feat(vf): add NetherColumn and Params

core/include/vf/NetherGen.h

@@ -0,0 +1,95 @@
+#pragma once
+
+#include <cstdint>
+
+#include "Noise.h"
+#include "NoiseAdv.h"
+#include "World.h"
+
+namespace vf {
+
+enum class NetherBiome : uint8_t {
+    NetherWastes = 0,
+    SoulSandValley = 1,
+    BasaltDeltas = 2,
+    CrimsonForest = 3,
+    Count,
+};
+
+// Vertical profile of a single Nether column. The cavern is the gap between
+// the top of the lower mass (floorHeight) and the underside of the roof mass
+// (ceilingHeight); everything at or below lavaLevel inside that gap is lava.
+struct NetherColumn {
+    NetherBiome biome = NetherBiome::NetherWastes;
+    int floorHeight = 0;
+    int ceilingHeight = 0;
+    int lavaLevel = 0;
+    bool drowned = false;
+
+    int cavernHeight() const { return ceilingHeight - floorHeight - 1; }
+};
+
+// Deterministic Nether generator: a solid rock volume between a bedrock floor
+// and a bedrock roof, hollowed out by a cavern profile plus 3D carving noise,
+// flooded with a lava sea at a fixed level, and surfaced per Nether biome.
+// The same seed and column always yield the same blocks.
+class NetherGenerator {
+public:
+    struct Params {
+        uint32_t seed = 1337u;
+        int floorY = 0;
+        int ceilingY = 128;
+        int lavaLevel = 31;
+        int bedrockThickness = 4;
+        int roofThickness = 12;
+        float biomeFrequency = 0.0046f;
+        float floorFrequency = 0.017f;
+        float ceilingFrequency = 0.013f;
+        float caveFrequency = 0.031f;
+        float caveThreshold = 0.87f;
+        float blobThreshold = 0.46f;
+        float quartzFrequency = 0.125f;
+        float quartzThreshold = 0.60f;
+        bool decorate = true;
+    };
+
+    NetherGenerator();
+    explicit NetherGenerator(const Params& netherParams);
+
+    const Params& settings() const { return params; }
+    int stackChunkCount() const { return (params.ceilingY - params.floorY) / chunkSize; }
+
+    NetherBiome biomeAt(int gx, int gz) const;
+    NetherColumn columnAt(int gx, int gz) const;
+
+    // Tunnel network cut through the solid mass, sampled independently of the
+    // column profile so it links the floor rock to the roof rock.
+    bool isCarved(int gx, int gy, int gz) const;
+    bool isBedrock(int gx, int gy, int gz) const;
+
+    Block blockAt(const NetherColumn& column, int gx, int gy, int gz) const;
+
+    void generateChunk(Chunk& chunk, const Vec3i& chunkCoord) const;
+    void generateColumn(World& world, int columnX, int columnZ) const;
+    void decorateColumn(World& world, int columnX, int columnZ) const;
+
+private:
+    bool isBlob(int gx, int gy, int gz) const;
+    Block topFor(NetherBiome biome) const;
+    Block fillerFor(NetherBiome biome) const;
+
+    void raiseBasaltPillar(World& world, int gx, int gz, const NetherColumn& column, uint32_t roll) const;
+    void pourLavafall(World& world, int gx, int gz, const NetherColumn& column) const;
+    void hangGlowstone(World& world, int gx, int gz, const NetherColumn& column, uint32_t roll) const;
+    void plantFungus(World& world, int gx, int gz, const NetherColumn& column, uint32_t roll) const;
+
+    Params params;
+    PerlinNoise floorNoise;
+    PerlinNoise ceilingNoise;
+    PerlinNoise caveNoise;
+    PerlinNoise blobNoise;
+    PerlinNoise oreNoise;
+    NoiseAdv biomeNoise;
+};
+
+} // namespace vf