rail_cmd.cpp

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/*
 * 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 <https://www.gnu.org/licenses/old-licenses/gpl-2.0>.
 */

 
#include "stdafx.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 "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 "core/container_func.hpp"
#include "timer/timer_game_calendar.h"
#include "strings_func.h"
#include "company_gui.h"
#include "object_map.h"
#include "rail_cmd.h"
#include "landscape_cmd.h"
 
#include "table/strings.h"
#include "table/railtypes.h"
#include "table/track_land.h"
 
#include "safeguards.h"

typedef std::vector<Train *> TrainList;
 
RailTypeInfo _railtypes[RAILTYPE_END];
std::vector<RailType> _sorted_railtypes; 
RailTypes _railtypes_hidden_mask;

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,
};

void ResetRailTypes()
{
  static_assert(std::size(_original_railtypes) <= std::size(_railtypes));
 
  auto insert = std::copy(std::begin(_original_railtypes), std::end(_original_railtypes), std::begin(_railtypes));
  std::fill(insert, std::end(_railtypes), RailTypeInfo{});
 
  _railtypes_hidden_mask = {};
}
 
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. */
  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_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},
  };
 
  for (SignalType type = SIGTYPE_BLOCK; 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;
    }
  }
}

static bool CompareRailTypes(const RailType &first, const RailType &second)
{
  return GetRailTypeInfo(first)->sorting_order < GetRailTypeInfo(second)->sorting_order;
}

void InitRailTypes()
{
  _sorted_railtypes.clear();
  for (RailTypeInfo &rti : _railtypes) {
    RailType rt = rti.Index();
 
    ResolveRailTypeGUISprites(&rti);
    _railtypes_hidden_mask.Set(rt, rti.flags.Test(RailTypeFlag::Hidden));
 
    if (rti.label == 0) continue;
    _sorted_railtypes.push_back(rt);
  }
  std::sort(_sorted_railtypes.begin(), _sorted_railtypes.end(), CompareRailTypes);
}

RailType AllocateRailType(RailTypeLabel label)
{
  auto it = std::ranges::find(_railtypes, 0, &RailTypeInfo::label);
  if (it == std::end(_railtypes)) return INVALID_RAILTYPE;
 
  RailTypeInfo &rti = *it;
  RailType rt = rti.Index();
 
  /* Set up new rail type based on default rail. */
  rti = _original_railtypes[RAILTYPE_RAIL];
  rti.label = label;
  rti.alternate_labels.clear();
 
  /* Make us compatible with ourself. */
  rti.powered_railtypes = rt;
  rti.compatible_railtypes = rt;
 
  /* We also introduce ourself. */
  rti.introduces_railtypes = 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;
}
 
static const uint8_t _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
 */

static CommandCost EnsureNoTrainOnTrack(TileIndex tile, Track track)
{
  TrackBits rail_bits = TrackToTrackBits(track);
  return EnsureNoTrainOnTrackBits(tile, rail_bits);
}

static CommandCost CheckTrackCombination(TileIndex tile, TrackBits to_build)
{
  if (!IsPlainRail(tile)) return CommandCost(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 CommandCost(STR_ERROR_ALREADY_BUILT);
  }
 
  /* Normally, we may overlap and any combination is valid */
  return CommandCost();
}
 

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,
};

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
};

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);
  }
}
 

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 CommandCost(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 CommandCost(STR_ERROR_LAND_SLOPED_IN_WRONG_DIRECTION);
  }
 
  Foundation f_old = GetRailFoundation(tileh, existing);
  return CommandCost(EXPENSES_CONSTRUCTION, f_new != f_old ? _price[Price::BuildFoundation] : (Money)0);
}
 
/* Validate functions for rail building */
static inline bool ValParamTrackOrientation(Track track)
{
  return IsValidTrack(track);
}

CommandCost CmdBuildSingleRail(DoCommandFlags flags, TileIndex tile, RailType railtype, Track track, bool auto_remove_signals)
{
  CommandCost cost(EXPENSES_CONSTRUCTION);
 
  if (!ValParamRailType(railtype) || !ValParamTrackOrientation(track)) return CMD_ERROR;
 
  Slope tileh = GetTileSlope(tile);
  TrackBits trackbit = TrackToTrackBits(track);
 
  switch (GetTileType(tile)) {
    case TileType::Railway: {
      CommandCost ret = CheckTileOwnership(tile);
      if (ret.Failed()) return ret;
 
      if (!IsPlainRail(tile)) return Command<Commands::LandscapeClear>::Do(flags, tile); // just get appropriate error message
 
      if (!IsCompatibleRail(GetRailType(tile), railtype)) return CommandCost(STR_ERROR_IMPOSSIBLE_TRACK_COMBINATION);
 
      ret = CheckTrackCombination(tile, trackbit);
      if (ret.Succeeded()) ret = EnsureNoTrainOnTrack(tile, track);
      if (ret.Failed()) return ret;
 
      ret = CheckRailSlope(tileh, trackbit, GetTrackBits(tile), tile);
      if (ret.Failed()) return ret;
      cost.AddCost(ret.GetCost());
 
      if (HasSignals(tile) && TracksOverlap(GetTrackBits(tile) | TrackToTrackBits(track))) {
        /* If adding the new track causes any overlap, all signals must be removed first */
        if (!auto_remove_signals) return CommandCost(STR_ERROR_MUST_REMOVE_SIGNALS_FIRST);
 
        for (Track track_it = TRACK_BEGIN; track_it < TRACK_END; track_it++) {
          if (HasTrack(tile, track_it) && HasSignalOnTrack(tile, track_it)) {
            CommandCost ret_remove_signals = Command<Commands::RemoveSignal>::Do(flags, tile, track_it);
            if (ret_remove_signals.Failed()) return ret_remove_signals;
            cost.AddCost(ret_remove_signals.GetCost());
          }
        }
      }
 
      /* 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 = Command<Commands::ConvertRail>::Do(flags, tile, tile, railtype, false);
          if (ret.Failed()) return ret;
          cost.AddCost(ret.GetCost());
        } else {
          return CMD_ERROR;
        }
      }
 
      if (flags.Test(DoCommandFlag::Execute)) {
        SetRailGroundType(tile, RailGroundType::Barren);
        TrackBits bits = GetTrackBits(tile);
        SetTrackBits(tile, bits | trackbit);
        /* 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 TileType::Road: {
      /* Level crossings may only be built on these slopes */
      if (!HasBit(VALID_LEVEL_CROSSING_SLOPES, tileh)) return CommandCost(STR_ERROR_LAND_SLOPED_IN_WRONG_DIRECTION);
 
      if (!_settings_game.construction.crossing_with_competitor && _current_company != OWNER_DEITY) {
        CommandCost ret = CheckTileOwnership(tile);
        if (ret.Failed()) return ret;
      }
 
      CommandCost ret = EnsureNoVehicleOnGround(tile);
      if (ret.Failed()) return ret;
 
      if (IsNormalRoad(tile)) {
        if (HasRoadWorks(tile)) return CommandCost(STR_ERROR_ROAD_WORKS_IN_PROGRESS);
 
        if (GetDisallowedRoadDirections(tile) != DRD_NONE) return CommandCost(STR_ERROR_CROSSING_ON_ONEWAY_ROAD);
 
        if (RailNoLevelCrossings(railtype)) return CommandCost(STR_ERROR_CROSSING_DISALLOWED_RAIL);
 
        RoadType roadtype_road = GetRoadTypeRoad(tile);
        RoadType roadtype_tram = GetRoadTypeTram(tile);
 
        if (roadtype_road != INVALID_ROADTYPE && RoadNoLevelCrossing(roadtype_road)) return CommandCost(STR_ERROR_CROSSING_DISALLOWED_ROAD);
        if (roadtype_tram != INVALID_ROADTYPE && RoadNoLevelCrossing(roadtype_tram)) return CommandCost(STR_ERROR_CROSSING_DISALLOWED_ROAD);
 
        RoadBits road = GetRoadBits(tile, RTT_ROAD);
        RoadBits tram = GetRoadBits(tile, RTT_TRAM);
        if ((track == TRACK_X && ((road | tram) & ROAD_X) == 0) ||
            (track == TRACK_Y && ((road | tram) & ROAD_Y) == 0)) {
          Owner road_owner = GetRoadOwner(tile, RTT_ROAD);
          Owner tram_owner = GetRoadOwner(tile, RTT_TRAM);
          /* Disallow breaking end-of-line of someone else
           * so trams can still reverse on this tile. */
          if (Company::IsValidID(tram_owner) && HasExactlyOneBit(tram)) {
            ret = CheckOwnership(tram_owner);
            if (ret.Failed()) return ret;
          }
 
          uint num_new_road_pieces = (road != ROAD_NONE) ? 2 - CountBits(road) : 0;
          if (num_new_road_pieces > 0) {
            cost.AddCost(num_new_road_pieces * RoadBuildCost(roadtype_road));
          }
 
          uint num_new_tram_pieces = (tram != ROAD_NONE) ? 2 - CountBits(tram) : 0;
          if (num_new_tram_pieces > 0) {
            cost.AddCost(num_new_tram_pieces * RoadBuildCost(roadtype_tram));
          }
 
          if (flags.Test(DoCommandFlag::Execute)) {
            MakeRoadCrossing(tile, road_owner, tram_owner, _current_company, (track == TRACK_X ? AXIS_Y : AXIS_X), railtype, roadtype_road, roadtype_tram, GetTownIndex(tile));
            UpdateLevelCrossing(tile, false);
            MarkDirtyAdjacentLevelCrossingTiles(tile, GetCrossingRoadAxis(tile));
            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) {
        return CommandCost(STR_ERROR_ALREADY_BUILT);
      }
      [[fallthrough]];
    }
 
    default: {
      /* Will there be flat water on the lower halftile? */
      bool water_ground = IsTileType(tile, TileType::Water) && IsSlopeWithOneCornerRaised(tileh);
 
      CommandCost ret = CheckRailSlope(tileh, trackbit, TRACK_BIT_NONE, tile);
      if (ret.Failed()) return ret;
      cost.AddCost(ret.GetCost());
 
      ret = Command<Commands::LandscapeClear>::Do(flags, tile);
      if (ret.Failed()) return ret;
      cost.AddCost(ret.GetCost());
 
      if (water_ground) {
        cost.AddCost(-_price[Price::ClearWater]);
        cost.AddCost(_price[Price::ClearRough]);
      }
 
      if (flags.Test(DoCommandFlag::Execute)) {
        MakeRailNormal(tile, _current_company, trackbit, railtype);
        if (water_ground) {
          SetRailGroundType(tile, RailGroundType::HalfTileWater);
          if (IsPossibleDockingTile(tile)) CheckForDockingTile(tile);
        }
        Company::Get(_current_company)->infrastructure.rail[railtype]++;
        DirtyCompanyInfrastructureWindows(_current_company);
      }
      break;
    }
  }
 
  if (flags.Test(DoCommandFlag::Execute)) {
    MarkTileDirtyByTile(tile);
    AddTrackToSignalBuffer(tile, track, _current_company);
    YapfNotifyTrackLayoutChange(tile, track);
  }
 
  cost.AddCost(RailBuildCost(railtype));
  return cost;
}

CommandCost CmdRemoveSingleRail(DoCommandFlags flags, TileIndex tile, Track track)
{
  CommandCost cost(EXPENSES_CONSTRUCTION);
  bool crossing = false;
 
  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 = nullptr;
 
  switch (GetTileType(tile)) {
    case TileType::Road: {
      if (!IsLevelCrossing(tile) || GetCrossingRailBits(tile) != trackbit) return CommandCost(STR_ERROR_THERE_IS_NO_RAILROAD_TRACK);
 
      if (_current_company != OWNER_WATER) {
        CommandCost ret = CheckTileOwnership(tile);
        if (ret.Failed()) return ret;
      }
 
      if (!flags.Test(DoCommandFlag::Bankrupt)) {
        CommandCost ret = EnsureNoVehicleOnGround(tile);
        if (ret.Failed()) return ret;
      }
 
      cost.AddCost(RailClearCost(GetRailType(tile)));
 
      if (flags.Test(DoCommandFlag::Execute)) {
        UpdateAdjacentLevelCrossingTilesOnLevelCrossingRemoval(tile, GetCrossingRoadAxis(tile));
 
        if (HasReservedTracks(tile, trackbit)) {
          v = GetTrainForReservation(tile, track);
          if (v != nullptr) FreeTrainTrackReservation(v);
        }
 
        owner = GetTileOwner(tile);
        Company::Get(owner)->infrastructure.rail[GetRailType(tile)] -= LEVELCROSSING_TRACKBIT_FACTOR;
        DirtyCompanyInfrastructureWindows(owner);
        MakeRoadNormal(tile, GetCrossingRoadBits(tile), GetRoadTypeRoad(tile), GetRoadTypeTram(tile), GetTownIndex(tile), GetRoadOwner(tile, RTT_ROAD), GetRoadOwner(tile, RTT_TRAM));
        DeleteNewGRFInspectWindow(GSF_RAILTYPES, tile.base());
      }
      break;
    }
 
    case TileType::Railway: {
      TrackBits present;
      /* There are no rails present at depots. */
      if (!IsPlainRail(tile)) return CommandCost(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 CommandCost(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(Command<Commands::RemoveSignal>::Do(flags, tile, track));
      }
 
      if (flags.Test(DoCommandFlag::Execute)) {
        if (HasReservedTracks(tile, trackbit)) {
          v = GetTrainForReservation(tile, track);
          if (v != nullptr) 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) == RailGroundType::HalfTileWater && IsSlopeWithOneCornerRaised(tileh)) {
            bool docking = IsDockingTile(tile);
            MakeShore(tile);
            SetDockingTile(tile, docking);
          } else {
            DoClearSquare(tile);
          }
          DeleteNewGRFInspectWindow(GSF_RAILTYPES, tile.base());
        } else {
          SetTrackBits(tile, present);
          SetTrackReservation(tile, GetRailReservationTrackBits(tile) & present);
        }
      }
      break;
    }
 
    default: return CommandCost(STR_ERROR_THERE_IS_NO_RAILROAD_TRACK);
  }
 
  if (flags.Test(DoCommandFlag::Execute)) {
    /* 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 != nullptr) TryPathReserve(v, true);
  }
 
  return cost;
}
 

bool FloodHalftile(TileIndex t)
{
  assert(IsPlainRailTile(t));
 
  bool flooded = false;
  if (GetRailGroundType(t) == RailGroundType::HalfTileWater) 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 != TRACK_BIT_NONE) {
      Backup<CompanyID> cur_company(_current_company, OWNER_WATER);
      flooded = Command<Commands::RemoveRail>::Do(DoCommandFlag::Execute, t, FindFirstTrack(to_remove)).Succeeded();
      cur_company.Restore();
      if (!flooded) return flooded; // not yet floodable
      rail_bits = rail_bits & ~to_remove;
      if (rail_bits == TRACK_BIT_NONE) {
        MakeShore(t);
        MarkTileDirtyByTile(t);
        return flooded;
      }
    }
 
    if (IsNonContinuousFoundation(GetRailFoundation(tileh, rail_bits))) {
      flooded = true;
      SetRailGroundType(t, RailGroundType::HalfTileWater);
      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, RailGroundType::HalfTileWater);
        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();
}

static CommandCost CmdRailTrackHelper(DoCommandFlags flags, TileIndex tile, TileIndex end_tile, RailType railtype, Track track, bool remove, bool auto_remove_signals, bool fail_on_obstacle)
{
  CommandCost total_cost(EXPENSES_CONSTRUCTION);
 
  if ((!remove && !ValParamRailType(railtype)) || !ValParamTrackOrientation(track)) return CMD_ERROR;
  if (end_tile >= Map::Size() || tile >= Map::Size()) return CMD_ERROR;
 
  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 (;;) {
    ret = remove ? Command<Commands::RemoveRail>::Do(flags, tile, TrackdirToTrack(trackdir)) : Command<Commands::BuildRail>::Do(flags, tile, railtype, TrackdirToTrack(trackdir), auto_remove_signals);
    if (!remove && !fail_on_obstacle && last_error.GetErrorMessage() == STR_ERROR_ALREADY_BUILT) had_success = true;
 
    if (ret.Failed()) {
      last_error = std::move(ret);
      if (last_error.GetErrorMessage() != STR_ERROR_ALREADY_BUILT && !remove) {
        if (fail_on_obstacle) return last_error;
        if (had_success) break; // Keep going if we haven't constructed any rail yet, skipping the start of the drag
      }
 
      /* Ownership errors are more important. */
      if (last_error.GetErrorMessage() == STR_ERROR_OWNED_BY && remove) break;
    } else {
      had_success = true;
      total_cost.AddCost(ret.GetCost());
    }
 
    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;
}

CommandCost CmdBuildRailroadTrack(DoCommandFlags flags, TileIndex end_tile, TileIndex start_tile, RailType railtype, Track track, bool auto_remove_signals, bool fail_on_obstacle)
{
  return CmdRailTrackHelper(flags, start_tile, end_tile, railtype, track, false, auto_remove_signals, fail_on_obstacle);
}

CommandCost CmdRemoveRailroadTrack(DoCommandFlags flags, TileIndex end_tile, TileIndex start_tile, Track track)
{
  return CmdRailTrackHelper(flags, start_tile, end_tile, INVALID_RAILTYPE, track, true, false, false);
}

CommandCost CmdBuildTrainDepot(DoCommandFlags flags, TileIndex tile, RailType railtype, DiagDirection dir)
{
  /* check railtype and valid direction for depot (0 through 3), 4 in total */
  if (!ValParamRailType(railtype) || !IsValidDiagDirection(dir)) return CMD_ERROR;
 
  Slope tileh = GetTileSlope(tile);
 
  CommandCost cost(EXPENSES_CONSTRUCTION);
 
  /* 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) {
    if (!_settings_game.construction.build_on_slopes || !CanBuildDepotByTileh(dir, tileh)) {
      return CommandCost(STR_ERROR_FLAT_LAND_REQUIRED);
    }
    cost.AddCost(_price[Price::BuildFoundation]);
  }
 
  /* Allow the user to rotate the depot instead of having to destroy it and build it again */
  bool rotate_existing_depot = false;
  if (IsRailDepotTile(tile) && railtype == GetRailType(tile)) {
    CommandCost ret = CheckTileOwnership(tile);
    if (ret.Failed()) return ret;
 
    if (dir == GetRailDepotDirection(tile)) return CommandCost();
 
    ret = EnsureNoVehicleOnGround(tile);
    if (ret.Failed()) return ret;
 
    rotate_existing_depot = true;
  }
 
  if (!rotate_existing_depot) {
    cost.AddCost(Command<Commands::LandscapeClear>::Do(flags, tile));
    if (cost.Failed()) return cost;
 
    if (IsBridgeAbove(tile)) return CommandCost(STR_ERROR_MUST_DEMOLISH_BRIDGE_FIRST);
 
    if (!Depot::CanAllocateItem()) return CMD_ERROR;
  }
 
  if (flags.Test(DoCommandFlag::Execute)) {
    if (rotate_existing_depot) {
      SetRailDepotExitDirection(tile, dir);
    } else {
      Depot *d = Depot::Create(tile);
 
      MakeRailDepot(tile, _current_company, d->index, dir, railtype);
      MakeDefaultName(d);
 
      Company::Get(_current_company)->infrastructure.rail[railtype]++;
      DirtyCompanyInfrastructureWindows(_current_company);
    }
 
    MarkTileDirtyByTile(tile);
    AddSideToSignalBuffer(tile, INVALID_DIAGDIR, _current_company);
    YapfNotifyTrackLayoutChange(tile, DiagDirToDiagTrack(dir));
  }
 
  cost.AddCost(_price[Price::BuildDepotTrain]);
  cost.AddCost(RailBuildCost(railtype));
  return cost;
}

CommandCost CmdBuildSingleSignal(DoCommandFlags flags, TileIndex tile, Track track, SignalType sigtype, SignalVariant sigvar, bool convert_signal, bool skip_existing_signals, bool ctrl_pressed, SignalType cycle_start, SignalType cycle_stop, uint8_t num_dir_cycle, uint8_t signals_copy)
{
  if (sigtype > SIGTYPE_LAST || sigvar > SIG_SEMAPHORE) return CMD_ERROR;
  if (cycle_start > cycle_stop || cycle_stop > SIGTYPE_LAST) return CMD_ERROR;
 
  if (ctrl_pressed) sigvar = (SignalVariant)(sigvar ^ SIG_SEMAPHORE);
 
  /* You can only build signals on plain rail tiles, and the selected track must exist */
  if (!ValParamTrackOrientation(track) || !IsPlainRailTile(tile) ||
      !HasTrack(tile, track)) {
    return CommandCost(STR_ERROR_THERE_IS_NO_RAILROAD_TRACK);
  }
  /* Protect against invalid signal copying */
  if (signals_copy != 0 && (signals_copy & SignalOnTrack(track)) == 0) return CMD_ERROR;
 
  CommandCost ret = CheckTileOwnership(tile);
  if (ret.Failed()) return ret;
 
  /* See if this is a valid track combination for signals (no overlap) */
  if (TracksOverlap(GetTrackBits(tile))) return CommandCost(STR_ERROR_NO_SUITABLE_RAILROAD_TRACK);
 
  /* In case we don't want to change an existing signal, return without error. */
  if (skip_existing_signals && HasSignalOnTrack(tile, track)) return CommandCost();
 
  /* you can not convert a signal if no signal is on track */
  if (convert_signal && !HasSignalOnTrack(tile, track)) return CommandCost(STR_ERROR_THERE_ARE_NO_SIGNALS);
 
  CommandCost cost;
  if (!HasSignalOnTrack(tile, track)) {
    /* build new signals */
    cost = CommandCost(EXPENSES_CONSTRUCTION, _price[Price::BuildSignals]);
  } else {
    if (signals_copy != 0 && sigvar != GetSignalVariant(tile, track)) {
      /* convert signals <-> semaphores */
      cost = CommandCost(EXPENSES_CONSTRUCTION, _price[Price::BuildSignals] + _price[Price::ClearSignals]);
 
    } else if (convert_signal) {
      /* convert button pressed */
      if (ctrl_pressed || GetSignalVariant(tile, track) != sigvar) {
        /* it costs money to change signal variant (light or semaphore) */
        cost = CommandCost(EXPENSES_CONSTRUCTION, _price[Price::BuildSignals] + _price[Price::ClearSignals]);
      } else {
        /* it is free to change signal type (block, exit, entry, combo, path, etc) */
        cost = CommandCost();
      }
 
    } else {
      /* it is free to change orientation or number of signals on the tile (for block/presignals which allow signals in both directions) */
      cost = CommandCost();
    }
  }
 
  if (flags.Test(DoCommandFlag::Execute)) {
    Train *v = nullptr;
    /* 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 != nullptr) 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 (signals_copy == 0) {
      if (!HasSignalOnTrack(tile, track)) {
        /* build new signals */
        SetPresentSignals(tile, GetPresentSignals(tile) | (IsPbsSignal(sigtype) ? KillFirstBit(SignalOnTrack(track)) : SignalOnTrack(track)));
        SetSignalType(tile, track, sigtype);
        SetSignalVariant(tile, track, sigvar);
        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 */
            SetSignalType(tile, track, sigtype);
            SetSignalVariant(tile, track, sigvar);
            if (IsPbsSignal(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;
 
          SetSignalType(tile, track, sigtype);
          if (IsPbsSignal(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)) | (signals_copy & SignalOnTrack(track)));
      SetSignalVariant(tile, track, sigvar);
      SetSignalType(tile, track, sigtype);
    }
 
    /* 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);
    AddTrackToSignalBuffer(tile, track, _current_company);
    YapfNotifyTrackLayoutChange(tile, track);
    if (v != nullptr && v->track != TRACK_BIT_DEPOT) {
      /* Extend the train's path if it's not stopped or loading, or not at a safe position. */
      if (!((v->vehstatus.Test(VehState::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 AdvanceSignalAutoFill(TileIndex &tile, Trackdir &trackdir, bool remove)
{
  /* We only process starting tiles of tunnels or bridges so jump to the other end before moving further. */
  if (IsTileType(tile, TileType::TunnelBridge)) tile = GetOtherTunnelBridgeEnd(tile);
 
  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 TileType::Railway:
      if (IsRailDepot(tile)) return false;
      if (!remove && HasSignalOnTrack(tile, TrackdirToTrack(trackdir))) return false;
      break;
 
    case TileType::Road:
      if (!IsLevelCrossing(tile)) return false;
      break;
 
    case TileType::TunnelBridge: {
      if (GetTunnelBridgeTransportType(tile) != TRANSPORT_RAIL) return false;
      if (GetTunnelBridgeDirection(tile) != TrackdirToExitdir(trackdir)) return false;
      break;
    }
 
    default: return false;
  }
  return true;
}

static CommandCost CmdSignalTrackHelper(DoCommandFlags flags, TileIndex tile, TileIndex end_tile, Track track, SignalType sigtype, SignalVariant sigvar, bool mode, bool remove, bool autofill, bool minimise_gaps, int signal_density)
{
  CommandCost total_cost(EXPENSES_CONSTRUCTION);
 
  if (end_tile >= Map::Size() || !ValParamTrackOrientation(track)) return CMD_ERROR;
  if (signal_density == 0 || signal_density > 20) return CMD_ERROR;
  if (!remove && (sigtype > SIGTYPE_LAST || sigvar > SIG_SEMAPHORE)) return CMD_ERROR;
 
  if (!IsPlainRailTile(tile)) return CommandCost(STR_ERROR_THERE_IS_NO_RAILROAD_TRACK);
  TileIndex start_tile = tile;
 
  /* Interpret signal_density as the logical length of said amount of tiles in X/Y direction. */
  signal_density *= TILE_AXIAL_DISTANCE;
 
  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;
 
  uint8_t 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) */
    sigvar = GetSignalVariant(tile, track);
 
    sigtype = GetSignalType(tile, track);
    /* Don't but copy entry or exit-signal type */
    if (sigtype == SIGTYPE_ENTRY || sigtype == SIGTYPE_EXIT) sigtype = SIGTYPE_BLOCK;
  } else { // no signals exist, drag a two-way signal stretch
    signals = IsPbsSignal(sigtype) ? SignalAlongTrackdir(trackdir) : SignalOnTrack(track);
  }
 
  uint8_t 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 = -signal_density; // to force signal at 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;
  auto build_signal = [&](TileIndex tile, Trackdir trackdir, bool test_only) {
    /* Pick the correct orientation for the track direction */
    uint8_t signals = 0;
    if (HasBit(signal_dir, 0)) signals |= SignalAlongTrackdir(trackdir);
    if (HasBit(signal_dir, 1)) signals |= SignalAgainstTrackdir(trackdir);
 
    DoCommandFlags do_flags = test_only ? DoCommandFlags{flags}.Reset(DoCommandFlag::Execute) : flags;
    CommandCost ret = remove ? Command<Commands::RemoveSignal>::Do(do_flags, tile, TrackdirToTrack(trackdir)) : Command<Commands::BuildSignal>::Do(do_flags, tile, TrackdirToTrack(trackdir), sigtype, sigvar, false, signal_ctr == 0, mode, SIGTYPE_BLOCK, SIGTYPE_BLOCK, 0, signals);
 
    if (test_only) return ret.Succeeded();
 
    if (ret.Succeeded()) {
      had_success = true;
      total_cost.AddCost(ret.GetCost());
    } 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;
      }
    }
    return ret.Succeeded();
  };
 
  for (;;) {
    if (remove) {
      /* In remove mode last_* stuff doesn't matter, we simply try to clear every tile. */
      build_signal(tile, trackdir, false);
    } else if (minimise_gaps) {
      /* We're trying to minimize gaps wherever possible, so keep track of last suitable
       * position and use it if current gap exceeds required signal density. */
 
      if (signal_ctr > last_used_ctr + signal_density && last_suitable_tile != INVALID_TILE) {
        /* We overshot so build a signal in last good location. */
        if (build_signal(last_suitable_tile, last_suitable_trackdir, false)) {
          last_suitable_tile = INVALID_TILE;
          last_used_ctr = last_suitable_ctr;
        }
      }
 
      if (signal_ctr == last_used_ctr + signal_density) {
        /* Current gap matches the required density, build a signal.  */
        if (build_signal(tile, trackdir, false)) {
          last_used_ctr = signal_ctr;
          last_suitable_tile = INVALID_TILE;
        }
      } else {
        /* Test tile for a potential signal spot. */
        if (build_signal(tile, trackdir, true)) {
          last_suitable_tile = tile;
          last_suitable_ctr = signal_ctr;
          last_suitable_trackdir = trackdir;
        }
      }
    } else if (signal_ctr >= last_used_ctr + signal_density) {
      /* We're always keeping regular interval between signals so doesn't matter whether we succeed or not. */
      build_signal(tile, trackdir, false);
      last_used_ctr = signal_ctr;
    }
 
    if (autofill) {
      switch (GetTileType(tile)) {
        case TileType::Railway:
          signal_ctr += (IsDiagonalTrackdir(trackdir) ? TILE_AXIAL_DISTANCE : TILE_CORNER_DISTANCE);
          break;
 
        case TileType::Road:
          signal_ctr += TILE_AXIAL_DISTANCE;
          break;
 
        case TileType::TunnelBridge: {
          uint len = (GetTunnelBridgeLength(tile, GetOtherTunnelBridgeEnd(tile)) + 2) * TILE_AXIAL_DISTANCE;
          if (remove || minimise_gaps) {
            signal_ctr += len;
          } else {
            /* To keep regular interval we need to emulate placing signals on a bridge.
             * We start with TILE_AXIAL_DISTANCE as one bridge tile gets processed in the main loop. */
            signal_ctr += TILE_AXIAL_DISTANCE;
            for (uint i = TILE_AXIAL_DISTANCE; i < len; i += TILE_AXIAL_DISTANCE) {
              if (signal_ctr >= last_used_ctr + signal_density) last_used_ctr = signal_ctr;
              signal_ctr += TILE_AXIAL_DISTANCE;
            }
          }
          break;
        }
 
        default: break;
      }
 
      if (!AdvanceSignalAutoFill(tile, trackdir, remove)) break;
 
      /* Prevent possible loops */
      if (tile == start_tile && trackdir == start_trackdir) break;
    } else {
      if (tile == end_tile) break;
 
      signal_ctr += (IsDiagonalTrackdir(trackdir) ? TILE_AXIAL_DISTANCE : TILE_CORNER_DISTANCE);
      /* toggle railbit for the non-diagonal tracks (|, -- tracks) */
 
      tile += ToTileIndexDiff(_trackdelta[trackdir]);
      if (!IsDiagonalTrackdir(trackdir)) ToggleBit(trackdir, 0);
    }
  }
 
  /* We may end up with the current gap exceeding the signal density so fix that if needed. */
  if (!remove && minimise_gaps && signal_ctr > last_used_ctr + signal_density && last_suitable_tile != INVALID_TILE) {
    build_signal(last_suitable_tile, last_suitable_trackdir, false);
  }
 
  return had_success ? total_cost : last_error;
}

CommandCost CmdBuildSignalTrack(DoCommandFlags flags, TileIndex tile, TileIndex end_tile, Track track, SignalType sigtype, SignalVariant sigvar, bool mode, bool autofill, bool minimise_gaps, uint8_t signal_density)
{
  return CmdSignalTrackHelper(flags, tile, end_tile, track, sigtype, sigvar, mode, false, autofill, minimise_gaps, signal_density);
}

CommandCost CmdRemoveSingleSignal(DoCommandFlags flags, TileIndex tile, Track track)
{
  if (!ValParamTrackOrientation(track) || !IsPlainRailTile(tile) || !HasTrack(tile, track)) {
    return CommandCost(STR_ERROR_THERE_IS_NO_RAILROAD_TRACK);
  }
  if (!HasSignalOnTrack(tile, track)) {
    return CommandCost(STR_ERROR_THERE_ARE_NO_SIGNALS);
  }
 
  /* Only water can remove signals from anyone */
  if (_current_company != OWNER_WATER) {
    CommandCost ret = CheckTileOwnership(tile);
    if (ret.Failed()) return ret;
  }
 
  /* Do it? */
  if (flags.Test(DoCommandFlag::Execute)) {
    Train *v = nullptr;
    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 == nullptr && 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));
        }
      }
    }
    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));
 
    /* 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 != nullptr) TryPathReserve(v, false);
 
    MarkTileDirtyByTile(tile);
  }
 
  return CommandCost(EXPENSES_CONSTRUCTION, _price[Price::ClearSignals]);
}

CommandCost CmdRemoveSignalTrack(DoCommandFlags flags, TileIndex tile, TileIndex end_tile, Track track, bool autofill)
{
  return CmdSignalTrackHelper(flags, tile, end_tile, track, SIGTYPE_BLOCK, SIG_ELECTRIC, false, true, autofill, false, 1); // bit 5 is remove bit
}

CommandCost CmdConvertRail(DoCommandFlags flags, TileIndex tile, TileIndex area_start, RailType totype, bool diagonal)
{
  TileIndex area_end = tile;
 
  if (!ValParamRailType(totype)) return CMD_ERROR;
  if (area_start >= Map::Size()) 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.
  bool found_convertible_track = false; // whether we actually did convert some track (see bug #7633)
 
  std::unique_ptr<TileIterator> iter = TileIterator::Create(area_start, area_end, diagonal);
  for (; (tile = *iter) != INVALID_TILE; ++(*iter)) {
    TileType tt = GetTileType(tile);
 
    /* Check if there is any track on tile */
    switch (tt) {
      case TileType::Railway:
        break;
      case TileType::Station:
        if (!HasStationRail(tile)) continue;
        break;
      case TileType::Road:
        if (!IsLevelCrossing(tile)) continue;
        if (RailNoLevelCrossings(totype)) {
          error.MakeError(STR_ERROR_CROSSING_DISALLOWED_RAIL);
          continue;
        }
        break;
      case TileType::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 = std::move(ret);
      continue;
    }
 
    std::vector<Train *> vehicles_affected;
 
    /* Vehicle on the tile when not converting Rail <-> ElRail
     * Tunnels and bridges have special check later */
    if (tt != TileType::TunnelBridge) {
      if (!IsCompatibleRail(type, totype)) {
        ret = IsPlainRailTile(tile) ? EnsureNoTrainOnTrackBits(tile, GetTrackBits(tile)) : EnsureNoVehicleOnGround(tile);
        if (ret.Failed()) {
          error = std::move(ret);
          continue;
        }
      }
      if (flags.Test(DoCommandFlag::Execute)) { // we can safely convert, too
        TrackBits reserved = GetReservedTrackbits(tile);
        Track     track;
        while ((track = RemoveFirstTrack(&reserved)) != INVALID_TRACK) {
          Train *v = GetTrainForReservation(tile, track);
          if (v != nullptr && !HasPowerOnRail(v->railtypes, totype)) {
            /* No power on new rail type, reroute. */
            FreeTrainTrackReservation(v);
            vehicles_affected.push_back(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);
        /* update power of train on this tile */
        for (Vehicle *v : VehiclesOnTile(tile)) {
          if (v->type == VEH_TRAIN) include(affected_trains, Train::From(v)->First());
        }
      }
    }
 
    switch (tt) {
      default: NOT_REACHED();
      case TileType::Railway:
        switch (GetRailTileType(tile)) {
          case RailTileType::Depot:
            if (flags.Test(DoCommandFlag::Execute)) {
              /* 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);
            }
            found_convertible_track = true;
            cost.AddCost(RailConvertCost(type, totype));
            break;
 
          default: // RailTileType::Normal, RailTileType::Signals
            if (flags.Test(DoCommandFlag::Execute)) {
              /* notify YAPF about the track layout change */
              TrackBits tracks = GetTrackBits(tile);
              while (tracks != TRACK_BIT_NONE) {
                YapfNotifyTrackLayoutChange(tile, RemoveFirstTrack(&tracks));
              }
            }
            found_convertible_track = true;
            cost.AddCost(RailConvertCost(type, totype) * CountBits(GetTrackBits(tile)));
            break;
        }
        break;
 
      case TileType::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)) {
          ret = TunnelBridgeIsFree(tile, endtile);
          if (ret.Failed()) {
            error = std::move(ret);
            continue;
          }
        }
 
        if (flags.Test(DoCommandFlag::Execute)) {
          Track track = DiagDirToDiagTrack(GetTunnelBridgeDirection(tile));
          if (HasTunnelBridgeReservation(tile)) {
            Train *v = GetTrainForReservation(tile, track);
            if (v != nullptr && !HasPowerOnRail(v->railtypes, totype)) {
              /* No power on new rail type, reroute. */
              FreeTrainTrackReservation(v);
              vehicles_affected.push_back(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);
 
          for (Vehicle *v : VehiclesOnTile(tile)) {
            if (v->type == VEH_TRAIN) include(affected_trains, Train::From(v)->First());
          }
          for (Vehicle *v : VehiclesOnTile(endtile)) {
            if (v->type == VEH_TRAIN) include(affected_trains, Train::From(v)->First());
          }
 
          YapfNotifyTrackLayoutChange(tile, track);
          YapfNotifyTrackLayoutChange(endtile, track);
 
          if (IsBridge(tile)) {
            MarkBridgeDirty(tile);
          } else {
            MarkTileDirtyByTile(tile);
            MarkTileDirtyByTile(endtile);
          }
        }
 
        found_convertible_track = true;
        cost.AddCost((GetTunnelBridgeLength(tile, endtile) + 2) * RailConvertCost(type, totype));
        break;
      }
 
      case TileType::Station:
      case TileType::Road:
        if (flags.Test(DoCommandFlag::Execute)) {
          Track track = ((tt == TileType::Station) ? GetRailStationTrack(tile) : GetCrossingRailTrack(tile));
          YapfNotifyTrackLayoutChange(tile, track);
        }
 
        found_convertible_track = true;
        cost.AddCost(RailConvertCost(type, totype));
        break;
    }
 
    for (uint i = 0; i < vehicles_affected.size(); ++i) {
      TryPathReserve(vehicles_affected[i], true);
    }
  }
 
  if (flags.Test(DoCommandFlag::Execute)) {
    /* Railtype changed, update trains as when entering different track */
    for (Train *v : affected_trains) {
      v->ConsistChanged(CCF_TRACK);
    }
  }
 
  return found_convertible_track ? cost : error;
}
 
static CommandCost RemoveTrainDepot(TileIndex tile, DoCommandFlags 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.Test(DoCommandFlag::Execute)) {
    /* read variables before the depot is removed */
    DiagDirection dir = GetRailDepotDirection(tile);
    Owner owner = GetTileOwner(tile);
    Train *v = nullptr;
 
    if (HasDepotReservation(tile)) {
      v = GetTrainForReservation(tile, DiagDirToDiagTrack(dir));
      if (v != nullptr) 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 != nullptr) TryPathReserve(v, true);
  }
 
  return CommandCost(EXPENSES_CONSTRUCTION, _price[Price::ClearDepotTrain]);
}
 
static CommandCost ClearTile_Track(TileIndex tile, DoCommandFlags flags)
{
  CommandCost cost(EXPENSES_CONSTRUCTION);
 
  if (flags.Test(DoCommandFlag::Auto)) {
    if (!IsTileOwner(tile, _current_company)) {
      return CommandCost(STR_ERROR_AREA_IS_OWNED_BY_ANOTHER);
    }
 
    if (IsPlainRail(tile)) {
      return CommandCost(STR_ERROR_MUST_REMOVE_RAILROAD_TRACK);
    } else {
      return CommandCost(STR_ERROR_BUILDING_MUST_BE_DEMOLISHED);
    }
  }
 
  switch (GetRailTileType(tile)) {
    case RailTileType::Signals:
    case RailTileType::Normal: {
      Slope tileh = GetTileSlope(tile);
      /* Is there flat water on the lower halftile that gets cleared expensively? */
      bool water_ground = (GetRailGroundType(tile) == RailGroundType::HalfTileWater && IsSlopeWithOneCornerRaised(tileh));
 
      TrackBits tracks = GetTrackBits(tile);
      while (tracks != TRACK_BIT_NONE) {
        Track track = RemoveFirstTrack(&tracks);
        CommandCost ret = Command<Commands::RemoveRail>::Do(flags, tile, track);
        if (ret.Failed()) return ret;
        cost.AddCost(ret.GetCost());
      }
 
      /* 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.Test(DoCommandFlag::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.Test(DoCommandFlag::Execute)) {
          DoClearSquare(tile);
        }
        cost.AddCost(_price[Price::ClearWater]);
      }
 
      return cost;
    }
 
    case RailTileType::Depot:
      return RemoveTrainDepot(tile, flags);
 
    default:
      return CMD_ERROR;
  }
}

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);
  if (sprite != 0) {
    sprite += image;
  } else {
    /* Normal electric signals are stored in a different sprite block than all other signals. */
    sprite = (type == SIGTYPE_BLOCK && 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, GetSaveSlopeZ(x, y, track), {{}, {1, 1, BB_HEIGHT_UNDER_BRIDGE}, {}});
}

struct FenceOffset : SpriteBounds {
  Corner height_ref; 
 
  constexpr FenceOffset(Corner height_ref, int8_t origin_x, int8_t origin_y, uint8_t extent_x, uint8_t extent_y) :
    SpriteBounds({origin_x, origin_y, 0}, {extent_x, extent_y, 4}, {}), height_ref(height_ref) {}
};

static const 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
};

static void DrawTrackFence(const TileInfo *ti, const PalSpriteID &psid, 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(psid.sprite + (rfo % num_sprites), psid.pal, ti->x, ti->y, z, _fence_offsets[rfo]);
}

static void DrawTrackFence_NW(const TileInfo *ti, const PalSpriteID &psid, 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, psid, num_sprites, rfo);
}

static void DrawTrackFence_SE(const TileInfo *ti, const PalSpriteID &psid, 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, psid, num_sprites, rfo);
}

static void DrawTrackFence_NE(const TileInfo *ti, const PalSpriteID &psid, 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, psid, num_sprites, rfo);
}

static void DrawTrackFence_SW(const TileInfo *ti, const PalSpriteID &psid, 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, psid, num_sprites, rfo);
}

static void DrawTrackDetails(const TileInfo *ti, const RailTypeInfo *rti, PaletteID pal)
{
  /* Base sprite for track fences.
   * Note: Halftile slopes only have fences on the upper part. */
  uint num_sprites = 0;
  PalSpriteID psid{
    .sprite = GetCustomRailSprite(rti, ti->tile, RTSG_FENCES, IsHalftileSlope(ti->tileh) ? TCX_UPPER_HALFTILE : TCX_NORMAL, &num_sprites),
    .pal = pal,
  };
  if (psid.sprite == 0) {
    psid.sprite = SPR_TRACK_FENCE_FLAT_X;
    num_sprites = 8;
  }
 
  assert(num_sprites > 0);
 
  switch (GetRailGroundType(ti->tile)) {
    case RailGroundType::FenceNW:     DrawTrackFence_NW(ti, psid, num_sprites); break;
    case RailGroundType::FenceSE:     DrawTrackFence_SE(ti, psid, num_sprites); break;
    case RailGroundType::FenceSENW:   DrawTrackFence_NW(ti, psid, num_sprites);
                                      DrawTrackFence_SE(ti, psid, num_sprites); break;
    case RailGroundType::FenceNE:     DrawTrackFence_NE(ti, psid, num_sprites); break;
    case RailGroundType::FenceSW:     DrawTrackFence_SW(ti, psid, num_sprites); break;
    case RailGroundType::FenceNESW:   DrawTrackFence_NE(ti, psid, num_sprites);
                                      DrawTrackFence_SW(ti, psid, num_sprites); break;
    case RailGroundType::FenceVert1:  DrawTrackFence(ti, psid, num_sprites, RFO_FLAT_LEFT);  break;
    case RailGroundType::FenceVert2:  DrawTrackFence(ti, psid, num_sprites, RFO_FLAT_RIGHT); break;
    case RailGroundType::FenceHoriz1: DrawTrackFence(ti, psid, num_sprites, RFO_FLAT_UPPER); break;
    case RailGroundType::FenceHoriz2: DrawTrackFence(ti, psid, num_sprites, RFO_FLAT_LOWER); break;
    case RailGroundType::HalfTileWater: {
      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, psid, num_sprites, RFO_FLAT_LEFT);  break;
        case CORNER_S: DrawTrackFence(ti, psid, num_sprites, RFO_FLAT_LOWER); break;
        case CORNER_E: DrawTrackFence(ti, psid, num_sprites, RFO_FLAT_RIGHT); break;
        case CORNER_N: DrawTrackFence(ti, psid, 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, nullptr, 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 == RailGroundType::HalfTileWater) {
    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 RailGroundType::Barren: image = SPR_FLAT_BARE_LAND; break;
      case RailGroundType::SnowOrDesert: image = SPR_FLAT_SNOW_DESERT_TILE; break;
      default: image = SPR_FLAT_GRASS_TILE; break;
    }
 
    image += SlopeToSpriteOffset(ti->tileh);
 
    DrawGroundSprite(image, PAL_NONE);
  }
 
  bool no_combine = ti->tileh == SLOPE_FLAT && rti->flags.Test(RailTypeFlag::NoSpriteCombine);
  SpriteID overlay = GetCustomRailSprite(rti, ti->tile, RTSG_OVERLAY);
  SpriteID ground = GetCustomRailSprite(rti, ti->tile, no_combine ? RTSG_GROUND_COMPLETE : 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 (no_combine) {
    /* Use trackbits as direct index from ground sprite, subtract 1
     * because there is no sprite for no bits. */
    DrawGroundSprite(ground + track - 1, 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);
  } 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 RailGroundType::Barren: image = SPR_FLAT_BARE_LAND; break;
      case RailGroundType::SnowOrDesert:
      case RailGroundType::HalfTileSnow: 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);
    }
  }
}

static int GetJunctionGroundSpriteOffset(TrackBits track)
{
  /* If none of the tracks end up in the NE corner, return the ground sprite
   * where the NE of the tile is not covered. Repeat for the other directions.
   * What remains are junctions where all directions are covered. */
  if ((track & TRACK_BIT_3WAY_NE) == 0) return 0;
  if ((track & TRACK_BIT_3WAY_SW) == 0) return 1;
  if ((track & TRACK_BIT_3WAY_NW) == 0) return 2;
  if ((track & TRACK_BIT_3WAY_SE) == 0) return 3;
  return 4;
}

static void DrawTrackBits(TileInfo *ti, TrackBits track)
{
  const RailTypeInfo *rti = GetRailTypeInfo(GetRailType(ti->tile));
 
  if (rti->UsesOverlay()) {
    DrawTrackBitsOverlay(ti, track, rti);
    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 = nullptr;
  bool junction = false;
 
  /* Select the sprite to use. */
  if (track == 0) {
    /* Clear ground (only track on halftile foundation) */
    if (rgt == RailGroundType::HalfTileWater) {
      if (IsSteepSlope(ti->tileh)) {
        DrawShoreTile(ti->tileh);
        image = 0;
      } else {
        image = SPR_FLAT_WATER_TILE;
      }
    } else {
      switch (rgt) {
        case RailGroundType::Barren: image = SPR_FLAT_BARE_LAND; break;
        case RailGroundType::SnowOrDesert: 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 */
      switch (track) {
        /* single track, select combined track + ground sprite*/
        case TRACK_BIT_Y:     image = rti->base_sprites.track_y;     break;
        case TRACK_BIT_X:     image = rti->base_sprites.track_y + 1; break;
        case TRACK_BIT_UPPER: image = rti->base_sprites.track_y + 2; break;
        case TRACK_BIT_LOWER: image = rti->base_sprites.track_y + 3; break;
        case TRACK_BIT_RIGHT: image = rti->base_sprites.track_y + 4; break;
        case TRACK_BIT_LEFT:  image = rti->base_sprites.track_y + 5; break;
        case TRACK_BIT_CROSS: image = rti->base_sprites.track_y + 6; break;
 
        /* double diagonal track, select combined track + ground sprite*/
        case TRACK_BIT_HORZ:  image = rti->base_sprites.track_ns;     break;
        case TRACK_BIT_VERT:  image = rti->base_sprites.track_ns + 1; break;
 
        /* junction, select only ground sprite, handle track sprite later */
        default:
          junction = true;
          image = rti->base_sprites.ground + GetJunctionGroundSpriteOffset(track);
          break;
      }
    }
 
    switch (rgt) {
      case RailGroundType::Barren: pal = PALETTE_TO_BARE_LAND; break;
      case RailGroundType::SnowOrDesert: image += rti->snow_offset; break;
      case RailGroundType::HalfTileWater: {
        /* 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, nullptr, 0, ti->tileh & SLOPE_N ? -(int)TILE_HEIGHT : 0);
    if (pbs & TRACK_BIT_LOWER) DrawGroundSprite(rti->base_sprites.single_s, PALETTE_CRASH, nullptr, 0, ti->tileh & SLOPE_S ? -(int)TILE_HEIGHT : 0);
    if (pbs & TRACK_BIT_LEFT)  DrawGroundSprite(rti->base_sprites.single_w, PALETTE_CRASH, nullptr, 0, ti->tileh & SLOPE_W ? -(int)TILE_HEIGHT : 0);
    if (pbs & TRACK_BIT_RIGHT) DrawGroundSprite(rti->base_sprites.single_e, PALETTE_CRASH, nullptr, 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 RailGroundType::Barren: pal = PALETTE_TO_BARE_LAND; break;
      case RailGroundType::SnowOrDesert:
      case RailGroundType::HalfTileSnow: 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 uint8_t _corner_to_track_sprite[] = {3, 1, 2, 0};
      DrawGroundSprite(_corner_to_track_sprite[halftile_corner] + rti->base_sprites.single_n, PALETTE_CRASH, nullptr, 0, -(int)TILE_HEIGHT);
    }
  }
}
 
static void DrawSignals(TileIndex tile, TrackBits rails, const RailTypeInfo *rti)
{
  auto MAYBE_DRAW_SIGNAL = [&](uint8_t signalbit, SignalOffsets image, uint pos, Track track) {
    if (IsSignalPresent(tile, signalbit)) DrawSingleSignal(tile, rti, track, GetSingleSignalState(tile, signalbit), image, pos);
  };
 
  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));
  BridgePillarFlags blocked_pillars{};
  PaletteID pal = GetCompanyPalette(GetTileOwner(ti->tile));
 
  if (IsPlainRail(ti->tile)) {
    TrackBits rails = GetTrackBits(ti->tile);
 
    DrawTrackBits(ti, rails);
 
    if (HasBit(_display_opt, DO_FULL_DETAIL)) DrawTrackDetails(ti, rti, pal);
 
    if (HasRailCatenaryDrawn(GetRailType(ti->tile))) DrawRailCatenary(ti);
 
    if (HasSignals(ti->tile)) DrawSignals(ti->tile, rails, rti);
 
    if (IsBridgeAbove(ti->tile)) {
      if ((rails & TRACK_BIT_3WAY_NE) != 0) blocked_pillars.Set(BridgePillarFlag::EdgeNE);
      if ((rails & TRACK_BIT_3WAY_SE) != 0) blocked_pillars.Set(BridgePillarFlag::EdgeSE);
      if ((rails & TRACK_BIT_3WAY_SW) != 0) blocked_pillars.Set(BridgePillarFlag::EdgeSW);
      if ((rails & TRACK_BIT_3WAY_NW) != 0) blocked_pillars.Set(BridgePillarFlag::EdgeNW);
    }
  } else {
    /* draw depot */
    const DrawTileSprites *dts;
    DiagDirection dir = GetRailDepotDirection(ti->tile);
 
    if (ti->tileh != SLOPE_FLAT) DrawFoundation(ti, FOUNDATION_LEVELED);
 
    if (IsInvisibilitySet(TO_BUILDINGS)) {
      /* Draw rail instead of depot */
      dts = &_depot_invisible_gfx_table[dir];
    } else {
      dts = &_depot_gfx_table[dir];
    }
 
    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 and snow. */
    if (IsSnowRailGround(ti->tile)) {
      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_NONE, pal));
 
    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);
    int relocation = depot_sprite != 0 ? depot_sprite - SPR_RAIL_DEPOT_SE_1 : rti->GetRailtypeSpriteOffset();
 
    if (HasRailCatenaryDrawn(GetRailType(ti->tile))) DrawRailCatenary(ti);
 
    DrawRailTileSeq(ti, dts, TO_BUILDINGS, relocation, 0, pal);
    /* Depots can't have bridges above so no blocked pillars. */
  }
  DrawBridgeMiddle(ti, blocked_pillars);
}
 
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_t offset = rti->GetRailtypeSpriteOffset();
 
  if (image != SPR_FLAT_GRASS_TILE) image += offset;
  PaletteID palette = GetCompanyPalette(_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, bool)
{
  if (IsPlainRail(tile)) {
    auto [tileh, z] = GetTilePixelSlope(tile);
    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);
}
 
static void TileLoop_Track(TileIndex tile)
{
  RailGroundType old_ground = GetRailGroundType(tile);
  RailGroundType new_ground;
 
  if (old_ground == RailGroundType::HalfTileWater) {
    TileLoop_Water(tile);
    return;
  }
 
  switch (_settings_game.game_creation.landscape) {
    case LandscapeType::Arctic: {
      auto [slope, z] = GetTileSlopeZ(tile);
      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 (IsSlopeWithThreeCornersRaised(slope)) 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 = RailGroundType::HalfTileSnow;
        } else {
          new_ground = RailGroundType::SnowOrDesert;
        }
        goto set_ground;
      }
      break;
      }
 
    case LandscapeType::Tropic:
      if (GetTropicZone(tile) == TROPICZONE_DESERT) {
        new_ground = RailGroundType::SnowOrDesert;
        goto set_ground;
      }
      break;
 
    default:
      break;
  }
 
  new_ground = RailGroundType::Grass;
 
  if (IsPlainRail(tile) && old_ground != RailGroundType::Barren) { // wait until bottom is green
    /* determine direction of fence */
    TrackBits rail = GetTrackBits(tile);
 
    Owner owner = GetTileOwner(tile);
    DiagDirections fences{};
 
    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, TileType::House) || IsTileType(tile2, TileType::Industry) ||
          IsTileType(tile2, TileType::Road) || (IsTileType(tile2, TileType::Object) && !IsObjectType(tile2, OBJECT_OWNED_LAND)) || IsTileType(tile2, TileType::TunnelBridge) || !IsTileOwner(tile2, owner)) {
        fences.Set(d);
      }
    }
 
    switch (fences.base()) {
      case DiagDirections{}.base(): break;
      case DiagDirections{DIAGDIR_NE}.base(): new_ground = RailGroundType::FenceNE; break;
      case DiagDirections{DIAGDIR_SE}.base(): new_ground = RailGroundType::FenceSE; break;
      case DiagDirections{DIAGDIR_SW}.base(): new_ground = RailGroundType::FenceSW; break;
      case DiagDirections{DIAGDIR_NW}.base(): new_ground = RailGroundType::FenceNW; break;
      case DiagDirections{DIAGDIR_NE, DIAGDIR_SW}.base(): new_ground = RailGroundType::FenceNESW; break;
      case DiagDirections{DIAGDIR_SE, DIAGDIR_NW}.base(): new_ground = RailGroundType::FenceSENW; break;
      case DiagDirections{DIAGDIR_NE, DIAGDIR_SE}.base(): new_ground = RailGroundType::FenceVert1; break;
      case DiagDirections{DIAGDIR_NE, DIAGDIR_NW}.base(): new_ground = RailGroundType::FenceHoriz2; break;
      case DiagDirections{DIAGDIR_SE, DIAGDIR_SW}.base(): new_ground = RailGroundType::FenceHoriz1; break;
      case DiagDirections{DIAGDIR_SW, DIAGDIR_NW}.base(): new_ground = RailGroundType::FenceVert2; 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, DiagDirection side)
{
  /* Case of half tile slope with water. */
  if (mode == TRANSPORT_WATER && IsPlainRail(tile) && GetRailGroundType(tile) == RailGroundType::HalfTileWater && 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 RailTileType::Normal:
      trackbits = GetTrackBits(tile);
      break;
 
    case RailTileType::Signals: {
      trackbits = GetTrackBits(tile);
      uint8_t 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 RailTileType::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 (!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 RailTileType::Normal:
      td.str = STR_LAI_RAIL_DESCRIPTION_TRACK;
      break;
 
    case RailTileType::Signals: {
      static const StringID signal_type[6][6] = {
        {
          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_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_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_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_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_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
        }
      };
 
      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];
      break;
    }
 
    case RailTileType::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 = std::min<uint16_t>(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 {
    Command<Commands::LandscapeClear>::Do({DoCommandFlag::Execute, DoCommandFlag::Bankrupt}, tile);
  }
}
 
static const uint8_t _fractcoords_behind[4] = { 0x8F, 0x8, 0x80, 0xF8 };
static const uint8_t _fractcoords_enter[4] = { 0x8A, 0x48, 0x84, 0xA8 };
static const int8_t _deltacoord_leaveoffset[8] = {
  -1,  0,  1,  0, /* x */
   0,  1,  0, -1  /* y */
};
 

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)));
    case DIAGDIR_NW: return  ((int)(v->y_pos & 0x0F) - ((_fractcoords_enter[dir] >> 4)   - (length + 1)));
    default: NOT_REACHED();
  }
}

static VehicleEnterTileStates 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 {};
 
  /* Depot direction. */
  DiagDirection dir = GetRailDepotDirection(tile);
 
  uint8_t fract_coord = (x & 0xF) + ((y & 0xF) << 4);
 
  /* Make sure a train is not entering the tile from behind. */
  if (_fractcoords_behind[dir] == fract_coord) return VehicleEnterTileState::CannotEnter;
 
  Train *v = Train::From(u);
 
  /* Leaving depot? */
  if (v->direction == DiagDirToDir(dir)) {
    /* Calculate the point where the following wagon should be activated. */
    int length = v->CalcNextVehicleOffset();
 
    uint8_t 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);
 
    if (fract_coord_leave == fract_coord) {
      /* Leave the depot. */
      if ((v = v->Next()) != nullptr) {
        v->vehstatus.Reset(VehState::Hidden);
        v->track = (DiagDirToAxis(dir) == AXIS_X ? TRACK_BIT_X : TRACK_BIT_Y);
      }
    }
  } else if (_fractcoords_enter[dir] == fract_coord) {
    /* Entering depot. */
    assert(DiagDirToDir(ReverseDiagDir(dir)) == v->direction);
    v->track = TRACK_BIT_DEPOT,
    v->vehstatus.Set(VehState::Hidden);
    v->direction = ReverseDir(v->direction);
    if (v->Next() == nullptr) VehicleEnterDepot(v->First());
    v->tile = tile;
 
    InvalidateWindowData(WC_VEHICLE_DEPOT, v->tile);
    return VehicleEnterTileState::EnteredWormhole;
  }
 
  return {};
}

static CommandCost TestAutoslopeOnRailTile(TileIndex tile, DoCommandFlags 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 CommandCost(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 CommandCost(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 CommandCost(STR_ERROR_MUST_REMOVE_RAILROAD_TRACK);
      return CommandCost(EXPENSES_CONSTRUCTION, _price[Price::BuildFoundation]);
  }
 
  /* 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 CommandCost(STR_ERROR_MUST_REMOVE_RAILROAD_TRACK);
 
  CommandCost cost = CommandCost(EXPENSES_CONSTRUCTION, _price[Price::BuildFoundation]);
  /* 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) == RailGroundType::HalfTileWater && IsSlopeWithOneCornerRaised(tileh_old)) cost.AddCost(_price[Price::ClearWater]);
    if (flags.Test(DoCommandFlag::Execute)) SetRailGroundType(tile, RailGroundType::Barren);
  }
  return  cost;
}
 
static CommandCost TerraformTile_Track(TileIndex tile, DoCommandFlags flags, int z_new, Slope tileh_new)
{
  auto [tileh_old, z_old] = GetTileSlopeZ(tile);
  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) == RailGroundType::HalfTileWater && IsSlopeWithOneCornerRaised(tileh_old));
 
    /* Allow clearing the water only if there is no ship */
    if (was_water && HasVehicleOnTile(tile, [](const Vehicle *v) {
        return v->type == VEH_SHIP;
      })) return CommandCost(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.Test(DoCommandFlag::Execute)) SetRailGroundType(tile, RailGroundType::Barren);
 
    /* allow terraforming */
    return CommandCost(EXPENSES_CONSTRUCTION, was_water ? _price[Price::ClearWater] : (Money)0);
  } else if (_settings_game.construction.build_on_slopes && AutoslopeEnabled() &&
      AutoslopeCheckForEntranceEdge(tile, z_new, tileh_new, GetRailDepotDirection(tile))) {
    return CommandCost(EXPENSES_CONSTRUCTION, _price[Price::BuildFoundation]);
  }
  return Command<Commands::LandscapeClear>::Do(flags, tile);
}
 
static CommandCost CheckBuildAbove_Track(TileIndex tile, DoCommandFlags flags, Axis, int)
{
  if (IsPlainRail(tile)) return CommandCost();
  return Command<Commands::LandscapeClear>::Do(flags, tile);
}
 
extern const TileTypeProcs _tile_type_rail_procs = {
  DrawTile_Track,           // draw_tile_proc
  GetSlopePixelZ_Track,     // get_slope_z_proc
  ClearTile_Track,          // clear_tile_proc
  nullptr,                     // add_accepted_cargo_proc
  GetTileDesc_Track,        // get_tile_desc_proc
  GetTileTrackStatus_Track, // get_tile_track_status_proc
  ClickTile_Track,          // click_tile_proc
  nullptr,                     // animate_tile_proc
  TileLoop_Track,           // tile_loop_proc
  ChangeTileOwner_Track,    // change_tile_owner_proc
  nullptr,                     // add_produced_cargo_proc
  VehicleEnter_Track,       // vehicle_enter_tile_proc
  GetFoundation_Track,      // get_foundation_proc
  TerraformTile_Track,      // terraform_tile_proc
  CheckBuildAbove_Track, // check_build_above_proc
};