(svn r160) -Codechange: made GetTileTrackStatus more readable (blathijs)

-Fix: some minor fixes around GetTileTrackStatus (blathijs)

20 files changed, 146 insertions, 80 deletions

diff --git a/ai.c b/ai.c
index 4039229a4..5b1650f4d 100644
--- a/ai.c
+++ b/ai.c
@@ -47,7 +47,7 @@ enum {
 #include "table/ai_rail.h"
 
 static byte GetRailTrackStatus(TileIndex tile) {
-	uint32 r = GetTileTrackStatus(tile, 0);
+	uint32 r = GetTileTrackStatus(tile, TRANSPORT_RAIL);
 	return (byte) (r | r >> 8);
 }
 
@@ -1849,7 +1849,7 @@ static bool AiDoFollowTrack(Player *p)
 	arpfd.tile2 = p->ai.cur_tile_a;
 	arpfd.flag = false;
 	arpfd.count = 0;
-	FollowTrack(p->ai.cur_tile_a + _tileoffs_by_dir[p->ai.cur_dir_a], 0x2000, p->ai.cur_dir_a^2, 
+	FollowTrack(p->ai.cur_tile_a + _tileoffs_by_dir[p->ai.cur_dir_a], 0x2000 | TRANSPORT_RAIL, p->ai.cur_dir_a^2, 
 		(TPFEnumProc*)AiEnumFollowTrack, NULL, &arpfd);
 	return arpfd.count > 8;
 }
@@ -2782,7 +2782,7 @@ bool AiCheckRoadFinished(Player *p)
 	are.dest = p->ai.cur_tile_b;
 	tile = TILE_MASK(p->ai.cur_tile_a + _tileoffs_by_dir[dir]);
 
-	bits = GetTileTrackStatus(tile, 2) & _ai_road_table_and[dir];
+	bits = GetTileTrackStatus(tile, TRANSPORT_ROAD) & _ai_road_table_and[dir];
 	if (bits == 0) {
 		return false;
 	}
@@ -2790,7 +2790,7 @@ bool AiCheckRoadFinished(Player *p)
 	are.best_dist = (uint)-1;
 
 	for_each_bit(i, bits) {
-		FollowTrack(tile, 0x3002, _dir_by_track[i], (TPFEnumProc*)AiEnumFollowRoad, NULL, &are);
+		FollowTrack(tile, 0x3000 | TRANSPORT_ROAD, _dir_by_track[i], (TPFEnumProc*)AiEnumFollowRoad, NULL, &are);
 	}
 
 	if (GetTileDist(tile, are.dest) <= are.best_dist)
diff --git a/clear_cmd.c b/clear_cmd.c
index 6b6445916..d7e742d5e 100644
--- a/clear_cmd.c
+++ b/clear_cmd.c
@@ -757,7 +757,7 @@ static void ClickTile_Clear(uint tile)
 	/* not used */
 }
 
-uint32 GetTileTrackStatus_Clear(uint tile, int mode)
+uint32 GetTileTrackStatus_Clear(uint tile, TransportType mode)
 {
 	return 0;
 }
diff --git a/disaster_cmd.c b/disaster_cmd.c
index bcb69e8f8..23c7e3fcb 100644
--- a/disaster_cmd.c
+++ b/disaster_cmd.c
@@ -641,7 +641,7 @@ static void DisasterTick_5_and_6(Vehicle *v)
 
 	tile = v->tile + _tileoffs_by_dir[v->direction >> 1];
 	if (IsValidTile(tile) &&
-			(r=GetTileTrackStatus(tile,4),(byte)(r+(r >> 8)) == 0x3F) &&
+			(r=GetTileTrackStatus(tile,TRANSPORT_WATER),(byte)(r+(r >> 8)) == 0x3F) &&
 			!CHANCE16(1,90)) {
 		GetNewVehiclePos(v, &gp);
 		SetDisasterVehiclePos(v, gp.x, gp.y, v->z_pos);
diff --git a/dummy_land.c b/dummy_land.c
index 590e48e78..0b0f4333f 100644
--- a/dummy_land.c
+++ b/dummy_land.c
@@ -53,7 +53,7 @@ static void ChangeTileOwner_Dummy(uint tile, byte old_player, byte new_player)
 	/* not used */
 }
 
-static uint32 GetTileTrackStatus_Dummy(uint tile, int mode)
+static uint32 GetTileTrackStatus_Dummy(uint tile, TransportType mode)
 {
 	return 0;
 }
diff --git a/functions.h b/functions.h
index 9cb23d52a..faf450e2c 100644
--- a/functions.h
+++ b/functions.h
@@ -20,7 +20,7 @@ void RunTileLoop();
 
 uint GetPartialZ(int x, int y, int corners);
 uint GetSlopeZ(int x, int y);
-uint32 GetTileTrackStatus(uint tile, int mode);
+uint32 GetTileTrackStatus(uint tile, TransportType mode);
 void GetAcceptedCargo(uint tile, AcceptedCargo *ac);
 void ChangeTileOwner(uint tile, byte old_player, byte new_player);
 void AnimateTile(uint tile);
diff --git a/industry_cmd.c b/industry_cmd.c
index bd955dbab..96ee9d98c 100644
--- a/industry_cmd.c
+++ b/industry_cmd.c
@@ -820,7 +820,7 @@ static void ClickTile_Industry(uint tile)
 	ShowIndustryViewWindow(_map2[tile]);
 }
 
-static uint32 GetTileTrackStatus_Industry(uint tile, int mode)
+static uint32 GetTileTrackStatus_Industry(uint tile, TransportType mode)
 {
 	return 0;
 }
diff --git a/landscape.c b/landscape.c
index 4c13d880b..b8e86dc5a 100644
--- a/landscape.c
+++ b/landscape.c
@@ -301,7 +301,7 @@ void DoClearSquare(uint tile)
 	);
 }
 
-uint32 GetTileTrackStatus(uint tile, int mode)
+uint32 GetTileTrackStatus(uint tile, TransportType mode)
 {
 	return _tile_type_procs[GET_TILETYPE(tile)]->get_tile_track_status_proc(tile, mode);
 }
diff --git a/pathfind.c b/pathfind.c
index 5a6ed2890..1a39aa376 100644
--- a/pathfind.c
+++ b/pathfind.c
@@ -190,7 +190,7 @@ static const int8 _get_tunlen_inc[5] = { -16, 0, 16, 0, -16 };
 /* Returns the end tile and the length of a tunnel. The length does not
  * include the starting tile (entry), it does include the end tile (exit).
  */
-FindLengthOfTunnelResult FindLengthOfTunnel(uint tile, int direction, byte type)
+FindLengthOfTunnelResult FindLengthOfTunnel(uint tile, int direction)
 {
 	FindLengthOfTunnelResult flotr;
 	int x,y;
@@ -213,7 +213,8 @@ FindLengthOfTunnelResult FindLengthOfTunnel(uint tile, int direction, byte type)
 
 		if (IS_TILETYPE(tile, MP_TUNNELBRIDGE) &&
 				(_map5[tile] & 0xF0) == 0 &&
-				((_map5[tile]>>1)&6) == type &&
+				//((_map5[tile]>>2)&3) == type && // This is
+				//not necesary to check, right?
 				((_map5[tile] & 3)^2) == direction &&
 				GetSlopeZ(x+8, y+8) == z)
 					break;
@@ -228,7 +229,7 @@ static const uint16 _tpfmode1_and[4] = { 0x1009, 0x16, 0x520, 0x2A00 };
 static uint SkipToEndOfTunnel(TrackPathFinder *tpf, uint tile, int direction) {
 	FindLengthOfTunnelResult flotr;
 	TPFSetTileBit(tpf, tile, 14);
-	flotr = FindLengthOfTunnel(tile, direction, tpf->tracktype);
+	flotr = FindLengthOfTunnel(tile, direction);
 	tpf->rd.cur_length += flotr.length;
 	TPFSetTileBit(tpf, flotr.tile, 14);
 	return flotr.tile;
@@ -601,7 +602,7 @@ restart:
 				/* We are not driving into the tunnel, or it
 				 * is an invalid tunnel */
 				goto popnext;
-			flotr = FindLengthOfTunnel(tile, direction, tpf->tracktype);
+			flotr = FindLengthOfTunnel(tile, direction);
 			si.cur_length += flotr.length;
 			tile = flotr.tile;
 		}
@@ -619,7 +620,7 @@ restart:
 
 		// not a regular rail tile?
 		if (!IS_TILETYPE(tile, MP_RAILWAY) || (bits = _map5[tile]) & 0xC0) {
-			bits = GetTileTrackStatus(tile, 0) & _tpfmode1_and[direction];
+			bits = GetTileTrackStatus(tile, TRANSPORT_RAIL) & _tpfmode1_and[direction];
 			bits = (bits | (bits >> 8)) & 0x3F;
 			break;
 		}
@@ -711,7 +712,7 @@ popnext:
 void NewTrainPathfind(uint tile, byte direction, TPFEnumProc *enum_proc, void *data, byte *cache)
 {
 	if (!_patches.new_pathfinding) {
-		FollowTrack(tile, 0x3000, direction, enum_proc, NULL, data);
+		FollowTrack(tile, 0x3000 | TRANSPORT_RAIL, direction, enum_proc, NULL, data);
 	} else {
 		NewTrackPathFinder *tpf;
 
diff --git a/pathfind.h b/pathfind.h
index 5f12568b4..2f947cab6 100644
--- a/pathfind.h
+++ b/pathfind.h
@@ -58,7 +58,7 @@ typedef struct {
 	uint tile;
 	int length;
 } FindLengthOfTunnelResult;
-FindLengthOfTunnelResult FindLengthOfTunnel(uint tile, int direction, byte type);
+FindLengthOfTunnelResult FindLengthOfTunnel(uint tile, int direction);
 
 void NewTrainPathfind(uint tile, byte direction, TPFEnumProc *enum_proc, void *data, byte *cache);
 
diff --git a/rail_cmd.c b/rail_cmd.c
index cff3cea8e..d4dc81725 100644
--- a/rail_cmd.c
+++ b/rail_cmd.c
@@ -1762,7 +1762,7 @@ bool UpdateSignalsOnSegment(uint tile, byte direction)
 		ssd.cur = ssd.presignal_exits = ssd.presignal_exits_free = 0;
 		ssd.has_presignal = false;
 
-		FollowTrack(tile, 0xC000, direction, (TPFEnumProc*)SetSignalsEnumProc, SetSignalsAfterProc, &ssd);
+		FollowTrack(tile, 0xC000 | TRANSPORT_RAIL, direction, (TPFEnumProc*)SetSignalsEnumProc, SetSignalsAfterProc, &ssd);
 		ChangeSignalStates(&ssd);
 
 		// remember the result only for the first iteration.
@@ -1933,11 +1933,11 @@ modify_me:;
 }
 
 
-static uint32 GetTileTrackStatus_Track(uint tile, int mode) {
+static uint32 GetTileTrackStatus_Track(uint tile, TransportType mode) {
 	byte m5, a, b;
 	uint32 ret;
 
-	if (mode != 0)
+	if (mode != TRANSPORT_RAIL)
 		return 0;
 
 	m5 = _map5[tile];
diff --git a/rail_gui.c b/rail_gui.c
index ae1e4dc54..980695604 100644
--- a/rail_gui.c
+++ b/rail_gui.c
@@ -145,7 +145,7 @@ static void GenericPlaceSignals(uint tile)
 	uint trackstat;
 	int i;
 
-	trackstat = (byte)GetTileTrackStatus(tile,0);
+	trackstat = (byte)GetTileTrackStatus(tile, TRANSPORT_RAIL);
 
 	if ((trackstat & 0x30) == 0x30) {
 		trackstat = (_tile_fract_coords.x <= _tile_fract_coords.y) ? 0x20 : 0x10;
diff --git a/road_cmd.c b/road_cmd.c
index fa3ea30f1..b4e9774da 100644
--- a/road_cmd.c
+++ b/road_cmd.c
@@ -6,6 +6,7 @@
 #include "player.h"
 #include "town.h"
 #include "gfx.h"
+#include "table/directions.h"
 
 /* When true, GetTrackStatus for roads will treat roads under reconstruction
  * as normal roads instead of impassable. This is used when detecting whether
@@ -119,7 +120,7 @@ bool IsRoadDepotTile(TileIndex tile)
 
 uint GetRoadBitsByTile(TileIndex tile)
 {
-	uint32 r = GetTileTrackStatus(tile, 2);
+	uint32 r = GetTileTrackStatus(tile, TRANSPORT_ROAD);
 	return (byte)(r | (r >> 8));
 }
 
@@ -1023,18 +1024,20 @@ static const byte _road_trackbits[16] = {
 	0x0, 0x0, 0x0, 0x10, 0x0, 0x2, 0x8, 0x1A, 0x0, 0x4, 0x1, 0x15, 0x20, 0x26, 0x29, 0x3F,
 };
 
-static uint32 GetTileTrackStatus_Road(uint tile, int mode)	{
-	if (mode == 0) {
+static uint32 GetTileTrackStatus_Road(uint tile, TransportType mode)	{
+	if (mode == TRANSPORT_RAIL) {
 		if ((_map5[tile] & 0xF0) != 0x10)
 			return 0;
 		return _map5[tile] & 8 ? 0x101 : 0x202;
-	} else if  (mode == 2) {
+	} else if  (mode == TRANSPORT_ROAD) {
 		byte b = _map5[tile];
 		if ((b & 0xF0) == 0) {
+			/* Ordinary road */
 			if (!_road_special_gettrackstatus && (_map2[tile]&7) >= 6)
 				return 0;
 			return _road_trackbits[b&0xF] * 0x101;
-		} else if ((b&0xE0) == 0) {
+		} else if ((b&0xF0) == 0x10) {
+			/* Crossing */
 			uint32 r = 0x101;
 			if (b&8) r <<= 1;
 				
@@ -1042,6 +1045,13 @@ static uint32 GetTileTrackStatus_Road(uint tile, int mode)	{
 				r *= 0x10001;
 			}			
 			return r;
+		} else if ((b&0xF0) == 0x20) {
+			/* Depot */
+			/* We reverse the dir because it points out of the
+			 * exit, and we want to get in. Maybe we should return
+			 * both dirs here? */
+			byte dir = _reverse_dir[b&3];
+			return 1 << _dir_to_straight_trackdir[dir];
 		}
 	}
 	return 0;
diff --git a/roadveh_cmd.c b/roadveh_cmd.c
index e3fec5681..cc8250ffc 100644
--- a/roadveh_cmd.c
+++ b/roadveh_cmd.c
@@ -371,7 +371,7 @@ static int FindClosestRoadDepot(Vehicle *v)
 
 	/* search in all directions */
 	for(i=0; i!=4; i++)
-		FollowTrack(tile, 0x2002, i, (TPFEnumProc*)EnumRoadSignalFindDepot, NULL, &rfdd);
+		FollowTrack(tile, 0x2000 | TRANSPORT_ROAD, i, (TPFEnumProc*)EnumRoadSignalFindDepot, NULL, &rfdd);
 
 	if (rfdd.best_length == (uint)-1)
 		return -1;
@@ -898,7 +898,7 @@ static bool FindRoadVehToOvertake(OvertakeData *od)
 {
 	uint32 bits;
 
-	bits = GetTileTrackStatus(od->tile, 2)&0x3F;
+	bits = GetTileTrackStatus(od->tile, TRANSPORT_ROAD)&0x3F;
 
 	if (!(od->tilebits & bits) || (bits&0x3C) || (bits & 0x3F3F0000))
 		return true;
@@ -924,7 +924,7 @@ static void RoadVehCheckOvertake(Vehicle *v, Vehicle *u)
 	if (v->u.road.state >= 32 || (v->u.road.state&7) > 1 )
 		return;
 
-	tt = (byte)(GetTileTrackStatus(v->tile, 2) & 0x3F);
+	tt = (byte)(GetTileTrackStatus(v->tile, TRANSPORT_ROAD) & 0x3F);
 	if ((tt & 3) == 0)
 		return;
 	if ((tt & 0x3C) != 0)
@@ -1020,31 +1020,24 @@ static int RoadFindPathToDest(Vehicle *v, uint tile, int direction)
 
 	{
 		uint32 r;
-		r = GetTileTrackStatus(tile, 2);
+			r = GetTileTrackStatus(tile, TRANSPORT_ROAD);
 		signal = (uint16)(r >> 16);
 		bitmask = (uint16)r;
 	}
 
-	if (IS_TILETYPE(tile, MP_STREET)) {
-		
-		if ((_map5[tile]&0xF0) == 0x20 && v->owner == _map_owner[tile])
-			bitmask |= _road_veh_fp_ax_or[_map5[tile]&3];
-
-	} else if (IS_TILETYPE(tile, MP_STATION)) {
-		if (_map_owner[tile] == OWNER_NONE || _map_owner[tile] == v->owner) {
-			Station *st = DEREF_STATION(_map2[tile]);
-			byte val = _map5[tile];
-
-			if (v->cargo_type != CT_PASSENGERS) {
-				if (IS_BYTE_INSIDE(val, 0x43, 0x47) && (_patches.roadveh_queue || st->truck_stop_status&3))
-					bitmask |= _road_veh_fp_ax_or[(val-0x43)&3];
-			} else {
-				if (IS_BYTE_INSIDE(val, 0x47, 0x4B) && (_patches.roadveh_queue || st->bus_stop_status&3))
-					bitmask |= _road_veh_fp_ax_or[(val-0x47)&3];
-			}
-		}
-	}
 
+	/* Most of the checks that used to be here, are now integrated into
+	 * GetTileTrackStatus now. The only thing still remaining is the
+	 * owner check for stations and depots, since GetTileTrackStatus
+	 * doesn't know about owner */
+	if (IS_TILETYPE(tile, MP_STREET) && (_map5[tile]&0xF0) == 0x20 && v->owner != _map_owner[tile])
+		/* Depot not owned by us */
+		bitmask = 0;
+	if (IS_TILETYPE(tile, MP_STATION) && _map_owner[tile] != OWNER_NONE && _map_owner[tile] != v->owner)
+		/* Station not owned by us */
+		bitmask = 0;
+
+	/* remove unreachable tracks */
 	bitmask &= _road_veh_fp_ax_and[direction];
 	if (bitmask == 0) {
 		// reverse
@@ -1096,7 +1089,7 @@ do_it:;
 			if (best_track == -1) best_track = i; // in case we don't find the path, just pick a direction
 			frd.maxtracklen = (uint)-1;
 			frd.mindist = (uint)-1;
-			FollowTrack(tile, 0x3002, _road_pf_directions[i], (TPFEnumProc*)EnumRoadTrackFindDist, NULL, &frd);
+			FollowTrack(tile, 0x3000 | TRANSPORT_ROAD, _road_pf_directions[i], (TPFEnumProc*)EnumRoadTrackFindDist, NULL, &frd);
 
 			if (frd.mindist < best_dist || (frd.mindist==best_dist && frd.maxtracklen < best_maxlen)) {
 				best_dist = frd.mindist;
diff --git a/ship_cmd.c b/ship_cmd.c
index 009f2f18b..de853968e 100644
--- a/ship_cmd.c
+++ b/ship_cmd.c
@@ -15,7 +15,7 @@ static const uint16 _ship_sprites[] = {0x0E5D, 0x0E55, 0x0E65, 0x0E6D};
 static const byte _ship_sometracks[4] = {0x19, 0x16, 0x25, 0x2A};
 
 static byte GetTileShipTrackStatus(uint tile) {
-	uint32 r = GetTileTrackStatus(tile, 4);
+	uint32 r = GetTileTrackStatus(tile, TRANSPORT_WATER);
 	return r | r >> 8;
 }
 
@@ -492,7 +492,7 @@ static uint FindShipTrack(Vehicle *v, uint tile, int dir, uint bits, uint skipti
 		pfs.best_bird_dist = (uint)-1;
 		pfs.best_length = (uint)-1;
 
-		FollowTrack(tile, 0x3804, _ship_search_directions[i][dir], (TPFEnumProc*)ShipTrackFollower, NULL, &pfs);
+		FollowTrack(tile, 0x3800 | TRANSPORT_WATER, _ship_search_directions[i][dir], (TPFEnumProc*)ShipTrackFollower, NULL, &pfs);
 		
 		if (best_track >= 0) {
 			if (pfs.best_bird_dist != 0) {
@@ -569,7 +569,7 @@ static int ShipGetNewDirection(Vehicle *v, int x, int y)
 
 static int GetAvailShipTracks(uint tile, int dir)
 {
-	uint32 r = GetTileTrackStatus(tile, 4);
+	uint32 r = GetTileTrackStatus(tile, TRANSPORT_WATER);
 	return (byte) ((r | r >> 8)) & _ship_sometracks[dir];
 }
 
diff --git a/station_cmd.c b/station_cmd.c
index b2bd2f54a..c34aeb620 100644
--- a/station_cmd.c
+++ b/station_cmd.c
@@ -12,6 +12,7 @@
 #include "economy.h"
 #include "player.h"
 #include "airport.h"
+#include "table/directions.h"
 
 // FIXME -- need to be embedded into Airport variable. Is dynamically
 // deducteable from graphics-tile array, so will not be needed
@@ -1837,21 +1838,34 @@ static void GetTileDesc_Station(uint tile, TileDesc *td)
 
 static const byte _tile_track_status_rail[8] = { 1,2,1,2,1,2,1,2 };
 
-static uint32 GetTileTrackStatus_Station(uint tile, int mode) {
+static uint32 GetTileTrackStatus_Station(uint tile, TransportType mode) {
 	uint i = _map5[tile];
 	uint j = 0;
 
-	if (mode == 0) {
+	if (mode == TRANSPORT_RAIL) {
 		if (i < 8)
 			j = _tile_track_status_rail[i];
-	} else if (mode == 2) {
-		// not needed
-	} else if (mode == 4) {
-		// buoy
+		j += (j << 8);
+	} else if (mode == TRANSPORT_ROAD) {
+		Station *st = DEREF_STATION(_map2[tile]);
+		if ( (IS_BYTE_INSIDE(i, 0x43, 0x47) && (_patches.roadveh_queue || st->truck_stop_status&3)) ||
+		(IS_BYTE_INSIDE(i, 0x47, 0x4B) && (_patches.roadveh_queue || st->bus_stop_status&3)) ) {
+			/* This is a bus/truck stop, and there is free space
+			 * (or we allow queueing) */
+			
+			/* We reverse the dir because it points out of the
+			 * exit, and we want to get in. Maybe we should return
+			 * both dirs here? */
+			byte dir = _reverse_dir[(i-0x43)&3];
+			j = 1 << _dir_to_straight_trackdir[dir];
+		}
+	} else if (mode == TRANSPORT_WATER) {
+		// buoy is coded as a station, it is always on open water
+		// (0x3F, all tracks available)
 		if (i == 0x52) j = 0x3F;
+		j += (j << 8);
 	}
-
-	return j + (j << 8);
+	return j;
 }
 
 static void TileLoop_Station(uint tile)
diff --git a/town_cmd.c b/town_cmd.c
index 719ba2b8b..6ed0b6151 100644
--- a/town_cmd.c
+++ b/town_cmd.c
@@ -319,7 +319,7 @@ static void GetTileDesc_Town(uint tile, TileDesc *td)
 	td->owner = OWNER_TOWN;
 }
 
-static uint32 GetTileTrackStatus_Town(uint tile, int mode)
+static uint32 GetTileTrackStatus_Town(uint tile, TransportType mode)
 {
 	/* not used */
 	return 0;
@@ -540,7 +540,7 @@ static void GrowTownInTile(uint *tile_ptr, uint mask, int block, Town *t1)
 
 		// Reached a tunnel? Then continue at the other side of it.
 		if (IS_TILETYPE(tile, MP_TUNNELBRIDGE) && (_map5[tile]&~3)==4) {
-			FindLengthOfTunnelResult flotr = FindLengthOfTunnel(tile, _map5[tile]&3, 2);
+			FindLengthOfTunnelResult flotr = FindLengthOfTunnel(tile, _map5[tile]&3);
 			*tile_ptr = flotr.tile;
 			return;
 		}
diff --git a/train_cmd.c b/train_cmd.c
index dd5bc6008..cb6306d91 100644
--- a/train_cmd.c
+++ b/train_cmd.c
@@ -2035,7 +2035,7 @@ static void TrainController(Vehicle *v)
 				
 				/* Get the status of the tracks in the new tile and mask
 				 * away the bits that aren't reachable. */
-				ts = GetTileTrackStatus(gp.new_tile, 0) & _reachable_tracks[dir >> 1];
+				ts = GetTileTrackStatus(gp.new_tile, TRANSPORT_RAIL) & _reachable_tracks[dir >> 1];
 
 				/* Combine the from & to directions.
 				 * Now, the lower byte contains the track status, and the byte at bit 16 contains
@@ -2347,7 +2347,7 @@ static void TrainCheckIfLineEnds(Vehicle *v)
 	/* Calculate next tile */
 	tile += _tileoffs_by_dir[t];
 	// determine the track status on the next tile.
-	ts = GetTileTrackStatus(tile, 0) & _reachable_tracks[t];
+ 	ts = GetTileTrackStatus(tile, TRANSPORT_RAIL) & _reachable_tracks[t];
 	
 	/* Calc position within the current tile ?? */
 	x = v->x_pos & 0xF;
diff --git a/ttd.h b/ttd.h
index 325292c16..1f0dd3752 100644
--- a/ttd.h
+++ b/ttd.h
@@ -86,6 +86,20 @@ enum MapTileTypes {
 	MP_UNMOVABLE
 };
 
+typedef enum TransportTypes {
+	/* These constants are for now linked to the representation of bridges
+	 * and tunnels, so they can be used by GetTileTrackStatus_TunnelBridge
+	 * to compare against the map5 array. In an ideal world, these
+	 * constants would be used everywhere when accessing tunnels and
+	 * bridges. For now, you should just not change the values for road
+	 * and rail.
+	 */
+        TRANSPORT_RAIL = 0,
+	TRANSPORT_ROAD = 1,
+	TRANSPORT_WATER,
+	TRANSPORT_MAX
+} TransportType;
+
 typedef struct TileInfo {
 	uint x;
 	uint y;
@@ -231,7 +245,26 @@ typedef uint GetSlopeZProc(TileInfo *ti);
 typedef int32 ClearTileProc(uint tile, byte flags);
 typedef void GetAcceptedCargoProc(uint tile, AcceptedCargo *res);
 typedef void GetTileDescProc(uint tile, TileDesc *td);
-typedef uint32 GetTileTrackStatusProc(uint tile, int mode);
+/* GetTileTrackStatusProcs return a value that contains the possible tracks
+ * that can be taken on a given tile by a given transport. The return value is
+ * composed as follows: 0xaabbccdd. ccdd and aabb are bitmasks of trackdirs,
+ * where bit n corresponds to trackdir n. ccdd are the trackdirs that are
+ * present in the tile (1==present, 0==not present), aabb is the signal
+ * status, if applicable (0==green/no signal, 1==red, note that this is
+ * reversed from map3/2[tile] for railway signals).
+ *
+ * The result (let's call it ts) is often used as follows:
+ * tracks = (byte)(ts | ts >>8)
+ * This effectively converts the present part of the result (ccdd) to a
+ * track bitmask, which disregards directions. Normally, this is the same as just
+ * doing (byte)ts I think, although I am not really sure 
+ *
+ * A trackdir is combination of a track and a dir, where the lower three bits
+ * are a track, the fourth bit is the direction. these give 12 (or 14)
+ * possible options: 0-5 and 8-13, so we need 14 bits for a trackdir bitmask
+ * above. 
+ */
+typedef uint32 GetTileTrackStatusProc(uint tile, TransportType mode);
 typedef void GetProducedCargoProc(uint tile, byte *b);
 typedef void ClickTileProc(uint tile);
 typedef void AnimateTileProc(uint tile);
diff --git a/tunnelbridge_cmd.c b/tunnelbridge_cmd.c
index 7a7af310a..2ded3e90c 100644
--- a/tunnelbridge_cmd.c
+++ b/tunnelbridge_cmd.c
@@ -1296,34 +1296,49 @@ static void ClickTile_TunnelBridge(uint tile)
 }
 
 
-static uint32 GetTileTrackStatus_TunnelBridge(uint tile, int mode)
+static uint32 GetTileTrackStatus_TunnelBridge(uint tile, TransportType mode)
 {
 	uint32 result;
-	byte t, m5 = _map5[tile];
+	byte m5 = _map5[tile];
 
 	if ((m5 & 0xF0) == 0) {
-		if (((m5 & 0xC) >> 1) == mode) { /* XXX: possible problem when switching mode constants */
+		/* This is a tunnel */
+		if (((m5 & 0xC) >> 2) == mode) { 
+			/* Tranport in the tunnel is compatible */
 			return m5&1 ? 0x202 : 0x101;
 		}
 	} else if (m5 & 0x80) {
+		/* This is a bridge */
 		result = 0;
-		if ((m5 & 6) == mode) {
+		if (((m5 & 0x6) >> 1) == mode) {
+			/* Transport over the bridge is compatible */
 			result = m5&1 ? 0x202 : 0x101;
 		}
 		if (m5 & 0x40) {
-			t = m5;
-			if (!(t & 0x20)) {
-				if ((t &= 0x18) != 8)
+			/* Bridge middle part */
+			if (!(m5 & 0x20)) {
+				/* Clear ground or water underneath */
+				if ((m5 &= 0x18) != 8)
+					/* Clear ground */
+					return result;
+				else	
+					if (mode != TRANSPORT_WATER)
+						return result;
+			} else {
+				/* Transport underneath */
+				if ((m5 & 0x18) >> 3 != mode)
+					/* Incompatible transport underneath */
 					return result;
-				t = (t&0xE7) | 0x30;
 			}
-
-			if ((t & 0x18) >> 2 != mode)
-				return result;
-
+			/* If we've not returned yet, there is a compatible
+			 * transport or water beneath, so we can add it to
+			 * result */
+			/* Why is this xor'd ? Can't it just be or'd? */
 			result ^= m5&1 ? 0x101 : 0x202;
 		}
 		return result;
+	} else {
+		assert(0); /* This should never occur */
 	}
 	return 0;
 }
diff --git a/water_cmd.c b/water_cmd.c
index a7740f3e1..fa22d5a1e 100644
--- a/water_cmd.c
+++ b/water_cmd.c
@@ -600,12 +600,12 @@ void TileLoop_Water(uint tile)
 static const byte _coast_tracks[16] = {0, 32, 4, 0, 16, 0, 0, 0, 8, 0, 0, 0, 0, 0, 0, 0};
 static const byte _shipdepot_tracks[4] = {1,1,2,2};
 static const byte _shiplift_tracks[12] = {1,2,1,2,1,2,1,2,1,2,1,2};
-static uint32 GetTileTrackStatus_Water(uint tile, int mode)
+static uint32 GetTileTrackStatus_Water(uint tile, TransportType mode)
 {
 	uint m5;
 	uint b;
 
-	if (mode != 4)
+	if (mode != TRANSPORT_WATER)
 		return 0;
 
 	m5 = _map5[tile];