Feature: Place rocks on "too steep" tiles when fixing slopes.

When generating maps or loading heightmaps, the terrain height is altered to prevent slopes that can't be represented.

During this, there is now a chance of these tiles being turned into a rocky tile.

Chance of placing rocks is based on the height. This gives a rocky mountain appearance without affecting all peaks.

src/clear_cmd.cpp

@@ -165,7 +165,7 @@ static void TileLoopClearAlps(TileIndex tile)
 		/* Below the snow line, do nothing if no snow. */
 		/* At or above the snow line, make snow tile if needed. */
 		if (k >= 0) {
-			MakeSnow(tile);
+			MakeSnow(tile, IsClearGround(tile, CLEAR_ROCKS) ? GetClearDensity(tile) : 0);
 			MarkTileDirtyByTile(tile);
 		}
 		return;

src/heightmap.cpp

@@ -400,7 +400,8 @@ void FixSlopes()
 {
 	uint width, height;
 	int row, col;
-	uint8_t current_tile;
+	uint8_t current_height;
+	uint8_t max_height = _settings_game.construction.map_height_limit;
 
 	/* Adjust height difference to maximum one horizontal/vertical change. */
 	width   = Map::SizeX();
@@ -409,21 +410,27 @@ void FixSlopes()
 	/* Top and left edge */
 	for (row = 0; (uint)row < height; row++) {
 		for (col = 0; (uint)col < width; col++) {
-			current_tile = MAX_TILE_HEIGHT;
+			current_height = MAX_TILE_HEIGHT;
 			if (col != 0) {
 				/* Find lowest tile; either the top or left one */
-				current_tile = TileHeight(TileXY(col - 1, row)); // top edge
+				current_height = TileHeight(TileXY(col - 1, row)); // top edge
 			}
 			if (row != 0) {
-				if (TileHeight(TileXY(col, row - 1)) < current_tile) {
+				if (TileHeight(TileXY(col, row - 1)) < current_height) {
-					current_tile = TileHeight(TileXY(col, row - 1)); // left edge
+					current_height = TileHeight(TileXY(col, row - 1)); // left edge
 				}
 			}
 
 			/* Does the height differ more than one? */
-			if (TileHeight(TileXY(col, row)) >= (uint)current_tile + 2) {
+			TileIndex tile = TileXY(col, row);
+			if (TileHeight(tile) >= (uint)current_height + 2) {
 				/* Then change the height to be no more than one */
-				SetTileHeight(TileXY(col, row), current_tile + 1);
+				SetTileHeight(tile, current_height + 1);
+				/* Height was changed so now there's a chance, more likely at higher altitude, of the
+				 * tile turning into rock. */
+				if (IsInnerTile(tile) && RandomRange(max_height) <= current_height) {
+					MakeClear(tile, CLEAR_ROCKS, 3);
+				}
 			}
 		}
 	}
@@ -431,22 +438,28 @@ void FixSlopes()
 	/* Bottom and right edge */
 	for (row = height - 1; row >= 0; row--) {
 		for (col = width - 1; col >= 0; col--) {
-			current_tile = MAX_TILE_HEIGHT;
+			current_height = MAX_TILE_HEIGHT;
 			if ((uint)col != width - 1) {
 				/* Find lowest tile; either the bottom and right one */
-				current_tile = TileHeight(TileXY(col + 1, row)); // bottom edge
+				current_height = TileHeight(TileXY(col + 1, row)); // bottom edge
 			}
 
 			if ((uint)row != height - 1) {
-				if (TileHeight(TileXY(col, row + 1)) < current_tile) {
+				if (TileHeight(TileXY(col, row + 1)) < current_height) {
-					current_tile = TileHeight(TileXY(col, row + 1)); // right edge
+					current_height = TileHeight(TileXY(col, row + 1)); // right edge
 				}
 			}
 
 			/* Does the height differ more than one? */
-			if (TileHeight(TileXY(col, row)) >= (uint)current_tile + 2) {
+			TileIndex tile = TileXY(col, row);
+			if (TileHeight(tile) >= (uint)current_height + 2) {
 				/* Then change the height to be no more than one */
-				SetTileHeight(TileXY(col, row), current_tile + 1);
+				SetTileHeight(tile, current_height + 1);
+				/* Height was changed so now there's a chance, more likely at higher altitude, of the
+				 * tile turning into rock. */
+				if (IsInnerTile(tile) && RandomRange(max_height) <= current_height) {
+					MakeClear(tile, CLEAR_ROCKS, 3);
+				}
 			}
 		}
 	}

src/landscape.cpp

@@ -1535,7 +1535,7 @@ bool GenerateLandscape(uint8_t mode)
 {
 	/* Number of steps of landscape generation */
 	static constexpr uint GLS_HEIGHTMAP = 3; ///< Loading a heightmap
-	static constexpr uint GLS_TERRAGENESIS = 5; ///< Terragenesis generator
+	static constexpr uint GLS_TERRAGENESIS = 4; ///< Terragenesis generator
 	static constexpr uint GLS_ORIGINAL = 2; ///< Original generator
 	static constexpr uint GLS_TROPIC = 12; ///< Extra steps needed for tropic landscape
 	static constexpr uint GLS_OTHER = 0; ///< Extra steps for other landscapes

src/tgp.cpp

@@ -884,8 +884,6 @@ static void HeightMapNormalize()
 	if (_settings_game.game_creation.variety > 0) {
 		HeightMapCurves(_settings_game.game_creation.variety);
 	}
-
-	HeightMapSmoothSlopes(I2H(1));
 }
 
 /**
@@ -1006,8 +1004,6 @@ void GenerateTerrainPerlin()
 		}
 	}
 
-	IncreaseGeneratingWorldProgress(GWP_LANDSCAPE);
-
 	FreeHeightMap();
 	GenerateWorldSetAbortCallback(nullptr);
 }