feat: add coal generation

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

tilemap/CMakeLists.txt

@@ -4,6 +4,7 @@ cmake_minimum_required(VERSION 3.27)
 set(ISTD_TILEMAP_SRC
 	src/pass/base_tile_type.cpp
 	src/pass/biome.cpp
+	src/pass/coal.cpp
 	src/pass/deepwater.cpp
 	src/pass/mineral_cluster.cpp
 	src/pass/mountain_hole_fill.cpp

tilemap/docs/api.md

@@ -17,7 +17,7 @@ public:
 
     std::uint8_t get_size() const;
     Chunk& get_chunk(std::uint8_t chunk_x, std::uint8_t chunk_y);
-    
+
     Tile& get_tile(TilePos pos);
     const Tile& get_tile(TilePos pos) const;
     void set_tile(TilePos pos, const Tile& tile);
@@ -31,10 +31,10 @@ public:
 ```cpp
 struct Chunk {
     static constexpr uint8_t size = 64;
-    
+
     Tile tiles[size][size];
     BiomeType biome[16][16];  // Sub-chunk biomes
-    
+
     BiomeType& get_biome(SubChunkPos pos);
 };
 ```
@@ -62,7 +62,7 @@ struct Tile {
 struct TilePos {
     uint8_t chunk_x, chunk_y;  // Chunk coordinates
     uint8_t local_x, local_y;  // Tile within chunk (0-63)
-    
+
     std::pair<std::uint16_t, std::uint16_t> to_global() const;
     static TilePos from_global(std::uint16_t global_x, std::uint16_t global_y);
 };
@@ -81,21 +81,7 @@ Configuration for terrain generation.
 ```cpp
 struct GenerationConfig {
     Seed seed;
-    
+	// For more options, see generation.h
-    // Noise parameters
-    double temperature_scale = 0.05;
-    double humidity_scale = 0.05;
-    double base_scale = 0.08;
-    
-    int temperature_octaves = 3;
-    int humidity_octaves = 3;
-    int base_octaves = 3;
-    
-    // Oil generation parameters
-    double oil_density = 0.8;           // Average oil fields per chunk
-    std::uint32_t oil_cluster_min_size = 2; // Minimum tiles per cluster
-    std::uint32_t oil_cluster_max_size = 6; // Maximum tiles per cluster
-    double oil_biome_preference = 2.0;  // Multiplier for preferred biomes
 };
 ```
 
@@ -110,7 +96,7 @@ void map_generate(TileMap& tilemap, const GenerationConfig& config);
 ```cpp
 struct Seed {
     std::uint64_t s[2];
-    
+
     static Seed from_string(const char* str);
     static Seed device_random();
 };

tilemap/examples/CMakeLists.txt

@@ -3,7 +3,7 @@ cmake_minimum_required(VERSION 3.27)
 # Examples for the tilemap library
 # Each example is built as a separate executable
 
-# Biome system demonstration
+# Tilemap system demonstration
 add_executable(tilemap_demo tilemap_demo.cpp)
 target_link_libraries(tilemap_demo PRIVATE istd_tilemap)
 target_include_directories(tilemap_demo PRIVATE ../include)

tilemap/examples/bmp.h

@@ -241,6 +241,7 @@ constexpr Color OIL(0, 0, 0);          // Black
 constexpr Color HEMATITE(255, 0, 0);          // Red
 constexpr Color TITANOMAGNETITE(128, 0, 128); // Purple
 constexpr Color GIBBSITE(255, 255, 0);        // Yellow
+constexpr Color COAL(64, 64, 64);             // Dark gray
 } // namespace BmpColors
 
 #endif // BMP_H

tilemap/examples/tilemap_demo.cpp

@@ -19,6 +19,8 @@ BmpColors::Color get_tile_color(const istd::Tile &tile) {
 		return BmpColors::TITANOMAGNETITE;
 	case istd::SurfaceTileType::Gibbsite:
 		return BmpColors::GIBBSITE;
+	case istd::SurfaceTileType::Coal:
+		return BmpColors::COAL;
 	case istd::SurfaceTileType::Empty:
 	default:
 		break; // Fall through to base tile color
@@ -101,6 +103,7 @@ void print_statistics(const istd::TileMap &tilemap) {
 	int hematite_count = 0;        // Count hematite surface tiles
 	int titanomagnetite_count = 0; // Count titanomagnetite surface tiles
 	int gibbsite_count = 0;        // Count gibbsite surface tiles
+	int coal_count = 0;            // Count coal surface tiles
 	int mountain_edge_count = 0;   // Count mountain edge tiles
 	const int chunks_per_side = tilemap.get_size();
 	const int tiles_per_chunk = istd::Chunk::size;
@@ -128,6 +131,9 @@ void print_statistics(const istd::TileMap &tilemap) {
 					case istd::SurfaceTileType::Gibbsite:
 						gibbsite_count++;
 						break;
+					case istd::SurfaceTileType::Coal:
+						coal_count++;
+						break;
 					default:
 						break;
 					}
@@ -195,6 +201,7 @@ void print_statistics(const istd::TileMap &tilemap) {
 	print_mineral_stats("Hematite", hematite_count);
 	print_mineral_stats("Titanomagnetite", titanomagnetite_count);
 	print_mineral_stats("Gibbsite", gibbsite_count);
+	print_mineral_stats("Coal", coal_count);
 
 	// Mountain edge statistics for mineral context
 	int mountain_count = tile_counts[static_cast<int>(

tilemap/include/tilemap/generation.h

@@ -47,16 +47,24 @@ struct GenerationConfig {
 	                                       // of 255)
 
 	// Mineral cluster generation parameters
-	std::uint16_t hematite_density = 450;        // ~1.8 per chunk (out of 255)
+	std::uint16_t hematite_density = 450;        // ~1.8 per chunk (n / 255)
-	std::uint16_t titanomagnetite_density = 300; // ~1.2 per chunk (out of 255)
+	std::uint16_t titanomagnetite_density = 300; // ~1.2 per chunk (n / 255)
-	std::uint16_t gibbsite_density = 235;        // ~0.9 per chunk (out of 255)
+	std::uint16_t gibbsite_density = 235;        // ~0.9 per chunk (n / 255)
 
 	std::uint8_t mineral_cluster_min_size = 2;   // Minimum tiles per mineral
 	                                             // cluster
 	std::uint8_t mineral_cluster_max_size = 5;   // Maximum tiles per mineral
 	                                             // cluster
-	std::uint8_t mineral_base_probe = 192;       // Base probability for mineral
+	std::uint8_t mineral_base_prob = 192;        // Base probability for mineral
 	                                             // placement
+
+	// Coal generation parameters
+	std::uint8_t coal_seeds_per_chunk = 3;   // Number of initial coal seeds per
+	                                         // chunk
+	std::uint8_t coal_evolution_steps = 6;   // Number of cellular automata
+	                                         // evolution steps
+	std::uint8_t coal_growth_base_prob = 21; // Base probability for coal
+	                                         // growth per neighbor (n / 255)
 };
 
 // Terrain generator class that manages the generation process
@@ -126,6 +134,12 @@ private:
 	 * @param tilemap The tilemap to process
 	 */
 	void mineral_cluster_pass(TileMap &tilemap);
+
+	/**
+	 * @brief Generate coal deposits on suitable terrain
+	 * @param tilemap The tilemap to process
+	 */
+	void coal_pass(TileMap &tilemap);
 };
 /**
  * @brief Generate a tilemap using the new biome-based system

tilemap/include/tilemap/pass/coal.h

@@ -0,0 +1,86 @@
+#ifndef TILEMAP_PASS_COAL_H
+#define TILEMAP_PASS_COAL_H
+
+#include "tilemap/generation.h"
+#include "tilemap/noise.h"
+
+namespace istd {
+
+/**
+ * @brief Generates coal deposits on suitable terrain using cellular automata
+ */
+class CoalGenerationPass {
+private:
+	const GenerationConfig &config_;
+	Xoroshiro128PP rng_;
+	DiscreteRandomNoise noise_;
+
+public:
+	/**
+	 * @brief Construct a coal generation pass
+	 * @param config Generation configuration parameters
+	 * @param rng Random number generator for coal placement
+	 * @param noise_rng Random number generator for noise-based operations
+	 */
+	CoalGenerationPass(
+		const GenerationConfig &config, Xoroshiro128PP rng,
+		Xoroshiro128PP noise_rng
+	);
+
+	/**
+	 * @brief Generate coal deposits using cellular automata
+	 * @param tilemap The tilemap to process
+	 */
+	void operator()(TileMap &tilemap);
+
+private:
+	/**
+	 * @brief Generate initial coal seed points for a chunk
+	 * @param tilemap The tilemap to analyze
+	 * @param chunk_x Chunk X coordinate
+	 * @param chunk_y Chunk Y coordinate
+	 * @param seeds Output vector to fill with seed positions
+	 */
+	void chunk_coal_seeds(
+		const TileMap &tilemap, std::uint8_t chunk_x, std::uint8_t chunk_y,
+		std::vector<TilePos> &seeds
+	);
+
+	/**
+	 * @brief Evolve coal deposits using cellular automata
+	 * @param tilemap The tilemap to modify
+	 * @param initial_seeds Initial coal seed positions
+	 */
+	void evolve_coal_deposits(
+		TileMap &tilemap, const std::vector<TilePos> &initial_seeds
+	);
+
+	/**
+	 * @brief Check if a tile is suitable for coal placement
+	 * @param tilemap The tilemap to check
+	 * @param pos Position to check
+	 * @return True if coal can be placed at this position
+	 */
+	bool is_suitable_for_coal(const TileMap &tilemap, TilePos pos) const;
+
+	/**
+	 * @brief Get the coal growth probability for a specific biome
+	 * @param biome The biome type
+	 * @return Growth probability multiplier (x / 255)
+	 */
+	std::uint8_t get_biome_coal_growth_probability(BiomeType biome) const;
+
+	/**
+	 * @brief Count coal neighbors around a position
+	 * @param tilemap The tilemap to check
+	 * @param pos Position to check around
+	 * @return Number of coal neighbors
+	 */
+	std::uint8_t count_coal_neighbors(
+		const TileMap &tilemap, TilePos pos
+	) const;
+};
+
+} // namespace istd
+
+#endif // TILEMAP_PASS_COAL_H

tilemap/include/tilemap/tile.h

@@ -20,6 +20,7 @@ enum class SurfaceTileType : std::uint8_t {
 	Hematite,
 	Titanomagnetite,
 	Gibbsite,
+	Coal,
 
 	// Player built structures
 	// (not used in generation, but can be placed by player)

tilemap/src/generation.cpp

@@ -13,6 +13,7 @@ void TerrainGenerator::operator()(TileMap &tilemap) {
 	deepwater_pass(tilemap);
 	oil_pass(tilemap);
 	mineral_cluster_pass(tilemap);
+	coal_pass(tilemap);
 }
 
 void map_generate(TileMap &tilemap, const GenerationConfig &config) {

tilemap/src/pass/coal.cpp

@@ -0,0 +1,207 @@
+#include "tilemap/pass/coal.h"
+#include "tilemap/biome.h"
+#include "tilemap/chunk.h"
+#include "tilemap/generation.h"
+#include "tilemap/noise.h"
+#include "tilemap/xoroshiro.h"
+#include <algorithm>
+#include <queue>
+#include <utility>
+
+namespace istd {
+
+CoalGenerationPass::CoalGenerationPass(
+	const GenerationConfig &config, Xoroshiro128PP rng, Xoroshiro128PP noise_rng
+)
+	: config_(config), rng_(rng), noise_(noise_rng) {}
+
+void CoalGenerationPass::operator()(TileMap &tilemap) {
+	std::uint8_t map_size = tilemap.get_size();
+	std::vector<TilePos> all_seeds;
+
+	// Generate coal seeds for each chunk
+	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) {
+			chunk_coal_seeds(tilemap, chunk_x, chunk_y, all_seeds);
+		}
+	}
+
+	// Evolve coal deposits using cellular automata
+	evolve_coal_deposits(tilemap, all_seeds);
+}
+
+void CoalGenerationPass::chunk_coal_seeds(
+	const TileMap &tilemap, std::uint8_t chunk_x, std::uint8_t chunk_y,
+	std::vector<TilePos> &seeds
+) {
+	// Use a max heap to keep top N positions by noise value
+	using PosNoisePair = std::pair<std::uint64_t, TilePos>;
+	std::priority_queue<PosNoisePair> heap;
+
+	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 candidate{chunk_x, chunk_y, local_x, local_y};
+			if (!is_suitable_for_coal(tilemap, candidate)) {
+				continue;
+			}
+
+			auto [global_x, global_y] = candidate.to_global();
+			auto noise_val = noise_.noise(global_x, global_y, 0x90);
+
+			heap.emplace(noise_val, candidate);
+			if (heap.size() > config_.coal_seeds_per_chunk) {
+				heap.pop();
+			}
+		}
+	}
+
+	while (!heap.empty()) {
+		seeds.push_back(heap.top().second);
+		heap.pop();
+	}
+}
+
+void CoalGenerationPass::evolve_coal_deposits(
+	TileMap &tilemap, const std::vector<TilePos> &initial_seeds
+) {
+	// Place initial seeds
+	for (const auto &seed : initial_seeds) {
+		Tile &tile = tilemap.get_tile(seed);
+		if (tile.surface == SurfaceTileType::Empty) {
+			tile.surface = SurfaceTileType::Coal;
+		}
+	}
+
+	// Evolve using cellular automata
+	for (std::uint8_t step = 1; step <= config_.coal_evolution_steps; ++step) {
+		std::vector<TilePos> new_coal_positions;
+		std::uint8_t map_size = tilemap.get_size();
+
+		// Iterate through all tiles
+		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) {
+				const Chunk &chunk = tilemap.get_chunk(chunk_x, 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};
+						const Tile &tile = tilemap.get_tile(pos);
+
+						// Skip if not suitable for coal
+						if (!is_suitable_for_coal(tilemap, pos)) {
+							continue;
+						}
+
+						// Skip if already has coal
+						if (tile.surface == SurfaceTileType::Coal) {
+							continue;
+						}
+
+						// Count coal neighbors
+						std::uint8_t coal_neighbors = count_coal_neighbors(
+							tilemap, pos
+						);
+
+						if (coal_neighbors > 0) {
+							// Get biome for this position
+							BiomeType biome = chunk.get_biome(local_x, local_y);
+							auto biome_probability
+								= get_biome_coal_growth_probability(biome);
+
+							// Base probability increases with more coal
+							// neighbors
+							std::uint32_t base_probability = coal_neighbors
+								* config_.coal_growth_base_prob;
+							std::uint8_t final_probability = std::clamp(
+								base_probability * biome_probability / 255, 0u,
+								255u
+							);
+
+							// Use noise to decide whether to grow coal here
+							auto [global_x, global_y] = pos.to_global();
+							std::uint8_t sample = 0xFF
+								& noise_.noise(global_x, global_y, step);
+
+							if (sample < final_probability) {
+								new_coal_positions.push_back(pos);
+							}
+						}
+					}
+				}
+			}
+		}
+
+		// Place new coal
+		for (const auto &pos : new_coal_positions) {
+			Tile &tile = tilemap.get_tile(pos);
+			if (tile.surface == SurfaceTileType::Empty) {
+				tile.surface = SurfaceTileType::Coal;
+			}
+		}
+	}
+}
+
+bool CoalGenerationPass::is_suitable_for_coal(
+	const TileMap &tilemap, TilePos pos
+) const {
+	const Tile &tile = tilemap.get_tile(pos);
+	return (tile.base == BaseTileType::Sand || tile.base == BaseTileType::Land)
+		&& tile.surface == SurfaceTileType::Empty;
+}
+
+// Returns the coal growth probability for a given biome.
+// Higher values mean coal is more likely to spread in that biome.
+std::uint8_t CoalGenerationPass::get_biome_coal_growth_probability(
+	BiomeType biome
+) const {
+	switch (biome) {
+	case BiomeType::Forest:
+		return 255;
+	case BiomeType::LukeOcean:
+		return 204;
+	case BiomeType::Savanna:
+		return 153;
+	case BiomeType::Plains:
+		return 128;
+	case BiomeType::SnowyPlains:
+	case BiomeType::Ocean:
+		return 102;
+	case BiomeType::SnowyPeeks:
+		return 77;
+	case BiomeType::Desert:
+		return 51;
+	case BiomeType::FrozenOcean:
+		return 26;
+	default:
+		std::unreachable();
+	}
+}
+
+std::uint8_t CoalGenerationPass::count_coal_neighbors(
+	const TileMap &tilemap, TilePos pos
+) const {
+	std::uint8_t count = 0;
+	auto neighbors = tilemap.get_neighbors(pos);
+
+	for (const auto neighbor_pos : neighbors) {
+		const Tile &neighbor_tile = tilemap.get_tile(neighbor_pos);
+		if (neighbor_tile.surface == SurfaceTileType::Coal) {
+			++count;
+		}
+	}
+
+	return count;
+}
+
+void TerrainGenerator::coal_pass(TileMap &tilemap) {
+	auto rng = master_rng_;
+	master_rng_ = master_rng_.jump_96();
+	auto noise_rng = master_rng_;
+	master_rng_ = master_rng_.jump_96();
+	CoalGenerationPass pass(config_, rng, noise_rng);
+	pass(tilemap);
+}
+
+} // namespace istd

tilemap/src/pass/mineral_cluster.cpp

@@ -87,7 +87,7 @@ std::vector<TilePos> MineralClusterGenerationPass::generate_mineral_centers(
 				mineral_type
 			) // Use mineral type as seed variation
 		);
-		if (sample < config_.mineral_base_probe) {
+		if (sample < config_.mineral_base_prob) {
 			centers.push_back(candidate);
 		}
 	}