(svn r1839) Move GetTileSlope() and GetTileZ() into tile.[ch] and use more explicit types as parameters

tile.c

@@ -13,3 +13,47 @@ uint GetMapExtraBits(TileIndex tile)
 	assert(tile < MapSize());
 	return (_map_extra_bits[tile >> 2] >> (tile & 3) * 2) & 3;
 }
+
+
+uint GetTileSlope(TileIndex tile, uint *h)
+{
+	uint a;
+	uint b;
+	uint c;
+	uint d;
+	uint min;
+	uint r;
+
+	assert(tile < MapSize());
+
+	if (TileX(tile) == MapMaxX() || TileY(tile) == MapMaxY()) {
+		if (h != NULL) *h = 0;
+		return 0;
+	}
+
+	min = a = TileHeight(tile);
+	b = TileHeight(tile + TILE_XY(1,0));
+	if (min >= b) min = b;
+	c = TileHeight(tile + TILE_XY(0,1));
+	if (min >= c) min = c;
+	d = TileHeight(tile + TILE_XY(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;
+}
+
+uint GetTileZ(TileIndex tile)
+{
+	uint h;
+	GetTileSlope(tile, &h);
+	return h;
+}