Turn a conditional into an assertion in ConLoad

[openttd/fttd.git] / src / bridge_cmd.cpp

/* $Id$ */

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

/**
 * @file bridge_cmd.cpp
 * This file deals with bridges (non-gui stuff)
 */

#include "stdafx.h"
#include "bridge.h"
#include "tunnelbridge.h"
#include "landscape.h"
#include "slope_func.h"
#include "command_func.h"
#include "date_func.h"
#include "economy_func.h"
#include "map/ground.h"
#include "map/water.h"
#include "map/rail.h"
#include "map/road.h"
#include "map/slope.h"
#include "map/tunnelbridge.h"
#include "viewport_func.h"
#include "transparency.h"
#include "rail.h"
#include "elrail_func.h"
#include "clear_func.h"
#include "water.h"

#include "newgrf_commons.h"
#include "newgrf_railtype.h"
#include "newgrf_object.h"
#include "newgrf_station.h"

#include "table/sprites.h"
#include "table/strings.h"
#include "table/bridge_land.h"


/** Data for CheckExtendedBridgeHead; see the function for details */
extern const uint32 bridgehead_valid_slopes[DIAGDIR_END][2] = {
        { (1 << SLOPE_W) | (1 << SLOPE_STEEP_W),
                (1 << SLOPE_S) | (1 << SLOPE_STEEP_S) },
        { (1 << SLOPE_N) | (1 << SLOPE_STEEP_N),
                (1 << SLOPE_W) | (1 << SLOPE_STEEP_W) },
        { (1 << SLOPE_E) | (1 << SLOPE_STEEP_E),
                (1 << SLOPE_N) | (1 << SLOPE_STEEP_N) },
        { (1 << SLOPE_S) | (1 << SLOPE_STEEP_S),
                (1 << SLOPE_E) | (1 << SLOPE_STEEP_E) },
};


/** Z position of the bridge sprites relative to bridge height (downwards) */
static const int BRIDGE_Z_START = 3;

BridgeSpec _bridge[MAX_BRIDGES]; ///< The specification of all bridges.

/** Reset the data been eventually changed by the grf loaded. */
void ResetBridges()
{
        /* First, free sprite table data */
        for (BridgeType i = 0; i < MAX_BRIDGES; i++) {
                if (_bridge[i].sprite_table != NULL) {
                        for (BridgePieces j = BRIDGE_PIECE_NORTH; j < BRIDGE_PIECE_INVALID; j++) free(_bridge[i].sprite_table[j]);
                        free(_bridge[i].sprite_table);
                }
        }

        /* Then, wipe out current bridges */
        memset(&_bridge, 0, sizeof(_bridge));
        /* And finally, reinstall default data */
        memcpy(&_bridge, &_orig_bridge, sizeof(_orig_bridge));
}

/**
 * Calculate the price factor for building a long bridge.
 * Basically the cost delta is 1,1, 1, 2,2, 3,3,3, 4,4,4,4, 5,5,5,5,5, 6,6,6,6,6,6,  7,7,7,7,7,7,7,  8,8,8,8,8,8,8,8,
 * @param length Length of the bridge.
 * @return Price factor for the bridge.
 */
int CalcBridgeLenCostFactor(int length)
{
        if (length <= 2) return length;

        length -= 2;
        int sum = 2;

        int delta;
        for (delta = 1; delta < length; delta++) {
                sum += delta * delta;
                length -= delta;
        }
        sum += delta * length;
        return sum;
}

/**
 * Get the foundation for a bridge.
 * @param tileh The slope to build the bridge on.
 * @param axis The axis of the bridge entrance.
 * @return The foundation required.
 */
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));
}

/**
 * Get the height ('z') of a bridge.
 * @param tile the bridge ramp tile to get the bridge height from
 * @return the height of the bridge.
 */
int GetBridgeHeight(TileIndex t)
{
        int h;
        Slope tileh = GetTileSlope(t, &h);
        Foundation f = GetBridgeFoundation(tileh, DiagDirToAxis(GetTunnelBridgeDirection(t)));

        /* one height level extra for the ramp */
        return h + 1 + ApplyFoundationToSlope(f, &tileh);
}

/**
 * Determines if the track on a bridge ramp is flat or goes up/down.
 *
 * @param tileh Slope of the tile under the bridge head
 * @param axis Orientation of bridge
 * @return true iff the track is flat.
 */
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);
}

/**
 * Check tiles validity for a bridge.
 *
 * @param tile1 Start tile
 * @param tile2 End tile
 * @param axis Pointer to receive bridge axis, or NULL
 * @return Null cost for success or an error
 */
CommandCost CheckBridgeTiles(TileIndex tile1, TileIndex tile2, Axis *axis)
{
        if (!IsValidTile(tile1) || !IsValidTile(tile2)) return_cmd_error(STR_ERROR_BRIDGE_THROUGH_MAP_BORDER);

        if (tile1 == tile2) {
                return_cmd_error(STR_ERROR_CAN_T_START_AND_END_ON);
        } else if (TileX(tile1) == TileX(tile2)) {
                if (axis != NULL) *axis = AXIS_Y;
        } else if (TileY(tile1) == TileY(tile2)) {
                if (axis != NULL) *axis = AXIS_X;
        } else {
                return_cmd_error(STR_ERROR_START_AND_END_MUST_BE_IN);
        }

        return CommandCost();
}

/**
 * Check if a bridge can be built over a tile.
 * @param tile The tile to check.
 * @param dir The direction of the bridge to be built.
 * @param z The height at which the bridge will be built.
 * @param Whether a bridge is buildable over the tile.
 */
static bool CheckBridgeTileBuildable (TileIndex tile, DiagDirection dir, int z)
{
        switch (GetTileType (tile)) {
                case TT_WATER:
                        return IsPlainWater (tile) || IsCoast (tile);

                case TT_MISC:
                        if (IsTileSubtype (tile, TT_MISC_TUNNEL)) return true;
                        if (IsTileSubtype (tile, TT_MISC_DEPOT)) return false;
                        assert_compile (TT_BRIDGE == TT_MISC_AQUEDUCT);
                        /* fall through */
                case TT_RAILWAY:
                case TT_ROAD:
                        if (!IsTileSubtype (tile, TT_BRIDGE)) return true;
                        if (DiagDirToAxis (dir) == DiagDirToAxis (GetTunnelBridgeDirection (tile))) return false;
                        return z >= GetBridgeHeight (tile);

                case TT_OBJECT: {
                        const ObjectSpec *spec = ObjectSpec::GetByTile(tile);
                        if ((spec->flags & OBJECT_FLAG_ALLOW_UNDER_BRIDGE) == 0) return false;
                        return z >= GetTileMaxZ (tile) + spec->height;
                }

                case TT_GROUND:
                        assert (IsGroundTile (tile));
                        return !IsTileSubtype (tile, TT_GROUND_TREES);

                case TT_STATION:
                        switch (GetStationType(tile)) {
                                case STATION_RAIL: {
                                        if (GetStationSpec (tile) != NULL) return false;
                                        uint gfx = GetStationGfx (tile);
                                        int h = (gfx < 2 ? 0 : gfx < 4 ? 1 : 3);
                                        return z >= (GetTileMaxZ (tile) + h);
                                }

                                case STATION_WAYPOINT:
                                        if (GetStationSpec (tile) != NULL) return false;
                                        return z >= (GetTileMaxZ (tile) + 2);

                                case STATION_DOCK:
                                        if (IsInsideMM (GetStationGfx (tile),
                                                        GFX_DOCK_BASE_WATER_PART,
                                                        GFX_DOCK_BUOY)) {
                                                /* water part */
                                                assert (IsTileFlat (tile));
                                                return z > GetTileZ (tile);
                                        } else {
                                                return z >= GetTileMaxZ (tile);
                                        }

                                case STATION_TRUCK:
                                case STATION_BUS:
                                        return z > GetTileMaxZ (tile);

                                case STATION_BUOY:
                                        assert (IsTileFlat (tile));
                                        return z >= GetTileZ (tile);

                                default:
                                        return false;
                        }

                default:
                        return false;
        }
}

/**
 * Check if a bridge can be built.
 *
 * @param tile1 Start tile
 * @param tile2 End tile
 * @param flags type of operation
 * @param clear1 Try to clear start tile
 * @param clear2 Try to clear end tile
 * @param height Pointer to store the height at which the bridge will be
 * @param restricted Force flat ramp (for aqueducts)
 * @return Terraforming cost for success or an error
 */
CommandCost CheckBridgeBuildable (TileIndex tile1, TileIndex tile2,
        DoCommandFlag flags, bool clear1, bool clear2, int *height,
        bool restricted)
{
        DiagDirection dir = DiagdirBetweenTiles(tile1, tile2);
        assert(IsValidDiagDirection(dir));

        int z1;
        int z2;
        Slope tileh1 = GetTileSlope(tile1, &z1);
        Slope tileh2 = GetTileSlope(tile2, &z2);

        CommandCost terraform1 = CheckBridgeSlope(dir, &tileh1, &z1);
        CommandCost terraform2 = CheckBridgeSlope(ReverseDiagDir(dir), &tileh2, &z2);

        if (restricted && (tileh1 == SLOPE_FLAT || tileh2 == SLOPE_FLAT)) return_cmd_error(STR_ERROR_LAND_SLOPED_IN_WRONG_DIRECTION);
        if (z1 != z2) return_cmd_error(STR_ERROR_BRIDGEHEADS_NOT_SAME_HEIGHT);

        bool allow_on_slopes = (_settings_game.construction.build_on_slopes && !restricted);

        CommandCost cost;

        if (clear1) {
                /* Try and clear the start landscape */
                CommandCost ret = DoCommand(tile1, 0, 0, flags, CMD_LANDSCAPE_CLEAR);
                if (ret.Failed()) return ret;
                cost.AddCost(ret);

                if (terraform1.Failed() || (terraform1.GetCost() != 0 && !allow_on_slopes)) return_cmd_error(STR_ERROR_LAND_SLOPED_IN_WRONG_DIRECTION);
                cost.AddCost(terraform1);
        } else {
                assert(terraform1.Succeeded());
        }

        if (clear2) {
                /* Try and clear the end landscape */
                CommandCost ret = DoCommand(tile2, 0, 0, flags, CMD_LANDSCAPE_CLEAR);
                if (ret.Failed()) return ret;
                cost.AddCost(ret);

                if (terraform2.Failed() || (terraform2.GetCost() != 0 && !allow_on_slopes)) return_cmd_error(STR_ERROR_LAND_SLOPED_IN_WRONG_DIRECTION);
                cost.AddCost(terraform2);
        } else {
                assert(terraform2.Succeeded());
        }

        const TileIndex heads[] = {tile1, tile2};
        for (int i = 0; i < 2; i++) {
                if (HasBridgeAbove(heads[i])) {
                        if (DiagDirToAxis(dir) == GetBridgeAxis(heads[i])) return_cmd_error(STR_ERROR_MUST_DEMOLISH_BRIDGE_FIRST);

                        if (z1 + 1 == GetBridgeHeight(GetNorthernBridgeEnd(heads[i]))) {
                                return_cmd_error(STR_ERROR_MUST_DEMOLISH_BRIDGE_FIRST);
                        }
                }
        }

        TileIndexDiff delta = TileOffsByDiagDir(dir);

        for (TileIndex tile = tile1 + delta; tile != tile2; tile += delta) {
                if (GetTileMaxZ(tile) > z1) return_cmd_error(STR_ERROR_BRIDGE_TOO_LOW_FOR_TERRAIN);

                if (z1 >= (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. z1 here is one heightlevel below the bridge level.
                         */
                        return_cmd_error(STR_ERROR_BRIDGE_TOO_HIGH_FOR_TERRAIN);
                }

                if (HasBridgeAbove(tile)) {
                        /* Disallow crossing bridges for the time being */
                        return_cmd_error(STR_ERROR_MUST_DEMOLISH_BRIDGE_FIRST);
                }

                if (!CheckBridgeTileBuildable (tile, dir, z1)) {
                        /* try and clear the middle landscape */
                        CommandCost ret = DoCommand (tile, 0, 0, flags, CMD_LANDSCAPE_CLEAR);
                        if (ret.Failed()) return ret;
                        cost.AddCost (ret);
                }
        }

        *height = z1 + 1;
        return cost;
}

/**
 * Is a bridge of the specified type and length available?
 * @param bridge_type Wanted type of bridge.
 * @param bridge_len  Wanted length of the bridge.
 * @return A succeeded (the requested bridge is available) or failed (it cannot be built) command.
 */
CommandCost CheckBridgeAvailability(BridgeType bridge_type, uint bridge_len, DoCommandFlag flags)
{
        if (flags & DC_QUERY_COST) {
                if (bridge_len <= _settings_game.construction.max_bridge_length) return CommandCost();
                return_cmd_error(STR_ERROR_BRIDGE_TOO_LONG);
        }

        if (bridge_type >= MAX_BRIDGES) return CMD_ERROR;

        const BridgeSpec *b = GetBridgeSpec(bridge_type);
        if (b->avail_year > _cur_year) return CMD_ERROR;

        uint max = 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_cmd_error(STR_ERROR_BRIDGE_TOO_LONG);
}

/**
 * Determines the foundation for a bridge head, and tests if the resulting slope is valid.
 *
 * @param dir Diagonal direction the bridge ramp will be facing
 * @param tileh Slope of the tile under the bridge head; returns slope on top of foundation
 * @param z TileZ corresponding to tileh, gets modified as well
 * @return Error or cost for bridge foundation
 */
CommandCost CheckBridgeSlope(DiagDirection dir, Slope *tileh, int *z)
{
        static const Slope inclined[DIAGDIR_END] = {
                SLOPE_SW,     ///< DIAGDIR_NE
                SLOPE_NW,     ///< DIAGDIR_SE
                SLOPE_NE,     ///< DIAGDIR_SW
                SLOPE_SE,     ///< DIAGDIR_NW
        };

        Foundation f = GetBridgeFoundation(*tileh, DiagDirToAxis(dir));
        *z += ApplyFoundationToSlope(f, tileh);

        if ((*tileh != SLOPE_FLAT) && (*tileh != inclined[dir])) return CMD_ERROR;

        if (f == FOUNDATION_NONE) return CommandCost();

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

/**
 * Mark the tiles that a bridge spans dirty.
 * @param start First tile of bridge.
 * @param end Last tile of bridge.
 * @param dir Direction from start to end.
 * @param first Do mark the first tile dirty, else skip it.
 */
void MarkBridgeTilesDirty (TileIndex start, TileIndex end, DiagDirection dir,
        bool first)
{
        assert (DiagdirBetweenTiles (start, end) == dir);

        if (first) MarkTileDirtyByTile (start);

        uint height = GetBridgeHeight (start);
        TileIndexDiff delta = TileOffsByDiagDir (dir);
        for (TileIndex tile = start + delta; tile != end; tile += delta) {
                MarkBridgeTileDirtyByTile (tile, height);
        }

        MarkTileDirtyByTile (end);
}

/**
 * Set bridge axis on a new bridge middle tiles, and mark them dirty
 *
 * @param tile1 Bridge start tile
 * @param tile2 Bridge end tile
 * @param direction Bridge axis
 * @param height Height of the bridge
 */
void SetBridgeMiddleTiles (TileIndex tile1, TileIndex tile2, Axis direction,
        int height)
{
        assert(tile1 < tile2);
        assert (height == GetBridgeHeight (tile1));

        MarkTileDirtyByTile(tile1);
        MarkTileDirtyByTile(tile2);

        TileIndexDiff delta = TileOffsByDiagDir(AxisToDiagDir(direction));
        for (TileIndex tile = tile1 + delta; tile < tile2; tile += delta) {
                SetBridgeMiddle(tile, direction);
                MarkBridgeTileDirtyByTile (tile, height);
        }
}

/**
 * Clear middle bridge tiles
 *
 * @param tile1 Bridge start tile
 * @param tile2 Bridge end tile
 */
void RemoveBridgeMiddleTiles(TileIndex tile1, TileIndex tile2)
{
        /* Call this function before clearing the endpoints. */
        assert(IsBridgeHeadTile(tile1));
        assert(IsBridgeHeadTile(tile2));

        TileIndexDiff delta = TileOffsByDiagDir(GetTunnelBridgeDirection(tile1));
        int height = GetBridgeHeight(tile1);

        for (TileIndex t = tile1 + delta; t != tile2; t += delta) {
                /* do not let trees appear from 'nowhere' after removing bridge */
                if (IsNormalRoadTile(t) && GetRoadside(t) == ROADSIDE_TREES) {
                        int minz = GetTileMaxZ(t) + 3;
                        if (height < minz) SetRoadside(t, ROADSIDE_PAVED);
                }
                ClearBridgeMiddle(t);
                MarkBridgeTileDirtyByTile (t, height);
        }
}


static inline const PalSpriteID *GetBridgeSpriteTable(int index, BridgePieces table)
{
        const BridgeSpec *bridge = GetBridgeSpec(index);
        assert(table < BRIDGE_PIECE_INVALID);
        if (bridge->sprite_table == NULL || bridge->sprite_table[table] == NULL) {
                return _bridge_sprite_table[index][table];
        } else {
                return bridge->sprite_table[table];
        }
}

/**
 * Draw a single pillar sprite.
 * @param vd        The viewport drawer to use
 * @param psid      Pillarsprite
 * @param x         Pillar X
 * @param y         Pillar Y
 * @param z         Pillar Z
 * @param w         Bounding box size in X direction
 * @param h         Bounding box size in Y direction
 * @param subsprite Optional subsprite for drawing halfpillars
 */
static inline void DrawPillar (ViewportDrawer *vd, 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; ///< Start offset of pillar wrt. bridge (downwards)
        AddSortableSpriteToDraw (vd, 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);
}

/**
 * Draw two bridge pillars (north and south).
 * @param z_bottom Bottom Z
 * @param z_top    Top Z
 * @param psid     Pillarsprite
 * @param x        Pillar X
 * @param y        Pillar Y
 * @param w        Bounding box size in X direction
 * @param h        Bounding box size in Y direction
 * @return Reached Z at the bottom
 */
static int DrawPillarColumn (ViewportDrawer *vd, 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 (vd, psid, x, y, cur_z, w, h, NULL);
        }
        return cur_z;
}

/**
 * Draws the pillars under high bridges.
 *
 * @param psid Image and palette of a bridge pillar.
 * @param ti #TileInfo of current bridge-middle-tile.
 * @param axis Orientation of bridge.
 * @param drawfarpillar Whether to draw the pillar at the back
 * @param x Sprite X position of front pillar.
 * @param y Sprite Y position of front pillar.
 * @param z_bridge Absolute height of bridge bottom.
 */
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}; ///< bounding box size of pillars along bridge direction
        static const int back_pillar_offset[2] = { 0, 9}; ///< sprite position offset of back facing pillar

        static const int INF = 1000; ///< big number compared to sprite size
        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 = max(z_front_north, z_front_south);
        int z_back = 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 (ti->vd, z_front, z_bridge, psid, x, y, w, h);
        if (z_front_north < z_front) DrawPillar (ti->vd, psid, x, y, bottom_z, w, h, &half_pillar_sub_sprite[axis][0]);
        if (z_front_south < z_front) DrawPillar (ti->vd, 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 (ti->vd, z_back, z_bridge_back, psid, x_back, y_back, w, h);
                if (z_back_north < z_back) DrawPillar (ti->vd, psid, x_back, y_back, bottom_z, w, h, &half_pillar_sub_sprite[axis][0]);
                if (z_back_south < z_back) DrawPillar (ti->vd, psid, x_back, y_back, bottom_z, w, h, &half_pillar_sub_sprite[axis][1]);
        }
}

/**
 * Compute bridge piece. Computes the bridge piece to display depending on the position inside the bridge.
 * bridges pieces sequence (middle parts).
 * Note that it is not covering the bridge heads, which are always referenced by the same sprite table.
 * bridge len 1: BRIDGE_PIECE_NORTH
 * bridge len 2: BRIDGE_PIECE_NORTH  BRIDGE_PIECE_SOUTH
 * bridge len 3: BRIDGE_PIECE_NORTH  BRIDGE_PIECE_MIDDLE_ODD   BRIDGE_PIECE_SOUTH
 * bridge len 4: BRIDGE_PIECE_NORTH  BRIDGE_PIECE_INNER_NORTH  BRIDGE_PIECE_INNER_SOUTH  BRIDGE_PIECE_SOUTH
 * bridge len 5: BRIDGE_PIECE_NORTH  BRIDGE_PIECE_INNER_NORTH  BRIDGE_PIECE_MIDDLE_EVEN  BRIDGE_PIECE_INNER_SOUTH  BRIDGE_PIECE_SOUTH
 * bridge len 6: BRIDGE_PIECE_NORTH  BRIDGE_PIECE_INNER_NORTH  BRIDGE_PIECE_INNER_SOUTH  BRIDGE_PIECE_INNER_NORTH  BRIDGE_PIECE_INNER_SOUTH  BRIDGE_PIECE_SOUTH
 * bridge len 7: BRIDGE_PIECE_NORTH  BRIDGE_PIECE_INNER_NORTH  BRIDGE_PIECE_INNER_SOUTH  BRIDGE_PIECE_MIDDLE_ODD   BRIDGE_PIECE_INNER_NORTH  BRIDGE_PIECE_INNER_SOUTH  BRIDGE_PIECE_SOUTH
 * #0 - always as first, #1 - always as last (if len>1)
 * #2,#3 are to pair in order
 * for odd bridges: #5 is going in the bridge middle if on even position, #4 on odd (counting from 0)
 * @param north Northernmost tile of bridge
 * @param south Southernmost tile of bridge
 * @return Index of bridge piece
 */
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;
        }
}

/**
 * Draws the trambits over an already drawn (lower end) of a bridge.
 * @param vd      the viewport drawer to use
 * @param x       the x of the bridge
 * @param y       the y of the bridge
 * @param z       the z of the bridge
 * @param offset  number representing whether to level or sloped and the direction
 * @param overlay do we want to still see the road?
 * @param head    are we drawing bridge head?
 */
void DrawBridgeTramBits (ViewportDrawer *vd, int x, int y, int z, int offset,
        bool overlay, bool head)
{
        struct SpriteData {
                SpriteID tram[2], back, front;
                uint size_x, size_y, front_bb_offset_x, front_bb_offset_y;
        };

#define S(x) (SPR_TRAMWAY_BASE + (x))
        static const SpriteData sprite_data[6] = {
                { { S(107), S( 4) }, S( 95), S( 97),  1, 16, 15,  0 },
                { { S(108), S( 5) }, S( 96), S( 98), 16,  1,  0, 15 },
                { { S(109), S(15) }, S( 99), S(103), 16,  1,  0, 15 },
                { { S(110), S(16) }, S(102), S(106),  1, 16, 15,  0 },
                { { S(111), S(17) }, S(100), S(104), 16,  1,  0, 15 },
                { { S(112), S(18) }, S(101), S(105),  1, 16, 15,  0 },
        };
#undef S

        const SpriteData *data = &sprite_data[offset];

        /* 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 */
        if (head || !IsInvisibilitySet(TO_BRIDGES)) {
                AddSortableSpriteToDraw (vd, data->tram[overlay], PAL_NONE,
                        x, y, data->size_x, data->size_y, 0x28, z,
                        !head && IsTransparencySet(TO_BRIDGES));
        }

        /* Do not draw catenary if it is set invisible */
        if (!IsInvisibilitySet(TO_CATENARY)) {
                AddSortableSpriteToDraw (vd, data->back, PAL_NONE,
                        x, y, data->size_x, data->size_y, 0x28, z,
                        IsTransparencySet(TO_CATENARY));
        }

        /* Start a new SpriteCombine for the front part */
        EndSpriteCombine (vd);
        StartSpriteCombine (vd);

        /* For sloped sprites the bounding box needs to be higher, as the pylons stop on a higher point */
        if (!IsInvisibilitySet(TO_CATENARY)) {
                AddSortableSpriteToDraw (vd, data->front, PAL_NONE,
                        x, y, data->size_x + data->front_bb_offset_x, data->size_y + data->front_bb_offset_y, 0x28, z,
                        IsTransparencySet(TO_CATENARY), data->front_bb_offset_x, data->front_bb_offset_y);
        }
}

/**
 * Draw the middle bits of a bridge.
 * @param ti Tile information of the tile to draw it on.
 */
void DrawBridgeMiddle(const TileInfo *ti)
{
        /* Sectional view of bridge bounding boxes:
         *
         *  1           2                                1,2 = SpriteCombine of Bridge front/(back&floor) and TramCatenary
         *  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 (!HasBridgeAbove(ti->tile)) return;

        TileIndex rampnorth = GetNorthernBridgeEnd(ti->tile);
        TileIndex rampsouth = GetSouthernBridgeEnd(ti->tile);

        Axis axis = GetBridgeAxis(ti->tile);
        BridgePieces piece = CalcBridgePiece(
                GetTunnelBridgeLength(ti->tile, rampnorth) + 1,
                GetTunnelBridgeLength(ti->tile, rampsouth) + 1
        );

        TransportType transport_type;
        const PalSpriteID *psid;
        bool drawfarpillar;

        if (IsTileType(rampsouth, TT_MISC)) {
                assert(IsAqueductTile(rampsouth));
                transport_type = TRANSPORT_WATER;
                psid = _aqueduct_sprites;
                drawfarpillar = true;
        } else {
                assert(IsTileSubtype(rampsouth, TT_BRIDGE));

                BridgeType type;
                uint base_offset;

                if (IsRailwayTile(rampsouth)) {
                        transport_type = TRANSPORT_RAIL;
                        type = GetRailBridgeType(rampsouth);
                        base_offset = GetRailTypeInfo(GetBridgeRailType(rampsouth))->bridge_offset;
                } else {
                        transport_type = TRANSPORT_ROAD;
                        type = GetRoadBridgeType(rampsouth);
                        base_offset = 8;
                }

                psid = base_offset + GetBridgeSpriteTable(type, piece);
                drawfarpillar = !HasBit(GetBridgeSpec(type)->flags, 0);
        }

        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 (ti->vd, 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 (ti->vd);

        /* Draw floor and far part of bridge*/
        if (!IsInvisibilitySet(TO_BRIDGES)) {
                if (axis == AXIS_X) {
                        AddSortableSpriteToDraw (ti->vd, psid->sprite, psid->pal, x, y, 16, 1, 0x28, z, IsTransparencySet(TO_BRIDGES), 0, 0, BRIDGE_Z_START);
                } else {
                        AddSortableSpriteToDraw (ti->vd, psid->sprite, psid->pal, x, y, 1, 16, 0x28, z, IsTransparencySet(TO_BRIDGES), 0, 0, BRIDGE_Z_START);
                }
        }

        psid++;

        if (transport_type == TRANSPORT_ROAD) {
                RoadBits bits = DiagDirToRoadBits(axis == AXIS_X ? DIAGDIR_NE : DIAGDIR_NW);

                if ((GetRoadBits(rampsouth, ROADTYPE_TRAM) & bits) != 0) {
                        /* DrawBridgeTramBits() calls EndSpriteCombine() and StartSpriteCombine() */
                        DrawBridgeTramBits (ti->vd, x, y, bridge_z, axis ^ 1, (GetRoadBits(rampsouth, ROADTYPE_ROAD) & bits) != 0, false);
                } else {
                        EndSpriteCombine (ti->vd);
                        StartSpriteCombine (ti->vd);
                }
        } else if (transport_type == TRANSPORT_RAIL) {
                const RailtypeInfo *rti = GetRailTypeInfo(GetBridgeRailType(rampsouth));
                if (rti->UsesOverlay() && !IsInvisibilitySet(TO_BRIDGES)) {
                        SpriteID surface = GetCustomRailSprite(rti, rampsouth, RTSG_BRIDGE, TCX_ON_BRIDGE);
                        if (surface != 0) {
                                AddSortableSpriteToDraw (ti->vd, 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) && HasBridgeMiddleReservation(rampnorth)) {
                        SpriteID image = rti->UsesOverlay() ?
                                        GetCustomRailSprite (rti, ti->tile, RTSG_OVERLAY) + RTO_X + axis :
                                        rti->base_sprites.single[AxisToTrack(axis)];
                        AddSortableSpriteToDraw (ti->vd, image, PALETTE_CRASH, ti->x, ti->y, 16, 16, 0, bridge_z, IsTransparencySet (TO_BRIDGES));
                }

                EndSpriteCombine (ti->vd);

                if (HasRailCatenaryDrawn (rti)) {
                        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 (ti->vd, 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 (ti->vd, 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 (ti->vd);

        /* Do not draw anything more if bridges are invisible */
        if (IsInvisibilitySet(TO_BRIDGES)) return;

        psid++;
        if (ti->z + 5 == z) {
                /* draw poles below for small bridges */
                if (psid->sprite != 0) {
                        SpriteID image = psid->sprite;
                        SpriteID pal   = psid->pal;
                        if (IsTransparencySet(TO_BRIDGES)) {
                                SetBit(image, PALETTE_MODIFIER_TRANSPARENT);
                                pal = PALETTE_TO_TRANSPARENT;
                        }

                        DrawGroundSpriteAt (ti, image, pal, x - ti->x, y - ti->y, z - ti->z);
                }
        } else {
                /* draw pillars below for high bridges */
                DrawBridgePillars(psid, ti, axis, drawfarpillar, x, y, z);
        }
}

void DrawBridgeGround(TileInfo *ti)
{
        DiagDirection dir = GetTunnelBridgeDirection(ti->tile);

        DrawFoundation(ti, GetBridgeFoundation(ti->tileh, DiagDirToAxis(dir)));

        if (IsOnSnow(ti->tile)) {
                DrawGroundSprite (ti, SPR_FLAT_SNOW_DESERT_TILE + SlopeToSpriteOffset(ti->tileh), PAL_NONE);
        } else {
                TileIndex next = ti->tile + TileOffsByDiagDir(dir);
                if (ti->tileh != SLOPE_FLAT && ti->z == 0 && HasTileWaterClass(next) && GetWaterClass(next) == WATER_CLASS_SEA) {
                        DrawShoreTile (ti);
                } else {
                        DrawClearLandTile(ti, 3);
                }
        }
}

const PalSpriteID *GetBridgeRampSprite(int index, int offset, Slope slope, DiagDirection dir)
{
        /* as the lower 3 bits are used for other stuff, make sure they are clear */
        assert((offset & 0x07) == 0x00);

        if (slope == SLOPE_FLAT) offset += 4; // sloped bridge head

        /* HACK Wizardry to convert the bridge ramp direction into a sprite offset */
        offset += (6 - dir) % 4;

        /* Table number BRIDGE_PIECE_HEAD always refers to the bridge heads for any bridge type */
        return offset + GetBridgeSpriteTable(index, BRIDGE_PIECE_HEAD);
}

void DrawAqueductRamp(TileInfo *ti)
{
        DrawBridgeGround(ti);

        assert(ti->tileh != SLOPE_FLAT);

        DiagDirection dir = GetTunnelBridgeDirection(ti->tile);

        /* HACK Wizardry to convert the bridge ramp direction into a sprite offset */
        const PalSpriteID *psid = _aqueduct_sprites + 8 + (6 - dir) % 4;

        /* 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 (ti->vd, psid->sprite, psid->pal, ti->x, ti->y, 16, 16, 8, ti->z);
}