(svn r3065) -Codechange/Add: Modified the bridge drawing code so that the basic offset is read from the RailTypeInfo struct. This is (hopefully) the last DrawTile change on the way to electrified railways. While being at it, de-mystified the function a bit and added some asserts.

4 files changed, 72 insertions, 29 deletions

diff --git a/openttd.h b/openttd.h
index 26f45f219..4e2119fbe 100644
--- a/openttd.h
+++ b/openttd.h
@@ -1,4 +1,5 @@
 /* $Id$ */
+/** @file openttd.h */
 
 #ifndef OPENTTD_H
 #define OPENTTD_H
@@ -71,8 +72,8 @@ typedef byte PlayerID;
 typedef byte OrderID;
 typedef byte CargoID;
 typedef uint16 StringID;
-typedef uint32 SpriteID;
-typedef uint32 PalSpriteID;
+typedef uint32 SpriteID;    //! The number of a sprite, without mapping bits and colortables
+typedef uint32 PalSpriteID; //! The number of a sprite plus all the mapping bits and colortables
 typedef uint32 CursorID;
 typedef uint16 EngineID; //! All enginenumbers should be of this type
 typedef uint16 UnitID;   //! All unitnumber stuff is of this type (or anyway, should be)
diff --git a/rail.h b/rail.h
index 8632fe368..96203e5ab 100644
--- a/rail.h
+++ b/rail.h
@@ -201,6 +201,11 @@ typedef struct RailtypeInfo {
 	 * @note: Something more flexible might be desirable in the future.
 	 */
 	SpriteID total_offset;
+
+	/**
+	  * Bridge offset
+	  */
+	SpriteID bridge_offset;
 } RailtypeInfo;
 
 extern const RailtypeInfo _railtypes[RAILTYPE_END];
@@ -592,5 +597,5 @@ static inline bool IsCompatibleRail(RailType enginetype, RailType tiletype)
 void DrawTrackBits(TileInfo *ti, TrackBits track, bool earth, bool snow, bool flat);
 void DrawTrainDepotSprite(int x, int y, int image, RailType railtype);
 void DrawDefaultWaypointSprite(int x, int y, RailType railtype);
-
 #endif /* RAIL_H */
+
diff --git a/railtypes.h b/railtypes.h
index bb1b6a10c..be097383c 100644
--- a/railtypes.h
+++ b/railtypes.h
@@ -41,6 +41,9 @@ const RailtypeInfo _railtypes[] = {
 
 		/* main offset */
 		0,
+
+		/* bridge offset */
+		0,
 	},
 
 	/** Monorail */
@@ -77,6 +80,9 @@ const RailtypeInfo _railtypes[] = {
 
 		/* main offset */
 		82,
+
+		/* bridge offset */
+		16,
 	},
 
 	/** Maglev */
@@ -113,6 +119,9 @@ const RailtypeInfo _railtypes[] = {
 
 		/* main offset */
 		164,
+
+		/* bridge offset */
+		24,
 	},
 };
 
diff --git a/tunnelbridge_cmd.c b/tunnelbridge_cmd.c
index dec5e6a3c..b5bcfe3d5 100644
--- a/tunnelbridge_cmd.c
+++ b/tunnelbridge_cmd.c
@@ -968,8 +968,8 @@ extern const byte _road_sloped_sprites[14];
 
 static void DrawBridgePillars(const TileInfo *ti, int x, int y, int z)
 {
-	const uint32 *b;
-	uint32 image;
+	const PalSpriteID *b;
+	PalSpriteID image;
 	int piece;
 
 	b = _bridge_poles_table[GetBridgeType(ti->tile)];
@@ -1030,11 +1030,27 @@ uint GetBridgeFoundation(uint tileh, byte direction) {
 	return 0;
 }
 
+/**
+  * Draws a tunnel of bridge tile.
+  * For tunnels, this is rather simple, as you only needa draw the entrance.
+  * Bridges are a bit more complex. base_offset is where the sprite selection comes into play
+  * and it works a bit like a bitmask.<p> For bridge heads:
+  * <ul><li>Bit 0: direction</li>
+  * <li>Bit 1: northern or southern heads</li>
+  * <li>Bit 2: Set if the bridge head is sloped</li>
+  * <li>Bit 3 and more: Railtype Specific subset</li>
+  * </ul>
+  * For middle parts:
+  * <ul><li>Bits 0-1: need to be 0</li>
+  * <li>Bit 2: direction</li>
+  * <li>Bit 3 and above: Railtype Specific subset</li>
+  * </ul>
+  * Please note that in this code, "roads" are treated as railtype 1, whilst the real railtypes are 0, 2 and 3
+  */
 static void DrawTile_TunnelBridge(TileInfo *ti)
 {
 	uint32 image;
-	uint tmp;
-	const uint32 *b;
+	const PalSpriteID *b;
 	bool ice = _m[ti->tile].m4 & 0x80;
 
 	// draw tunnel?
@@ -1053,19 +1069,24 @@ static void DrawTile_TunnelBridge(TileInfo *ti)
 		AddSortableSpriteToDraw(image+1, ti->x + 15, ti->y + 15, 1, 1, 8, (byte)ti->z);
 	// draw bridge?
 	} else if ((byte)ti->map5 & 0x80) {
-		// get type of track on the bridge.
-		tmp = _m[ti->tile].m3;
-		if (ti->map5 & 0x40) tmp >>= 4;
-		tmp &= 0xF;
+		RailType rt;
+		int base_offset;
+
+		if (HASBIT(ti->map5, 1)) { /* This is a road bridge */
+			base_offset = 8;
+		} else { /* Rail bridge */
+			if (HASBIT(ti->map5, 6)) { /* The bits we need depend on the fact whether it is a bridge head or not */
+				rt = GB(_m[ti->tile].m3, 4, 3);
+			} else {
+				rt = GB(_m[ti->tile].m3, 0, 3);
+			}
 
-		// 0 = rail bridge
-		// 1 = road bridge
-		// 2 = monorail bridge
-		// 3 = maglev bridge
+			base_offset = GetRailTypeInfo(rt)->bridge_offset;
+			assert(base_offset != 8); /* This one is used for roads */
+		}
 
-		// add direction and fix stuff.
-		if (tmp != 0) tmp++;
-		tmp = (ti->map5&3) + (tmp*2);
+		/* as the lower 3 bits are used for other stuff, make sure they are clear */
+		assert( (base_offset & 0x07) == 0x00);
 
 		if (!(ti->map5 & 0x40)) {	// bridge ramps
 
@@ -1077,14 +1098,14 @@ static void DrawTile_TunnelBridge(TileInfo *ti)
 				if (ti->tileh != 0) image = SPR_RAIL_TRACK_Y + _track_sloped_sprites[ti->tileh - 1];
 			}
 
-			// bridge ending.
-			b = GetBridgeSpriteTable(GetBridgeType(ti->tile), 6);
-			b += (tmp&(3<<1))*4; /* actually ((tmp>>2)&3)*8 */
-			b += (tmp&1); // direction
-			if (ti->tileh == 0) b += 4; // sloped "entrance" ?
-			if (ti->map5 & 0x20) b += 2; // which side
+			/* Cope for the direction of the bridge */
+			if (HASBIT(ti->map5, 0)) base_offset++;
+
+			if (ti->map5 & 0x20) base_offset += 2; // which side
+			if (ti->tileh == 0) base_offset += 4; // sloped bridge head
 
-			image = *b;
+			/* Table number 6 always refers to the bridge heads for any bridge type */
+			image = GetBridgeSpriteTable(GetBridgeType(ti->tile), 6)[base_offset];
 
 			if (!ice) {
 				DrawClearLandTile(ti, 3);
@@ -1101,6 +1122,7 @@ static void DrawTile_TunnelBridge(TileInfo *ti)
 			int x,y;
 
 			image = GB(ti->map5, 3, 2); // type of stuff under bridge (only defined for 0,1)
+			/** @todo So why do we even WASTE that one bit?! (map5, bit 4) */
 			assert(image <= 1);
 
 			if (!(ti->map5 & 0x20)) {
@@ -1134,16 +1156,22 @@ static void DrawTile_TunnelBridge(TileInfo *ti)
 					// road
 					image = SPR_ROAD_Y + (ti->map5 & 1);
 					if (ti->tileh != 0) image = _road_sloped_sprites[ti->tileh - 1] + 0x53F;
-					if (ice) image += 19; // ice?
+					if (ice) image += 19;
 				}
 				DrawGroundSprite(image);
 			}
+
+			/* Cope for the direction of the bridge */
+			if (HASBIT(ti->map5, 0)) base_offset += 4;
+
+			/*  base_offset needs to be 0 due to the structure of the sprite table see table/bridge_land.h */
+			assert( (base_offset & 0x03) == 0x00);
 			// get bridge sprites
-			b = GetBridgeSpriteTable(GetBridgeType(ti->tile), GetBridgePiece(ti->tile)) + tmp * 4;
+			b = GetBridgeSpriteTable(GetBridgeType(ti->tile), GetBridgePiece(ti->tile)) + base_offset;
 
 			z = GetBridgeHeight(ti) + 5;
 
-			// draw rail
+			// draw rail or road component
 			image = b[0];
 			if (_display_opt & DO_TRANS_BUILDINGS) MAKE_TRANSPARENT(image);
 			AddSortableSpriteToDraw(image, ti->x, ti->y, (ti->map5&1)?11:16, (ti->map5&1)?16:11, 1, z);
@@ -1153,7 +1181,7 @@ static void DrawTile_TunnelBridge(TileInfo *ti)
 			image = b[1];
 			if (_display_opt & DO_TRANS_BUILDINGS) MAKE_TRANSPARENT(image);
 
-			// draw roof
+			// draw roof, the component of the bridge which is logically between the vehicle and the camera
 			if (ti->map5&1) {
 				x += 12;
 				if (image & SPRITE_MASK) AddSortableSpriteToDraw(image, x,y, 1, 16, 0x28, z);