feat(core): add biome selection from noise-driven sampling

core/include/vf/BiomeGen.h

@@ -0,0 +1,105 @@
+#pragma once
+
+#include <array>
+#include <cstdint>
+#include "Block.h"
+#include "NoiseAdv.h"
+
+namespace vf {
+
+// Standalone climate-driven biome catalogue. Deliberately named BiomeKind,
+// distinct from vf::Biome in WorldGen.h, so this header can be included
+// alongside WorldGen.h without redefinition.
+enum class BiomeKind : uint8_t {
+    Ocean = 0,
+    Beach = 1,
+    Desert = 2,
+    Plains = 3,
+    Forest = 4,
+    Taiga = 5,
+    Tundra = 6,
+    Swamp = 7,
+    Jungle = 8,
+    Savanna = 9,
+    Mountains = 10,
+    Count,
+};
+
+const char* biomeKindName(BiomeKind biome);
+
+// Five-axis climate sample at a world column, each roughly in [-1, 1].
+struct ClimateSample {
+    float temperature = 0.0f;
+    float humidity = 0.0f;
+    float continentalness = 0.0f;  // low = ocean, high = deep inland
+    float erosion = 0.0f;          // low = jagged/mountainous, high = flat
+    float weirdness = 0.0f;        // near 0 carves a river valley
+};
+
+struct BiomeGenParams {
+    uint32_t seed = 1337u;
+    float climateFrequency = 0.003f;
+    float erosionFrequency = 0.006f;
+    float weirdnessFrequency = 0.01f;
+    float riverWidth = 0.045f;
+    int seaLevel = 26;
+};
+
+struct SurfaceLayers {
+    Block top = Block::Grass;
+    Block filler = Block::Dirt;
+    int fillerDepth = 3;
+};
+
+struct DecoratorDensity {
+    float treeDensity = 0.0f;
+    float bushDensity = 0.0f;
+    float caneDensity = 0.0f;  // cactus in desert, reeds in swamp/jungle
+};
+
+// Vote-blended biome weights over a neighbourhood, used to smooth borders
+// (surface colour, height blending) instead of a hard biome edge.
+struct BiomeWeights {
+    std::array<float, static_cast<std::size_t>(BiomeKind::Count)> weight{};
+
+    float weightOf(BiomeKind biome) const { return weight[static_cast<std::size_t>(biome)]; }
+};
+
+// Climate-parameter biome classifier with river carving, surface builders
+// and decorator density tables. Independent of vf::WorldGen: samples are
+// pure functions of world column coordinates, so identical seed and column
+// always yield an identical result.
+class BiomeGen {
+public:
+    explicit BiomeGen(const BiomeGenParams& params = {});
+
+    ClimateSample climateAt(int gx, int gz) const;
+    BiomeKind biomeFromClimate(const ClimateSample& climate) const;
+    BiomeKind biomeAt(int gx, int gz) const;
+
+    bool isRiver(int gx, int gz) const;
+
+    SurfaceLayers surfaceFor(BiomeKind biome) const;
+
+    // Surface block at height `height` for the column at (gx, gz): river
+    // water/sand overrides the biome's ordinary top block.
+    Block surfaceBlockAt(int gx, int gz, int height) const;
+
+    DecoratorDensity decoratorsFor(BiomeKind biome) const;
+
+    // Box-blurred biome vote over a (2*radius+1)^2 neighbourhood, weights
+    // sum to 1.
+    BiomeWeights biomeBlend(int gx, int gz, int radius) const;
+
+    const BiomeGenParams& settings() const { return params; }
+
+private:
+    BiomeGenParams params;
+    NoiseAdv temperatureNoise;
+    NoiseAdv humidityNoise;
+    NoiseAdv continentalnessNoise;
+    NoiseAdv erosionNoise;
+    NoiseAdv weirdnessNoise;
+};
+
+} // namespace vf