(svn r15685) -Fix [FS#2720]: do not crash when someone substitutes the "map generation" sprites with garbage.

src/heightmap.cpp

@@ -352,7 +352,7 @@ static void GrayscaleToMapHeights(uint img_width, uint img_height, byte *map)
  * This function takes care of the fact that land in OpenTTD can never differ
  * more than 1 in height
  */
-static void FixSlopes()
+void FixSlopes()
 {
 	uint width, height;
 	int row, col;

src/heightmap.h

@@ -37,4 +37,10 @@ void LoadHeightmap(char *filename);
  */
 void FlatEmptyWorld(byte tile_height);
 
+/**
+ * This function takes care of the fact that land in OpenTTD can never differ
+ * more than 1 in height
+ */
+void FixSlopes();
+
 #endif /* HEIGHTMAP_H */

src/landscape.cpp

@@ -766,7 +766,7 @@ static void GenerateTerrain(int type, uint flag)
 				Tile *tile_cur = tile;
 
 				for (uint w_cur = w; w_cur != 0; --w_cur) {
-					if (*p >= tile_cur->type_height) tile_cur->type_height = *p;
+					if (GB(*p, 0, 4) >= tile_cur->type_height) tile_cur->type_height = GB(*p, 0, 4);
 					p++;
 					tile_cur++;
 				}
@@ -779,7 +779,7 @@ static void GenerateTerrain(int type, uint flag)
 				Tile *tile_cur = tile;
 
 				for (uint h_cur = h; h_cur != 0; --h_cur) {
-					if (*p >= tile_cur->type_height) tile_cur->type_height = *p;
+					if (GB(*p, 0, 4) >= tile_cur->type_height) tile_cur->type_height = GB(*p, 0, 4);
 					p++;
 					tile_cur += TileDiffXY(0, 1);
 				}
@@ -793,7 +793,7 @@ static void GenerateTerrain(int type, uint flag)
 				Tile *tile_cur = tile;
 
 				for (uint w_cur = w; w_cur != 0; --w_cur) {
-					if (*p >= tile_cur->type_height) tile_cur->type_height = *p;
+					if (GB(*p, 0, 4) >= tile_cur->type_height) tile_cur->type_height = GB(*p, 0, 4);
 					p++;
 					tile_cur--;
 				}
@@ -807,7 +807,7 @@ static void GenerateTerrain(int type, uint flag)
 				Tile *tile_cur = tile;
 
 				for (uint h_cur = h; h_cur != 0; --h_cur) {
-					if (*p >= tile_cur->type_height) tile_cur->type_height = *p;
+					if (GB(*p, 0, 4) >= tile_cur->type_height) tile_cur->type_height = GB(*p, 0, 4);
 					p++;
 					tile_cur -= TileDiffXY(0, 1);
 				}
@@ -815,6 +815,8 @@ static void GenerateTerrain(int type, uint flag)
 			} while (--w != 0);
 			break;
 	}
+
+	FixSlopes();
 }