feat: add island smoothing pass and update biome properties for improved terrain generation

Signed-off-by: szdytom <szdytom@qq.com>

tilemap/CMakeLists.txt

@@ -7,6 +7,7 @@ set(ISTD_TILEMAP_SRC
 	src/pass/deepwater.cpp
 	src/pass/mountain_hole_fill.cpp
 	src/pass/smoothen_mountain.cpp
+	src/pass/smoothen_island.cpp
 	src/generation.cpp
 	src/tilemap.cpp
 	src/noise.cpp

tilemap/examples/biome_demo.cpp

@@ -134,7 +134,7 @@ int main(int argc, char *argv[]) {
 	istd::Seed seed
 		= istd::Seed::from_string(argc >= 2 ? argv[1] : "hello_world");
 	std::string output_filename = argc >= 3 ? argv[2] : "output.bmp";
-	int chunks_per_side = 4; // Default value
+	int chunks_per_side = 8; // Default value
 
 	// Parse optional chunks_per_side parameter
 	if (argc == 4) {

tilemap/include/generation.h

@@ -5,9 +5,7 @@
 #include "chunk.h"
 #include "noise.h"
 #include "tilemap.h"
-#include <array>
 #include <cstdint>
-#include <queue>
 #include <vector>
 
 namespace istd {
@@ -28,13 +26,18 @@ struct GenerationConfig {
 	double humidity_persistence = 0.4; // Persistence for humidity noise
 
 	double base_scale = 0.08;          // Scale for base terrain noise
-	int base_octaves = 3;          // Number of octaves for base terrain noise
-	double base_persistence = 0.5; // Persistence for base terrain noise
+	int base_octaves = 3;            // Number of octaves for base terrain noise
+	double base_persistence = 0.5;   // Persistence for base terrain noise
+
+	int mountain_smoothen_steps = 2; // Number of steps for mountain smoothing
+	                                 // cellular automata
+	std::uint32_t mountain_remove_threshold = 10; // Threshold for mountain
+	                                              // removal
+
+	int island_smoothen_steps = 8; // Number of steps for island smoothing
+	                               // cellular automata
+	std::uint32_t island_remove_threshold = 8; // Threshold for island removal
 
-	int mountain_smoothen_steps
-		= 2;  // Number of steps for mountain smoothing cellular automata
-	std::uint32_t mountain_remove_threshold
-		= 10; // Threshold for mountain removal
 	std::uint32_t fill_threshold = 10;  // Fill holes smaller than this size
 	std::uint32_t deepwater_radius = 2; // Radius for deepwater generation
 };
@@ -222,6 +225,72 @@ public:
 	void operator()(TileMap &tilemap);
 };
 
+class SmoothenIslandPass {
+private:
+	const GenerationConfig &config_;
+	DiscreteRandomNoise noise_;
+
+	/**
+	 * @brief Perform BFS to find connected component size for islands
+	 * @param tilemap The tilemap to search
+	 * @param start_pos Starting position for BFS
+	 * @param visited 2D array tracking visited tiles
+	 * @param positions Output vector of positions in this component
+	 * @return Size of the connected component
+	 */
+	std::uint32_t bfs_component_size(
+		TileMap &tilemap, TilePos start_pos,
+		std::vector<std::vector<bool>> &visited, std::vector<TilePos> &positions
+	);
+
+	/**
+	 * @brief Remove small island components to create smoother terrain
+	 * @param tilemap The tilemap to process
+	 */
+	void remove_small_island(TileMap &tilemap);
+
+	/**
+	 * @brief Smoothen islands with cellular automata
+	 * @param tilemap The tilemap to process
+	 */
+	void smoothen_islands(TileMap &tilemap, std::uint32_t step_i);
+
+	void smoothen_islands_subchunk(
+		TileMap &tilemap, std::uint8_t chunk_x, std::uint8_t chunk_y,
+		SubChunkPos sub_pos, std::uint32_t step_i,
+		std::vector<std::pair<TilePos, Tile>> &replacements
+	);
+
+	struct CACtx {
+		BiomeType biome;
+		std::uint8_t rand;
+		int adj_land, adj_sand, adj_water; // Adjacent tile counts
+	};
+
+	Tile ca_tile(TilePos pos, Tile tile, const CACtx &ctx) const;
+
+	/**
+	 * @brief Check if a tile is part of an island (Land or Sand)
+	 * @param tile The tile to check
+	 * @return True if the tile is Land or Sand
+	 */
+	bool is_island_tile(const Tile &tile) const;
+
+public:
+	/**
+	 * @brief Construct an island smoothing pass
+	 * @param config Generation configuration parameters
+	 * @param rng Random number generator for terrain replacement
+	 */
+	SmoothenIslandPass(const GenerationConfig &config, Xoroshiro128PP rng);
+
+	/**
+	 * @brief Smoothen islands in the terrain
+	 * @param tilemap The tilemap to process
+	 */
+	void operator()(TileMap &tilemap);
+};
+
 // Terrain generator class that manages the generation process
 class TerrainGenerator {
 private:
@@ -260,6 +329,12 @@ private:
 	 */
 	void smoothen_mountains_pass(TileMap &tilemap);
 
+	/**
+	 * @brief Smoothen islands in the terrain
+	 * @param tilemap The tilemap to process
+	 */
+	void smoothen_islands_pass(TileMap &tilemap);
+
 	/**
 	 * @brief Fill small holes in the terrain
 	 * @param tilemap The tilemap to process

tilemap/include/tile.h

@@ -33,6 +33,7 @@ static_assert(surface_tile_count <= 16, "Surface tile don't fit in 4 bits");
 struct Tile {
 	BaseTileType base : 4;
 	SurfaceTileType surface : 4;
+	friend bool operator==(Tile lhs, Tile rhs) = default;
 };
 
 static_assert(sizeof(Tile) == 1);

tilemap/src/biome.cpp

@@ -36,10 +36,10 @@ constexpr BiomeProperties biome_properties[] = {
      .temperature = BiomeTemperature::Cold,
      .humidity = BiomeHumidity::Wet,
      .is_ocean = true,
-     .water_ratio = .1,
-     .ice_ratio = .7,
-     .sand_ratio = .25,
-     .land_ratio = .05,
+     .water_ratio = .15,
+     .ice_ratio = .8,
+     .sand_ratio = .05,
+     .land_ratio = .0,
 	 },
 	// Plains (Temperate & Dry)
 	{
@@ -69,10 +69,10 @@ constexpr BiomeProperties biome_properties[] = {
      .temperature = BiomeTemperature::Temperate,
      .humidity = BiomeHumidity::Wet,
      .is_ocean = true,
-     .water_ratio = .8,
+     .water_ratio = .95,
      .ice_ratio = .0,
-     .sand_ratio = .15,
-     .land_ratio = .05,
+     .sand_ratio = .03,
+     .land_ratio = .02,
 	 },
 	// Desert (Hot & Dry)
 	{
@@ -82,7 +82,7 @@ constexpr BiomeProperties biome_properties[] = {
      .is_ocean = false,
      .water_ratio = .0,
      .ice_ratio = .0,
-     .sand_ratio = .8,
+     .sand_ratio = .85,
      .land_ratio = .0,
 	 },
 	// Savanna (Hot & Moderate)
@@ -102,10 +102,10 @@ constexpr BiomeProperties biome_properties[] = {
      .temperature = BiomeTemperature::Hot,
      .humidity = BiomeHumidity::Wet,
      .is_ocean = true,
-     .water_ratio = .8,
+     .water_ratio = .95,
      .ice_ratio = .0,
-     .sand_ratio = .05,
-     .land_ratio = .15,
+     .sand_ratio = .01,
+     .land_ratio = .04,
 	 },
 };
 

tilemap/src/generation.cpp

@@ -1,5 +1,4 @@
 #include "generation.h"
-#include "biome.h"
 
 namespace istd {
 TerrainGenerator::TerrainGenerator(const GenerationConfig &config)
@@ -9,6 +8,7 @@ void TerrainGenerator::operator()(TileMap &tilemap) {
 	biome_pass(tilemap);
 	base_tile_type_pass(tilemap);
 	smoothen_mountains_pass(tilemap);
+	smoothen_islands_pass(tilemap);
 	mountain_hole_fill_pass(tilemap);
 	deepwater_pass(tilemap);
 }

tilemap/src/pass/base_tile_type.cpp

@@ -1,6 +1,7 @@
 #include "biome.h"
 #include "chunk.h"
 #include "generation.h"
+#include <utility>
 
 namespace istd {
 
@@ -57,12 +58,14 @@ void BaseTileTypeGenerationPass::generate_subchunk(
 			double global_y = chunk_y * Chunk::size + local_y;
 
 			// Generate base terrain noise value using uniform distribution
-			double base_noise_value
-				= base_noise_.uniform_noise(global_x, global_y);
+			double base_noise_value = base_noise_.uniform_noise(
+				global_x, global_y
+			);
 
 			// Determine base terrain type
-			BaseTileType base_type
-				= determine_base_type(base_noise_value, properties);
+			BaseTileType base_type = determine_base_type(
+				base_noise_value, properties
+			);
 
 			// Create tile with base and surface components
 			Tile tile;

tilemap/src/pass/smoothen_island.cpp

@@ -0,0 +1,274 @@
+#include "biome.h"
+#include "generation.h"
+#include "tile.h"
+#include <algorithm>
+#include <queue>
+
+namespace istd {
+
+SmoothenIslandPass::SmoothenIslandPass(
+	const GenerationConfig &config, Xoroshiro128PP rng
+)
+	: config_(config), noise_(rng) {}
+
+void SmoothenIslandPass::operator()(TileMap &tilemap) {
+	remove_small_island(tilemap);
+	for (int i = 1; i <= config_.island_smoothen_steps; ++i) {
+		smoothen_islands(tilemap, i);
+	}
+	remove_small_island(tilemap);
+}
+
+bool SmoothenIslandPass::is_island_tile(const Tile &tile) const {
+	return !(
+		tile.base == BaseTileType::Water || tile.base == BaseTileType::Deepwater
+		|| tile.base == BaseTileType::Ice
+	);
+}
+
+void SmoothenIslandPass::remove_small_island(TileMap &tilemap) {
+	std::uint8_t map_size = tilemap.get_size();
+	std::vector<std::vector<bool>> visited(
+		map_size * Chunk::size, std::vector<bool>(map_size * Chunk::size, false)
+	);
+
+	for (std::uint8_t chunk_x = 0; chunk_x < map_size; ++chunk_x) {
+		for (std::uint8_t chunk_y = 0; chunk_y < map_size; ++chunk_y) {
+			for (std::uint8_t local_x = 0; local_x < Chunk::size; ++local_x) {
+				for (std::uint8_t local_y = 0; local_y < Chunk::size;
+				     ++local_y) {
+					TilePos pos{chunk_x, chunk_y, local_x, local_y};
+					auto [global_x, global_y] = pos.to_global();
+
+					// Skip if already visited
+					if (visited[global_x][global_y]) {
+						continue;
+					}
+
+					const Tile &tile = tilemap.get_tile(pos);
+					if (!is_island_tile(tile)) {
+						visited[global_x][global_y] = true;
+						continue;
+					}
+
+					// Find connected component of island tiles
+					std::vector<TilePos> component_positions;
+					std::uint32_t component_size = bfs_component_size(
+						tilemap, pos, visited, component_positions
+					);
+
+					// If the component touches the boundary, skip it
+					bool touches_boundary = false;
+					for (auto component_pos : component_positions) {
+						if (tilemap.is_at_boundary(component_pos)) {
+							touches_boundary = true;
+							break;
+						}
+					}
+
+					// Skip if it touches the boundary
+					if (touches_boundary) {
+						continue;
+					}
+
+					// If the component is too small, convert it to water
+					if (component_size <= config_.island_remove_threshold) {
+						for (const auto &island_pos : component_positions) {
+							Tile tile = tilemap.get_tile(island_pos);
+							tile.base = BaseTileType::Water;
+							tilemap.set_tile(island_pos, tile);
+						}
+					}
+				}
+			}
+		}
+	}
+}
+
+std::uint32_t SmoothenIslandPass::bfs_component_size(
+	TileMap &tilemap, TilePos start_pos,
+	std::vector<std::vector<bool>> &visited, std::vector<TilePos> &positions
+) {
+	std::queue<TilePos> queue;
+	queue.push(start_pos);
+
+	auto [start_global_x, start_global_y] = start_pos.to_global();
+	visited[start_global_x][start_global_y] = true;
+
+	std::uint32_t size = 0;
+	positions.clear();
+
+	while (!queue.empty()) {
+		TilePos current = queue.front();
+		queue.pop();
+		positions.push_back(current);
+		++size;
+
+		// Check all neighbors
+		std::vector<TilePos> neighbors = tilemap.get_neighbors(current, true);
+		for (const auto neighbor : neighbors) {
+			auto [neighbor_global_x, neighbor_global_y] = neighbor.to_global();
+			if (visited[neighbor_global_x][neighbor_global_y]) {
+				continue;
+			}
+
+			const Tile &neighbor_tile = tilemap.get_tile(neighbor);
+			if (is_island_tile(neighbor_tile)) {
+				visited[neighbor_global_x][neighbor_global_y] = true;
+				queue.push(neighbor);
+			}
+		}
+	}
+
+	return size;
+}
+
+Tile SmoothenIslandPass::ca_tile(
+	TilePos pos, Tile tile, const CACtx &ctx
+) const {
+	constexpr std::uint8_t as_water_chance_map[9] = {
+		0, 0, 0, 8, 16, 32, 64, 128, 255
+	};
+
+	// Sand -> Water
+	auto as_water_chance = as_water_chance_map[ctx.adj_water];
+	if (as_water_chance > 0 && tile.base == BaseTileType::Sand) {
+		if (ctx.rand < as_water_chance) {
+			tile.base = BaseTileType::Water;
+			return tile;
+		}
+	}
+
+	// Water -> Sand
+	if (!is_island_tile(tile)) {
+		int as_sand_chance = std::clamp(
+			ctx.adj_sand * 8 + ctx.adj_land * 32, 0, 255
+		);
+
+		if (ctx.rand < as_sand_chance) {
+			tile.base = BaseTileType::Sand;
+		}
+		return tile;
+	}
+
+	// Sand -> Land
+	if (tile.base == BaseTileType::Sand && ctx.biome == BiomeType::LukeOcean) {
+		int as_land_chance = std::clamp(
+			256 - ctx.adj_water * 32 - ctx.adj_sand * 12, 0, 255
+		);
+
+		if (ctx.rand < as_land_chance) {
+			tile.base = BaseTileType::Land;
+		}
+		return tile;
+	}
+
+	// Land -> Sand
+	if (tile.base == BaseTileType::Land) {
+		int as_sand_chance = std::clamp(
+			ctx.adj_water * 32 + ctx.adj_sand * 8, 0, 255
+		);
+
+		if (ctx.rand < as_sand_chance) {
+			tile.base = BaseTileType::Sand;
+		}
+	}
+
+	return tile;
+}
+
+void SmoothenIslandPass::smoothen_islands_subchunk(
+	TileMap &tilemap, std::uint8_t chunk_x, std::uint8_t chunk_y,
+	SubChunkPos sub_pos, std::uint32_t step_i,
+	std::vector<std::pair<TilePos, Tile>> &replacements
+) {
+	const auto &chunk = tilemap.get_chunk(chunk_x, chunk_y);
+	auto biome = chunk.get_biome(sub_pos);
+	auto biome_props = get_biome_properties(biome);
+	if (!biome_props.is_ocean) {
+		// Only process ocean biomes
+		return;
+	}
+
+	auto [start_x, start_y] = subchunk_to_tile_start(sub_pos);
+	for (std::uint8_t local_x = start_x;
+	     local_x < start_x + Chunk::subchunk_size; ++local_x) {
+		for (std::uint8_t local_y = start_y;
+		     local_y < start_y + Chunk::subchunk_size; ++local_y) {
+			TilePos pos{chunk_x, chunk_y, local_x, local_y};
+
+			Tile tile = tilemap.get_tile(pos);
+
+			auto neighbors = tilemap.get_neighbors(pos, true);
+			if (neighbors.size() < 8) {
+				continue;
+			}
+
+			int adj_land = 0, adj_sand = 0, adj_water = 0;
+			for (auto neighbor : neighbors) {
+				const Tile &neighbor_tile = tilemap.get_tile(neighbor);
+				switch (neighbor_tile.base) {
+				case BaseTileType::Land:
+					++adj_land;
+					break;
+				case BaseTileType::Sand:
+					++adj_sand;
+					break;
+				case BaseTileType::Water:
+				case BaseTileType::Deepwater:
+				case BaseTileType::Ice:
+					++adj_water;
+					break;
+				default:
+					break; // Ignore other tile types
+				}
+			}
+
+			auto [global_x, global_y] = pos.to_global();
+			std::uint8_t rand = noise_.noise(global_x, global_y, step_i);
+
+			CACtx ctx{
+				biome, rand, adj_land, adj_sand, adj_water,
+			};
+
+			Tile new_tile = ca_tile(pos, tile, ctx);
+			if (new_tile != tile) {
+				replacements.emplace_back(pos, new_tile);
+			}
+		}
+	}
+
+	for (auto [pos, new_tile] : replacements) {
+		tilemap.set_tile(pos, new_tile);
+	}
+}
+
+void SmoothenIslandPass::smoothen_islands(
+	TileMap &tilemap, std::uint32_t step_i
+) {
+	std::vector<std::pair<TilePos, Tile>> replacements;
+
+	for (std::uint8_t chunk_x = 0; chunk_x < tilemap.get_size(); ++chunk_x) {
+		for (std::uint8_t chunk_y = 0; chunk_y < tilemap.get_size();
+		     ++chunk_y) {
+			for (std::uint8_t sub_x = 0; sub_x < Chunk::subchunk_count;
+			     ++sub_x) {
+				for (std::uint8_t sub_y = 0; sub_y < Chunk::subchunk_count;
+				     ++sub_y) {
+					SubChunkPos sub_pos{sub_x, sub_y};
+					smoothen_islands_subchunk(
+						tilemap, chunk_x, chunk_y, sub_pos, step_i, replacements
+					);
+				}
+			}
+		}
+	}
+}
+
+void TerrainGenerator::smoothen_islands_pass(TileMap &tilemap) {
+	SmoothenIslandPass pass(config_, master_rng_);
+	master_rng_ = master_rng_.jump_96();
+	pass(tilemap);
+}
+
+} // namespace istd