COMBO_PBSSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_PBSSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_PBS_NOENTRYSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_PBS_LOGICSIGNALS
                                },
                                {
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_NORMAL_NOENTRYSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_PRE_NOENTRYSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_EXIT_NOENTRYSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_COMBO_NOENTRYSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_PBS_NOENTRYSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_NOENTRYSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_NOENTRY_LOGICSIGNALS
                                },
                                {
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_NORMAL_LOGICSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_PRE_LOGICSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_EXIT_LOGICSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_COMBO_LOGICSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_PBS_LOGICSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_NOENTRY_LOGICSIGNALS,
                                        STR_LAI_RAIL_DESCRIPTION_TRACK_WITH_LOGICSIGNALS
                                }
                        };

                        SignalType primary_signal;
                        SignalType secondary_signal;
                        if (HasSignalOnTrack(tile, TRACK_UPPER)) {
                                primary_signal = GetSignalType(tile, TRACK_UPPER);
                                secondary_signal = HasSignalOnTrack(tile, TRACK_LOWER) ? GetSignalType(tile, TRACK_LOWER) : primary_signal;
                        } else {
                                secondary_signal = primary_signal = GetSignalType(tile, TRACK_LOWER);
                        }

                        td->str = signal_type[secondary_signal][primary_signal];

                        if (IsRestrictedSignal(tile)) {
                                SetDParamX(td->dparam, 0, td->str);
                                SetDParamX(td->dparam, 1, rti->strings.name);
                                td->str = STR_LAI_RAIL_DESCRIPTION_RESTRICTED_SIGNAL;
                        }
                        break;
                }

                case RAIL_TILE_DEPOT:
                        td->str = STR_LAI_RAIL_DESCRIPTION_TRAIN_DEPOT;
                        if (_settings_game.vehicle.train_acceleration_model != AM_ORIGINAL) {
                                if (td->rail_speed > 0) {
                                        td->rail_speed = min(td->rail_speed, 61);
                                } else {
                                        td->rail_speed = 61;
                                }
                        }
                        td->build_date = Depot::GetByTile(tile)->build_date;
                        break;

                default:
                        NOT_REACHED();
        }
}

static void ChangeTileOwner_Track(TileIndex tile, Owner old_owner, Owner new_owner)
{
        if (!IsTileOwner(tile, old_owner)) return;

        if (new_owner != INVALID_OWNER) {
                /* Update company infrastructure counts. No need to dirty windows here, we'll redraw the whole screen anyway. */
                uint num_pieces = 1;
                if (IsPlainRail(tile)) {
                        TrackBits bits = GetTrackBits(tile);
                        num_pieces = CountBits(bits);
                        if (TracksOverlap(bits)) num_pieces *= num_pieces;
                }
                RailType rt = GetRailType(tile);
                Company::Get(old_owner)->infrastructure.rail[rt] -= num_pieces;
                Company::Get(new_owner)->infrastructure.rail[rt] += num_pieces;

                if (HasSignals(tile)) {
                        uint num_sigs = CountBits(GetPresentSignals(tile));
                        Company::Get(old_owner)->infrastructure.signal -= num_sigs;
                        Company::Get(new_owner)->infrastructure.signal += num_sigs;
                }

                SetTileOwner(tile, new_owner);
        } else {
                DoCommand(tile, 0, 0, DC_EXEC | DC_BANKRUPT, CMD_LANDSCAPE_CLEAR);
        }
}

static const byte _fractcoords_behind[4] = { 0x8F, 0x8, 0x80, 0xF8 };
static const byte _fractcoords_enter[4] = { 0x8A, 0x48, 0x84, 0xA8 };
static const int8 _deltacoord_leaveoffset[8] = {
        -1,  0,  1,  0, /* x */
         0,  1,  0, -1  /* y */
};


/**
 * Compute number of ticks when next wagon will leave a depot.
 * Negative means next wagon should have left depot n ticks before.
 * @param v vehicle outside (leaving) the depot
 * @return number of ticks when the next wagon will leave
 */
int TicksToLeaveDepot(const Train *v)
{
        DiagDirection dir = GetRailDepotDirection(v->tile);
        int length = v->CalcNextVehicleOffset();

        switch (dir) {
                case DIAGDIR_NE: return  ((int)(v->x_pos & 0x0F) - ((_fractcoords_enter[dir] & 0x0F) - (length + 1)));
                case DIAGDIR_SE: return -((int)(v->y_pos & 0x0F) - ((_fractcoords_enter[dir] >> 4)   + (length + 1)));
                case DIAGDIR_SW: return -((int)(v->x_pos & 0x0F) - ((_fractcoords_enter[dir] & 0x0F) + (length + 1)));
                default:
                case DIAGDIR_NW: return  ((int)(v->y_pos & 0x0F) - ((_fractcoords_enter[dir] >> 4)   - (length + 1)));
        }

        return 0; // make compilers happy
}

/**
 * Tile callback routine when vehicle enters tile
 * @see vehicle_enter_tile_proc
 */
static VehicleEnterTileStatus VehicleEnter_Track(Vehicle *u, TileIndex tile, int x, int y)
{
        /* this routine applies only to trains in depot tiles */
        if (u->type != VEH_TRAIN || !IsRailDepotTile(tile)) return VETSB_CONTINUE;

        Train *v = Train::From(u);

        /* depot direction */
        DiagDirection dir = GetRailDepotDirection(tile);

        /* Calculate the point where the following wagon should be activated. */
        int length = v->CalcNextVehicleOffset();

        byte fract_coord_leave =
                ((_fractcoords_enter[dir] & 0x0F) + // x
                        (length + 1) * _deltacoord_leaveoffset[dir]) +
                (((_fractcoords_enter[dir] >> 4) +  // y
                        ((length + 1) * _deltacoord_leaveoffset[dir + 4])) << 4);

        byte fract_coord = (x & 0xF) + ((y & 0xF) << 4);

        if (_fractcoords_behind[dir] == fract_coord) {
                /* make sure a train is not entering the tile from behind */
                return VETSB_CANNOT_ENTER;
        } else if (_fractcoords_enter[dir] == fract_coord) {
                if (DiagDirToDir(ReverseDiagDir(dir)) == v->direction) {
                        /* enter the depot */
                        v->track = TRACK_BIT_DEPOT,
                        v->vehstatus |= VS_HIDDEN; // hide it
                        v->direction = ReverseDir(v->direction);
                        if (v->Next() == NULL) VehicleEnterDepot(v->First());
                        v->tile = tile;

                        InvalidateWindowData(WC_VEHICLE_DEPOT, v->tile);
                        return VETSB_ENTERED_WORMHOLE;
                }
        } else if (fract_coord_leave == fract_coord) {
                if (DiagDirToDir(dir) == v->direction) {
                        /* leave the depot? */
                        if ((v = v->Next()) != NULL) {
                                v->vehstatus &= ~VS_HIDDEN;
                                v->track = (DiagDirToAxis(dir) == AXIS_X ? TRACK_BIT_X : TRACK_BIT_Y);
                        }
                }
        }

        return VETSB_CONTINUE;
}

/**
 * Tests if autoslope is allowed.
 *
 * @param tile The tile.
 * @param flags Terraform command flags.
 * @param z_old Old TileZ.
 * @param tileh_old Old TileSlope.
 * @param z_new New TileZ.
 * @param tileh_new New TileSlope.
 * @param rail_bits Trackbits.
 */
static CommandCost TestAutoslopeOnRailTile(TileIndex tile, uint flags, int z_old, Slope tileh_old, int z_new, Slope tileh_new, TrackBits rail_bits)
{
        if (!_settings_game.construction.build_on_slopes || !AutoslopeEnabled()) return_cmd_error(STR_ERROR_MUST_REMOVE_RAILROAD_TRACK);

        /* Is the slope-rail_bits combination valid in general? I.e. is it safe to call GetRailFoundation() ? */
        if (CheckRailSlope(tileh_new, rail_bits, TRACK_BIT_NONE, tile).Failed()) return_cmd_error(STR_ERROR_MUST_REMOVE_RAILROAD_TRACK);

        /* Get the slopes on top of the foundations */
        z_old += ApplyFoundationToSlope(GetRailFoundation(tileh_old, rail_bits), &tileh_old);
        z_new += ApplyFoundationToSlope(GetRailFoundation(tileh_new, rail_bits), &tileh_new);

        Corner track_corner;
        switch (rail_bits) {
                case TRACK_BIT_LEFT:  track_corner = CORNER_W; break;
                case TRACK_BIT_LOWER: track_corner = CORNER_S; break;
                case TRACK_BIT_RIGHT: track_corner = CORNER_E; break;
                case TRACK_BIT_UPPER: track_corner = CORNER_N; break;

                /* Surface slope must not be changed */
                default:
                        if (z_old != z_new || tileh_old != tileh_new) return_cmd_error(STR_ERROR_MUST_REMOVE_RAILROAD_TRACK);
                        return CommandCost(EXPENSES_CONSTRUCTION, _price[PR_BUILD_FOUNDATION]);
        }

        /* The height of the track_corner must not be changed. The rest ensures GetRailFoundation() already. */
        z_old += GetSlopeZInCorner(RemoveHalftileSlope(tileh_old), track_corner);
        z_new += GetSlopeZInCorner(RemoveHalftileSlope(tileh_new), track_corner);
        if (z_old != z_new) return_cmd_error(STR_ERROR_MUST_REMOVE_RAILROAD_TRACK);

        CommandCost cost = CommandCost(EXPENSES_CONSTRUCTION, _price[PR_BUILD_FOUNDATION]);
        /* Make the ground dirty, if surface slope has changed */
        if (tileh_old != tileh_new) {
                /* If there is flat water on the lower halftile add the cost for clearing it */
                if (GetRailGroundType(tile) == RAIL_GROUND_WATER && IsSlopeWithOneCornerRaised(tileh_old)) cost.AddCost(_price[PR_CLEAR_WATER]);
                if ((flags & DC_EXEC) != 0) SetRailGroundType(tile, RAIL_GROUND_BARREN);
        }
        return  cost;
}

/**
 * Test-procedure for HasVehicleOnPos to check for a ship.
 */
static Vehicle *EnsureNoShipProc(Vehicle *v, void *data)
{
        return v->type == VEH_SHIP ? v : NULL;
}

static CommandCost TerraformTile_Track(TileIndex tile, DoCommandFlag flags, int z_new, Slope tileh_new)
{
        int z_old;
        Slope tileh_old = GetTileSlope(tile, &z_old);
        if (IsPlainRail(tile)) {
                TrackBits rail_bits = GetTrackBits(tile);
                /* Is there flat water on the lower halftile that must be cleared expensively? */
                bool was_water = (GetRailGroundType(tile) == RAIL_GROUND_WATER && IsSlopeWithOneCornerRaised(tileh_old));

                /* Allow clearing the water only if there is no ship */
                if (was_water && HasVehicleOnPos(tile, NULL, &EnsureNoShipProc)) return_cmd_error(STR_ERROR_SHIP_IN_THE_WAY);

                /* First test autoslope. However if it succeeds we still have to test the rest, because non-autoslope terraforming is cheaper. */
                CommandCost autoslope_result = TestAutoslopeOnRailTile(tile, flags, z_old, tileh_old, z_new, tileh_new, rail_bits);

                /* When there is only a single horizontal/vertical track, one corner can be terraformed. */
                Corner allowed_corner;
                switch (rail_bits) {
                        case TRACK_BIT_RIGHT: allowed_corner = CORNER_W; break;
                        case TRACK_BIT_UPPER: allowed_corner = CORNER_S; break;
                        case TRACK_BIT_LEFT:  allowed_corner = CORNER_E; break;
                        case TRACK_BIT_LOWER: allowed_corner = CORNER_N; break;
                        default: return autoslope_result;
                }

                Foundation f_old = GetRailFoundation(tileh_old, rail_bits);

                /* Do not allow terraforming if allowed_corner is part of anti-zig-zag foundations */
                if (tileh_old != SLOPE_NS && tileh_old != SLOPE_EW && IsSpecialRailFoundation(f_old)) return autoslope_result;

                /* Everything is valid, which only changes allowed_corner */
                for (Corner corner = (Corner)0; corner < CORNER_END; corner = (Corner)(corner + 1)) {
                        if (allowed_corner == corner) continue;
                        if (z_old + GetSlopeZInCorner(tileh_old, corner) != z_new + GetSlopeZInCorner(tileh_new, corner)) return autoslope_result;
                }

                /* Make the ground dirty */
                if ((flags & DC_EXEC) != 0) SetRailGroundType(tile, RAIL_GROUND_BARREN);

                /* allow terraforming */
                return CommandCost(EXPENSES_CONSTRUCTION, was_water ? _price[PR_CLEAR_WATER] : (Money)0);
        } else if (_settings_game.construction.build_on_slopes && AutoslopeEnabled() &&
                        AutoslopeCheckForEntranceEdge(tile, z_new, tileh_new, GetRailDepotDirection(tile))) {
                return CommandCost(EXPENSES_CONSTRUCTION, _price[PR_BUILD_FOUNDATION]);
        }
        return DoCommand(tile, 0, 0, flags, CMD_LANDSCAPE_CLEAR);
}


extern const TileTypeProcs _tile_type_rail_procs = {
        DrawTile_Track,           // draw_tile_proc
        GetSlopePixelZ_Track,     // get_slope_z_proc
        ClearTile_Track,          // clear_tile_proc
        NULL,                     // add_accepted_cargo_proc
        GetTileDesc_Track,        // get_tile_desc_proc
        GetTileTrackStatus_Track, // get_tile_track_status_proc
        ClickTile_Track,          // click_tile_proc
        NULL,                     // animate_tile_proc
        TileLoop_Track,           // tile_loop_proc
        ChangeTileOwner_Track,    // change_tile_owner_proc
        NULL,                     // add_produced_cargo_proc
        VehicleEnter_Track,       // vehicle_enter_tile_proc
        GetFoundation_Track,      // get_foundation_proc
        TerraformTile_Track,      // terraform_tile_proc
};