Feature: Place rocks on "too steep" tiles when fixing slopes. (#13462)

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) {
-					current_tile = TileHeight(TileXY(col, row - 1)); // left edge
+				if (TileHeight(TileXY(col, row - 1)) < current_height) {
+					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) {
-					current_tile = TileHeight(TileXY(col, row + 1)); // right edge
+				if (TileHeight(TileXY(col, row + 1)) < current_height) {
+					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);
 }