(svn r3992) -Fix: Rewrote the code to determine whether a rail-tile can be terraformed.

Fixes a bug where you could terraform a tunnel (fixed by r3228, but reverted that one)
Fixes a bug introduced by r3228 which allowed steep rail tiles resulting in ... unwanted effects such as display artifacts.
That means the terraform feature should not work as intended; it also uses _valid_tileh_slopes to determine valid configurations instead of hand-brewn stuff.
TODO: _terraform_err_tile and similar TileIndices should have INVALID_TILE as "unused", not 0. (0 is a valid tile).

5 files changed, 53 insertions, 57 deletions

diff --git a/clear_cmd.c b/clear_cmd.c
index c7142bb56..364e7733b 100644
--- a/clear_cmd.c
+++ b/clear_cmd.c
@@ -88,38 +88,13 @@ static void TerraformAddDirtyTileAround(TerraformerState *ts, TileIndex tile)
 static int TerraformProc(TerraformerState *ts, TileIndex tile, int mode)
 {
 	int r;
-	bool skip_clear = false;
 
 	assert(tile < MapSize());
 
 	if ((r=TerraformAllowTileProcess(ts, tile)) <= 0)
 		return r;
 
-	if (IsTileType(tile, MP_RAILWAY)) {
-		static const TrackBits _railway_modes[] = { TRACK_BIT_LOWER, TRACK_BIT_LEFT, TRACK_BIT_UPPER, TRACK_BIT_RIGHT };
-		static const byte _railway_dangslopes[4] = {0xd, 0xe, 7, 0xb};
-		static const byte _railway_dangslopes2[4] = {0x2, 0x1, 0x8, 0x4};
-
-		// Nothing could be built at the steep slope - this avoids a bug
-		// when you have a single diagonal track in one corner on a
-		// basement and then you raise/lower the other corner.
-		int tileh = GetTileSlope(tile, NULL) & 0xF;
-		if (tileh == _railway_dangslopes[mode] ||
-				tileh == _railway_dangslopes2[mode]) {
-			_terraform_err_tile = tile;
-			_error_message = STR_1008_MUST_REMOVE_RAILROAD_TRACK;
-			return -1;
-		}
-
-		// If we have a single diagonal track there, the other side of
-		// tile can be terraformed.
-		if (IsPlainRailTile(tile) && GetTrackBits(tile) == _railway_modes[mode]) {
-			if (ts->direction == 1) return 0;
-			skip_clear = true;
-		}
-	}
-
-	if (!skip_clear) {
+	if (!IsTileType(tile, MP_RAILWAY)) {
 		int32 ret = DoCommandByTile(tile, 0,0, ts->flags & ~DC_EXEC, CMD_LANDSCAPE_CLEAR);
 
 		if (CmdFailed(ret)) {
@@ -261,26 +236,35 @@ int32 CmdTerraformLand(int x, int y, uint32 flags, uint32 p1, uint32 p2)
 					return CMD_ERROR;
 	}
 
-	if (direction == -1) {
-		/* Check if tunnel would take damage */
+	{ /* Check if tunnel or track would take damage */
 		int count;
 		TileIndex *ti = ts.tile_table;
 
 		for (count = ts.tile_table_count; count != 0; count--, ti++) {
-			uint z, t;
+			uint a, b, c, d, r, min;
 			TileIndex tile = *ti;
 
-			z = TerraformGetHeightOfTile(&ts, tile + TileDiffXY(0, 0));
-			t = TerraformGetHeightOfTile(&ts, tile + TileDiffXY(1, 0));
-			if (t <= z) z = t;
-			t = TerraformGetHeightOfTile(&ts, tile + TileDiffXY(1, 1));
-			if (t <= z) z = t;
-			t = TerraformGetHeightOfTile(&ts, tile + TileDiffXY(0, 1));
-			if (t <= z) z = t;
+			_terraform_err_tile = tile;
+
+			a = TerraformGetHeightOfTile(&ts, tile + TileDiffXY(0, 0));
+			b = TerraformGetHeightOfTile(&ts, tile + TileDiffXY(1, 0));
+			c = TerraformGetHeightOfTile(&ts, tile + TileDiffXY(0, 1));
+			d = TerraformGetHeightOfTile(&ts, tile + TileDiffXY(1, 1));
+
+			r = GetTileh(a, b, c, d, &min);
 
-			if (IsTunnelInWay(tile, z * 8)) {
-				return_cmd_error(STR_1002_EXCAVATION_WOULD_DAMAGE);
+			if (IsTileType(tile, MP_RAILWAY)) {
+				if (IsSteepTileh(r)) return_cmd_error(STR_1008_MUST_REMOVE_RAILROAD_TRACK);
+
+				if (IsPlainRailTile(tile)) {
+					extern const TrackBits _valid_tileh_slopes[2][15];
+					if (GetTrackBits(tile) & ~_valid_tileh_slopes[0][r]) return_cmd_error(STR_1008_MUST_REMOVE_RAILROAD_TRACK);
+				} else return_cmd_error(STR_5800_OBJECT_IN_THE_WAY);
 			}
+
+			if (direction == -1 && IsTunnelInWay(tile, min)) return_cmd_error(STR_1002_EXCAVATION_WOULD_DAMAGE);
+
+			_terraform_err_tile = 0;
 		}
 	}
 
diff --git a/rail_cmd.c b/rail_cmd.c
index 3c79ff0d9..a89717d78 100644
--- a/rail_cmd.c
+++ b/rail_cmd.c
@@ -130,7 +130,7 @@ static bool CheckTrackCombination(TileIndex tile, TrackBits to_build, uint flags
 }
 
 
-static const TrackBits _valid_tileh_slopes[][15] = {
+const TrackBits _valid_tileh_slopes[2][15] = {
 
 // set of normal ones
 {
diff --git a/tile.c b/tile.c
index 7d2f680b8..f18932c3f 100644
--- a/tile.c
+++ b/tile.c
@@ -15,6 +15,30 @@ uint GetMapExtraBits(TileIndex tile)
 	return GB(_m[tile].extra, 0, 2);
 }
 
+/** Converts the heights of 4 corners into a tileh, and returns the minimum height of the tile
+  * @param n,w,e,s the four corners
+  * @param h uint pointer to write the height to
+  * @return the tileh
+*/
+uint GetTileh(uint n, uint w, uint e, uint s, uint *h)
+{
+	uint min = n;
+	uint r;
+
+	if (min >= w) min = w;
+	if (min >= e) min = e;
+	if (min >= s) min = s;
+
+	r = 0;
+	if ((n -= min) != 0) r += (--n << 4) + 8;
+	if ((e -= min) != 0) r += (--e << 4) + 4;
+	if ((s -= min) != 0) r += (--s << 4) + 2;
+	if ((w -= min) != 0) r += (--w << 4) + 1;
+
+	if (h != NULL) *h = min * 8;
+
+	return r;
+}
 
 uint GetTileSlope(TileIndex tile, uint *h)
 {
@@ -22,8 +46,6 @@ uint GetTileSlope(TileIndex tile, uint *h)
 	uint b;
 	uint c;
 	uint d;
-	uint min;
-	uint r;
 
 	assert(tile < MapSize());
 
@@ -32,23 +54,12 @@ uint GetTileSlope(TileIndex tile, uint *h)
 		return 0;
 	}
 
-	min = a = TileHeight(tile);
+	a = TileHeight(tile);
 	b = TileHeight(tile + TileDiffXY(1, 0));
-	if (min >= b) min = b;
 	c = TileHeight(tile + TileDiffXY(0, 1));
-	if (min >= c) min = c;
 	d = TileHeight(tile + TileDiffXY(1, 1));
-	if (min >= d) min = d;
-
-	r = 0;
-	if ((a -= min) != 0) r += (--a << 4) + 8;
-	if ((c -= min) != 0) r += (--c << 4) + 4;
-	if ((d -= min) != 0) r += (--d << 4) + 2;
-	if ((b -= min) != 0) r += (--b << 4) + 1;
-
-	if (h != NULL) *h = min * 8;
 
-	return r;
+	return GetTileh(a, b, c, d, h);
 }
 
 uint GetTileZ(TileIndex tile)
diff --git a/tile.h b/tile.h
index af6c0e1f1..e3a0d45d6 100644
--- a/tile.h
+++ b/tile.h
@@ -24,6 +24,7 @@ typedef enum TileTypes {
 void SetMapExtraBits(TileIndex tile, byte flags);
 uint GetMapExtraBits(TileIndex tile);
 
+uint GetTileh(uint n, uint w, uint e, uint s, uint *h);
 uint GetTileSlope(TileIndex tile, uint *h);
 uint GetTileZ(TileIndex tile);
 
diff --git a/viewport.c b/viewport.c
index 7d88bb33a..c87e8e01f 100644
--- a/viewport.c
+++ b/viewport.c
@@ -634,7 +634,7 @@ static void DrawTileSelection(const TileInfo *ti)
 #endif
 
 	// Draw a red error square?
-	if (_thd.redsq != 0 && _thd.redsq == ti->tile) {
+	if (_thd.redsq != INVALID_TILE && _thd.redsq == ti->tile) {
 		DrawSelectionSprite(PALETTE_TILE_RED_PULSATING | (SPR_SELECT_TILE + _tileh_to_sprite[ti->tileh]), ti);
 		return;
 	}
@@ -1812,8 +1812,8 @@ void SetRedErrorSquare(TileIndex tile)
 	_thd.redsq = tile;
 
 	if (tile != old) {
-		if (tile != 0) MarkTileDirtyByTile(tile);
-		if (old  != 0) MarkTileDirtyByTile(old);
+		if (tile != INVALID_TILE) MarkTileDirtyByTile(tile);
+		if (old  != INVALID_TILE) MarkTileDirtyByTile(old);
 	}
 }