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[openttd/fttd.git] / src / elrail.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 elrail.cpp
 * This file deals with displaying wires and pylons for electric railways.
 * <h2>Basics</h2>
 *
 * <h3>Tile Types</h3>
 *
 * We have two different types of tiles in the drawing code:
 * Normal Railway Tiles (NRTs) which can have more than one track on it, and
 * Special Railways tiles (SRTs) which have only one track (like crossings, depots
 * stations, etc).
 *
 * <h3>Location Categories</h3>
 *
 * All tiles are categorized into three location groups (TLG):
 * Group 0: Tiles with both an even X coordinate and an even Y coordinate
 * Group 1: Tiles with an even X and an odd Y coordinate
 * Group 2: Tiles with an odd X and an even Y coordinate
 * Group 3: Tiles with both an odd X and Y coordinate.
 *
 * <h3>Pylon Points</h3>
 * <h4>Control Points</h4>
 * A Pylon Control Point (PCP) is a position where a wire (or rather two)
 * is mounted onto a pylon.
 * Each NRT does contain 4 PCPs which are bitmapped to a byte
 * variable and are represented by the DiagDirection enum
 *
 * Each track ends on two PCPs and thus requires one pylon on each end. However,
 * there is one exception: Straight-and-level tracks only have one pylon every
 * other tile.
 *
 * Now on each edge there are two PCPs: One from each adjacent tile. Both PCPs
 * are merged using an OR operation (i. e. if one tile needs a PCP at the position
 * in question, both tiles get it).
 *
 * <h4>Position Points</h4>
 * A Pylon Position Point (PPP) is a position where a pylon is located on the
 * ground.  Each PCP owns 8 in (45 degree steps) PPPs that are located around
 * it. PPPs are represented using the Direction enum. Each track bit has PPPs
 * that are impossible (because the pylon would be situated on the track) and
 * some that are preferred (because the pylon would be rectangular to the track).
 *
 * @image html elrail_tile.png
 * @image html elrail_track.png
 *
 */

#include "stdafx.h"

#include <utility>

#include "map/rail.h"
#include "map/road.h"
#include "map/slope.h"
#include "map/bridge.h"
#include "map/tunnelbridge.h"
#include "viewport_func.h"
#include "train.h"
#include "rail_gui.h"
#include "bridge.h"
#include "elrail_func.h"
#include "company_base.h"
#include "newgrf_railtype.h"
#include "station_func.h"


/** Which PPPs are possible at all on a given PCP */
static const byte AllowedPPPonPCP[DIAGDIR_END] = {
        1 << DIR_N | 1 << DIR_E  | 1 << DIR_SE | 1 << DIR_S | 1 << DIR_W  | 1 << DIR_NW,
        1 << DIR_N | 1 << DIR_NE | 1 << DIR_E  | 1 << DIR_S | 1 << DIR_SW | 1 << DIR_W,
        1 << DIR_N | 1 << DIR_E  | 1 << DIR_SE | 1 << DIR_S | 1 << DIR_W  | 1 << DIR_NW,
        1 << DIR_N | 1 << DIR_NE | 1 << DIR_E  | 1 << DIR_S | 1 << DIR_SW | 1 << DIR_W,
};


/* Geometric placement of the PCP relative to the tile origin */
static const int8 x_pcp_offsets[DIAGDIR_END] = {0,  8, 16, 8};
static const int8 y_pcp_offsets[DIAGDIR_END] = {8, 16,  8, 0};
/* Geometric placement of the PPP relative to the PCP*/
static const int8 x_ppp_offsets[DIR_END] = {-2, -4, -2,  0,  2,  4,  2,  0};
static const int8 y_ppp_offsets[DIR_END] = {-2,  0,  2,  4,  2,  0, -2, -4};

/* The type of pylon to draw at each PPP */
static const uint8 pylon_sprites[DIR_END] = { 4, 0, 7, 3, 5, 1, 6, 2, };

/**
 * Offset for wire sprites from the base wire sprite.
 */
enum WireSpriteOffset {
        WSO_X_SHORT,
        WSO_Y_SHORT,
        WSO_EW_SHORT,
        WSO_NS_SHORT,
        WSO_X_SHORT_DOWN,
        WSO_Y_SHORT_UP,
        WSO_X_SHORT_UP,
        WSO_Y_SHORT_DOWN,

        WSO_X_SW,
        WSO_Y_SE,
        WSO_EW_E,
        WSO_NS_S,
        WSO_X_SW_DOWN,
        WSO_Y_SE_UP,
        WSO_X_SW_UP,
        WSO_Y_SE_DOWN,

        WSO_X_NE,
        WSO_Y_NW,
        WSO_EW_W,
        WSO_NS_N,
        WSO_X_NE_DOWN,
        WSO_Y_NW_UP,
        WSO_X_NE_UP,
        WSO_Y_NW_DOWN,

        WSO_ENTRANCE_NE,
        WSO_ENTRANCE_SE,
        WSO_ENTRANCE_SW,
        WSO_ENTRANCE_NW,
};

struct SortableSpriteStructM {
        int8 x_offset;
        int8 y_offset;
        int8 x_size;
        int8 y_size;
        int8 z_offset;
        uint8 image_offset[3];
};

/** Distance between wire and rail */
static const uint ELRAIL_ELEVATION = 10;
/** Wires that a draw one level higher than the north corner. */
static const uint ELRAIL_ELEVRAISE = ELRAIL_ELEVATION + TILE_HEIGHT;

static const SortableSpriteStructM CatenarySpriteData[TRACK_END] = {
        {  0,  7, 15,  1, ELRAIL_ELEVATION, { WSO_X_NE, WSO_X_SW, WSO_X_SHORT  } }, // X flat
        {  7,  0,  1, 15, ELRAIL_ELEVATION, { WSO_Y_SE, WSO_Y_NW, WSO_Y_SHORT  } }, // Y flat
        {  7,  0,  1,  1, ELRAIL_ELEVATION, { WSO_EW_W, WSO_EW_E, WSO_EW_SHORT } }, // UPPER
        { 15,  8,  3,  3, ELRAIL_ELEVATION, { WSO_EW_E, WSO_EW_W, WSO_EW_SHORT } }, // LOWER
        {  8,  0,  8,  8, ELRAIL_ELEVATION, { WSO_NS_S, WSO_NS_N, WSO_NS_SHORT } }, // LEFT
        {  0,  8,  8,  8, ELRAIL_ELEVATION, { WSO_NS_N, WSO_NS_S, WSO_NS_SHORT } }, // RIGHT
};

static const SortableSpriteStructM CatenarySpriteDataSW =
        {  0,  7, 15,  8, ELRAIL_ELEVRAISE, { WSO_X_NE_UP,   WSO_X_SW_UP,   WSO_X_SHORT_UP   } }; // X up

static const SortableSpriteStructM CatenarySpriteDataSE =
        {  7,  0,  8, 15, ELRAIL_ELEVRAISE, { WSO_Y_SE_UP,   WSO_Y_NW_UP,   WSO_Y_SHORT_UP   } }; // Y up

static const SortableSpriteStructM CatenarySpriteDataNW =
        {  7,  0,  8, 15, ELRAIL_ELEVATION, { WSO_Y_SE_DOWN, WSO_Y_NW_DOWN, WSO_Y_SHORT_DOWN } }; // Y down

static const SortableSpriteStructM CatenarySpriteDataNE =
        {  0,  7, 15,  8, ELRAIL_ELEVATION, { WSO_X_NE_DOWN, WSO_X_SW_DOWN, WSO_X_SHORT_DOWN } }; // X down


/**
 * Check if a tile is on an odd X coordinate.
 * @param t The tile to check
 * @return Whether the tile is on an odd X coordinate
 */
static inline bool IsOddX (TileIndex t)
{
        return HasBit (TileX(t), 0);
}

/**
 * Check if a tile is on an odd Y coordinate.
 * @param t The tile to check
 * @return Whether the tile is on an odd Y coordinate
 */
static inline bool IsOddY (TileIndex t)
{
        return HasBit (TileY(t), 0);
}

/**
 * Test if a rail type has catenary
 * @param rt Rail type to test
 */
static inline bool HasRailCatenary (RailType rt)
{
        return HasRailCatenary (GetRailTypeInfo (rt));
}

/** Get the electrified track bits on a railway tile. */
static TrackBits GetElectrifiedTrackBits (TileIndex t)
{
        TrackBits present = GetTrackBits(t);
        TrackBits result = TRACK_BIT_NONE;
        if (HasRailCatenary (GetRailType (t, TRACK_UPPER))) result |= present & (TRACK_BIT_CROSS | TRACK_BIT_UPPER | TRACK_BIT_LEFT);
        if (HasRailCatenary (GetRailType (t, TRACK_LOWER))) result |= present & (TRACK_BIT_LOWER | TRACK_BIT_RIGHT);
        return result;
}

/**
 * Masks out track bits when neighbouring tiles are unelectrified.
 */
static TrackBits MaskWireBits(TileIndex t, TrackBits tracks)
{
        if (!IsNormalRailTile(t)) return tracks;

        TrackdirBits neighbour_tdb = TRACKDIR_BIT_NONE;
        for (DiagDirection d = DIAGDIR_BEGIN; d < DIAGDIR_END; d++) {
                /* If the neighbour tile is either not electrified or has no tracks that can be reached
                 * from this tile, mark all trackdirs that can be reached from the neighbour tile
                 * as needing no catenary. We make an exception for blocked station tiles with a matching
                 * axis that still display wires to preserve visual continuity. */
                TileIndex next_tile = TileAddByDiagDir(t, d);
                TrackBits reachable = TrackStatusToTrackBits(GetTileRailwayStatus(next_tile)) & DiagdirReachesTracks(d);
                RailType rt;
                if ((reachable != TRACK_BIT_NONE) ?
                                ((rt = GetRailType(next_tile, FindFirstTrack(reachable))) == INVALID_RAILTYPE || !HasRailCatenary(rt)) :
                                (!HasStationTileRail(next_tile) || GetRailStationAxis(next_tile) != DiagDirToAxis(d) || !CanStationTileHaveWires(next_tile))) {
                        neighbour_tdb |= DiagdirReachesTrackdirs(ReverseDiagDir(d));
                }
        }

        /* If the tracks from either a diagonal crossing or don't overlap, both
         * trackdirs have to be marked to mask the corresponding track bit. Else
         * one marked trackdir is enough the mask the track bit. */
        TrackBits mask;
        if (tracks == TRACK_BIT_CROSS || !TracksOverlap(tracks)) {
                /* If the tracks form either a diagonal crossing or don't overlap, both
                 * trackdirs have to be marked to mask the corresponding track bit. */
                mask = ~(TrackBits)((neighbour_tdb & (neighbour_tdb >> 8)) & TRACK_BIT_MASK);
                /* If that results in no masked tracks and it is not a diagonal crossing,
                 * require only one marked trackdir to mask. */
                if (tracks != TRACK_BIT_CROSS && (mask & TRACK_BIT_MASK) == TRACK_BIT_MASK) mask = ~TrackdirBitsToTrackBits(neighbour_tdb);
        } else {
                /* Require only one marked trackdir to mask the track. */
                mask = ~TrackdirBitsToTrackBits(neighbour_tdb);
                /* If that results in an empty set, require both trackdirs for diagonal track. */
                if ((tracks & mask) == TRACK_BIT_NONE) {
                        if ((neighbour_tdb & TRACKDIR_BIT_X_NE) == 0 || (neighbour_tdb & TRACKDIR_BIT_X_SW) == 0) mask |= TRACK_BIT_X;
                        if ((neighbour_tdb & TRACKDIR_BIT_Y_NW) == 0 || (neighbour_tdb & TRACKDIR_BIT_Y_SE) == 0) mask |= TRACK_BIT_Y;
                        /* If that still is not enough, require both trackdirs for any track. */
                        if ((tracks & mask) == TRACK_BIT_NONE) mask = ~(TrackBits)((neighbour_tdb & (neighbour_tdb >> 8)) & TRACK_BIT_MASK);
                }
        }

        /* Mask the tracks only if at least one track bit would remain. */
        return (tracks & mask) != TRACK_BIT_NONE ? tracks & mask : tracks;
}

/** Get the base wire sprite to use. */
static inline SpriteID GetWireBase (const RailtypeInfo *rti, TileIndex tile,
        TileContext context = TCX_NORMAL)
{
        SpriteID wires = GetCustomRailSprite (rti, tile, RTSG_WIRES, context);
        return wires == 0 ? SPR_WIRE_BASE : wires;
}

/** Get the base pylon sprite to use. */
static inline SpriteID GetPylonBase (const RailtypeInfo *rti, TileIndex tile,
        TileContext context = TCX_NORMAL)
{
        SpriteID pylons = GetCustomRailSprite (rti, tile, RTSG_PYLONS, context);
        return pylons == 0 ? SPR_PYLON_BASE : pylons;
}

/**
 * Draws wires on a rail tunnel or depot tile.
 * @param ti The TileInfo to draw the tile for.
 * @param rti The rail type information of the rail.
 * @param depot The tile is a depot, else a tunnel.
 * @param dir The direction of the tunnel or depot.
 */
void DrawRailTunnelDepotCatenary (const TileInfo *ti, const RailtypeInfo *rti,
        bool depot, DiagDirection dir)
{
        struct SortableSpriteStruct {
                struct { int8 x, y, w, h; } bb[2];
                int8 x_offset;
                int8 y_offset;
        };

        static const SortableSpriteStruct data[2] = {
                { { {  0, -6, 16,  8 }, { 0, 0, 15, 1 } }, 0, 7 }, //! Wire along X axis
                { { { -6,  0,  8, 16 }, { 0, 0, 1, 15 } }, 7, 0 }, //! Wire along Y axis
        };

        assert_compile (WSO_ENTRANCE_NE == WSO_ENTRANCE_NE + DIAGDIR_NE);
        assert_compile (WSO_ENTRANCE_SE == WSO_ENTRANCE_NE + DIAGDIR_SE);
        assert_compile (WSO_ENTRANCE_SW == WSO_ENTRANCE_NE + DIAGDIR_SW);
        assert_compile (WSO_ENTRANCE_NW == WSO_ENTRANCE_NE + DIAGDIR_NW);

        const SortableSpriteStruct *sss = &data[DiagDirToAxis(dir)];
        int dz = depot ? 0 : BB_Z_SEPARATOR - ELRAIL_ELEVATION;
        int z = depot ? GetTileMaxPixelZ (ti->tile) : GetTilePixelZ (ti->tile);
        /* This wire is not visible with the default depot sprites. */
        AddSortableSpriteToDraw (ti->vd,
                GetWireBase (rti, ti->tile) + WSO_ENTRANCE_NE + dir, PAL_NONE,
                ti->x + sss->x_offset, ti->y + sss->y_offset,
                sss->bb[depot].w, sss->bb[depot].h, dz + 1,
                z + ELRAIL_ELEVATION, IsTransparencySet (TO_CATENARY),
                sss->bb[depot].x, sss->bb[depot].y, dz);
}


struct SideTrackData {
        byte track;     ///< a track that incides at this side
        byte preferred; ///< preferred pylon position points for it
};

static const uint NUM_TRACKS_PER_SIDE = 3;

/* Side track data, 3 tracks per side. */
static const SideTrackData side_tracks[DIAGDIR_END][NUM_TRACKS_PER_SIDE] = {
        {    // NE
                { TRACK_X,     1 << DIR_NE | 1 << DIR_SE | 1 << DIR_NW },
                { TRACK_UPPER, 1 << DIR_E  | 1 << DIR_N  | 1 << DIR_S  },
                { TRACK_RIGHT, 1 << DIR_N  | 1 << DIR_E  | 1 << DIR_W  },
        }, { // SE
                { TRACK_Y,     1 << DIR_NE | 1 << DIR_SE | 1 << DIR_SW },
                { TRACK_LOWER, 1 << DIR_E  | 1 << DIR_N  | 1 << DIR_S  },
                { TRACK_RIGHT, 1 << DIR_S  | 1 << DIR_E  | 1 << DIR_W  },
        }, { // SW
                { TRACK_X,     1 << DIR_SE | 1 << DIR_SW | 1 << DIR_NW },
                { TRACK_LOWER, 1 << DIR_W  | 1 << DIR_N  | 1 << DIR_S  },
                { TRACK_LEFT,  1 << DIR_S  | 1 << DIR_E  | 1 << DIR_W  },
        }, { // NW
                { TRACK_Y,     1 << DIR_SW | 1 << DIR_NW | 1 << DIR_NE },
                { TRACK_UPPER, 1 << DIR_W  | 1 << DIR_N  | 1 << DIR_S  },
                { TRACK_LEFT,  1 << DIR_N  | 1 << DIR_E  | 1 << DIR_W  },
        },
};

/* Mask of positions at which pylons can be built per track. */
static const byte allowed_ppp[TRACK_END] = {
        1 << DIR_N  | 1 << DIR_E  | 1 << DIR_SE | 1 << DIR_S  | 1 << DIR_W  | 1 << DIR_NW, // X
        1 << DIR_N  | 1 << DIR_NE | 1 << DIR_E  | 1 << DIR_S  | 1 << DIR_SW | 1 << DIR_W,  // Y
        1 << DIR_N  | 1 << DIR_NE | 1 << DIR_SE | 1 << DIR_S  | 1 << DIR_SW | 1 << DIR_NW, // UPPER
        1 << DIR_N  | 1 << DIR_NE | 1 << DIR_SE | 1 << DIR_S  | 1 << DIR_SW | 1 << DIR_NW, // LOWER
        1 << DIR_NE | 1 << DIR_E  | 1 << DIR_SE | 1 << DIR_SW | 1 << DIR_W  | 1 << DIR_NW, // LEFT
        1 << DIR_NE | 1 << DIR_E  | 1 << DIR_SE | 1 << DIR_SW | 1 << DIR_W  | 1 << DIR_NW, // RIGHT
};

/**
 * Mask preferred and allowed pylon position points on a tile side.
 * @param tracks Tracks present on the tile.
 * @param wires Electrified tracks present on the tile.
 * @param side Tile side to check.
 * @param preferred Pointer to preferred positions to mask.
 * @param allowed Pointer to allowed positions to mask.
 * @return Whether the pylon control point is in use from this tile.
 */
static bool CheckCatenarySide (TrackBits tracks, TrackBits wires,
        DiagDirection side, byte *preferred, byte *allowed)
{
        bool pcp_in_use = false;
        byte pmask = 0xFF;
        byte amask = 0xFF;

        for (uint k = 0; k < NUM_TRACKS_PER_SIDE; k++) {
                /* We check whether the track in question is present. */
                const SideTrackData *data = &side_tracks[side][k];
                byte track = data->track;
                if (HasBit(wires, track)) {
                        /* track found */
                        pcp_in_use = true;
                        pmask &= data->preferred;
                }
                if (HasBit(tracks, track)) {
                        amask &= allowed_ppp[track];
                }
        }

        *preferred &= pmask;
        *allowed &= amask;
        return pcp_in_use;
}

/**
 * Mask preferred and allowed pylon position points on a tile side,
 * when there is a single track along an axis on the tile.
 * @param axis Axis of the track.
 * @param side Tile side to check.
 * @param preferred Pointer to preferred positions to mask.
 * @return Whether the pylon control point is in use from this tile.
 */
static inline bool CheckCatenarySideAxis (Axis axis, DiagDirection side,
        byte *preferred)
{
        /* We check whether the track in question is present. */
        if (DiagDirToAxis (side) != axis) return false;

        /* track found */
        *preferred &= side_tracks[side][0].preferred;
        return true;
}

/**
 * Check if the pylon on a tile side should be elided on long track runs.
 * @param side Tile side to check.
 * @param preferred Preferred pylon positions.
 * @param odd Array of tile coordinate parity per axis.
 * @param level Whether the land is level (for tracks running along an axis).
 * @return Whether the pylon should be elided.
 */
static bool CheckPylonElision (DiagDirection side, byte preferred,
        const bool *odd, bool level)
{
        Axis axis = DiagDirToAxis (side);
        bool ignore;
        switch (preferred) {
                case 1 << DIR_NW | 1 << DIR_SE:
                        if (!level) return false;
                        ignore = false; // must be X axis
                        break;

                case 1 << DIR_NE | 1 << DIR_SW:
                        if (!level) return false;
                        ignore = true;  // must be Y axis
                        break;

                case 1 << DIR_E | 1 << DIR_W:
                        /* Non-orthogonal tracks must always be level. */
                        ignore = (axis == AXIS_X) ? !odd[AXIS_Y] : odd[AXIS_X];
                        break;

                case 1 << DIR_N | 1 << DIR_S:
                        /* Non-orthogonal tracks must always be level. */
                        ignore = !odd[OtherAxis(axis)];
                        break;

                default:
                        return false;
        }

        /* This configuration may be subject to pylon elision. */
        /* Toggle ignore if we are in an odd row, or heading the other way. */
        return (ignore ^ odd[axis] ^ HasBit(side, 1));
}

/** Possible return values for CheckNeighbourPCP below. */
enum {
        PCP_NB_NONE,      ///< PCP not in use from the neighbour tile
        PCP_NB_TUNNEL,    ///< PCP in use by a tunnel from the neighbour tile
        PCP_NB_TRY_ELIDE, ///< PCP is in use and may be subject to elision
};

/**
 * Check whether a pylon is also in use from a railway tile at the other side.
 * @param tile The neighbour railway tile to check.
 * @param side The tile side to check from this tile.
 * @param preferred Pointer to preferred positions to mask.
 * @param allowed Pointer to allowed positions to mask.
 * @param slope Pointer to store the tile slope if pylon elision is possible.
 * @return A value representing the PCP state at the given side.
 */
static uint CheckRailNeighbourPCP (TileIndex tile, DiagDirection side,
        byte *preferred, byte *allowed, Slope *slope)
{
        assert (IsRailwayTile (tile));

        bool is_bridge = IsTileSubtype (tile, TT_BRIDGE);
        if (is_bridge && GetTunnelBridgeDirection (tile) == side) {
                return PCP_NB_NONE;
        }

        TrackBits nb_tracks = GetElectrifiedTrackBits (tile);
        if (nb_tracks == TRACK_BIT_NONE) return PCP_NB_NONE;
        TrackBits nb_wires = MaskWireBits (tile, nb_tracks);

        /* Tracks inciding from the neighbour tile */
        if (!CheckCatenarySide (nb_tracks, nb_wires, side, preferred, allowed)) {
                return PCP_NB_NONE;
        }

        /* Read the foundations if they are present, and adjust the tileh */
        assert_compile (TRACK_BIT_X == 1);
        assert_compile (TRACK_BIT_Y == 2);

        Slope nb_slope;
        if (nb_tracks > 2) {
                /* Anything having more than a single X or Y track must be
                 * flat (or a half tile slope, but we treat those as flat). */
                nb_slope = SLOPE_FLAT;
        } else if (!is_bridge) {
                nb_slope = GetTileSlope (tile);
                Foundation f = GetRailFoundation (nb_slope, nb_tracks);
                ApplyFoundationToSlope (f, &nb_slope);
        } else {
                nb_slope = GetTileSlope (tile);
                /* With a single X or Y track, bridge must
                 * head away from our side. */
                nb_slope = HasBridgeFlatRamp (nb_slope, DiagDirToAxis (side)) ?
                                SLOPE_FLAT :
                                InclinedSlope (ReverseDiagDir (side));
        }

        *slope = nb_slope;
        return PCP_NB_TRY_ELIDE;
}

/**
 * Check whether a pylon is also in use from the other side.
 * @param tile The neighbour tile to check.
 * @param side The tile side to check from this tile.
 * @param preferred Pointer to preferred positions to mask.
 * @param allowed Pointer to allowed positions to mask.
 * @param slope Pointer to store the tile slope if pylon elision is possible.
 * @return A value representing the PCP state at the given side.
 */
static uint CheckNeighbourPCP (TileIndex tile, DiagDirection side,
        byte *preferred, byte *allowed, Slope *slope)
{
        Axis axis;
        switch (GetTileType (tile)) {
                case TT_RAILWAY:
                        return CheckRailNeighbourPCP (tile, side,
                                                preferred, allowed, slope);

                case TT_MISC:
                        switch (GetTileSubtype (tile)) {
                                default: return PCP_NB_NONE;

                                case TT_MISC_CROSSING:
                                        if (!HasRailCatenary (GetRailType (tile))) return PCP_NB_NONE;
                                        axis = GetCrossingRailAxis (tile);
                                        break;

                                case TT_MISC_TUNNEL:
                                        if (GetTunnelTransportType (tile) != TRANSPORT_RAIL) return PCP_NB_NONE;
                                        if (!HasRailCatenary (GetRailType (tile))) return PCP_NB_NONE;
                                        /* ignore tunnels facing the wrong way for neighbouring tiles */
                                        if (GetTunnelBridgeDirection (tile) != ReverseDiagDir (side)) return PCP_NB_NONE;
                                        /* force tunnels to always have a pylon (no elision) */
                                        *preferred = 0;
                                        return PCP_NB_TUNNEL;
                        }
                        break;

                case TT_STATION:
                        if (!HasStationRail (tile)) return PCP_NB_NONE;
                        if (!HasRailCatenary (GetRailType (tile))) return PCP_NB_NONE;
                        /* Ignore neighbouring station tiles that allow neither wires nor pylons. */
                        if (!CanStationTileHavePylons (tile) && !CanStationTileHaveWires (tile)) return PCP_NB_NONE;
                        axis = GetRailStationAxis (tile);
                        break;

                default:
                        return PCP_NB_NONE;
        }

        /* Crossing or station tile, so just one flat track along an axis. */
        if (!CheckCatenarySideAxis (axis, side, preferred)) {
                return PCP_NB_NONE;
        }

        *slope = SLOPE_FLAT;
        return PCP_NB_TRY_ELIDE;
}

/** Possible return values for CheckSidePCP below. */
enum {
        PCP_NONE,        ///< PCP is not in use
        PCP_IN_USE,      ///< PCP is in use from this tile
        PCP_IN_USE_BOTH, ///< PCP is in use also from the neighbour tile
};

/**
 * Check whether there should be a pylon at a tile side.
 * @param tile The tile to check.
 * @param home_tracks Tracks present on the home tile.
 * @param home_wires Electrified tracks present on the home tile.
 * @param home_slope Slope of the home tile, adjusted for foundations.
 * @param side The side to check.
 * @param odd Array of tile coordinate parity per axis.
 * @return A value representing the PCP state at the given side, plus
 *  a bitmask of allowed directions for the pylon, if any.
 */
static std::pair <uint, byte> CheckSidePCP (TileIndex tile,
        TrackBits home_tracks, TrackBits home_wires, Slope home_slope,
        DiagDirection side, const bool *odd)
{
        /* We cycle through all the existing tracks at a PCP and see what
         * PPPs we want to have, or may not have at all */
        byte PPPpreferred = 0xFF; // We start with preferring everything (end-of-line in any direction)
        byte PPPallowed = AllowedPPPonPCP[side];

        /* Tracks inciding from the home tile */
        if (!CheckCatenarySide (home_tracks, home_wires, side, &PPPpreferred, &PPPallowed)) {
                /* PCP not used at all from this tile. */
                return std::make_pair (PCP_NONE, 0);
        }

        bool pcp_neighbour;
        Slope nb_slope;
        switch (CheckNeighbourPCP (tile + TileOffsByDiagDir (side),
                                ReverseDiagDir (side),
                                &PPPpreferred, &PPPallowed, &nb_slope)) {
                default: // PCP_NB_TRY_ELIDE
                        if (CheckPylonElision (side, PPPpreferred, odd, home_slope == nb_slope)) {
                                return std::make_pair (PCP_NONE, 0);
                        }
                        /* fall through */
                case PCP_NB_TUNNEL:
                        pcp_neighbour = true;
                        break;

                case PCP_NB_NONE:
                        pcp_neighbour = false;
                        break;
        }

        /* Now decide where we draw our pylons. First try the preferred PPPs,
         * but they may not exist. In that case, we try the any of the allowed
         * ones. if they don't exist either, don't draw anything. Note that
         * the preferred PPPs still contain the end-of-line markers. Remove
         * those (simply by ANDing with allowed, since these markers are never
         * allowed) */
        if (PPPallowed == 0) return std::make_pair (PCP_NONE, 0);

        if ((PPPallowed & PPPpreferred) != 0) PPPallowed &= PPPpreferred;
        return std::make_pair (pcp_neighbour ? PCP_IN_USE_BOTH : PCP_IN_USE, PPPallowed);
}

/**
 * Choose the pylon position point to use for a pylon.
 * @param side Tile side where the pylon will be drawn.
 * @param allowed Mask of allowed pylon position points.
 * @param order Possible pylon positions arranged by preference.
 * @param nb Whether there is a neighbour tile that could draw this pylon.
 * @return The pylon position point to use, or -1 for none.
 * @note Use the overloaded variant below.
 */
static int ChoosePylonPosition (DiagDirection side, byte allowed,
        const Direction *order, bool nb)
{
        /* Which of the PPPs are inside the tile. For the two PPPs on the tile
         * border the following system is used: if you rotate the PCP so that
         * it is in the north, the eastern PPP belongs to the tile. */
        static const byte owned[DIAGDIR_END] = {
                1 << DIR_SE | 1 << DIR_S  | 1 << DIR_SW | 1 << DIR_W,
                1 << DIR_N  | 1 << DIR_SW | 1 << DIR_W  | 1 << DIR_NW,
                1 << DIR_N  | 1 << DIR_NE | 1 << DIR_E  | 1 << DIR_NW,
                1 << DIR_NE | 1 << DIR_E  | 1 << DIR_SE | 1 << DIR_S,
        };

        assert (allowed != 0);

        for (Direction k = DIR_BEGIN; k < DIR_END; k++) {
                byte pos = order[k];

                if (!HasBit(allowed, pos)) continue;

                /* Don't build the pylon if it would be outside the tile */
                if (HasBit(owned[side], pos)) return pos;

                /* We have a neighbour that will draw it, bail out */
                if (nb) return -1;
        }

        NOT_REACHED();
}

/**
 * Choose the pylon position point to use for a pylon.
 * @param side Tile side where the pylon will be drawn.
 * @param allowed Mask of allowed pylon position points.
 * @param odd_x Whether the tile is on an odd X coordinate.
 * @param odd_y Whether the tile is on an odd Y coordinate.
 * @param nb Whether there is a neighbour tile that could draw this pylon.
 * @return The pylon position point to use.
 */
static inline int ChoosePylonPosition (DiagDirection side, byte allowed,
        bool odd_x, bool odd_y, bool nb)
{
        /* Several PPPs maybe exist, here they are sorted in order of preference. */
        static const Direction order[2][2][DIAGDIR_END][DIR_END] = {
                {    // X even
                        {    // Y even
                                {DIR_NE, DIR_NW, DIR_SE, DIR_SW, DIR_N, DIR_E, DIR_S, DIR_W}, // NE
                                {DIR_NE, DIR_NW, DIR_SE, DIR_SW, DIR_S, DIR_E, DIR_N, DIR_W}, // SE
                                {DIR_NE, DIR_NW, DIR_SE, DIR_SW, DIR_S, DIR_W, DIR_N, DIR_E}, // SW
                                {DIR_NE, DIR_NW, DIR_SE, DIR_SW, DIR_N, DIR_W, DIR_S, DIR_E}, // NW
                        }, { // Y odd
                                {DIR_NE, DIR_SE, DIR_SW, DIR_NW, DIR_S, DIR_W, DIR_N, DIR_E}, // NE
                                {DIR_NE, DIR_SE, DIR_SW, DIR_NW, DIR_N, DIR_W, DIR_S, DIR_E}, // SE
                                {DIR_NE, DIR_SE, DIR_SW, DIR_NW, DIR_N, DIR_E, DIR_S, DIR_W}, // SW
                                {DIR_NE, DIR_SE, DIR_SW, DIR_NW, DIR_S, DIR_E, DIR_N, DIR_W}, // NW
                        }
                }, { // X odd
                        {    // Y even
                                {DIR_SW, DIR_NW, DIR_NE, DIR_SE, DIR_S, DIR_W, DIR_N, DIR_E}, // NE
                                {DIR_SW, DIR_NW, DIR_NE, DIR_SE, DIR_N, DIR_W, DIR_S, DIR_E}, // SE
                                {DIR_SW, DIR_NW, DIR_NE, DIR_SE, DIR_N, DIR_E, DIR_S, DIR_W}, // SW
                                {DIR_SW, DIR_NW, DIR_NE, DIR_SE, DIR_S, DIR_E, DIR_N, DIR_W}, // NW
                        }, { // Y odd
                                {DIR_SW, DIR_SE, DIR_NE, DIR_NW, DIR_N, DIR_E, DIR_S, DIR_W}, // NE
                                {DIR_SW, DIR_SE, DIR_NE, DIR_NW, DIR_S, DIR_E, DIR_N, DIR_W}, // SE
                                {DIR_SW, DIR_SE, DIR_NE, DIR_NW, DIR_S, DIR_W, DIR_N, DIR_E}, // SW
                                {DIR_SW, DIR_SE, DIR_NE, DIR_NW, DIR_N, DIR_W, DIR_S, DIR_E}, // NW
                        }
                }
        };

        return ChoosePylonPosition (side, allowed, order[odd_x][odd_y][side], nb);
}

/*
 * Add a pylon sprite for a tile.
 * @param ti The TileInfo struct of the tile being drawn.
 * @param pylon The sprite to draw.
 * @param x X position of the sprite.
 * @param y Y position of the sprite.
 * @param z Z position of the sprite.
 */
static void AddPylonSprite (const TileInfo *ti, SpriteID pylon,
        int x, int y, int z)
{
        AddSortableSpriteToDraw (ti->vd, pylon, PAL_NONE, x, y, 1, 1,
                        BB_HEIGHT_UNDER_BRIDGE, z,
                        IsTransparencySet (TO_CATENARY), -1, -1);
}

/**
 * Draw a pylon at a tile side.
 * @param ti The TileInfo struct of the tile being drawn.
 * @param side Side where to draw the pylon.
 * @param dir Pylon position point.
 * @param pylon_base Pylon sprite base.
 */
static void DrawPylon (const TileInfo *ti, DiagDirection side, Direction dir,
        SpriteID pylon_base)
{
        uint x = ti->x + x_pcp_offsets[side] + x_ppp_offsets[dir];
        uint y = ti->y + y_pcp_offsets[side] + y_ppp_offsets[dir];

        /* The elevation of the "pylon"-sprite should be the elevation
         * at the PCP. PCPs are always on a tile edge.
         *
         * This position can be outside of the tile, i.e.
         * ?_pcp_offset == TILE_SIZE > TILE_SIZE - 1.
         * So we have to move it inside the tile, because if the neighboured
         * tile has a foundation, that does not smoothly connect to the
         * current tile, we will get a wrong elevation from GetSlopePixelZ().
         *
         * When we move the position inside the tile, we will get a wrong
         * elevation if we have a slope. To catch all cases we round the Z
         * position to the next (TILE_HEIGHT / 2). This will return the
         * correct elevation for slopes and will also detect non-continuous
         * elevation on edges.
         *
         * Also note that the result of GetSlopePixelZ() is very special on
         * bridge-ramps.
         */

        TileIndex tile = ti->tile;
        int z = GetSlopePixelZ (TileX(tile) * TILE_SIZE + min(x_pcp_offsets[side], TILE_SIZE - 1), TileY(tile) * TILE_SIZE + min(y_pcp_offsets[side], TILE_SIZE - 1));
        int elevation = (z + 2) & ~3; // this means z = (z + TILE_HEIGHT / 4) / (TILE_HEIGHT / 2) * (TILE_HEIGHT / 2);

        AddPylonSprite (ti, pylon_base + pylon_sprites[dir], x, y, elevation);
}

/**
 * Add a wire sprite for a tile.
 * @param ti The TileInfo struct of the tile being drawn.
 * @param wire_base The base of the wire sprite to draw.
 * @param sss The sprite data for the wire.
 * @param config The configuration to use for the wire.
 * @param z Base Z position of the sprite.
 */
static inline void AddWireSprite (const TileInfo *ti, SpriteID wire_base,
        const SortableSpriteStructM *sss, uint config, int z)
{
        AddSortableSpriteToDraw (ti->vd,
                        wire_base + sss->image_offset[config - 1], PAL_NONE,
                        ti->x + sss->x_offset, ti->y + sss->y_offset,
                        sss->x_size, sss->y_size, 1,
                        z + sss->z_offset, IsTransparencySet (TO_CATENARY));
}

/**
 * Draws overhead wires and pylons for electric railways.
 * @param ti The TileInfo struct of the tile being drawn.
 * @param rti The rail type information of the rail.
 * @param tracks Tracks on which to draw.
 * @param wires Wires to draw.
 * @param slope Slope of the track surface for pylon elision.
 * @param draw_pylons Whether to draw pylons (some stations disable this).
 * @param draw_wires Whether to draw wires (some stations disable this).
 * @param context Tile context for GetWireBase and GetPylonBase.
 * @param bridge Bridge direction, if any.
 */
static void DrawRailCatenary (const TileInfo *ti, const RailtypeInfo *rti,
        TrackBits tracks, TrackBits wires, Slope slope,
        bool draw_pylons, bool draw_wires, TileContext context = TCX_NORMAL,
        DiagDirection bridge = INVALID_DIAGDIR)
{
        bool odd[AXIS_END];
        odd[AXIS_X] = IsOddX(ti->tile);
        odd[AXIS_Y] = IsOddY(ti->tile);

        byte pcp_status = 0;

        SpriteID pylon_base = GetPylonBase (rti, ti->tile, context);

        for (DiagDirection side = DIAGDIR_BEGIN; side < DIAGDIR_END; side++) {
                bool pcp_neighbour;
                byte ppp_allowed;
                if (side != bridge) {
                        std::pair <uint, byte> pcp_state = CheckSidePCP (ti->tile,
                                        tracks, wires, slope, side, odd);
                        if (pcp_state.first == PCP_NONE) continue;
                        pcp_neighbour = (pcp_state.first == PCP_IN_USE_BOTH);
                        ppp_allowed = pcp_state.second;
                        SetBit(pcp_status, side);
                } else {
                        /* Bridge tile. */
                        TrackBits bridge_tracks = DiagdirReachesTracks (ReverseDiagDir (side));
                        if ((tracks & bridge_tracks) == TRACK_BIT_NONE) continue;
                        SetBit(pcp_status, side);
                        /* Pylon is drawn by the middle part if there is any. */
                        if (GetTunnelBridgeLength (ti->tile, GetOtherBridgeEnd (ti->tile)) > 0) continue;
                        pcp_neighbour = true;
                        ppp_allowed = AllowedPPPonPCP[side];
                }

                if (!draw_pylons) continue;

                if (HasBridgeAbove(ti->tile)) {
                        if (GetBridgeAxis (ti->tile) == DiagDirToAxis (side)) {
                                int height = GetBridgeHeight (GetNorthernBridgeEnd (ti->tile));
                                if (height <= GetTileMaxZ (ti->tile) + 1) {
                                        continue;
                                }
                        }
                }

                int pos = ChoosePylonPosition (side, ppp_allowed,
                        odd[AXIS_X], odd[AXIS_Y], pcp_neighbour);
                if (pos >= 0) {
                        DrawPylon (ti, side, (Direction)pos, pylon_base);
                }
        }

        /* Don't draw a wire if the station tile does not want any */
        if (!draw_wires) return;

        /* Don't draw a wire under a low bridge */
        if (HasBridgeAbove(ti->tile) && !IsTransparencySet(TO_BRIDGES)) {
                int height = GetBridgeHeight(GetNorthernBridgeEnd(ti->tile));

                if (height <= GetTileMaxZ(ti->tile) + 1) return;
        }

        /* Drawing of pylons is finished, now draw the wires */
        SpriteID wire_base = GetWireBase (rti, ti->tile, context);

        Track t;
        FOR_EACH_SET_TRACK(t, wires) {
                /* Map a track bit onto its two tile sides. */
                static const byte track_sides[TRACK_END][2] = {
                        {DIAGDIR_NE, DIAGDIR_SW}, // X
                        {DIAGDIR_SE, DIAGDIR_NW}, // Y
                        {DIAGDIR_NW, DIAGDIR_NE}, // UPPER
                        {DIAGDIR_SE, DIAGDIR_SW}, // LOWER
                        {DIAGDIR_SW, DIAGDIR_NW}, // LEFT
                        {DIAGDIR_NE, DIAGDIR_SE}, // RIGHT
                };

                byte pcp_config = HasBit(pcp_status, track_sides[t][0]) +
                        (HasBit(pcp_status, track_sides[t][1]) << 1);

                assert(pcp_config != 0); // We have a pylon on neither end of the wire, that doesn't work (since we have no sprites for that)
                assert(!IsSteepSlope(slope));

                const SortableSpriteStructM *sss;
                switch (slope) {
                        case SLOPE_SW: sss = &CatenarySpriteDataSW;  break;
                        case SLOPE_SE: sss = &CatenarySpriteDataSE;  break;
                        case SLOPE_NW: sss = &CatenarySpriteDataNW;  break;
                        case SLOPE_NE: sss = &CatenarySpriteDataNE;  break;
                        default:       sss = &CatenarySpriteData[t]; break;
                }

                /*
                 * The "wire"-sprite position is inside the tile, i.e. 0 <= sss->?_offset < TILE_SIZE.
                 * Therefore it is safe to use GetSlopePixelZ() for the elevation.
                 * Also note that the result of GetSlopePixelZ() is very special for bridge-ramps.
                 */
                AddWireSprite (ti, wire_base, sss, pcp_config,
                        GetSlopePixelZ (ti->x + sss->x_offset, ti->y + sss->y_offset));
        }
}

/**
 * Draws overhead wires and pylons for electric railways.
 * @param ti The TileInfo struct of the tile being drawn
 */
void DrawRailwayCatenary (const TileInfo *ti)
{
        assert (IsRailwayTile (ti->tile));

        /* Find which rail bits are present, and select the override points. */
        DiagDirection overridePCP = IsTileSubtype (ti->tile, TT_BRIDGE) ? GetTunnelBridgeDirection (ti->tile) : INVALID_DIAGDIR;
        TrackBits tracks = GetElectrifiedTrackBits (ti->tile);
        TrackBits wires = MaskWireBits (ti->tile, tracks);

        /* Note that ti->tileh has already been adjusted for Foundations */
        Slope slope = ti->tileh;

        const RailtypeInfo *rti, *halftile_rti;
        Track halftile_track;
        TileContext halftile_context;
        if (IsHalftileSlope (slope)) {
                switch (GetHalftileSlopeCorner (slope)) {
                        default: NOT_REACHED();
                        case CORNER_W: halftile_track = TRACK_LEFT;  break;
                        case CORNER_S: halftile_track = TRACK_LOWER; break;
                        case CORNER_E: halftile_track = TRACK_RIGHT; break;
                        case CORNER_N: halftile_track = TRACK_UPPER; break;
                }
                halftile_rti = GetRailTypeInfo (GetRailType (ti->tile, halftile_track));
                halftile_context = TCX_UPPER_HALFTILE;
                Track opposite = TrackToOppositeTrack (halftile_track);
                rti = !HasBit(tracks, opposite) ? NULL :
                                GetRailTypeInfo (GetRailType (ti->tile, opposite));
                slope = SLOPE_FLAT;
        } else {
                RailType rt1 = GetRailType (ti->tile, TRACK_UPPER);
                RailType rt2 = GetRailType (ti->tile, TRACK_LOWER);
                rti = GetRailTypeInfo (rt1);
                if (rt1 == rt2) {
                        halftile_track = INVALID_TRACK;
                } else {
                        const RailtypeInfo *rti2 = GetRailTypeInfo (rt2);
                        switch (tracks) {
                                case TRACK_BIT_HORZ:
                                        halftile_rti = rti2;
                                        halftile_track = TRACK_LOWER;
                                        break;
                                case TRACK_BIT_VERT:
                                        halftile_rti = rti2;
                                        halftile_track = TRACK_RIGHT;
                                        break;
                                case TRACK_BIT_LOWER:
                                case TRACK_BIT_RIGHT:
                                        rti = rti2;
                                        /* fall through */
                                default: // TRACK_BIT_UPPER or TRACK_BIT_LEFT
                                        halftile_track = INVALID_TRACK;
                                        break;
                        }
                }
                halftile_context = TCX_NORMAL;
        }

        if (halftile_track != INVALID_TRACK) {
                TrackBits tracks = TrackToTrackBits (halftile_track);
                if (HasRailCatenary (halftile_rti)) {
                        DrawRailCatenary (ti, halftile_rti, tracks, tracks,
                                        SLOPE_FLAT, true, true,
                                        halftile_context);
                }
                if (rti == NULL) return;
                tracks &= ~tracks;
                wires = tracks;
        }

        if (HasRailCatenary (rti)) {
                DrawRailCatenary (ti, rti, tracks, wires, slope, true, true,
                                TCX_NORMAL, overridePCP);
        }
}

/**
 * Draws overhead wires and pylons on a normal (non-custom) bridge head.
 * @param ti The TileInfo struct of the tile being drawn.
 * @param rti The rail type information of the rail.
 * @param dir The direction of the bridge.
 */
void DrawRailBridgeHeadCatenary (const TileInfo *ti, const RailtypeInfo *rti,
        DiagDirection dir)
{
        TrackBits tracks = DiagDirToDiagTrackBits (dir);

        DrawRailCatenary (ti, rti, tracks, tracks, (ti->tileh != SLOPE_FLAT) ?
                                        SLOPE_FLAT : InclinedSlope (dir),
                        true, true, TCX_NORMAL, dir);
}

/**
 * Draws overhead wires and pylons for electric railways along an axis
 * (for crossings and station tiles).
 * @param ti The TileInfo struct of the tile being drawn.
 * @param rti The rail type information of the rail.
 * @param axis The axis along which to draw the wire.
 * @param draw_pylons Whether to draw pylons (some stations disable this).
 * @param draw_wire Whether to draw the wire (some stations disable this).
 */
void DrawRailAxisCatenary (const TileInfo *ti, const RailtypeInfo *rti,
        Axis axis, bool draw_pylons, bool draw_wire)
{
        /* Note that ti->tileh has already been adjusted for Foundations */
        assert (ti->tileh == SLOPE_FLAT);

        TrackBits tracks = AxisToTrackBits (axis);
        DrawRailCatenary (ti, rti, tracks, tracks, SLOPE_FLAT, draw_pylons, draw_wire);
}

/**
 * Draws overhead wires and pylons at a tunnel entrance.
 * @param ti The TileInfo struct of the tile being drawn.
 * @param dir The direction of the tunnel.
 */
void DrawRailTunnelCatenary (const TileInfo *ti, DiagDirection dir)
{
        /* Draw pylon. */
        TileIndex tile = ti->tile;
        DiagDirection rev = ReverseDiagDir (dir);

        byte dummy_preferred, dummy_allowed;
        Slope dummy_slope;
        bool pcp_neighbour = CheckNeighbourPCP (tile + TileOffsByDiagDir (rev),
                                dir, &dummy_preferred, &dummy_allowed, &dummy_slope);

        int pos = ChoosePylonPosition (rev, AllowedPPPonPCP[rev],
                        IsOddX(tile), IsOddY(tile), pcp_neighbour);

        const RailtypeInfo *rti = GetRailTypeInfo (GetRailType (tile));
        if (pos >= 0) {
                DrawPylon (ti, rev, (Direction)pos,
                                GetPylonBase (rti, tile, TCX_NORMAL));
        }

        /* Draw wire. */
        StartSpriteCombine (ti->vd);
        DrawRailTunnelDepotCatenary (ti, rti, false, dir);
}

/**
 * Draws wires on a tunnel tile
 *
 * DrawTile_TunnelBridge() calls this function to draw the wires on the bridge.
 *
 * @param ti The Tileinfo to draw the tile for
 */
void DrawRailCatenaryOnBridge(const TileInfo *ti)
{
        TileIndex start = GetNorthernBridgeEnd(ti->tile);
        bool odd = ((GetTunnelBridgeLength (ti->tile, start) + 1) % 2) != 0;

        TileIndex end = GetSouthernBridgeEnd(ti->tile);
        bool last = (GetTunnelBridgeLength (ti->tile, end) == 0);

        const RailtypeInfo *rti = GetRailTypeInfo (GetBridgeRailType (end));

        Axis axis = GetBridgeAxis(ti->tile);

        uint config;
        if (odd && last) {
                /* Draw the "short" wire on the southern end of the bridge
                 * only needed if the length of the bridge is odd */
                config = 3;
        } else {
                /* Draw "long" wires on all other tiles of the bridge (one pylon every two tiles) */
                config = 2 - odd;
        }

        uint height = GetBridgePixelHeight(end);

        AddWireSprite (ti, GetWireBase (rti, end, TCX_ON_BRIDGE),
                        &CatenarySpriteData[AxisToTrack(axis)], config, height);

        /* Finished with wires, draw pylons */
        if (!odd && !last) return; /* no pylons to draw */

        DiagDirection PCPpos;
        Direction PPPpos;
        if (axis == AXIS_X) {
                PCPpos = DIAGDIR_NE;
                PPPpos = IsOddY(ti->tile) ? DIR_SE : DIR_NW;
        } else {
                PCPpos = DIAGDIR_NW;
                PPPpos = IsOddX(ti->tile) ? DIR_SW : DIR_NE;
        }

        SpriteID pylon = GetPylonBase (rti, end, TCX_ON_BRIDGE) + pylon_sprites[PPPpos];
        uint x = ti->x + x_ppp_offsets[PPPpos];
        uint y = ti->y + y_ppp_offsets[PPPpos];

        /* every other tile needs a pylon on the northern end */
        if (odd) {
                AddPylonSprite (ti, pylon, x + x_pcp_offsets[PCPpos],
                                y + y_pcp_offsets[PCPpos], height);
        }

        /* need a pylon on the southern end of the bridge */
        if (last) {
                PCPpos = ReverseDiagDir(PCPpos);
                AddPylonSprite (ti, pylon, x + x_pcp_offsets[PCPpos],
                                y + y_pcp_offsets[PCPpos], height);
        }
}

bool SettingsDisableElrail(int32 p1)
{
        Company *c;
        Train *t;
        bool disable = (p1 != 0);

        /* we will now walk through all electric train engines and change their railtypes if it is the wrong one*/
        const RailType old_railtype = disable ? RAILTYPE_ELECTRIC : RAILTYPE_RAIL;
        const RailType new_railtype = disable ? RAILTYPE_RAIL : RAILTYPE_ELECTRIC;

        /* walk through all train engines */
        Engine *e;
        FOR_ALL_ENGINES_OF_TYPE(e, VEH_TRAIN) {
                RailVehicleInfo *rv_info = &e->u.rail;
                /* if it is an electric rail engine and its railtype is the wrong one */
                if (rv_info->engclass == 2 && rv_info->railtype == old_railtype) {
                        /* change it to the proper one */
                        rv_info->railtype = new_railtype;
                }
        }

        /* when disabling elrails, make sure that all existing trains can run on
         *  normal rail too */
        if (disable) {
                FOR_ALL_TRAINS(t) {
                        if (t->railtype == RAILTYPE_ELECTRIC) {
                                /* this railroad vehicle is now compatible only with elrail,
                                 *  so add there also normal rail compatibility */
                                t->compatible_railtypes |= RAILTYPES_RAIL;
                                t->railtype = RAILTYPE_RAIL;
                                SetBit(t->flags, VRF_EL_ENGINE_ALLOWED_NORMAL_RAIL);
                        }
                }
        }

        /* Fix the total power and acceleration for trains */
        FOR_ALL_TRAINS(t) {
                /* power and acceleration is cached only for front engines */
                if (t->IsFrontEngine()) {
                        t->ConsistChanged(CCF_TRACK);
                }
        }

        FOR_ALL_COMPANIES(c) c->avail_railtypes = GetCompanyRailtypes(c->index);

        /* This resets the _last_built_railtype, which will be invalid for electric
         * rails. It may have unintended consequences if that function is ever
         * extended, though. */
        ReinitGuiAfterToggleElrail(disable);
        return true;
}