Feature: Wide rivers

src/landscape.cpp

@@ -88,6 +88,12 @@ extern const byte _slope_to_sprite_offset[32] = {
  */
 static SnowLine *_snow_line = nullptr;
 
+/** The current spring during river generation */
+static TileIndex _current_spring = INVALID_TILE;
+
+/** Whether the current river is a big river that others flow into */
+static bool _is_main_river = false;
+
 /**
  * Map 2D viewport or smallmap coordinate to 3D world or tile coordinate.
  * Function takes into account height of tiles and foundations.
@@ -1073,6 +1079,25 @@ static bool MakeLake(TileIndex tile, void *user_data)
 	return false;
 }
 
+/**
+ * Widen a river by expanding into adjacent tiles via circular tile search.
+ * @param tile The tile to try expanding the river into.
+ * @param data The tile to try surrounding the river around.
+ * @return Always false, so it continues searching.
+ */
+static bool RiverMakeWider(TileIndex tile, void *data)
+{
+	if (IsValidTile(tile) && !IsWaterTile(tile) && GetTileSlope(tile) == GetTileSlope(*(TileIndex*)data)) {
+		MakeRiver(tile, Random());
+		/* Remove desert directly around the river tile. */
+		TileIndex cur_tile = tile;
+
+		MarkTileDirtyByTile(cur_tile);
+		CircularTileSearch(&cur_tile, RIVER_OFFSET_DESERT_DISTANCE, RiverModifyDesertZone, nullptr);
+	}
+	return false;
+}
+
 /**
  * Check whether a river at begin could (logically) flow down to end.
  * @param begin The origin of the flow.
@@ -1132,13 +1157,33 @@ static void River_GetNeighbours(AyStar *aystar, OpenListNode *current)
 /* AyStar callback when an route has been found. */
 static void River_FoundEndNode(AyStar *aystar, OpenListNode *current)
 {
+	/* Count river length. */
+	uint length = 0;
 	for (PathNode *path = &current->path; path != nullptr; path = path->parent) {
+		length++;
+	}
+
+	uint cur_pos = 0;
+	for (PathNode* path = &current->path; path != nullptr; path = path->parent, cur_pos++) {
 		TileIndex tile = path->node.tile;
 		if (!IsWaterTile(tile)) {
 			MakeRiver(tile, Random());
+
+			/* Check if we should widen river depending on how far we are away from the source. */
+			const uint current_river_length = DistanceManhattan(_current_spring, path->node.tile);
+			const uint long_river_length = _settings_game.game_creation.min_river_length * 4;
+			const uint radius = std::min(3u, (current_river_length / (long_river_length / 3u)) + 1u);
+
 			MarkTileDirtyByTile(tile);
-			/* Remove desert directly around the river tile. */
-			CircularTileSearch(&tile, RIVER_OFFSET_DESERT_DISTANCE, RiverModifyDesertZone, nullptr);
+
+			/* If building a main river, try to widen it. */
+			if (_is_main_river && (radius > 1)) {
+				CircularTileSearch(&tile, radius + RandomRange(1), RiverMakeWider, (void*)&path->node.tile);
+			}
+			else {
+				/* Remove desert directly around the river tile. */
+				CircularTileSearch(&tile, RIVER_OFFSET_DESERT_DISTANCE, RiverModifyDesertZone, nullptr);
+			}
 		}
 	}
 }
@@ -1185,15 +1230,22 @@ static void BuildRiver(TileIndex begin, TileIndex end)
  * Try to flow the river down from a given begin.
  * @param spring The springing point of the river.
  * @param begin  The begin point we are looking from; somewhere down hill from the spring.
+ * @param min_river_length The minimum length for the river.
  * @return True iff a river could/has been built, otherwise false.
  */
-static bool FlowRiver(TileIndex spring, TileIndex begin)
+static bool FlowRiver(TileIndex spring, TileIndex begin, uint min_river_length)
 {
 #	define SET_MARK(x) marks.insert(x)
 #	define IS_MARKED(x) (marks.find(x) != marks.end())
 
 	uint height = TileHeight(begin);
-	if (IsWaterTile(begin)) return DistanceManhattan(spring, begin) > _settings_game.game_creation.min_river_length;
+	if (IsWaterTile(begin))
+	{
+		if (GetTileZ(begin) == 0) {
+			_is_main_river = true;
+		}
+		return DistanceManhattan(spring, begin) > min_river_length;
+	}
 
 	std::set<TileIndex> marks;
 	SET_MARK(begin);
@@ -1227,7 +1279,7 @@ static bool FlowRiver(TileIndex spring, TileIndex begin)
 
 	if (found) {
 		/* Flow further down hill. */
-		found = FlowRiver(spring, end);
+		found = FlowRiver(spring, end, min_river_length);
 	} else if (count > 32) {
 		/* Maybe we can make a lake. Find the Nth of the considered tiles. */
 		TileIndex lakeCenter = 0;
@@ -1246,7 +1298,7 @@ static bool FlowRiver(TileIndex spring, TileIndex begin)
 				/* We don't want lakes in the desert. */
 				(_settings_game.game_creation.landscape != LT_TROPIC || GetTropicZone(lakeCenter) != TROPICZONE_DESERT) &&
 				/* We only want a lake if the river is long enough. */
-				DistanceManhattan(spring, lakeCenter) > _settings_game.game_creation.min_river_length) {
+				DistanceManhattan(spring, lakeCenter) > min_river_length) {
 			end = lakeCenter;
 			MakeRiver(lakeCenter, Random());
 			MarkTileDirtyByTile(lakeCenter);
@@ -1276,14 +1328,30 @@ static void CreateRivers()
 	if (amount == 0) return;
 
 	uint wells = ScaleByMapSize(4 << _settings_game.game_creation.amount_of_rivers);
+	const uint num_short_rivers = wells - std::max(1u, wells / 10);
 	SetGeneratingWorldProgress(GWP_RIVER, wells + 256 / 64); // Include the tile loop calls below.
 
+	/* Try to create long rivers. */
+	for (; wells > num_short_rivers; wells--) {
+		IncreaseGeneratingWorldProgress(GWP_RIVER);
+		for (int tries = 0; tries < 512; tries++) {
+			TileIndex t = RandomTile();
+			if (!CircularTileSearch(&t, 8, FindSpring, nullptr)) continue;
+			_current_spring = t;
+			_is_main_river = false;
+			if (FlowRiver(t, t, _settings_game.game_creation.min_river_length * 4)) break;
+		}
+	}
+
+	/* Try to create short rivers. */
 	for (; wells != 0; wells--) {
 		IncreaseGeneratingWorldProgress(GWP_RIVER);
 		for (int tries = 0; tries < 128; tries++) {
 			TileIndex t = RandomTile();
 			if (!CircularTileSearch(&t, 8, FindSpring, nullptr)) continue;
-			if (FlowRiver(t, t)) break;
+			_current_spring = t;
+			_is_main_river = false;
+			if (FlowRiver(t, t, _settings_game.game_creation.min_river_length)) break;
 		}
 	}