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docs: add developer guide for tilemap library and reduce api doc

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tilemap/docs/api.md
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# Tilemap Library API Documentation
# Tilemap Library API
## Overview
The tilemap library provides a flexible system for generating and managing tile-based terrain with biome support. The library consists of several main components:
- **TileMap**: The main map container holding chunks of tiles
- **Chunk**: 64x64 tile containers with biome information
- **Tile**: Individual map tiles with base and surface types
- **TerrainGenerator**: Pass-based procedural terrain generation system
- **Generation Passes**: Modular generation components (biome, base terrain, hole filling)
- **Biome System**: Climate-based terrain variation
The tilemap library provides a system for generating and managing tile-based terrain with biome support.
## Core Classes
### TileMap
The main container for the entire map, organized as an n×n grid of chunks.
Main container for the map, organized as chunks.
```cpp
class TileMap {
@ -24,446 +17,108 @@ public:
std::uint8_t get_size() const;
Chunk& get_chunk(std::uint8_t chunk_x, std::uint8_t chunk_y);
const Chunk& get_chunk(std::uint8_t chunk_x, std::uint8_t chunk_y) const;
Tile& get_tile(TilePos pos);
const Tile& get_tile(TilePos pos) const;
void set_tile(TilePos pos, const Tile& tile);
bool is_at_boundary(TilePos pos) const;
std::vector<TilePos> get_neighbors(TilePos pos, bool chebyshev = false) const;
};
```
**Constructor Parameters:**
- `size`: Number of chunks per side (max 100), creating an n×n grid
**New Methods:**
- `is_at_boundary()`: Checks if a tile position is at the map boundary
- `get_neighbors()`: Returns neighboring tile positions with optional Chebyshev distance support
### Chunk
Each chunk contains 64×64 tiles and sub-chunk biome information.
64×64 tile container with biome information.
```cpp
struct Chunk {
static constexpr uint8_t size = 64; // Tiles per side
static constexpr uint8_t subchunk_size = 4; // Tiles per sub-chunk side
static constexpr uint8_t subchunk_count = size / subchunk_size; // Sub-chunks per side
static constexpr uint8_t size = 64;
Tile tiles[size][size]; // 64x64 tile grid
BiomeType biome[subchunk_count][subchunk_count]; // Sub-chunk biomes
Tile tiles[size][size];
BiomeType biome[16][16]; // Sub-chunk biomes
// Methods for biome access
BiomeType& get_biome(SubChunkPos pos);
const BiomeType& get_biome(SubChunkPos pos) const;
};
```
### Tile
Individual map tiles with base terrain and surface features.
Individual map tile with terrain types.
```cpp
struct Tile {
BaseTileType base : 4; // Base terrain type
BaseTileType base : 4; // Base terrain
SurfaceTileType surface : 4; // Surface features
};
```
**Base Tile Types:**
- `Land`: Standard ground terrain
- `Mountain`: Rocky elevated terrain
- `Sand`: Desert/beach terrain
- `Water`: Water bodies
- `Ice`: Frozen terrain
- `Land`, `Mountain`, `Sand`, `Water`, `Ice`
**Surface Tile Types:**
- `Empty`: No surface features
- `Wood`: Trees/vegetation
- `Structure`: Player-built structures
- `Empty`, `Wood`, `Structure`
### TilePos
Position structure for locating tiles within the map with enhanced coordinate conversion support.
### Position Types
```cpp
struct TilePos {
uint8_t chunk_x; // Chunk X coordinate
uint8_t chunk_y; // Chunk Y coordinate
uint8_t local_x; // Tile X within chunk (0-63)
uint8_t local_y; // Tile Y within chunk (0-63)
uint8_t chunk_x, chunk_y; // Chunk coordinates
uint8_t local_x, local_y; // Tile within chunk (0-63)
// Coordinate conversion methods
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);
};
// Three-way comparison operator for ordering
std::strong_ordering operator<=>(const TilePos& lhs, const TilePos& rhs);
```
### SubChunkPos
Position within a chunk's sub-chunk grid.
```cpp
struct SubChunkPos {
std::uint8_t sub_x;
std::uint8_t sub_y;
constexpr SubChunkPos(std::uint8_t x, std::uint8_t y);
std::uint8_t sub_x, sub_y;
};
std::pair<std::uint8_t, std::uint8_t> subchunk_to_tile_start(
SubChunkPos pos
);
```
## Terrain Generation
The terrain generation system has been refactored into a modular pass-based architecture, providing better separation of concerns and more flexible generation control.
### GenerationConfig
Configuration parameters for terrain generation.
Configuration for terrain generation.
```cpp
struct GenerationConfig {
Seed seed; // 128-bit seed for random generation
Seed seed;
// Temperature noise parameters
double temperature_scale = 0.05; // Scale for temperature noise
int temperature_octaves = 3; // Number of octaves for temperature noise
double temperature_persistence = 0.4; // Persistence for temperature noise
// Noise parameters
double temperature_scale = 0.05;
double humidity_scale = 0.05;
double base_scale = 0.08;
// Humidity noise parameters
double humidity_scale = 0.05; // Scale for humidity noise
int humidity_octaves = 3; // Number of octaves for humidity noise
double humidity_persistence = 0.4; // Persistence for humidity noise
// Base terrain noise parameters
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
// Mountain smoothing parameters
std::uint32_t mountain_remove_threshold = 10; // Remove mountain components smaller than this size
// Hole filling parameters
std::uint32_t fill_threshold = 10; // Fill holes smaller than this size
int temperature_octaves = 3;
int humidity_octaves = 3;
int base_octaves = 3;
};
```
**Parameters:**
- `seed`: 128-bit seed for all noise generators (see Seed structure)
- `temperature_scale`: Controls the scale/frequency of temperature variation across the map
- `temperature_octaves`: Number of noise octaves for temperature (more octaves = more detail)
- `temperature_persistence`: How much each octave contributes to temperature noise (0.0-1.0)
- `humidity_scale`: Controls the scale/frequency of humidity variation across the map
- `humidity_octaves`: Number of noise octaves for humidity
- `humidity_persistence`: How much each octave contributes to humidity noise (0.0-1.0)
- `base_scale`: Controls the scale/frequency of base terrain variation across the map
- `base_octaves`: Number of noise octaves for base terrain
- `base_persistence`: How much each octave contributes to base terrain noise (0.0-1.0)
- `mountain_remove_threshold`: Maximum size of mountain components to remove for terrain smoothing
- `fill_threshold`: Maximum size of holes to fill with mountains
### Generation Passes
The generation system is organized into distinct passes, each responsible for a specific aspect of terrain generation.
#### BiomeGenerationPass
Generates biome data for all sub-chunks based on temperature and humidity noise.
```cpp
class BiomeGenerationPass {
public:
BiomeGenerationPass(
const GenerationConfig& config,
Xoroshiro128PP r1,
Xoroshiro128PP r2
);
void operator()(TileMap& tilemap);
private:
std::pair<double, double> get_climate(double global_x, double global_y) const;
};
```
**Key Features:**
- **Climate Generation**: Uses separate noise generators for temperature and humidity
- **Sub-chunk Resolution**: Assigns biomes to 16×16 sub-chunks for efficient generation
- **Climate Mapping**: Maps noise values to temperature/humidity ranges
- **Biome Determination**: Uses climate values to determine appropriate biomes
#### BaseTileTypeGenerationPass
Generates base terrain types for all tiles based on their sub-chunk biomes.
```cpp
class BaseTileTypeGenerationPass {
public:
BaseTileTypeGenerationPass(const GenerationConfig& config, Xoroshiro128PP rng);
void operator()(TileMap& tilemap);
void generate_chunk(TileMap& tilemap, std::uint8_t chunk_x, std::uint8_t chunk_y);
void generate_subchunk(
TileMap& tilemap, std::uint8_t chunk_x, std::uint8_t chunk_y,
SubChunkPos sub_pos, BiomeType biome
);
private:
BaseTileType determine_base_type(
double noise_value, const BiomeProperties& properties
) const;
};
```
**Key Features:**
- **Biome-aware Generation**: Uses biome properties to control terrain type ratios
- **Hierarchical Processing**: Processes chunks, then sub-chunks, then individual tiles
- **Noise-based Distribution**: Uses calibrated noise for balanced terrain distribution
- **Tile-level Detail**: Generates terrain at individual tile resolution
#### HoleFillPass
Fills small holes in the terrain using breadth-first search (BFS) algorithm.
```cpp
class HoleFillPass {
public:
explicit HoleFillPass(const GenerationConfig& config);
void operator()(TileMap& tilemap);
private:
bool is_passable(BaseTileType type) const;
std::uint32_t bfs_component_size(
TileMap& tilemap, TilePos start_pos,
std::vector<std::vector<bool>>& visited,
std::vector<TilePos>& positions
);
std::vector<TilePos> get_neighbors(TileMap& tilemap, TilePos pos) const;
bool is_at_boundary(TileMap& tilemap, TilePos pos) const;
};
```
**Key Features:**
- **BFS Algorithm**: Uses breadth-first search to identify connected components
- **Boundary Awareness**: Preserves holes that touch the map boundary
- **Size-based Filtering**: Only fills holes smaller than `fill_threshold`
- **Mountain-as-Impassable**: Treats mountains as impassable terrain for connectivity
- **Hole Filling**: Converts small isolated areas to mountains for cleaner terrain
#### SmoothenMountainsPass
Removes small mountain components to create smoother terrain using BFS and replacement strategies.
```cpp
class SmoothenMountainsPass {
public:
SmoothenMountainsPass(const GenerationConfig& config, Xoroshiro128PP rng);
void operator()(TileMap& tilemap);
private:
std::uint32_t bfs_component_size(
TileMap& tilemap, TilePos start_pos,
std::vector<std::vector<bool>>& visited,
std::vector<TilePos>& positions
);
void demountainize(TileMap& tilemap, const std::vector<TilePos>& positions);
};
```
**Key Features:**
- **Mountain Component Detection**: Uses BFS to find connected mountain regions
- **Size-based Removal**: Removes mountain components smaller than `mountain_remove_threshold`
- **Boundary Preservation**: Preserves mountain components that touch the map boundary
- **Intelligent Replacement**: Replaces mountains with terrain types based on neighboring tiles
- **Smooth Terrain**: Creates more natural-looking terrain without isolated mountain clusters
### TerrainGenerator
Main orchestrator class that manages the generation process using multiple passes.
```cpp
class TerrainGenerator {
public:
explicit TerrainGenerator(const GenerationConfig& config);
void operator()(TileMap& tilemap);
private:
void biome_pass(TileMap& tilemap);
void base_tile_type_pass(TileMap& tilemap);
void smoothen_mountains_pass(TileMap& tilemap);
void hole_fill_pass(TileMap& tilemap);
};
```
**Generation Order:**
1. **Biome Pass**: Generates climate-based biome data for sub-chunks
2. **Base Tile Type Pass**: Generates base terrain types based on biomes
3. **Smoothen Mountains Pass**: Removes small mountain components for smoother terrain
4. **Hole Fill Pass**: Fills small holes in the terrain
**Key Features:**
- **Multi-pass Architecture**: Separates generation concerns for better control
- **RNG Management**: Uses independent RNGs for each pass with proper seeding
- **Deterministic Results**: Same seed produces identical terrain across runs
- **Configurable**: All passes use parameters from GenerationConfig
**Generation Flow:**
1. **Biome Pass**: Generate climate data and assign biomes to sub-chunks
2. **Base Tile Type Pass**: Generate base terrain types based on biomes and noise
3. **Hole Fill Pass**: Fill small holes in the terrain using BFS algorithm
### Generation Function
Convenience function for complete map generation.
```cpp
void map_generate(TileMap& tilemap, const GenerationConfig& config);
```
## Random Number Generation
### Seed
128-bit seed structure for random number generation.
```cpp
struct Seed {
std::uint64_t s[2]; // 128-bit seed value (two 64-bit components)
std::uint64_t s[2];
static Seed from_string(const char* str); // Create seed from string
static Seed device_random(); // Create seed from hardware random device
static Seed from_string(const char* str);
static Seed device_random();
};
```
**Key Features:**
- **128-bit precision**: Uses two 64-bit integers for extended seed space
- **String generation**: Deterministic seed creation from text strings
- **Hardware random**: True random seed generation using system entropy
### Xoroshiro128++
High-performance random number generator using the Xoroshiro128++ algorithm.
```cpp
class Xoroshiro128PP {
public:
Xoroshiro128PP() = default;
Xoroshiro128PP(Seed seed);
// STL RandomEngine interface
using result_type = std::uint64_t;
static constexpr result_type min();
static constexpr result_type max();
result_type operator()();
std::uint64_t next(); // Generate next random number
Xoroshiro128PP jump_64() const; // Jump equivalent to 2^64 calls
Xoroshiro128PP jump_96() const; // Jump equivalent to 2^96 calls
};
```
**Key Features:**
- **High Performance**: Optimized for speed with excellent statistical properties
- **128-bit State**: Internal state provides long period (2^128 - 1)
- **Jump Functions**: Enable parallel random number generation
- **STL Compatible**: Implements standard random engine interface
## Noise System
### DiscreteRandomNoise
Discrete random noise generator using Xoroshiro128++ for terrain replacement operations.
```cpp
class DiscreteRandomNoise {
public:
explicit DiscreteRandomNoise(Xoroshiro128PP rng);
std::uint64_t noise(std::uint32_t x, std::uint32_t y, std::uint32_t z = 0) const;
};
```
**Key Features:**
- **Discrete Output**: Produces integer values for discrete selections
- **High Quality**: Based on Xoroshiro128++ random number generation
- **3D Support**: Supports optional Z coordinate for 3D noise
- **Fast**: Optimized for performance in terrain processing
### PerlinNoise
Standard Perlin noise implementation using Xoroshiro128++ for procedural generation.
```cpp
class PerlinNoise {
public:
explicit PerlinNoise(Xoroshiro128PP rng);
double noise(double x, double y) const;
double octave_noise(double x, double y, int octaves = 4, double persistence = 0.5) const;
};
```
### UniformPerlinNoise
Advanced noise generator using Xoroshiro128++ that provides uniform distribution mapping.
```cpp
class UniformPerlinNoise {
public:
explicit UniformPerlinNoise(Xoroshiro128PP rng);
void calibrate(double scale, int octaves = 1, double persistence = 0.5, int sample_size = 10000);
double uniform_noise(double x, double y) const;
bool is_calibrated() const;
};
```
**Key Features:**
- **Calibration**: Samples noise distribution to build CDF
- **Uniform Mapping**: Maps raw Perlin values to uniform [0,1] distribution
- **Balanced Output**: Ensures even distribution across all value ranges
- **Automatic Use**: TerrainGenerator uses this internally for balanced terrain
- **Xoroshiro128++ Backend**: Uses high-quality random number generation
## Biome System
## Biomes
### BiomeType
Available biome types based on temperature and humidity.
```cpp
enum class BiomeType : std::uint8_t {
SnowyPeeks, // Cold & Dry
SnowyPlains, // Cold & Moderate
FrozenOcean, // Cold & Wet
Plains, // Temperate & Dry
Forest, // Temperate & Moderate
Ocean, // Temperate & Wet
Desert, // Hot & Dry
Savanna, // Hot & Moderate
LukeOcean, // Hot & Wet
};
```
### BiomeProperties
Properties that control terrain generation for each biome.
```cpp
struct BiomeProperties {
std::string_view name; // Biome name
double water_ratio; // Water generation ratio
double ice_ratio; // Ice generation ratio
double sand_ratio; // Sand generation ratio
double land_ratio; // Land generation ratio
int base_octaves = 3; // Noise octaves
double base_persistence = 0.5; // Noise persistence
SnowyPeaks, SnowyPlains, FrozenOcean,
Plains, Forest, Ocean,
Desert, Savanna, LukeOcean
};
```
@ -476,201 +131,32 @@ BiomeType determine_biome(double temperature, double humidity);
## Usage Examples
### Basic Map Generation
### Basic Usage
```cpp
#include "tilemap.h"
#include "generation.h"
// Create a 4x4 chunk map
istd::TileMap tilemap(4);
// Configure generation
istd::GenerationConfig config;
config.seed = istd::Seed::from_string("hello_world"); // 128-bit seed from string
// Temperature noise settings
config.temperature_scale = 0.05;
config.temperature_octaves = 3;
config.temperature_persistence = 0.4;
// Humidity noise settings
config.humidity_scale = 0.05;
config.humidity_octaves = 3;
config.humidity_persistence = 0.4;
// Base terrain noise settings
config.base_scale = 0.08;
config.base_octaves = 3;
config.base_persistence = 0.5;
// Mountain smoothing settings
config.mountain_remove_threshold = 10; // Remove mountain components smaller than 10 tiles
// Hole filling settings
config.fill_threshold = 10; // Fill holes smaller than 10 tiles
// Create map
istd::TileMap tilemap(4); // 4x4 chunks
// Generate terrain
istd::GenerationConfig config;
config.seed = istd::Seed::from_string("my_world");
istd::map_generate(tilemap, config);
// Access tiles
for (int chunk_y = 0; chunk_y < tilemap.get_size(); ++chunk_y) {
for (int chunk_x = 0; chunk_x < tilemap.get_size(); ++chunk_x) {
const auto& chunk = tilemap.get_chunk(chunk_x, chunk_y);
// Process chunk tiles...
}
}
```
### Advanced Generation with Custom Passes
```cpp
#include "tilemap.h"
#include "generation.h"
// Create map and config
istd::TileMap tilemap(2);
istd::GenerationConfig config;
config.seed = istd::Seed::from_string("custom_world");
// Use TerrainGenerator for step-by-step control
istd::TerrainGenerator generator(config);
// Generate terrain (runs both biome and base tile passes)
generator(tilemap);
// Access biome data
const auto& chunk = tilemap.get_chunk(0, 0);
for (int sub_y = 0; sub_y < istd::Chunk::subchunk_count; ++sub_y) {
for (int sub_x = 0; sub_x < istd::Chunk::subchunk_count; ++sub_x) {
istd::SubChunkPos pos(sub_x, sub_y);
istd::BiomeType biome = chunk.get_biome(pos);
const auto& props = istd::get_biome_properties(biome);
// Process biome...
}
}
```
```
### Seed Usage Examples
```cpp
// Create seed from string (deterministic)
istd::Seed seed1 = istd::Seed::from_string("my_world");
// Create random seed from hardware
istd::Seed seed2 = istd::Seed::device_random();
// Manual seed creation
istd::Seed seed3;
seed3.s[0] = 0x123456789abcdef0;
seed3.s[1] = 0xfedcba9876543210;
// Use seed in generation
istd::GenerationConfig config;
config.seed = seed1;
```
### Accessing Individual Tiles
```cpp
// Using TilePos
istd::TilePos pos{0, 0, 32, 32}; // Chunk (0,0), tile (32,32)
istd::TilePos pos{0, 0, 32, 32}; // Chunk (0,0), tile (32,32)
const auto& tile = tilemap.get_tile(pos);
// Direct chunk access
const auto& chunk = tilemap.get_chunk(0, 0);
const auto& tile2 = chunk.tiles[32][32];
```
### Working with Biomes
```cpp
// Method 1: Direct array access (traditional way)
const auto& chunk = tilemap.get_chunk(0, 0);
istd::BiomeType biome = chunk.biome[1][1]; // Sub-chunk (1,1)
istd::SubChunkPos sub_pos(1, 1);
istd::BiomeType biome = chunk.get_biome(sub_pos);
// Method 2: Using SubChunkPos and get_biome method (recommended)
istd::SubChunkPos pos(1, 1); // Sub-chunk (1,1)
istd::BiomeType biome2 = chunk.get_biome(pos);
// Modify biome using the new method
auto& mutable_chunk = tilemap.get_chunk(0, 0);
mutable_chunk.get_biome(pos) = istd::BiomeType::Forest;
// Get biome properties
const auto& props = istd::get_biome_properties(biome);
std::cout << "Biome: " << props.name << std::endl;
```
## Performance Notes
- Each chunk contains 4,096 tiles (64×64)
- Sub-chunks provide efficient biome management
- Tiles are packed into 1 byte each for memory efficiency
- Generation uses Xoroshiro128++ random number generator with uniform distribution mapping for balanced terrain
- Noise calibration is performed once during generator construction
- 128-bit seeds provide excellent randomness and reproducibility
## Noise Distribution
The library uses an advanced noise system based on Xoroshiro128++ random number generation that addresses the non-uniform distribution of Perlin noise:
### Problem with Raw Perlin Noise
Raw Perlin noise follows a bell-curve distribution, with most values concentrated around 0.5. This leads to unbalanced terrain generation where certain tile types (like Land) dominate the map.
### Solution: Xoroshiro128++ + Uniform Distribution Mapping
The library combines two key improvements:
1. **Xoroshiro128++ RNG**: High-quality pseudo-random number generator with:
- **Long Period**: 2^128 - 1 sequence length before repetition
- **High Performance**: Optimized for speed and memory efficiency
- **Excellent Statistics**: Passes rigorous randomness tests
- **128-bit State**: Two 64-bit values providing extensive seed space
2. **Uniform Distribution Mapping**: The `UniformPerlinNoise` class:
- **Samples** the noise distribution during calibration
- **Builds a CDF** (Cumulative Distribution Function) from the samples
- **Maps raw noise values** to uniform [0,1] distribution using quantiles
- **Ensures balanced** terrain type distribution according to biome properties
### Usage in Terrain Generation
```cpp
// The terrain generator automatically uses Xoroshiro128++ and uniform noise
istd::Seed seed = istd::Seed::from_string("consistent_world");
istd::GenerationConfig config;
config.seed = seed;
// TerrainGenerator handles pass coordination and RNG management
istd::TerrainGenerator generator(config);
generator(tilemap); // Uses calibrated uniform noise with Xoroshiro128++
// Or use the convenience function
istd::map_generate(tilemap, config);
```
### Pass-based Architecture Benefits
The new pass-based system provides:
1. **Separation of Concerns**: Each pass handles a specific aspect of generation
2. **RNG Independence**: Each pass uses independent random number generators
3. **Reproducible Results**: Same seed produces identical results across passes
4. **Extensibility**: Easy to add new passes or modify existing ones
5. **Performance**: Efficient memory access patterns and reduced redundant calculations
6. **Terrain Quality**: SmoothenMountainsPass creates more natural-looking terrain
### Recent Improvements
**Mountain Smoothing**: The new `SmoothenMountainsPass` removes small isolated mountain components to create more natural terrain formations. Small mountain clusters that don't connect to the boundary are replaced with terrain types based on their neighboring areas.
**Enhanced TileMap**: Added utility methods for boundary detection and neighbor finding, supporting both Manhattan and Chebyshev distance calculations.
**Improved Noise**: Added `DiscreteRandomNoise` for high-quality discrete value generation used in terrain replacement operations.
## Thread Safety
The library is not inherently thread-safe. External synchronization is required for concurrent access to TileMap objects.

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# Tilemap Library Developer Guide
## Project Overview
The tilemap library is a C++ terrain generation system that creates tile-based worlds with biome support. It uses a multi-pass generation pipeline to create realistic, balanced terrain.
## Project Structure
```
tilemap/
├── include/ # Public headers
│ ├── tilemap.h # Main map container
│ ├── chunk.h # 64x64 tile chunks
│ ├── tile.h # Individual tile types
│ ├── generation.h # Generation system
│ ├── biome.h # Biome system
│ ├── noise.h # Noise generators
│ └── xoroshiro.h # RNG implementation
├── src/ # Implementation files
│ ├── tilemap.cpp # TileMap implementation
│ ├── chunk.cpp # Chunk utilities
│ ├── generation.cpp # Main generation orchestrator
│ ├── biome.cpp # Biome mapping logic
│ ├── noise.cpp # Noise implementations
│ ├── xoroshiro.cpp # Xoroshiro128++ RNG
│ └── pass/ # Generation passes
│ ├── biome.cpp # Climate-based biome generation
│ ├── base_tile_type.cpp # Base terrain generation
│ ├── smoothen_mountain.cpp # Mountain smoothing
│ ├── mountain_hole_fill.cpp # Hole filling
│ └── deepwater.cpp # Deep water placement
├── examples/ # Usage examples
└── docs/ # Documentation
```
## Core Architecture
### Data Organization
The system uses a hierarchical structure:
- **TileMap**: n×n grid of chunks
- **Chunk**: 64×64 tiles with biome metadata
- **Tile**: Individual terrain cell (1 byte packed)
Each chunk also contains a 16×16 grid of sub-chunk biomes, providing efficient biome lookup without per-tile storage.
### Pass-Based Generation
Terrain generation uses a multi-pass pipeline for modularity and control:
1. **Biome Pass**: Generates climate data and assigns biomes to sub-chunks
2. **Base Tile Type Pass**: Creates base terrain based on biomes
3. **Mountain Smoothing Pass**: Removes isolated mountain clusters
4. **Hole Fill Pass**: Fills small terrain holes
5. **Deep Water Pass**: Places deep water areas
Each pass operates independently with its own RNG state, ensuring deterministic results.
## Terrain Generation Pipeline
### Climate Generation
The biome pass uses dual noise generators for temperature and humidity:
- Separate Perlin noise for temperature/humidity at sub-chunk resolution
- Climate values mapped to 9 biome types in a 3×3 grid
- Sub-chunks store biome data for efficient terrain generation
### Noise System
The library addresses Perlin noise distribution issues:
- **Problem**: Raw Perlin noise has bell-curve distribution
- **Solution**: UniformPerlinNoise calibrates distribution to uniform [0,1]
- **Result**: Balanced terrain type ratios according to biome properties
### Terrain Generation Process
1. **Climate Sampling**: Sample temperature/humidity at sub-chunk centers
2. **Biome Assignment**: Map climate values to biome types
3. **Terrain Generation**: Generate tiles based on biome properties and noise
4. **Post-processing**: Apply smoothing and hole-filling algorithms
### Connected Component Analysis
Several passes use BFS (Breadth-First Search) for terrain analysis:
- **Mountain Smoothing**: Find and remove small mountain components
- **Hole Filling**: Identify and fill isolated terrain holes
- Components touching map boundaries are preserved
## Random Number Generation
### Xoroshiro128++ Implementation
High-quality PRNG with excellent statistical properties:
- 128-bit internal state
- Period of 2^128 - 1
- Jump functions for parallel generation
- STL-compatible interface
### Seed Management
128-bit seeds provide extensive randomness:
- String-based deterministic seed creation
- Hardware random seed generation
- Independent RNG streams for each generation pass
## Biome System
### Climate Mapping
Biomes are determined by temperature/humidity combinations:
```
Dry Moderate Wet
Cold Snowy Snowy Frozen
Peaks Plains Ocean
Temp Plains Forest Ocean
Hot Desert Savanna Luke Ocean
```
### Biome Properties
Each biome defines terrain generation ratios:
- Water/Ice/Sand/Land ratios
- Noise parameters (octaves, persistence)
- Used by base terrain generation pass
## Performance Considerations
### Memory Layout
- Tiles packed into 1 byte (4 bits base + 4 bits surface)
- Chunks use contiguous 64×64 arrays for cache efficiency
- Sub-chunk biomes reduce memory overhead vs per-tile storage
### Generation Efficiency
- Sub-chunk resolution for biome generation (16×16 vs 64×64)
- Single-pass algorithms where possible
- Efficient connected component analysis using BFS
### Determinism
- Same seed produces identical results
- Independent RNG streams prevent cross-pass contamination
- Floating-point operations use consistent precision
## Adding New Generation Passes
To add a new generation pass:
1. **Create Pass Implementation**: Add new file in `src/pass/`
2. **Add to Pipeline**: Update `TerrainGenerator::operator()`
3. **RNG Management**: Use jump functions for independent RNG streams
4. **Configuration**: Add parameters to `GenerationConfig` if needed
Example pass structure:
```cpp
void TerrainGenerator::my_custom_pass(TileMap &tilemap) {
auto rng = master_rng_.jump_96(); // Independent RNG stream
// Process tilemap...
for (auto chunk_y = 0; chunk_y < tilemap.get_size(); ++chunk_y) {
for (auto chunk_x = 0; chunk_x < tilemap.get_size(); ++chunk_x) {
auto& chunk = tilemap.get_chunk(chunk_x, chunk_y);
// Process chunk...
}
}
}
```
## Testing and Validation
### Determinism Testing
Verify same seed produces identical output across runs:
```cpp
auto seed = Seed::from_string("test");
TileMap map1(4), map2(4);
map_generate(map1, {seed});
map_generate(map2, {seed});
// Verify map1 == map2
```
### Distribution Analysis
Check terrain type distributions match biome properties:
- Count tile types per biome
- Verify ratios within acceptable tolerance
- Test with multiple seeds for statistical significance
### Visual Validation
Export maps to image formats for visual inspection:
- Check for realistic terrain patterns
- Verify biome transitions look natural
- Ensure no artifacts from generation passes
## Future Extensions
### Potential Improvements
- **Surface Feature Generation**: Trees, structures, resources
- **Elevation System**: Height maps for 3D terrain
- **River Generation**: Connected water systems
- **Chunk Streaming**: Dynamic loading for large worlds
- **Multithreading**: Parallel chunk generation
### API Stability
Core interfaces (TileMap, Chunk, Tile) are stable. Generation system is designed for extensibility without breaking existing code.