tunnelbridge_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 <http://www.gnu.org/licenses/>.
 */
 
#include "stdafx.h"
#include "newgrf_object.h"
#include "viewport_func.h"
#include "command_func.h"
#include "town.h"
#include "train.h"
#include "ship.h"
#include "roadveh.h"
#include "pathfinder/yapf/yapf_cache.h"
#include "pathfinder/water_regions.h"
#include "newgrf_sound.h"
#include "autoslope.h"
#include "tunnelbridge_map.h"
#include "strings_func.h"
#include "timer/timer_game_calendar.h"
#include "clear_func.h"
#include "vehicle_func.h"
#include "sound_func.h"
#include "tunnelbridge.h"
#include "cheat_type.h"
#include "elrail_func.h"
#include "pbs.h"
#include "company_base.h"
#include "newgrf_railtype.h"
#include "newgrf_roadtype.h"
#include "object_base.h"
#include "water.h"
#include "company_gui.h"
#include "station_func.h"
#include "tunnelbridge_cmd.h"
#include "landscape_cmd.h"
#include "terraform_cmd.h"
 
#include "table/strings.h"
#include "table/bridge_land.h"
 
#include "safeguards.h"
 
BridgeSpec _bridge[MAX_BRIDGES]; 
TileIndex _build_tunnel_endtile; 
 
static const int BRIDGE_Z_START = 3;
 
 
void MarkBridgeDirty(TileIndex begin, TileIndex end, DiagDirection direction, uint bridge_height)
{
  TileIndexDiff delta = TileOffsByDiagDir(direction);
  for (TileIndex t = begin; t != end; t += delta) {
    MarkTileDirtyByTile(t, bridge_height - TileHeight(t));
  }
  MarkTileDirtyByTile(end);
}
void MarkBridgeDirty(TileIndex begin, TileIndex end, DiagDirection direction, uint bridge_height) {…}
 
void MarkBridgeDirty(TileIndex tile)
{
  MarkBridgeDirty(tile, GetOtherTunnelBridgeEnd(tile), GetTunnelBridgeDirection(tile), GetBridgeHeight(tile));
}
void MarkBridgeDirty(TileIndex tile) {…}
 
void ResetBridges()
{
  std::ranges::copy(_orig_bridge, std::begin(_bridge));
}
void ResetBridges() {…}
 
int CalcBridgeLenCostFactor(int length)
{
  if (length < 2) return length;
 
  length -= 2;
  int sum = 2;
  for (int delta = 1;; delta++) {
    for (int count = 0; count < delta; count++) {
      if (length == 0) return sum;
      sum += delta;
      length--;
    }
  }
}
int CalcBridgeLenCostFactor(int length) {…}
 
Foundation GetBridgeFoundation(Slope tileh, Axis axis)
{
  if (tileh == SLOPE_FLAT ||
      ((tileh == SLOPE_NE || tileh == SLOPE_SW) && axis == AXIS_X) ||
      ((tileh == SLOPE_NW || tileh == SLOPE_SE) && axis == AXIS_Y)) return FOUNDATION_NONE;
 
  return (HasSlopeHighestCorner(tileh) ? InclinedFoundation(axis) : FlatteningFoundation(tileh));
}
Foundation GetBridgeFoundation(Slope tileh, Axis axis) {…}
 
bool HasBridgeFlatRamp(Slope tileh, Axis axis)
{
  ApplyFoundationToSlope(GetBridgeFoundation(tileh, axis), tileh);
  /* If the foundation slope is flat the bridge has a non-flat ramp and vice versa. */
  return (tileh != SLOPE_FLAT);
}
bool HasBridgeFlatRamp(Slope tileh, Axis axis) {…}
 
static inline std::span<const PalSpriteID> GetBridgeSpriteTable(int index, BridgePieces table)
{
  const BridgeSpec *bridge = GetBridgeSpec(index);
  assert(table < NUM_BRIDGE_PIECES);
  if (table < bridge->sprite_table.size() && !bridge->sprite_table[table].empty()) return bridge->sprite_table[table];
 
  return _bridge_sprite_table[index][table];
}
 
 
static CommandCost CheckBridgeSlope(BridgePieces bridge_piece, Axis axis, Slope &tileh, int &z)
{
  assert(bridge_piece == BRIDGE_PIECE_NORTH || bridge_piece == BRIDGE_PIECE_SOUTH);
 
  Foundation f = GetBridgeFoundation(tileh, axis);
  z += ApplyFoundationToSlope(f, tileh);
 
  Slope valid_inclined;
  if (bridge_piece == BRIDGE_PIECE_NORTH) {
    valid_inclined = (axis == AXIS_X ? SLOPE_NE : SLOPE_NW);
  } else {
    valid_inclined = (axis == AXIS_X ? SLOPE_SW : SLOPE_SE);
  }
  if ((tileh != SLOPE_FLAT) && (tileh != valid_inclined)) return CMD_ERROR;
 
  if (f == FOUNDATION_NONE) return CommandCost();
 
  return CommandCost(EXPENSES_CONSTRUCTION, _price[PR_BUILD_FOUNDATION]);
}
static CommandCost CheckBridgeSlope(BridgePieces bridge_piece, Axis axis, Slope &tileh, int &z) {…}
 
CommandCost CheckBridgeAvailability(BridgeType bridge_type, uint bridge_len, DoCommandFlags flags)
{
  if (flags.Test(DoCommandFlag::QueryCost)) {
    if (bridge_len <= _settings_game.construction.max_bridge_length) return CommandCost();
    return CommandCost(STR_ERROR_BRIDGE_TOO_LONG);
  }
 
  if (bridge_type >= MAX_BRIDGES) return CMD_ERROR;
 
  const BridgeSpec *b = GetBridgeSpec(bridge_type);
  if (b->avail_year > TimerGameCalendar::year) return CMD_ERROR;
 
  uint max = std::min(b->max_length, _settings_game.construction.max_bridge_length);
 
  if (b->min_length > bridge_len) return CMD_ERROR;
  if (bridge_len <= max) return CommandCost();
  return CommandCost(STR_ERROR_BRIDGE_TOO_LONG);
}
CommandCost CheckBridgeAvailability(BridgeType bridge_type, uint bridge_len, DoCommandFlags flags) {…}
 
static Money TunnelBridgeClearCost(TileIndex tile, Price base_price)
{
  Money base_cost = _price[base_price];
 
  /* Add the cost of the transport that is on the tunnel/bridge. */
  switch (GetTunnelBridgeTransportType(tile)) {
    case TRANSPORT_ROAD: {
      RoadType road_rt = GetRoadTypeRoad(tile);
      RoadType tram_rt = GetRoadTypeTram(tile);
 
      if (road_rt != INVALID_ROADTYPE) {
        base_cost += 2 * RoadClearCost(road_rt);
      }
      if (tram_rt != INVALID_ROADTYPE) {
        base_cost += 2 * RoadClearCost(tram_rt);
      }
    } break;
 
    case TRANSPORT_RAIL: base_cost += RailClearCost(GetRailType(tile)); break;
    /* Aquaducts have their own clear price. */
    case TRANSPORT_WATER: base_cost = _price[PR_CLEAR_AQUEDUCT]; break;
    default: break;
  }
 
  return base_cost;
}
static Money TunnelBridgeClearCost(TileIndex tile, Price base_price) {…}
 
CommandCost CmdBuildBridge(DoCommandFlags flags, TileIndex tile_end, TileIndex tile_start, TransportType transport_type, BridgeType bridge_type, uint8_t road_rail_type)
{
  CompanyID company = _current_company;
 
  RailType railtype = INVALID_RAILTYPE;
  RoadType roadtype = INVALID_ROADTYPE;
 
  if (!IsValidTile(tile_start)) return CommandCost(STR_ERROR_BRIDGE_THROUGH_MAP_BORDER);
 
  /* type of bridge */
  switch (transport_type) {
    case TRANSPORT_ROAD:
      roadtype = (RoadType)road_rail_type;
      if (!ValParamRoadType(roadtype)) return CMD_ERROR;
      break;
 
    case TRANSPORT_RAIL:
      railtype = (RailType)road_rail_type;
      if (!ValParamRailType(railtype)) return CMD_ERROR;
      break;
 
    case TRANSPORT_WATER:
      break;
 
    default:
      /* Airports don't have bridges. */
      return CMD_ERROR;
  }
 
  if (company == OWNER_DEITY) {
    if (transport_type != TRANSPORT_ROAD) return CMD_ERROR;
    const Town *town = CalcClosestTownFromTile(tile_start);
 
    company = OWNER_TOWN;
 
    /* If we are not within a town, we are not owned by the town */
    if (town == nullptr || DistanceSquare(tile_start, town->xy) > town->cache.squared_town_zone_radius[to_underlying(HouseZone::TownEdge)]) {
      company = OWNER_NONE;
    }
  }
 
  if (tile_start == tile_end) {
    return CommandCost(STR_ERROR_CAN_T_START_AND_END_ON);
  }
 
  Axis direction;
  if (TileX(tile_start) == TileX(tile_end)) {
    direction = AXIS_Y;
  } else if (TileY(tile_start) == TileY(tile_end)) {
    direction = AXIS_X;
  } else {
    return CommandCost(STR_ERROR_START_AND_END_MUST_BE_IN);
  }
 
  if (tile_end < tile_start) std::swap(tile_start, tile_end);
 
  uint bridge_len = GetTunnelBridgeLength(tile_start, tile_end);
  if (transport_type != TRANSPORT_WATER) {
    /* set and test bridge length, availability */
    CommandCost ret = CheckBridgeAvailability(bridge_type, bridge_len, flags);
    if (ret.Failed()) return ret;
  } else {
    if (bridge_len > _settings_game.construction.max_bridge_length) return CommandCost(STR_ERROR_BRIDGE_TOO_LONG);
  }
  bridge_len += 2; // begin and end tiles/ramps
 
  auto [tileh_start, z_start] = GetTileSlopeZ(tile_start);
  auto [tileh_end, z_end] = GetTileSlopeZ(tile_end);
  bool pbs_reservation = false;
 
  CommandCost terraform_cost_north = CheckBridgeSlope(BRIDGE_PIECE_NORTH, direction, tileh_start, z_start);
  CommandCost terraform_cost_south = CheckBridgeSlope(BRIDGE_PIECE_SOUTH, direction, tileh_end,   z_end);
 
  /* Aqueducts can't be built of flat land. */
  if (transport_type == TRANSPORT_WATER && (tileh_start == SLOPE_FLAT || tileh_end == SLOPE_FLAT)) return CommandCost(STR_ERROR_LAND_SLOPED_IN_WRONG_DIRECTION);
  if (z_start != z_end) return CommandCost(STR_ERROR_BRIDGEHEADS_NOT_SAME_HEIGHT);
 
  CommandCost cost(EXPENSES_CONSTRUCTION);
  Owner owner;
  bool is_new_owner;
  RoadType road_rt = INVALID_ROADTYPE;
  RoadType tram_rt = INVALID_ROADTYPE;
  if (IsBridgeTile(tile_start) && IsBridgeTile(tile_end) &&
      GetOtherBridgeEnd(tile_start) == tile_end &&
      GetTunnelBridgeTransportType(tile_start) == transport_type) {
    /* Replace a current bridge. */
 
    switch (transport_type) {
      case TRANSPORT_RAIL:
        /* Keep the reservation, the path stays valid. */
        pbs_reservation = HasTunnelBridgeReservation(tile_start);
        break;
 
      case TRANSPORT_ROAD:
        /* Do not remove road types when upgrading a bridge */
        road_rt = GetRoadTypeRoad(tile_start);
        tram_rt = GetRoadTypeTram(tile_start);
        break;
 
      default: break;
    }
 
    /* If this is a railway bridge, make sure the railtypes match. */
    if (transport_type == TRANSPORT_RAIL && GetRailType(tile_start) != railtype) {
      return CommandCost(STR_ERROR_MUST_DEMOLISH_BRIDGE_FIRST);
    }
 
    /* If this is a road bridge, make sure the roadtype matches. */
    if (transport_type == TRANSPORT_ROAD) {
      RoadType existing_rt = RoadTypeIsRoad(roadtype) ? road_rt : tram_rt;
      if (existing_rt != roadtype && existing_rt != INVALID_ROADTYPE) {
        return CommandCost(STR_ERROR_MUST_DEMOLISH_BRIDGE_FIRST);
      }
    }
 
    if (!flags.Test(DoCommandFlag::QueryCost)) {
      /* Do not replace the bridge with the same bridge type. */
      if ((bridge_type == GetBridgeType(tile_start)) && (transport_type != TRANSPORT_ROAD || road_rt == roadtype || tram_rt == roadtype)) {
        return CommandCost(STR_ERROR_ALREADY_BUILT);
      }
 
      /* Do not replace town bridges with lower speed bridges, unless in scenario editor. */
      if (IsTileOwner(tile_start, OWNER_TOWN) && _game_mode != GM_EDITOR) {
        Town *t = ClosestTownFromTile(tile_start, UINT_MAX);
        if (t == nullptr) return CMD_ERROR;
 
        if (GetBridgeSpec(bridge_type)->speed < GetBridgeSpec(GetBridgeType(tile_start))->speed) {
          return CommandCostWithParam(STR_ERROR_LOCAL_AUTHORITY_REFUSES_TO_ALLOW_THIS, t->index);
        } else {
          ChangeTownRating(t, RATING_TUNNEL_BRIDGE_UP_STEP, RATING_MAXIMUM, flags);
        }
      }
    }
 
    /* Do not allow replacing another company's bridges. */
    if (!IsTileOwner(tile_start, company) && !IsTileOwner(tile_start, OWNER_TOWN) && !IsTileOwner(tile_start, OWNER_NONE)) {
      return CommandCost(STR_ERROR_AREA_IS_OWNED_BY_ANOTHER);
    }
 
    /* The cost of clearing the current bridge. */
    cost.AddCost(bridge_len * TunnelBridgeClearCost(tile_start, PR_CLEAR_BRIDGE));
    owner = GetTileOwner(tile_start);
 
    /* If bridge belonged to bankrupt company, it has a new owner now */
    is_new_owner = (owner == OWNER_NONE);
    if (is_new_owner) owner = company;
  } else {
    /* Build a new bridge. */
 
    bool allow_on_slopes = (_settings_game.construction.build_on_slopes && transport_type != TRANSPORT_WATER);
 
    /* Try and clear the start landscape */
    CommandCost ret = Command<CMD_LANDSCAPE_CLEAR>::Do(flags, tile_start);
    if (ret.Failed()) return ret;
    cost = ret;
 
    if (terraform_cost_north.Failed() || (terraform_cost_north.GetCost() != 0 && !allow_on_slopes)) return CommandCost(STR_ERROR_LAND_SLOPED_IN_WRONG_DIRECTION);
    cost.AddCost(terraform_cost_north.GetCost());
 
    /* Try and clear the end landscape */
    ret = Command<CMD_LANDSCAPE_CLEAR>::Do(flags, tile_end);
    if (ret.Failed()) return ret;
    cost.AddCost(ret.GetCost());
 
    /* false - end tile slope check */
    if (terraform_cost_south.Failed() || (terraform_cost_south.GetCost() != 0 && !allow_on_slopes)) return CommandCost(STR_ERROR_LAND_SLOPED_IN_WRONG_DIRECTION);
    cost.AddCost(terraform_cost_south.GetCost());
 
    /* Check for bridges above the bridge ramps. */
    for (TileIndex tile : {tile_start, tile_end}) {
      if (!IsBridgeAbove(tile)) continue;
 
      if (direction == GetBridgeAxis(tile)) return CommandCost(STR_ERROR_MUST_DEMOLISH_BRIDGE_FIRST);
 
      if (z_start + 1 == GetBridgeHeight(GetNorthernBridgeEnd(tile))) return CommandCost(STR_ERROR_MUST_DEMOLISH_BRIDGE_FIRST);
    }
 
    TileIndexDiff delta = TileOffsByAxis(direction);
    for (TileIndex tile = tile_start + delta; tile != tile_end; tile += delta) {
      if (GetTileMaxZ(tile) > z_start) return CommandCost(STR_ERROR_BRIDGE_TOO_LOW_FOR_TERRAIN);
 
      if (z_start >= (GetTileZ(tile) + _settings_game.construction.max_bridge_height)) {
        /*
         * Disallow too high bridges.
         * Properly rendering a map where very high bridges (might) exist is expensive.
         * See http://www.tt-forums.net/viewtopic.php?f=33&t=40844&start=980#p1131762
         * for a detailed discussion. z_start here is one heightlevel below the bridge level.
         */
        return CommandCost(STR_ERROR_BRIDGE_TOO_HIGH_FOR_TERRAIN);
      }
 
      if (IsBridgeAbove(tile)) {
        /* Disallow crossing bridges for the time being */
        return CommandCost(STR_ERROR_MUST_DEMOLISH_BRIDGE_FIRST);
      }
 
      switch (GetTileType(tile)) {
        case MP_WATER:
          if (!IsWater(tile) && !IsCoast(tile)) goto not_valid_below;
          break;
 
        case MP_RAILWAY:
          if (!IsPlainRail(tile)) goto not_valid_below;
          break;
 
        case MP_ROAD:
          if (IsRoadDepot(tile)) goto not_valid_below;
          break;
 
        case MP_TUNNELBRIDGE:
          if (IsTunnel(tile)) break;
          if (direction == DiagDirToAxis(GetTunnelBridgeDirection(tile))) goto not_valid_below;
          if (z_start < GetBridgeHeight(tile)) goto not_valid_below;
          break;
 
        case MP_OBJECT: {
          const ObjectSpec *spec = ObjectSpec::GetByTile(tile);
          if (!spec->flags.Test(ObjectFlag::AllowUnderBridge)) goto not_valid_below;
          if (GetTileMaxZ(tile) + spec->height > z_start) goto not_valid_below;
          break;
        }
 
        case MP_CLEAR:
          break;
 
        default:
  not_valid_below:;
          /* try and clear the middle landscape */
          ret = Command<CMD_LANDSCAPE_CLEAR>::Do(flags, tile);
          if (ret.Failed()) return ret;
          cost.AddCost(ret.GetCost());
          break;
      }
 
      if (flags.Test(DoCommandFlag::Execute)) {
        /* We do this here because when replacing a bridge with another
         * type calling SetBridgeMiddle isn't needed. After all, the
         * tile already has the has_bridge_above bits set. */
        SetBridgeMiddle(tile, direction);
      }
    }
 
    owner = company;
    is_new_owner = true;
  }
 
  bool hasroad = road_rt != INVALID_ROADTYPE;
  bool hastram = tram_rt != INVALID_ROADTYPE;
  if (transport_type == TRANSPORT_ROAD) {
    if (RoadTypeIsRoad(roadtype)) road_rt = roadtype;
    if (RoadTypeIsTram(roadtype)) tram_rt = roadtype;
  }
 
  /* do the drill? */
  if (flags.Test(DoCommandFlag::Execute)) {
    DiagDirection dir = AxisToDiagDir(direction);
 
    Company *c = Company::GetIfValid(company);
    switch (transport_type) {
      case TRANSPORT_RAIL:
        /* Add to company infrastructure count if required. */
        if (is_new_owner && c != nullptr) c->infrastructure.rail[railtype] += bridge_len * TUNNELBRIDGE_TRACKBIT_FACTOR;
        MakeRailBridgeRamp(tile_start, owner, bridge_type, dir,                 railtype);
        MakeRailBridgeRamp(tile_end,   owner, bridge_type, ReverseDiagDir(dir), railtype);
        SetTunnelBridgeReservation(tile_start, pbs_reservation);
        SetTunnelBridgeReservation(tile_end,   pbs_reservation);
        break;
 
      case TRANSPORT_ROAD: {
        if (is_new_owner) {
          /* Also give unowned present roadtypes to new owner */
          if (hasroad && GetRoadOwner(tile_start, RTT_ROAD) == OWNER_NONE) hasroad = false;
          if (hastram && GetRoadOwner(tile_start, RTT_TRAM) == OWNER_NONE) hastram = false;
        }
        if (c != nullptr) {
          /* Add all new road types to the company infrastructure counter. */
          if (!hasroad && road_rt != INVALID_ROADTYPE) {
            /* A full diagonal road tile has two road bits. */
            c->infrastructure.road[road_rt] += bridge_len * 2 * TUNNELBRIDGE_TRACKBIT_FACTOR;
          }
          if (!hastram && tram_rt != INVALID_ROADTYPE) {
            /* A full diagonal road tile has two road bits. */
            c->infrastructure.road[tram_rt] += bridge_len * 2 * TUNNELBRIDGE_TRACKBIT_FACTOR;
          }
        }
        Owner owner_road = hasroad ? GetRoadOwner(tile_start, RTT_ROAD) : company;
        Owner owner_tram = hastram ? GetRoadOwner(tile_start, RTT_TRAM) : company;
        MakeRoadBridgeRamp(tile_start, owner, owner_road, owner_tram, bridge_type, dir, road_rt, tram_rt);
        MakeRoadBridgeRamp(tile_end,   owner, owner_road, owner_tram, bridge_type, ReverseDiagDir(dir), road_rt, tram_rt);
        break;
      }
 
      case TRANSPORT_WATER:
        if (is_new_owner && c != nullptr) c->infrastructure.water += bridge_len * TUNNELBRIDGE_TRACKBIT_FACTOR;
        MakeAqueductBridgeRamp(tile_start, owner, dir);
        MakeAqueductBridgeRamp(tile_end,   owner, ReverseDiagDir(dir));
        CheckForDockingTile(tile_start);
        CheckForDockingTile(tile_end);
        break;
 
      default:
        NOT_REACHED();
    }
 
    /* Mark all tiles dirty */
    MarkBridgeDirty(tile_start, tile_end, AxisToDiagDir(direction), z_start);
    DirtyCompanyInfrastructureWindows(company);
  }
 
  if (flags.Test(DoCommandFlag::Execute) && transport_type == TRANSPORT_RAIL) {
    Track track = AxisToTrack(direction);
    AddSideToSignalBuffer(tile_start, INVALID_DIAGDIR, company);
    YapfNotifyTrackLayoutChange(tile_start, track);
  }
 
  /* Human players that build bridges get a selection to choose from (DoCommandFlag::QueryCost)
   * It's unnecessary to execute this command every time for every bridge.
   * So it is done only for humans and cost is computed in bridge_gui.cpp.
   * For (non-spectated) AI, Towns this has to be of course calculated. */
  Company *c = Company::GetIfValid(company);
  if (!flags.Test(DoCommandFlag::QueryCost) || (c != nullptr && c->is_ai && company != _local_company)) {
    switch (transport_type) {
      case TRANSPORT_ROAD:
        if (road_rt != INVALID_ROADTYPE) {
          cost.AddCost(bridge_len * 2 * RoadBuildCost(road_rt));
        }
        if (tram_rt != INVALID_ROADTYPE) {
          cost.AddCost(bridge_len * 2 * RoadBuildCost(tram_rt));
        }
        break;
 
      case TRANSPORT_RAIL: cost.AddCost(bridge_len * RailBuildCost(railtype)); break;
      default: break;
    }
 
    if (c != nullptr) bridge_len = CalcBridgeLenCostFactor(bridge_len);
 
    if (transport_type != TRANSPORT_WATER) {
      cost.AddCost((int64_t)bridge_len * _price[PR_BUILD_BRIDGE] * GetBridgeSpec(bridge_type)->price >> 8);
    } else {
      /* Aqueducts use a separate base cost. */
      cost.AddCost((int64_t)bridge_len * _price[PR_BUILD_AQUEDUCT]);
    }
 
  }
 
  return cost;
}
CommandCost CmdBuildBridge(DoCommandFlags flags, TileIndex tile_end, TileIndex tile_start, TransportType transport_type, BridgeType bridge_type, uint8_t road_rail_type) {…}
 
 
CommandCost CmdBuildTunnel(DoCommandFlags flags, TileIndex start_tile, TransportType transport_type, uint8_t road_rail_type)
{
  CompanyID company = _current_company;
 
  RailType railtype = INVALID_RAILTYPE;
  RoadType roadtype = INVALID_ROADTYPE;
  _build_tunnel_endtile = TileIndex{};
  switch (transport_type) {
    case TRANSPORT_RAIL:
      railtype = (RailType)road_rail_type;
      if (!ValParamRailType(railtype)) return CMD_ERROR;
      break;
 
    case TRANSPORT_ROAD:
      roadtype = (RoadType)road_rail_type;
      if (!ValParamRoadType(roadtype)) return CMD_ERROR;
      break;
 
    default: return CMD_ERROR;
  }
 
  if (company == OWNER_DEITY) {
    if (transport_type != TRANSPORT_ROAD) return CMD_ERROR;
    const Town *town = CalcClosestTownFromTile(start_tile);
 
    company = OWNER_TOWN;
 
    /* If we are not within a town, we are not owned by the town */
    if (town == nullptr || DistanceSquare(start_tile, town->xy) > town->cache.squared_town_zone_radius[to_underlying(HouseZone::TownEdge)]) {
      company = OWNER_NONE;
    }
  }
 
  auto [start_tileh, start_z] = GetTileSlopeZ(start_tile);
  DiagDirection direction = GetInclinedSlopeDirection(start_tileh);
  if (direction == INVALID_DIAGDIR) return CommandCost(STR_ERROR_SITE_UNSUITABLE_FOR_TUNNEL);
 
  if (HasTileWaterGround(start_tile)) return CommandCost(STR_ERROR_CAN_T_BUILD_ON_WATER);
 
  CommandCost ret = Command<CMD_LANDSCAPE_CLEAR>::Do(flags, start_tile);
  if (ret.Failed()) return ret;
 
  /* XXX - do NOT change 'ret' in the loop, as it is used as the price
   * for the clearing of the entrance of the tunnel. Assigning it to
   * cost before the loop will yield different costs depending on start-
   * position, because of increased-cost-by-length: 'cost += cost >> 3' */
 
  TileIndexDiff delta = TileOffsByDiagDir(direction);
  DiagDirection tunnel_in_way_dir;
  if (DiagDirToAxis(direction) == AXIS_Y) {
    tunnel_in_way_dir = (TileX(start_tile) < (Map::MaxX() / 2)) ? DIAGDIR_SW : DIAGDIR_NE;
  } else {
    tunnel_in_way_dir = (TileY(start_tile) < (Map::MaxX() / 2)) ? DIAGDIR_SE : DIAGDIR_NW;
  }
 
  TileIndex end_tile = start_tile;
 
  /* Tile shift coefficient. Will decrease for very long tunnels to avoid exponential growth of price*/
  int tiles_coef = 3;
  /* Number of tiles from start of tunnel */
  int tiles = 0;
  /* Number of tiles at which the cost increase coefficient per tile is halved */
  int tiles_bump = 25;
 
  CommandCost cost(EXPENSES_CONSTRUCTION);
  Slope end_tileh;
  int end_z;
  for (;;) {
    end_tile += delta;
    if (!IsValidTile(end_tile)) return CommandCost(STR_ERROR_TUNNEL_THROUGH_MAP_BORDER);
    std::tie(end_tileh, end_z) = GetTileSlopeZ(end_tile);
 
    if (start_z == end_z) break;
 
    if (!_cheats.crossing_tunnels.value && IsTunnelInWayDir(end_tile, start_z, tunnel_in_way_dir)) {
      return CommandCost(STR_ERROR_ANOTHER_TUNNEL_IN_THE_WAY);
    }
 
    tiles++;
    if (tiles == tiles_bump) {
      tiles_coef++;
      tiles_bump *= 2;
    }
 
    cost.AddCost(_price[PR_BUILD_TUNNEL]);
    cost.AddCost(cost.GetCost() >> tiles_coef); // add a multiplier for longer tunnels
  }
 
  /* Add the cost of the entrance */
  cost.AddCost(_price[PR_BUILD_TUNNEL]);
  cost.AddCost(ret.GetCost());
 
  /* if the command fails from here on we want the end tile to be highlighted */
  _build_tunnel_endtile = end_tile;
 
  if (tiles > _settings_game.construction.max_tunnel_length) return CommandCost(STR_ERROR_TUNNEL_TOO_LONG);
 
  if (HasTileWaterGround(end_tile)) return CommandCost(STR_ERROR_CAN_T_BUILD_ON_WATER);
 
  /* Clear the tile in any case */
  ret = Command<CMD_LANDSCAPE_CLEAR>::Do(flags, end_tile);
  if (ret.Failed()) return CommandCost(STR_ERROR_UNABLE_TO_EXCAVATE_LAND);
  cost.AddCost(ret.GetCost());
 
  /* slope of end tile must be complementary to the slope of the start tile */
  if (end_tileh != ComplementSlope(start_tileh)) {
    /* Mark the tile as already cleared for the terraform command.
     * Do this for all tiles (like trees), not only objects. */
    ClearedObjectArea *coa = FindClearedObject(end_tile);
    if (coa == nullptr) {
      coa = &_cleared_object_areas.emplace_back(end_tile, TileArea(end_tile, 1, 1));
    }
 
    /* Hide the tile from the terraforming command */
    TileIndex old_first_tile = coa->first_tile;
    coa->first_tile = INVALID_TILE;
 
    /* CMD_TERRAFORM_LAND may append further items to _cleared_object_areas,
     * however it will never erase or re-order existing items.
     * _cleared_object_areas is a value-type self-resizing vector, therefore appending items
     * may result in a backing-store re-allocation, which would invalidate the coa pointer.
     * The index of the coa pointer into the _cleared_object_areas vector remains valid,
     * and can be used safely after the CMD_TERRAFORM_LAND operation.
     * Deliberately clear the coa pointer to avoid leaving dangling pointers which could
     * inadvertently be dereferenced.
     */
    ClearedObjectArea *begin = _cleared_object_areas.data();
    assert(coa >= begin && coa < begin + _cleared_object_areas.size());
    size_t coa_index = coa - begin;
    assert(coa_index < UINT_MAX); // more than 2**32 cleared areas would be a bug in itself
    coa = nullptr;
 
    ret = std::get<0>(Command<CMD_TERRAFORM_LAND>::Do(flags, end_tile, end_tileh & start_tileh, false));
    _cleared_object_areas[(uint)coa_index].first_tile = old_first_tile;
    if (ret.Failed()) return CommandCost(STR_ERROR_UNABLE_TO_EXCAVATE_LAND);
    cost.AddCost(ret.GetCost());
  }
  cost.AddCost(_price[PR_BUILD_TUNNEL]);
 
  /* Pay for the rail/road in the tunnel including entrances */
  switch (transport_type) {
    case TRANSPORT_ROAD: cost.AddCost((tiles + 2) * RoadBuildCost(roadtype) * 2); break;
    case TRANSPORT_RAIL: cost.AddCost((tiles + 2) * RailBuildCost(railtype)); break;
    default: NOT_REACHED();
  }
 
  if (flags.Test(DoCommandFlag::Execute)) {
    Company *c = Company::GetIfValid(company);
    uint num_pieces = (tiles + 2) * TUNNELBRIDGE_TRACKBIT_FACTOR;
    if (transport_type == TRANSPORT_RAIL) {
      if (c != nullptr) c->infrastructure.rail[railtype] += num_pieces;
      MakeRailTunnel(start_tile, company, direction,                 railtype);
      MakeRailTunnel(end_tile,   company, ReverseDiagDir(direction), railtype);
      AddSideToSignalBuffer(start_tile, INVALID_DIAGDIR, company);
      YapfNotifyTrackLayoutChange(start_tile, DiagDirToDiagTrack(direction));
    } else {
      if (c != nullptr) c->infrastructure.road[roadtype] += num_pieces * 2; // A full diagonal road has two road bits.
      RoadType road_rt = RoadTypeIsRoad(roadtype) ? roadtype : INVALID_ROADTYPE;
      RoadType tram_rt = RoadTypeIsTram(roadtype) ? roadtype : INVALID_ROADTYPE;
      MakeRoadTunnel(start_tile, company, direction,                 road_rt, tram_rt);
      MakeRoadTunnel(end_tile,   company, ReverseDiagDir(direction), road_rt, tram_rt);
    }
    DirtyCompanyInfrastructureWindows(company);
  }
 
  return cost;
}
CommandCost CmdBuildTunnel(DoCommandFlags flags, TileIndex start_tile, TransportType transport_type, uint8_t road_rail_type) {…}
 
 
static inline CommandCost CheckAllowRemoveTunnelBridge(TileIndex tile)
{
  /* Floods can remove anything as well as the scenario editor */
  if (_current_company == OWNER_WATER || _game_mode == GM_EDITOR) return CommandCost();
 
  switch (GetTunnelBridgeTransportType(tile)) {
    case TRANSPORT_ROAD: {
      RoadType road_rt = GetRoadTypeRoad(tile);
      RoadType tram_rt = GetRoadTypeTram(tile);
      Owner road_owner = _current_company;
      Owner tram_owner = _current_company;
 
      if (road_rt != INVALID_ROADTYPE) road_owner = GetRoadOwner(tile, RTT_ROAD);
      if (tram_rt != INVALID_ROADTYPE) tram_owner = GetRoadOwner(tile, RTT_TRAM);
 
      /* We can remove unowned road and if the town allows it */
      if (road_owner == OWNER_TOWN && _current_company != OWNER_TOWN && !(_settings_game.construction.extra_dynamite || _cheats.magic_bulldozer.value)) {
        /* Town does not allow */
        return CheckTileOwnership(tile);
      }
      if (road_owner == OWNER_NONE || road_owner == OWNER_TOWN) road_owner = _current_company;
      if (tram_owner == OWNER_NONE) tram_owner = _current_company;
 
      CommandCost ret = CheckOwnership(road_owner, tile);
      if (ret.Succeeded()) ret = CheckOwnership(tram_owner, tile);
      return ret;
    }
 
    case TRANSPORT_RAIL:
      return CheckOwnership(GetTileOwner(tile));
 
    case TRANSPORT_WATER: {
      /* Always allow to remove aqueducts without owner. */
      Owner aqueduct_owner = GetTileOwner(tile);
      if (aqueduct_owner == OWNER_NONE) aqueduct_owner = _current_company;
      return CheckOwnership(aqueduct_owner);
    }
 
    default: NOT_REACHED();
  }
}
static inline CommandCost CheckAllowRemoveTunnelBridge(TileIndex tile) {…}
 
static CommandCost DoClearTunnel(TileIndex tile, DoCommandFlags flags)
{
  CommandCost ret = CheckAllowRemoveTunnelBridge(tile);
  if (ret.Failed()) return ret;
 
  TileIndex endtile = GetOtherTunnelEnd(tile);
 
  ret = TunnelBridgeIsFree(tile, endtile);
  if (ret.Failed()) return ret;
 
  _build_tunnel_endtile = endtile;
 
  Town *t = nullptr;
  if (IsTileOwner(tile, OWNER_TOWN) && _game_mode != GM_EDITOR) {
    t = ClosestTownFromTile(tile, UINT_MAX); // town penalty rating
 
    /* Check if you are allowed to remove the tunnel owned by a town
     * Removal depends on difficulty settings */
    ret = CheckforTownRating(flags, t, TUNNELBRIDGE_REMOVE);
    if (ret.Failed()) return ret;
  }
 
  /* checks if the owner is town then decrease town rating by RATING_TUNNEL_BRIDGE_DOWN_STEP until
   * you have a "Poor" (0) town rating */
  if (IsTileOwner(tile, OWNER_TOWN) && _game_mode != GM_EDITOR) {
    ChangeTownRating(t, RATING_TUNNEL_BRIDGE_DOWN_STEP, RATING_TUNNEL_BRIDGE_MINIMUM, flags);
  }
 
  Money base_cost = TunnelBridgeClearCost(tile, PR_CLEAR_TUNNEL);
  uint len = GetTunnelBridgeLength(tile, endtile) + 2; // Don't forget the end tiles.
 
  if (flags.Test(DoCommandFlag::Execute)) {
    if (GetTunnelBridgeTransportType(tile) == TRANSPORT_RAIL) {
      /* We first need to request values before calling DoClearSquare */
      DiagDirection dir = GetTunnelBridgeDirection(tile);
      Track track = DiagDirToDiagTrack(dir);
      Owner owner = GetTileOwner(tile);
 
      Train *v = nullptr;
      if (HasTunnelBridgeReservation(tile)) {
        v = GetTrainForReservation(tile, track);
        if (v != nullptr) FreeTrainTrackReservation(v);
      }
 
      if (Company::IsValidID(owner)) {
        Company::Get(owner)->infrastructure.rail[GetRailType(tile)] -= len * TUNNELBRIDGE_TRACKBIT_FACTOR;
        DirtyCompanyInfrastructureWindows(owner);
      }
 
      DoClearSquare(tile);
      DoClearSquare(endtile);
 
      /* cannot use INVALID_DIAGDIR for signal update because the tunnel doesn't exist anymore */
      AddSideToSignalBuffer(tile,    ReverseDiagDir(dir), owner);
      AddSideToSignalBuffer(endtile, dir,                 owner);
 
      YapfNotifyTrackLayoutChange(tile,    track);
      YapfNotifyTrackLayoutChange(endtile, track);
 
      if (v != nullptr) TryPathReserve(v);
    } else {
      /* A full diagonal road tile has two road bits. */
      UpdateCompanyRoadInfrastructure(GetRoadTypeRoad(tile), GetRoadOwner(tile, RTT_ROAD), -(int)(len * 2 * TUNNELBRIDGE_TRACKBIT_FACTOR));
      UpdateCompanyRoadInfrastructure(GetRoadTypeTram(tile), GetRoadOwner(tile, RTT_TRAM), -(int)(len * 2 * TUNNELBRIDGE_TRACKBIT_FACTOR));
 
      DoClearSquare(tile);
      DoClearSquare(endtile);
    }
  }
 
  return CommandCost(EXPENSES_CONSTRUCTION, len * base_cost);
}
static CommandCost DoClearTunnel(TileIndex tile, DoCommandFlags flags) {…}
 
 
static CommandCost DoClearBridge(TileIndex tile, DoCommandFlags flags)
{
  CommandCost ret = CheckAllowRemoveTunnelBridge(tile);
  if (ret.Failed()) return ret;
 
  TileIndex endtile = GetOtherBridgeEnd(tile);
 
  ret = TunnelBridgeIsFree(tile, endtile);
  if (ret.Failed()) return ret;
 
  DiagDirection direction = GetTunnelBridgeDirection(tile);
  TileIndexDiff delta = TileOffsByDiagDir(direction);
 
  Town *t = nullptr;
  if (IsTileOwner(tile, OWNER_TOWN) && _game_mode != GM_EDITOR) {
    t = ClosestTownFromTile(tile, UINT_MAX); // town penalty rating
 
    /* Check if you are allowed to remove the bridge owned by a town
     * Removal depends on difficulty settings */
    ret = CheckforTownRating(flags, t, TUNNELBRIDGE_REMOVE);
    if (ret.Failed()) return ret;
  }
 
  /* checks if the owner is town then decrease town rating by RATING_TUNNEL_BRIDGE_DOWN_STEP until
   * you have a "Poor" (0) town rating */
  if (IsTileOwner(tile, OWNER_TOWN) && _game_mode != GM_EDITOR) {
    ChangeTownRating(t, RATING_TUNNEL_BRIDGE_DOWN_STEP, RATING_TUNNEL_BRIDGE_MINIMUM, flags);
  }
 
  Money base_cost = TunnelBridgeClearCost(tile, PR_CLEAR_BRIDGE);
  uint len = GetTunnelBridgeLength(tile, endtile) + 2; // Don't forget the end tiles.
 
  if (flags.Test(DoCommandFlag::Execute)) {
    /* read this value before actual removal of bridge */
    bool rail = GetTunnelBridgeTransportType(tile) == TRANSPORT_RAIL;
    Owner owner = GetTileOwner(tile);
    int height = GetBridgeHeight(tile);
    Train *v = nullptr;
 
    if (rail && HasTunnelBridgeReservation(tile)) {
      v = GetTrainForReservation(tile, DiagDirToDiagTrack(direction));
      if (v != nullptr) FreeTrainTrackReservation(v);
    }
 
    /* Update company infrastructure counts. */
    if (rail) {
      if (Company::IsValidID(owner)) Company::Get(owner)->infrastructure.rail[GetRailType(tile)] -= len * TUNNELBRIDGE_TRACKBIT_FACTOR;
    } else if (GetTunnelBridgeTransportType(tile) == TRANSPORT_ROAD) {
      /* A full diagonal road tile has two road bits. */
      UpdateCompanyRoadInfrastructure(GetRoadTypeRoad(tile), GetRoadOwner(tile, RTT_ROAD), -(int)(len * 2 * TUNNELBRIDGE_TRACKBIT_FACTOR));
      UpdateCompanyRoadInfrastructure(GetRoadTypeTram(tile), GetRoadOwner(tile, RTT_TRAM), -(int)(len * 2 * TUNNELBRIDGE_TRACKBIT_FACTOR));
    } else { // Aqueduct
      if (Company::IsValidID(owner)) Company::Get(owner)->infrastructure.water -= len * TUNNELBRIDGE_TRACKBIT_FACTOR;
    }
    DirtyCompanyInfrastructureWindows(owner);
 
    DoClearSquare(tile);
    DoClearSquare(endtile);
 
    for (TileIndex c = tile + delta; c != endtile; c += delta) {
      /* do not let trees appear from 'nowhere' after removing bridge */
      if (IsNormalRoadTile(c) && GetRoadside(c) == ROADSIDE_TREES) {
        int minz = GetTileMaxZ(c) + 3;
        if (height < minz) SetRoadside(c, ROADSIDE_PAVED);
      }
      ClearBridgeMiddle(c);
      MarkTileDirtyByTile(c, height - TileHeight(c));
    }
 
    if (rail) {
      /* cannot use INVALID_DIAGDIR for signal update because the bridge doesn't exist anymore */
      AddSideToSignalBuffer(tile,    ReverseDiagDir(direction), owner);
      AddSideToSignalBuffer(endtile, direction,                 owner);
 
      Track track = DiagDirToDiagTrack(direction);
      YapfNotifyTrackLayoutChange(tile,    track);
      YapfNotifyTrackLayoutChange(endtile, track);
 
      if (v != nullptr) TryPathReserve(v, true);
    }
  }
 
  return CommandCost(EXPENSES_CONSTRUCTION, len * base_cost);
}
static CommandCost DoClearBridge(TileIndex tile, DoCommandFlags flags) {…}
 
static CommandCost ClearTile_TunnelBridge(TileIndex tile, DoCommandFlags flags)
{
  if (IsTunnel(tile)) {
    if (flags.Test(DoCommandFlag::Auto)) return CommandCost(STR_ERROR_MUST_DEMOLISH_TUNNEL_FIRST);
    return DoClearTunnel(tile, flags);
  } else { // IsBridge(tile)
    if (flags.Test(DoCommandFlag::Auto)) return CommandCost(STR_ERROR_MUST_DEMOLISH_BRIDGE_FIRST);
    return DoClearBridge(tile, flags);
  }
}
static CommandCost ClearTile_TunnelBridge(TileIndex tile, DoCommandFlags flags) {…}
 
static inline void DrawPillar(const PalSpriteID *psid, int x, int y, int z, int w, int h, const SubSprite *subsprite)
{
  static const int PILLAR_Z_OFFSET = TILE_HEIGHT - BRIDGE_Z_START; 
  AddSortableSpriteToDraw(psid->sprite, psid->pal, x, y, w, h, BB_HEIGHT_UNDER_BRIDGE - PILLAR_Z_OFFSET, z, IsTransparencySet(TO_BRIDGES), 0, 0, -PILLAR_Z_OFFSET, subsprite);
}
static inline void DrawPillar(const PalSpriteID *psid, int x, int y, int z, int w, int h, const SubSprite *subsprite) {…}
 
static int DrawPillarColumn(int z_bottom, int z_top, const PalSpriteID *psid, int x, int y, int w, int h)
{
  int cur_z;
  for (cur_z = z_top; cur_z >= z_bottom; cur_z -= TILE_HEIGHT) {
    DrawPillar(psid, x, y, cur_z, w, h, nullptr);
  }
  return cur_z;
}
static int DrawPillarColumn(int z_bottom, int z_top, const PalSpriteID *psid, int x, int y, int w, int h) {…}
 
static void DrawBridgePillars(const PalSpriteID *psid, const TileInfo *ti, Axis axis, bool drawfarpillar, int x, int y, int z_bridge)
{
  static const int bounding_box_size[2]  = {16, 2}; 
  static const int back_pillar_offset[2] = { 0, 9}; 
 
  static const int INF = 1000; 
  static const SubSprite half_pillar_sub_sprite[2][2] = {
    { {  -14, -INF, INF, INF }, { -INF, -INF, -15, INF } }, // X axis, north and south
    { { -INF, -INF,  15, INF }, {   16, -INF, INF, INF } }, // Y axis, north and south
  };
 
  if (psid->sprite == 0) return;
 
  /* Determine ground height under pillars */
  DiagDirection south_dir = AxisToDiagDir(axis);
  int z_front_north = ti->z;
  int z_back_north = ti->z;
  int z_front_south = ti->z;
  int z_back_south = ti->z;
  GetSlopePixelZOnEdge(ti->tileh, south_dir, z_front_south, z_back_south);
  GetSlopePixelZOnEdge(ti->tileh, ReverseDiagDir(south_dir), z_front_north, z_back_north);
 
  /* Shared height of pillars */
  int z_front = std::max(z_front_north, z_front_south);
  int z_back = std::max(z_back_north, z_back_south);
 
  /* x and y size of bounding-box of pillars */
  int w = bounding_box_size[axis];
  int h = bounding_box_size[OtherAxis(axis)];
  /* sprite position of back facing pillar */
  int x_back = x - back_pillar_offset[axis];
  int y_back = y - back_pillar_offset[OtherAxis(axis)];
 
  /* Draw front pillars */
  int bottom_z = DrawPillarColumn(z_front, z_bridge, psid, x, y, w, h);
  if (z_front_north < z_front) DrawPillar(psid, x, y, bottom_z, w, h, &half_pillar_sub_sprite[axis][0]);
  if (z_front_south < z_front) DrawPillar(psid, x, y, bottom_z, w, h, &half_pillar_sub_sprite[axis][1]);
 
  /* Draw back pillars, skip top two parts, which are hidden by the bridge */
  int z_bridge_back = z_bridge - 2 * (int)TILE_HEIGHT;
  if (drawfarpillar && (z_back_north <= z_bridge_back || z_back_south <= z_bridge_back)) {
    bottom_z = DrawPillarColumn(z_back, z_bridge_back, psid, x_back, y_back, w, h);
    if (z_back_north < z_back) DrawPillar(psid, x_back, y_back, bottom_z, w, h, &half_pillar_sub_sprite[axis][0]);
    if (z_back_south < z_back) DrawPillar(psid, x_back, y_back, bottom_z, w, h, &half_pillar_sub_sprite[axis][1]);
  }
}
static void DrawBridgePillars(const PalSpriteID *psid, const TileInfo *ti, Axis axis, bool drawfarpillar, int x, int y, int z_bridge) {…}
 
static void GetBridgeRoadCatenary(const RoadTypeInfo *rti, TileIndex head_tile, int offset, bool head, SpriteID &spr_back, SpriteID &spr_front)
{
  static const SpriteID back_offsets[6]  = { 95,  96,  99, 102, 100, 101 };
  static const SpriteID front_offsets[6] = { 97,  98, 103, 106, 104, 105 };
 
  /* Simplified from DrawRoadTypeCatenary() to remove all the special cases required for regular ground road */
  spr_back = GetCustomRoadSprite(rti, head_tile, ROTSG_CATENARY_BACK, head ? TCX_NORMAL : TCX_ON_BRIDGE);
  spr_front = GetCustomRoadSprite(rti, head_tile, ROTSG_CATENARY_FRONT, head ? TCX_NORMAL : TCX_ON_BRIDGE);
  if (spr_back == 0 && spr_front == 0) {
    spr_back = SPR_TRAMWAY_BASE + back_offsets[offset];
    spr_front = SPR_TRAMWAY_BASE + front_offsets[offset];
  } else {
    if (spr_back != 0) spr_back += 23 + offset;
    if (spr_front != 0) spr_front += 23 + offset;
  }
}
static void GetBridgeRoadCatenary(const RoadTypeInfo *rti, TileIndex head_tile, int offset, bool head, SpriteID &spr_back, SpriteID &spr_front) {…}
 
static void DrawBridgeRoadBits(TileIndex head_tile, int x, int y, int z, int offset, bool head)
{
  RoadType road_rt = GetRoadTypeRoad(head_tile);
  RoadType tram_rt = GetRoadTypeTram(head_tile);
  const RoadTypeInfo *road_rti = road_rt == INVALID_ROADTYPE ? nullptr : GetRoadTypeInfo(road_rt);
  const RoadTypeInfo *tram_rti = tram_rt == INVALID_ROADTYPE ? nullptr : GetRoadTypeInfo(tram_rt);
 
  SpriteID seq_back[4] = { 0 };
  bool trans_back[4] = { false };
  SpriteID seq_front[4] = { 0 };
  bool trans_front[4] = { false };
 
  static const SpriteID overlay_offsets[6] = {   0,   1,  11,  12,  13,  14 };
  if (head || !IsInvisibilitySet(TO_BRIDGES)) {
    /* Road underlay takes precedence over tram */
    trans_back[0] = !head && IsTransparencySet(TO_BRIDGES);
    if (road_rti != nullptr) {
      if (road_rti->UsesOverlay()) {
        seq_back[0] = GetCustomRoadSprite(road_rti, head_tile, ROTSG_BRIDGE, head ? TCX_NORMAL : TCX_ON_BRIDGE) + offset;
      }
    } else if (tram_rti != nullptr) {
      if (tram_rti->UsesOverlay()) {
        seq_back[0] = GetCustomRoadSprite(tram_rti, head_tile, ROTSG_BRIDGE, head ? TCX_NORMAL : TCX_ON_BRIDGE) + offset;
      } else {
        seq_back[0] = SPR_TRAMWAY_BRIDGE + offset;
      }
    }
 
    /* Draw road overlay */
    trans_back[1] = !head && IsTransparencySet(TO_BRIDGES);
    if (road_rti != nullptr) {
      if (road_rti->UsesOverlay()) {
        seq_back[1] = GetCustomRoadSprite(road_rti, head_tile, ROTSG_OVERLAY, head ? TCX_NORMAL : TCX_ON_BRIDGE);
        if (seq_back[1] != 0) seq_back[1] += overlay_offsets[offset];
      }
    }
 
    /* Draw tram overlay */
    trans_back[2] = !head && IsTransparencySet(TO_BRIDGES);
    if (tram_rti != nullptr) {
      if (tram_rti->UsesOverlay()) {
        seq_back[2] = GetCustomRoadSprite(tram_rti, head_tile, ROTSG_OVERLAY, head ? TCX_NORMAL : TCX_ON_BRIDGE);
        if (seq_back[2] != 0) seq_back[2] += overlay_offsets[offset];
      } else if (road_rti != nullptr) {
        seq_back[2] = SPR_TRAMWAY_OVERLAY + overlay_offsets[offset];
      }
    }
 
    /* Road catenary takes precedence over tram */
    trans_back[3] = IsTransparencySet(TO_CATENARY);
    trans_front[0] = IsTransparencySet(TO_CATENARY);
    if (road_rti != nullptr && HasRoadCatenaryDrawn(road_rt)) {
      GetBridgeRoadCatenary(road_rti, head_tile, offset, head, seq_back[3], seq_front[0]);
    } else if (tram_rti != nullptr && HasRoadCatenaryDrawn(tram_rt)) {
      GetBridgeRoadCatenary(tram_rti, head_tile, offset, head, seq_back[3], seq_front[0]);
    }
  }
 
  static const uint size_x[6] = {  1, 16, 16,  1, 16,  1 };
  static const uint size_y[6] = { 16,  1,  1, 16,  1, 16 };
  static const uint front_bb_offset_x[6] = { 15,  0,  0, 15,  0, 15 };
  static const uint front_bb_offset_y[6] = {  0, 15, 15,  0, 15,  0 };
 
  /* The sprites under the vehicles are drawn as SpriteCombine. StartSpriteCombine() has already been called
   * The bounding boxes here are the same as for bridge front/roof */
  for (uint i = 0; i < lengthof(seq_back); ++i) {
    if (seq_back[i] != 0) {
      AddSortableSpriteToDraw(seq_back[i], PAL_NONE,
        x, y, size_x[offset], size_y[offset], 0x28, z,
        trans_back[i]);
    }
  }
 
  /* Start a new SpriteCombine for the front part */
  EndSpriteCombine();
  StartSpriteCombine();
 
  for (uint i = 0; i < lengthof(seq_front); ++i) {
    if (seq_front[i] != 0) {
      AddSortableSpriteToDraw(seq_front[i], PAL_NONE,
        x, y, size_x[offset] + front_bb_offset_x[offset], size_y[offset] + front_bb_offset_y[offset], 0x28, z,
        trans_front[i],
        front_bb_offset_x[offset], front_bb_offset_y[offset]);
    }
  }
}
static void DrawBridgeRoadBits(TileIndex head_tile, int x, int y, int z, int offset, bool head) {…}
 
static void DrawTile_TunnelBridge(TileInfo *ti)
{
  TransportType transport_type = GetTunnelBridgeTransportType(ti->tile);
  DiagDirection tunnelbridge_direction = GetTunnelBridgeDirection(ti->tile);
 
  if (IsTunnel(ti->tile)) {
    /* Front view of tunnel bounding boxes:
     *
     *   122223  <- BB_Z_SEPARATOR
     *   1    3
     *   1    3                1,3 = empty helper BB
     *   1    3                  2 = SpriteCombine of tunnel-roof and catenary (tram & elrail)
     *
     */
 
    static const int _tunnel_BB[4][12] = {
      /*  tunnnel-roof  |  Z-separator  | tram-catenary
       * w  h  bb_x bb_y| x   y   w   h |bb_x bb_y w h */
      {  1,  0, -15, -14,  0, 15, 16,  1, 0, 1, 16, 15 }, // NE
      {  0,  1, -14, -15, 15,  0,  1, 16, 1, 0, 15, 16 }, // SE
      {  1,  0, -15, -14,  0, 15, 16,  1, 0, 1, 16, 15 }, // SW
      {  0,  1, -14, -15, 15,  0,  1, 16, 1, 0, 15, 16 }, // NW
    };
    const int *BB_data = _tunnel_BB[tunnelbridge_direction];
 
    bool catenary = false;
 
    SpriteID image;
    SpriteID railtype_overlay = 0;
    if (transport_type == TRANSPORT_RAIL) {
      const RailTypeInfo *rti = GetRailTypeInfo(GetRailType(ti->tile));
      image = rti->base_sprites.tunnel;
      if (rti->UsesOverlay()) {
        /* Check if the railtype has custom tunnel portals. */
        railtype_overlay = GetCustomRailSprite(rti, ti->tile, RTSG_TUNNEL_PORTAL);
        if (railtype_overlay != 0) image = SPR_RAILTYPE_TUNNEL_BASE; // Draw blank grass tunnel base.
      }
    } else {
      image = SPR_TUNNEL_ENTRY_REAR_ROAD;
    }
 
    if (HasTunnelBridgeSnowOrDesert(ti->tile)) image += railtype_overlay != 0 ? 8 : 32;
 
    image += tunnelbridge_direction * 2;
    DrawGroundSprite(image, PAL_NONE);
 
    if (transport_type == TRANSPORT_ROAD) {
      RoadType road_rt = GetRoadTypeRoad(ti->tile);
      RoadType tram_rt = GetRoadTypeTram(ti->tile);
      const RoadTypeInfo *road_rti = road_rt == INVALID_ROADTYPE ? nullptr : GetRoadTypeInfo(road_rt);
      const RoadTypeInfo *tram_rti = tram_rt == INVALID_ROADTYPE ? nullptr : GetRoadTypeInfo(tram_rt);
      uint sprite_offset = DiagDirToAxis(tunnelbridge_direction) == AXIS_X ? 1 : 0;
      bool draw_underlay = true;
 
      /* Road underlay takes precedence over tram */
      if (road_rti != nullptr) {
        if (road_rti->UsesOverlay()) {
          SpriteID ground = GetCustomRoadSprite(road_rti, ti->tile, ROTSG_TUNNEL);
          if (ground != 0) {
            DrawGroundSprite(ground + tunnelbridge_direction, PAL_NONE);
            draw_underlay = false;
          }
        }
      } else {
        if (tram_rti->UsesOverlay()) {
          SpriteID ground = GetCustomRoadSprite(tram_rti, ti->tile, ROTSG_TUNNEL);
          if (ground != 0) {
            DrawGroundSprite(ground + tunnelbridge_direction, PAL_NONE);
            draw_underlay = false;
          }
        }
      }
 
      DrawRoadOverlays(ti, PAL_NONE, road_rti, tram_rti, sprite_offset, sprite_offset, draw_underlay);
 
      /* Road catenary takes precedence over tram */
      SpriteID catenary_sprite_base = 0;
      if (road_rti != nullptr && HasRoadCatenaryDrawn(road_rt)) {
        catenary_sprite_base = GetCustomRoadSprite(road_rti, ti->tile, ROTSG_CATENARY_FRONT);
        if (catenary_sprite_base == 0) {
          catenary_sprite_base = SPR_TRAMWAY_TUNNEL_WIRES;
        } else {
          catenary_sprite_base += 19;
        }
      } else if (tram_rti != nullptr && HasRoadCatenaryDrawn(tram_rt)) {
        catenary_sprite_base = GetCustomRoadSprite(tram_rti, ti->tile, ROTSG_CATENARY_FRONT);
        if (catenary_sprite_base == 0) {
          catenary_sprite_base = SPR_TRAMWAY_TUNNEL_WIRES;
        } else {
          catenary_sprite_base += 19;
        }
      }
 
      if (catenary_sprite_base != 0) {
        catenary = true;
        StartSpriteCombine();
        AddSortableSpriteToDraw(catenary_sprite_base + tunnelbridge_direction, PAL_NONE, ti->x, ti->y, BB_data[10], BB_data[11], TILE_HEIGHT, ti->z, IsTransparencySet(TO_CATENARY), BB_data[8], BB_data[9], BB_Z_SEPARATOR);
      }
    } else {
      const RailTypeInfo *rti = GetRailTypeInfo(GetRailType(ti->tile));
      if (rti->UsesOverlay()) {
        SpriteID surface = GetCustomRailSprite(rti, ti->tile, RTSG_TUNNEL);
        if (surface != 0) DrawGroundSprite(surface + tunnelbridge_direction, PAL_NONE);
      }
 
      /* PBS debugging, draw reserved tracks darker */
      if (_game_mode != GM_MENU && _settings_client.gui.show_track_reservation && HasTunnelBridgeReservation(ti->tile)) {
        if (rti->UsesOverlay()) {
          SpriteID overlay = GetCustomRailSprite(rti, ti->tile, RTSG_OVERLAY);
          DrawGroundSprite(overlay + RTO_X + DiagDirToAxis(tunnelbridge_direction), PALETTE_CRASH);
        } else {
          DrawGroundSprite(DiagDirToAxis(tunnelbridge_direction) == AXIS_X ? rti->base_sprites.single_x : rti->base_sprites.single_y, PALETTE_CRASH);
        }
      }
 
      if (HasRailCatenaryDrawn(GetRailType(ti->tile))) {
        /* Maybe draw pylons on the entry side */
        DrawRailCatenary(ti);
 
        catenary = true;
        StartSpriteCombine();
        /* Draw wire above the ramp */
        DrawRailCatenaryOnTunnel(ti);
      }
    }
 
    if (railtype_overlay != 0 && !catenary) StartSpriteCombine();
 
    AddSortableSpriteToDraw(image + 1, PAL_NONE, ti->x + TILE_SIZE - 1, ti->y + TILE_SIZE - 1, BB_data[0], BB_data[1], TILE_HEIGHT, ti->z, false, BB_data[2], BB_data[3], BB_Z_SEPARATOR);
    /* Draw railtype tunnel portal overlay if defined. */
    if (railtype_overlay != 0) AddSortableSpriteToDraw(railtype_overlay + tunnelbridge_direction, PAL_NONE, ti->x + TILE_SIZE - 1, ti->y + TILE_SIZE - 1, BB_data[0], BB_data[1], TILE_HEIGHT, ti->z, false, BB_data[2], BB_data[3], BB_Z_SEPARATOR);
 
    if (catenary || railtype_overlay != 0) EndSpriteCombine();
 
    /* Add helper BB for sprite sorting that separates the tunnel from things beside of it. */
    AddSortableSpriteToDraw(SPR_EMPTY_BOUNDING_BOX, PAL_NONE, ti->x,              ti->y,              BB_data[6], BB_data[7], TILE_HEIGHT, ti->z);
    AddSortableSpriteToDraw(SPR_EMPTY_BOUNDING_BOX, PAL_NONE, ti->x + BB_data[4], ti->y + BB_data[5], BB_data[6], BB_data[7], TILE_HEIGHT, ti->z);
 
    DrawBridgeMiddle(ti);
  } else { // IsBridge(ti->tile)
    const PalSpriteID *psid;
    int base_offset;
    bool ice = HasTunnelBridgeSnowOrDesert(ti->tile);
 
    if (transport_type == TRANSPORT_RAIL) {
      base_offset = GetRailTypeInfo(GetRailType(ti->tile))->bridge_offset;
      assert(base_offset != 8); // This one is used for roads
    } else {
      base_offset = 8;
    }
 
    /* as the lower 3 bits are used for other stuff, make sure they are clear */
    assert( (base_offset & 0x07) == 0x00);
 
    DrawFoundation(ti, GetBridgeFoundation(ti->tileh, DiagDirToAxis(tunnelbridge_direction)));
 
    /* HACK Wizardry to convert the bridge ramp direction into a sprite offset */
    base_offset += (6 - tunnelbridge_direction) % 4;
 
    /* Table number BRIDGE_PIECE_HEAD always refers to the bridge heads for any bridge type */
    if (transport_type != TRANSPORT_WATER) {
      if (ti->tileh == SLOPE_FLAT) base_offset += 4; // sloped bridge head
      psid = &GetBridgeSpriteTable(GetBridgeType(ti->tile), BRIDGE_PIECE_HEAD)[base_offset];
    } else {
      psid = _aqueduct_sprites + base_offset;
    }
 
    if (!ice) {
      TileIndex next = ti->tile + TileOffsByDiagDir(tunnelbridge_direction);
      if (ti->tileh != SLOPE_FLAT && ti->z == 0 && HasTileWaterClass(next) && GetWaterClass(next) == WATER_CLASS_SEA) {
        DrawShoreTile(ti->tileh);
      } else {
        DrawClearLandTile(ti, 3);
      }
    } else {
      DrawGroundSprite(SPR_FLAT_SNOW_DESERT_TILE + SlopeToSpriteOffset(ti->tileh), PAL_NONE);
    }
 
    /* draw ramp */
 
    /* Draw Trambits and PBS Reservation as SpriteCombine */
    if (transport_type == TRANSPORT_ROAD || transport_type == TRANSPORT_RAIL) StartSpriteCombine();
 
    /* HACK set the height of the BB of a sloped ramp to 1 so a vehicle on
     * it doesn't disappear behind it
     */
    /* Bridge heads are drawn solid no matter how invisibility/transparency is set */
    AddSortableSpriteToDraw(psid->sprite, psid->pal, ti->x, ti->y, 16, 16, ti->tileh == SLOPE_FLAT ? 0 : 8, ti->z);
 
    if (transport_type == TRANSPORT_ROAD) {
      uint offset = tunnelbridge_direction;
      int z = ti->z;
      if (ti->tileh != SLOPE_FLAT) {
        offset = (offset + 1) & 1;
        z += TILE_HEIGHT;
      } else {
        offset += 2;
      }
 
      /* DrawBridgeRoadBits() calls EndSpriteCombine() and StartSpriteCombine() */
      DrawBridgeRoadBits(ti->tile, ti->x, ti->y, z, offset, true);
 
      EndSpriteCombine();
    } else if (transport_type == TRANSPORT_RAIL) {
      const RailTypeInfo *rti = GetRailTypeInfo(GetRailType(ti->tile));
      if (rti->UsesOverlay()) {
        SpriteID surface = GetCustomRailSprite(rti, ti->tile, RTSG_BRIDGE);
        if (surface != 0) {
          if (HasBridgeFlatRamp(ti->tileh, DiagDirToAxis(tunnelbridge_direction))) {
            AddSortableSpriteToDraw(surface + ((DiagDirToAxis(tunnelbridge_direction) == AXIS_X) ? RTBO_X : RTBO_Y), PAL_NONE, ti->x, ti->y, 16, 16, 0, ti->z + 8);
          } else {
            AddSortableSpriteToDraw(surface + RTBO_SLOPE + tunnelbridge_direction, PAL_NONE, ti->x, ti->y, 16, 16, 8, ti->z);
          }
        }
        /* Don't fallback to non-overlay sprite -- the spec states that
         * if an overlay is present then the bridge surface must be
         * present. */
      }
 
      /* PBS debugging, draw reserved tracks darker */
      if (_game_mode != GM_MENU && _settings_client.gui.show_track_reservation && HasTunnelBridgeReservation(ti->tile)) {
        if (rti->UsesOverlay()) {
          SpriteID overlay = GetCustomRailSprite(rti, ti->tile, RTSG_OVERLAY);
          if (HasBridgeFlatRamp(ti->tileh, DiagDirToAxis(tunnelbridge_direction))) {
            AddSortableSpriteToDraw(overlay + RTO_X + DiagDirToAxis(tunnelbridge_direction), PALETTE_CRASH, ti->x, ti->y, 16, 16, 0, ti->z + 8);
          } else {
            AddSortableSpriteToDraw(overlay + RTO_SLOPE_NE + tunnelbridge_direction, PALETTE_CRASH, ti->x, ti->y, 16, 16, 8, ti->z);
          }
        } else {
          if (HasBridgeFlatRamp(ti->tileh, DiagDirToAxis(tunnelbridge_direction))) {
            AddSortableSpriteToDraw(DiagDirToAxis(tunnelbridge_direction) == AXIS_X ? rti->base_sprites.single_x : rti->base_sprites.single_y, PALETTE_CRASH, ti->x, ti->y, 16, 16, 0, ti->z + 8);
          } else {
            AddSortableSpriteToDraw(rti->base_sprites.single_sloped + tunnelbridge_direction, PALETTE_CRASH, ti->x, ti->y, 16, 16, 8, ti->z);
          }
        }
      }
 
      EndSpriteCombine();
      if (HasRailCatenaryDrawn(GetRailType(ti->tile))) {
        DrawRailCatenary(ti);
      }
    }
 
    DrawBridgeMiddle(ti);
  }
}
static void DrawTile_TunnelBridge(TileInfo *ti) {…}
 
 
static BridgePieces CalcBridgePiece(uint north, uint south)
{
  if (north == 1) {
    return BRIDGE_PIECE_NORTH;
  } else if (south == 1) {
    return BRIDGE_PIECE_SOUTH;
  } else if (north < south) {
    return north & 1 ? BRIDGE_PIECE_INNER_SOUTH : BRIDGE_PIECE_INNER_NORTH;
  } else if (north > south) {
    return south & 1 ? BRIDGE_PIECE_INNER_NORTH : BRIDGE_PIECE_INNER_SOUTH;
  } else {
    return north & 1 ? BRIDGE_PIECE_MIDDLE_EVEN : BRIDGE_PIECE_MIDDLE_ODD;
  }
}
static BridgePieces CalcBridgePiece(uint north, uint south) {…}
 
void DrawBridgeMiddle(const TileInfo *ti)
{
  /* Sectional view of bridge bounding boxes:
   *
   *  1           2                                1,2 = SpriteCombine of Bridge front/(back&floor) and RoadCatenary
   *  1           2                                  3 = empty helper BB
   *  1     7     2                                4,5 = pillars under higher bridges
   *  1 6 88888 6 2                                  6 = elrail-pylons
   *  1 6 88888 6 2                                  7 = elrail-wire
   *  1 6 88888 6 2  <- TILE_HEIGHT                  8 = rail-vehicle on bridge
   *  3333333333333  <- BB_Z_SEPARATOR
   *                 <- unused
   *    4       5    <- BB_HEIGHT_UNDER_BRIDGE
   *    4       5
   *    4       5
   *
   */
 
  if (!IsBridgeAbove(ti->tile)) return;
 
  TileIndex rampnorth = GetNorthernBridgeEnd(ti->tile);
  TileIndex rampsouth = GetSouthernBridgeEnd(ti->tile);
  TransportType transport_type = GetTunnelBridgeTransportType(rampsouth);
 
  Axis axis = GetBridgeAxis(ti->tile);
  BridgePieces piece = CalcBridgePiece(
    GetTunnelBridgeLength(ti->tile, rampnorth) + 1,
    GetTunnelBridgeLength(ti->tile, rampsouth) + 1
  );
 
  const PalSpriteID *psid;
  bool drawfarpillar;
  if (transport_type != TRANSPORT_WATER) {
    BridgeType type =  GetBridgeType(rampsouth);
    drawfarpillar = !HasBit(GetBridgeSpec(type)->flags, 0);
 
    uint base_offset;
    if (transport_type == TRANSPORT_RAIL) {
      base_offset = GetRailTypeInfo(GetRailType(rampsouth))->bridge_offset;
    } else {
      base_offset = 8;
    }
 
    psid = &GetBridgeSpriteTable(type, piece)[base_offset];
  } else {
    drawfarpillar = true;
    psid = _aqueduct_sprites;
  }
 
  if (axis != AXIS_X) psid += 4;
 
  int x = ti->x;
  int y = ti->y;
  uint bridge_z = GetBridgePixelHeight(rampsouth);
  int z = bridge_z - BRIDGE_Z_START;
 
  /* Add a bounding box that separates the bridge from things below it. */
  AddSortableSpriteToDraw(SPR_EMPTY_BOUNDING_BOX, PAL_NONE, x, y, 16, 16, 1, bridge_z - TILE_HEIGHT + BB_Z_SEPARATOR);
 
  /* Draw Trambits as SpriteCombine */
  if (transport_type == TRANSPORT_ROAD || transport_type == TRANSPORT_RAIL) StartSpriteCombine();
 
  /* Draw floor and far part of bridge*/
  if (!IsInvisibilitySet(TO_BRIDGES)) {
    if (axis == AXIS_X) {
      AddSortableSpriteToDraw(psid->sprite, psid->pal, x, y, 16, 1, 0x28, z, IsTransparencySet(TO_BRIDGES), 0, 0, BRIDGE_Z_START);
    } else {
      AddSortableSpriteToDraw(psid->sprite, psid->pal, x, y, 1, 16, 0x28, z, IsTransparencySet(TO_BRIDGES), 0, 0, BRIDGE_Z_START);
    }
  }
 
  psid++;
 
  if (transport_type == TRANSPORT_ROAD) {
    /* DrawBridgeRoadBits() calls EndSpriteCombine() and StartSpriteCombine() */
    DrawBridgeRoadBits(rampsouth, x, y, bridge_z, axis ^ 1, false);
  } else if (transport_type == TRANSPORT_RAIL) {
    const RailTypeInfo *rti = GetRailTypeInfo(GetRailType(rampsouth));
    if (rti->UsesOverlay() && !IsInvisibilitySet(TO_BRIDGES)) {
      SpriteID surface = GetCustomRailSprite(rti, rampsouth, RTSG_BRIDGE, TCX_ON_BRIDGE);
      if (surface != 0) {
        AddSortableSpriteToDraw(surface + axis, PAL_NONE, x, y, 16, 16, 0, bridge_z, IsTransparencySet(TO_BRIDGES));
      }
    }
 
    if (_game_mode != GM_MENU && _settings_client.gui.show_track_reservation && !IsInvisibilitySet(TO_BRIDGES) && HasTunnelBridgeReservation(rampnorth)) {
      if (rti->UsesOverlay()) {
        SpriteID overlay = GetCustomRailSprite(rti, ti->tile, RTSG_OVERLAY);
        AddSortableSpriteToDraw(overlay + RTO_X + axis, PALETTE_CRASH, ti->x, ti->y, 16, 16, 0, bridge_z, IsTransparencySet(TO_BRIDGES));
      } else {
        AddSortableSpriteToDraw(axis == AXIS_X ? rti->base_sprites.single_x : rti->base_sprites.single_y, PALETTE_CRASH, ti->x, ti->y, 16, 16, 0, bridge_z, IsTransparencySet(TO_BRIDGES));
      }
    }
 
    EndSpriteCombine();
 
    if (HasRailCatenaryDrawn(GetRailType(rampsouth))) {
      DrawRailCatenaryOnBridge(ti);
    }
  }
 
  /* draw roof, the component of the bridge which is logically between the vehicle and the camera */
  if (!IsInvisibilitySet(TO_BRIDGES)) {
    if (axis == AXIS_X) {
      y += 12;
      if (psid->sprite & SPRITE_MASK) AddSortableSpriteToDraw(psid->sprite, psid->pal, x, y, 16, 4, 0x28, z, IsTransparencySet(TO_BRIDGES), 0, 3, BRIDGE_Z_START);
    } else {
      x += 12;
      if (psid->sprite & SPRITE_MASK) AddSortableSpriteToDraw(psid->sprite, psid->pal, x, y, 4, 16, 0x28, z, IsTransparencySet(TO_BRIDGES), 3, 0, BRIDGE_Z_START);
    }
  }
 
  /* Draw TramFront as SpriteCombine */
  if (transport_type == TRANSPORT_ROAD) EndSpriteCombine();
 
  /* Do not draw anything more if bridges are invisible */
  if (IsInvisibilitySet(TO_BRIDGES)) return;
 
  psid++;
  DrawBridgePillars(psid, ti, axis, drawfarpillar, x, y, z);
}
void DrawBridgeMiddle(const TileInfo *ti) {…}
 
 
static int GetSlopePixelZ_TunnelBridge(TileIndex tile, uint x, uint y, bool ground_vehicle)
{
  auto [tileh, z] = GetTilePixelSlope(tile);
 
  x &= 0xF;
  y &= 0xF;
 
  if (IsTunnel(tile)) {
    /* In the tunnel entrance? */
    if (ground_vehicle) return z;
  } else { // IsBridge(tile)
    DiagDirection dir = GetTunnelBridgeDirection(tile);
    z += ApplyPixelFoundationToSlope(GetBridgeFoundation(tileh, DiagDirToAxis(dir)), tileh);
 
    /* On the bridge ramp? */
    if (ground_vehicle) {
      if (tileh != SLOPE_FLAT) return z + TILE_HEIGHT;
 
      switch (dir) {
        default: NOT_REACHED();
        case DIAGDIR_NE: tileh = SLOPE_NE; break;
        case DIAGDIR_SE: tileh = SLOPE_SE; break;
        case DIAGDIR_SW: tileh = SLOPE_SW; break;
        case DIAGDIR_NW: tileh = SLOPE_NW; break;
      }
    }
  }
 
  return z + GetPartialPixelZ(x, y, tileh);
}
 
static Foundation GetFoundation_TunnelBridge(TileIndex tile, Slope tileh)
{
  return IsTunnel(tile) ? FOUNDATION_NONE : GetBridgeFoundation(tileh, DiagDirToAxis(GetTunnelBridgeDirection(tile)));
}
 
static void GetTileDesc_TunnelBridge(TileIndex tile, TileDesc &td)
{
  TransportType tt = GetTunnelBridgeTransportType(tile);
 
  if (IsTunnel(tile)) {
    td.str = (tt == TRANSPORT_RAIL) ? STR_LAI_TUNNEL_DESCRIPTION_RAILROAD : STR_LAI_TUNNEL_DESCRIPTION_ROAD;
  } else { // IsBridge(tile)
    td.str = (tt == TRANSPORT_WATER) ? STR_LAI_BRIDGE_DESCRIPTION_AQUEDUCT : GetBridgeSpec(GetBridgeType(tile))->transport_name[tt];
  }
  td.owner[0] = GetTileOwner(tile);
 
  Owner road_owner = INVALID_OWNER;
  Owner tram_owner = INVALID_OWNER;
  RoadType road_rt = (tt == TRANSPORT_ROAD) ? GetRoadTypeRoad(tile) : INVALID_ROADTYPE;
  RoadType tram_rt = (tt == TRANSPORT_ROAD) ? GetRoadTypeTram(tile) : INVALID_ROADTYPE;
  if (road_rt != INVALID_ROADTYPE) {
    const RoadTypeInfo *rti = GetRoadTypeInfo(road_rt);
    td.roadtype = rti->strings.name;
    td.road_speed = rti->max_speed / 2;
    road_owner = GetRoadOwner(tile, RTT_ROAD);
  }
  if (tram_rt != INVALID_ROADTYPE) {
    const RoadTypeInfo *rti = GetRoadTypeInfo(tram_rt);
    td.tramtype = rti->strings.name;
    td.tram_speed = rti->max_speed / 2;
    tram_owner = GetRoadOwner(tile, RTT_TRAM);
  }
 
  /* Is there a mix of owners? */
  if ((tram_owner != INVALID_OWNER && tram_owner != td.owner[0]) ||
      (road_owner != INVALID_OWNER && road_owner != td.owner[0])) {
    uint i = 1;
    if (road_owner != INVALID_OWNER) {
      td.owner_type[i] = STR_LAND_AREA_INFORMATION_ROAD_OWNER;
      td.owner[i] = road_owner;
      i++;
    }
    if (tram_owner != INVALID_OWNER) {
      td.owner_type[i] = STR_LAND_AREA_INFORMATION_TRAM_OWNER;
      td.owner[i] = tram_owner;
    }
  }
 
  if (tt == TRANSPORT_RAIL) {
    const RailTypeInfo *rti = GetRailTypeInfo(GetRailType(tile));
    td.rail_speed = rti->max_speed;
    td.railtype = rti->strings.name;
 
    if (!IsTunnel(tile)) {
      uint16_t spd = GetBridgeSpec(GetBridgeType(tile))->speed;
      /* rail speed special-cases 0 as unlimited, hides display of limit etc. */
      if (spd == UINT16_MAX) spd = 0;
      if (td.rail_speed == 0 || spd < td.rail_speed) {
        td.rail_speed = spd;
      }
    }
  } else if (tt == TRANSPORT_ROAD && !IsTunnel(tile)) {
    uint16_t spd = GetBridgeSpec(GetBridgeType(tile))->speed;
    /* road speed special-cases 0 as unlimited, hides display of limit etc. */
    if (spd == UINT16_MAX) spd = 0;
    if (road_rt != INVALID_ROADTYPE && (td.road_speed == 0 || spd < td.road_speed)) td.road_speed = spd;
    if (tram_rt != INVALID_ROADTYPE && (td.tram_speed == 0 || spd < td.tram_speed)) td.tram_speed = spd;
  }
}
 
 
static void TileLoop_TunnelBridge(TileIndex tile)
{
  bool snow_or_desert = HasTunnelBridgeSnowOrDesert(tile);
  switch (_settings_game.game_creation.landscape) {
    case LandscapeType::Arctic: {
      /* As long as we do not have a snow density, we want to use the density
       * from the entry edge. For tunnels this is the lowest point for bridges the highest point.
       * (Independent of foundations) */
      int z = IsBridge(tile) ? GetTileMaxZ(tile) : GetTileZ(tile);
      if (snow_or_desert != (z > GetSnowLine())) {
        SetTunnelBridgeSnowOrDesert(tile, !snow_or_desert);
        MarkTileDirtyByTile(tile);
      }
      break;
    }
 
    case LandscapeType::Tropic:
      if (GetTropicZone(tile) == TROPICZONE_DESERT && !snow_or_desert) {
        SetTunnelBridgeSnowOrDesert(tile, true);
        MarkTileDirtyByTile(tile);
      }
      break;
 
    default:
      break;
  }
}
 
static TrackStatus GetTileTrackStatus_TunnelBridge(TileIndex tile, TransportType mode, uint sub_mode, DiagDirection side)
{
  TransportType transport_type = GetTunnelBridgeTransportType(tile);
  if (transport_type != mode || (transport_type == TRANSPORT_ROAD && !HasTileRoadType(tile, (RoadTramType)sub_mode))) return 0;
 
  DiagDirection dir = GetTunnelBridgeDirection(tile);
  if (side != INVALID_DIAGDIR && side != ReverseDiagDir(dir)) return 0;
  return CombineTrackStatus(TrackBitsToTrackdirBits(DiagDirToDiagTrackBits(dir)), TRACKDIR_BIT_NONE);
}
 
static void ChangeTileOwner_TunnelBridge(TileIndex tile, Owner old_owner, Owner new_owner)
{
  TileIndex other_end = GetOtherTunnelBridgeEnd(tile);
  /* Set number of pieces to zero if it's the southern tile as we
   * don't want to update the infrastructure counts twice. */
  uint num_pieces = tile < other_end ? (GetTunnelBridgeLength(tile, other_end) + 2) * TUNNELBRIDGE_TRACKBIT_FACTOR : 0;
 
  TransportType tt = GetTunnelBridgeTransportType(tile);
 
  if (tt == TRANSPORT_ROAD) {
    for (RoadTramType rtt : _roadtramtypes) {
      /* Update all roadtypes, no matter if they are present */
      if (GetRoadOwner(tile, rtt) == old_owner) {
        RoadType rt = GetRoadType(tile, rtt);
        if (rt != INVALID_ROADTYPE) {
          /* Update company infrastructure counts. A full diagonal road tile has two road bits.
           * No need to dirty windows here, we'll redraw the whole screen anyway. */
          Company::Get(old_owner)->infrastructure.road[rt] -= num_pieces * 2;
          if (new_owner != INVALID_OWNER) Company::Get(new_owner)->infrastructure.road[rt] += num_pieces * 2;
        }
 
        SetRoadOwner(tile, rtt, new_owner == INVALID_OWNER ? OWNER_NONE : new_owner);
      }
    }
  }
 
  if (!IsTileOwner(tile, old_owner)) return;
 
  /* Update company infrastructure counts for rail and water as well.
   * No need to dirty windows here, we'll redraw the whole screen anyway. */
  Company *old = Company::Get(old_owner);
  if (tt == TRANSPORT_RAIL) {
    old->infrastructure.rail[GetRailType(tile)] -= num_pieces;
    if (new_owner != INVALID_OWNER) Company::Get(new_owner)->infrastructure.rail[GetRailType(tile)] += num_pieces;
  } else if (tt == TRANSPORT_WATER) {
    old->infrastructure.water -= num_pieces;
    if (new_owner != INVALID_OWNER) Company::Get(new_owner)->infrastructure.water += num_pieces;
  }
 
  if (new_owner != INVALID_OWNER) {
    SetTileOwner(tile, new_owner);
  } else {
    if (tt == TRANSPORT_RAIL) {
      /* Since all of our vehicles have been removed, it is safe to remove the rail
       * bridge / tunnel. */
      [[maybe_unused]] CommandCost ret = Command<CMD_LANDSCAPE_CLEAR>::Do({DoCommandFlag::Execute, DoCommandFlag::Bankrupt}, tile);
      assert(ret.Succeeded());
    } else {
      /* In any other case, we can safely reassign the ownership to OWNER_NONE. */
      SetTileOwner(tile, OWNER_NONE);
    }
  }
}
 
template <typename T>
static void PrepareToEnterBridge(T *gv)
{
  if (HasBit(gv->gv_flags, GVF_GOINGUP_BIT)) {
    gv->z_pos++;
    ClrBit(gv->gv_flags, GVF_GOINGUP_BIT);
  } else {
    ClrBit(gv->gv_flags, GVF_GOINGDOWN_BIT);
  }
}
static void PrepareToEnterBridge(T *gv) {…}
 
static const uint8_t TUNNEL_SOUND_FRAME = 1;
 
extern const uint8_t _tunnel_visibility_frame[DIAGDIR_END] = {12, 8, 8, 12};
 
static VehicleEnterTileStates VehicleEnter_TunnelBridge(Vehicle *v, TileIndex tile, int x, int y)
{
  int z = GetSlopePixelZ(x, y, true) - v->z_pos;
 
  if (abs(z) > 2) return VehicleEnterTileState::CannotEnter;
  /* Direction into the wormhole */
  const DiagDirection dir = GetTunnelBridgeDirection(tile);
  /* Direction of the vehicle */
  const DiagDirection vdir = DirToDiagDir(v->direction);
  /* New position of the vehicle on the tile */
  uint8_t pos = (DiagDirToAxis(vdir) == AXIS_X ? x : y) & TILE_UNIT_MASK;
  /* Number of units moved by the vehicle since entering the tile */
  uint8_t frame = (vdir == DIAGDIR_NE || vdir == DIAGDIR_NW) ? TILE_SIZE - 1 - pos : pos;
 
  if (IsTunnel(tile)) {
    if (v->type == VEH_TRAIN) {
      Train *t = Train::From(v);
 
      if (t->track != TRACK_BIT_WORMHOLE && dir == vdir) {
        if (t->IsFrontEngine() && frame == TUNNEL_SOUND_FRAME) {
          if (!PlayVehicleSound(t, VSE_TUNNEL) && RailVehInfo(t->engine_type)->engclass == 0) {
            SndPlayVehicleFx(SND_05_TRAIN_THROUGH_TUNNEL, v);
          }
          return {};
        }
        if (frame == _tunnel_visibility_frame[dir]) {
          t->tile = tile;
          t->track = TRACK_BIT_WORMHOLE;
          t->vehstatus.Set(VehState::Hidden);
          return VehicleEnterTileState::EnteredWormhole;
        }
      }
 
      if (dir == ReverseDiagDir(vdir) && frame == TILE_SIZE - _tunnel_visibility_frame[dir] && z == 0) {
        /* We're at the tunnel exit ?? */
        t->tile = tile;
        t->track = DiagDirToDiagTrackBits(vdir);
        assert(t->track);
        t->vehstatus.Reset(VehState::Hidden);
        return VehicleEnterTileState::EnteredWormhole;
      }
    } else if (v->type == VEH_ROAD) {
      RoadVehicle *rv = RoadVehicle::From(v);
 
      /* Enter tunnel? */
      if (rv->state != RVSB_WORMHOLE && dir == vdir) {
        if (frame == _tunnel_visibility_frame[dir]) {
          /* Frame should be equal to the next frame number in the RV's movement */
          assert(frame == rv->frame + 1);
          rv->tile = tile;
          rv->state = RVSB_WORMHOLE;
          rv->vehstatus.Set(VehState::Hidden);
          return VehicleEnterTileState::EnteredWormhole;
        } else {
          return {};
        }
      }
 
      /* We're at the tunnel exit ?? */
      if (dir == ReverseDiagDir(vdir) && frame == TILE_SIZE - _tunnel_visibility_frame[dir] && z == 0) {
        rv->tile = tile;
        rv->state = DiagDirToDiagTrackdir(vdir);
        rv->frame = frame;
        rv->vehstatus.Reset(VehState::Hidden);
        return VehicleEnterTileState::EnteredWormhole;
      }
    }
  } else { // IsBridge(tile)
    if (v->type != VEH_SHIP) {
      /* modify speed of vehicle */
      uint16_t spd = GetBridgeSpec(GetBridgeType(tile))->speed;
 
      if (v->type == VEH_ROAD) spd *= 2;
      Vehicle *first = v->First();
      first->cur_speed = std::min(first->cur_speed, spd);
    }
 
    if (vdir == dir) {
      /* Vehicle enters bridge at the last frame inside this tile. */
      if (frame != TILE_SIZE - 1) return {};
      switch (v->type) {
        case VEH_TRAIN: {
          Train *t = Train::From(v);
          t->track = TRACK_BIT_WORMHOLE;
          PrepareToEnterBridge(t);
          break;
        }
 
        case VEH_ROAD: {
          RoadVehicle *rv = RoadVehicle::From(v);
          rv->state = RVSB_WORMHOLE;
          PrepareToEnterBridge(rv);
          break;
        }
 
        case VEH_SHIP:
          Ship::From(v)->state = TRACK_BIT_WORMHOLE;
          break;
 
        default: NOT_REACHED();
      }
      return VehicleEnterTileState::EnteredWormhole;
    } else if (vdir == ReverseDiagDir(dir)) {
      v->tile = tile;
      switch (v->type) {
        case VEH_TRAIN: {
          Train *t = Train::From(v);
          if (t->track == TRACK_BIT_WORMHOLE) {
            t->track = DiagDirToDiagTrackBits(vdir);
            return VehicleEnterTileState::EnteredWormhole;
          }
          break;
        }
 
        case VEH_ROAD: {
          RoadVehicle *rv = RoadVehicle::From(v);
          if (rv->state == RVSB_WORMHOLE) {
            rv->state = DiagDirToDiagTrackdir(vdir);
            rv->frame = 0;
            return VehicleEnterTileState::EnteredWormhole;
          }
          break;
        }
 
        case VEH_SHIP: {
          Ship *ship = Ship::From(v);
          if (ship->state == TRACK_BIT_WORMHOLE) {
            ship->state = DiagDirToDiagTrackBits(vdir);
            return VehicleEnterTileState::EnteredWormhole;
          }
          break;
        }
 
        default: NOT_REACHED();
      }
    }
  }
  return {};
}
 
static CommandCost TerraformTile_TunnelBridge(TileIndex tile, DoCommandFlags flags, int z_new, Slope tileh_new)
{
  if (_settings_game.construction.build_on_slopes && AutoslopeEnabled() && IsBridge(tile) && GetTunnelBridgeTransportType(tile) != TRANSPORT_WATER) {
    DiagDirection direction = GetTunnelBridgeDirection(tile);
    Axis axis = DiagDirToAxis(direction);
    CommandCost res;
    auto [tileh_old, z_old] = GetTileSlopeZ(tile);
 
    /* Check if new slope is valid for bridges in general (so we can safely call GetBridgeFoundation()) */
    if ((direction == DIAGDIR_NW) || (direction == DIAGDIR_NE)) {
      CheckBridgeSlope(BRIDGE_PIECE_SOUTH, axis, tileh_old, z_old);
      res = CheckBridgeSlope(BRIDGE_PIECE_SOUTH, axis, tileh_new, z_new);
    } else {
      CheckBridgeSlope(BRIDGE_PIECE_NORTH, axis, tileh_old, z_old);
      res = CheckBridgeSlope(BRIDGE_PIECE_NORTH, axis, tileh_new, z_new);
    }
 
    /* Surface slope is valid and remains unchanged? */
    if (res.Succeeded() && (z_old == z_new) && (tileh_old == tileh_new)) return CommandCost(EXPENSES_CONSTRUCTION, _price[PR_BUILD_FOUNDATION]);
  }
 
  return Command<CMD_LANDSCAPE_CLEAR>::Do(flags, tile);
}
 
extern const TileTypeProcs _tile_type_tunnelbridge_procs = {
  DrawTile_TunnelBridge,           // draw_tile_proc
  GetSlopePixelZ_TunnelBridge,     // get_slope_z_proc
  ClearTile_TunnelBridge,          // clear_tile_proc
  nullptr,                            // add_accepted_cargo_proc
  GetTileDesc_TunnelBridge,        // get_tile_desc_proc
  GetTileTrackStatus_TunnelBridge, // get_tile_track_status_proc
  nullptr,                            // click_tile_proc
  nullptr,                            // animate_tile_proc
  TileLoop_TunnelBridge,           // tile_loop_proc
  ChangeTileOwner_TunnelBridge,    // change_tile_owner_proc
  nullptr,                            // add_produced_cargo_proc
  VehicleEnter_TunnelBridge,       // vehicle_enter_tile_proc
  GetFoundation_TunnelBridge,      // get_foundation_proc
  TerraformTile_TunnelBridge,      // terraform_tile_proc
};