feat(biome): Milestone 2 — Biome Colors + Mountains 10x Height

src/engine/ChunkManager.ts

@@ -17,7 +17,7 @@ export interface ChunkGPUData {
 const RESOLUTION = 129
 export const CHUNK_SIZE = 512
 export const HEIGHT_SCALE = 64
-const UNIFORM_BUFFER_SIZE = 128  // 64 (viewProj mat4) + 16 (worldOffset) + 16 (cameraPos) + 16 (fogParams) + 16 padding
+const UNIFORM_BUFFER_SIZE = 144  // 64 (viewProj mat4) + 16 (worldOffset) + 16 (cameraPos) + 16 (fogParams) + 16 padding + 16 (biomeData)
 
 export default class ChunkManager {
   private device: GPUDevice
@@ -100,6 +100,9 @@ export default class ChunkManager {
     const worldOffset = new Float32Array([cx * CHUNK_SIZE, 0, cz * CHUNK_SIZE, 0])
     this.device.queue.writeBuffer(uniformBuffer, 64, worldOffset)
 
+    const biomeData = new Float32Array([biomeId ?? 0, 0, 0, 0])
+    this.device.queue.writeBuffer(uniformBuffer, 128, biomeData)
+
     const bindGroup = this.device.createBindGroup({
       layout: this.bindGroupLayout,
       entries: [{ binding: 0, resource: { buffer: uniformBuffer } }],

src/shaders/terrain.frag.wgsl

@@ -3,27 +3,44 @@ struct Uniforms {
   worldOffset: vec4<f32>,
   cameraPos:   vec4<f32>,
   fogParams:   vec4<f32>,
+  _pad:        vec4<f32>,
+  biomeData:   vec4<f32>,
 }
 @group(0) @binding(0) var<uniform> uniforms: Uniforms;
 
-@group(1) @binding(0) var terrainSampler: sampler;
-@group(1) @binding(1) var grassTex: texture_2d<f32>;
-@group(1) @binding(2) var rockTex:  texture_2d<f32>;
-
 struct FragInput {
   @location(0) normal:   vec3<f32>,
   @location(1) uv:       vec2<f32>,
   @location(2) worldPos: vec3<f32>,
 }
 
+fn getBiomeColor(id: f32) -> vec3f {
+    let biome = i32(round(id));
+    if (biome == 1) { return vec3f(0.86, 0.76, 0.42); } // Desert
+    if (biome == 2) { return vec3f(0.55, 0.50, 0.45); } // Mountains
+    if (biome == 3) { return vec3f(0.42, 0.60, 0.24); } // Valley
+    if (biome == 4) { return vec3f(0.22, 0.28, 0.14); } // Swamp
+    if (biome == 5) { return vec3f(0.20, 0.40, 0.12); } // Forest
+    return vec3f(0.34, 0.52, 0.18); // Grassland (default)
+}
+
+fn getHeightBlendedColor(biomeId: f32, worldY: f32) -> vec3f {
+    let baseColor = getBiomeColor(biomeId);
+    let rockColor = vec3f(0.52, 0.48, 0.44);
+    let snowColor = vec3f(0.92, 0.93, 0.95);
+
+    // Blend toward rock at mid-heights (>= 60 world units)
+    let rockBlend = clamp((worldY - 60.0) / 120.0, 0.0, 1.0);
+    let midColor = mix(baseColor, rockColor, rockBlend);
+
+    // Blend toward snow at very high elevations (>= 300 world units)
+    let snowBlend = clamp((worldY - 300.0) / 150.0, 0.0, 1.0);
+    return mix(midColor, snowColor, snowBlend);
+}
+
 @fragment
 fn fs_main(f: FragInput) -> @location(0) vec4<f32> {
-  let grassColor = textureSample(grassTex, terrainSampler, f.uv * 8.0).rgb;
-  let rockColor  = textureSample(rockTex,  terrainSampler, f.uv * 6.0).rgb;
-
-  let slope  = clamp(f.normal.y, 0.0, 1.0);
-  let blend  = smoothstep(0.55, 0.80, slope);
-  let albedo = mix(rockColor, grassColor, blend);
+  let albedo = getHeightBlendedColor(uniforms.biomeData.x, f.worldPos.y);
 
   let lightDir = normalize(vec3<f32>(0.5, 1.2, 0.4));
   let diffuse  = max(dot(normalize(f.normal), lightDir), 0.0);

src/shaders/terrain.vert.wgsl

@@ -3,6 +3,8 @@ struct Uniforms {
   worldOffset: vec4<f32>,
   cameraPos:   vec4<f32>,
   fogParams:   vec4<f32>,
+  _pad:        vec4<f32>,
+  biomeData:   vec4<f32>,
 }
 @group(0) @binding(0) var<uniform> uniforms: Uniforms;
 

wasm/biome/biome_test.go

@@ -215,6 +215,30 @@ t.Errorf("vertical spike at (%d,%d): diff=%.4f > %.4f", row, col, diff, maxAllow
 }
 }
 
+func TestBiomeNoiseProvidesVariety(t *testing.T) {
+	seed := 42
+	biomesSeen := make(map[biome.BiomeType]bool)
+	var minTemp, maxTemp float64 = 1.0, 0.0
+	for x := -10000.0; x <= 10000; x += 500 {
+		for z := -10000.0; z <= 10000; z += 500 {
+			temp, _ := biome.GetBiomeParams(x, z, seed)
+			if temp < minTemp {
+				minTemp = temp
+			}
+			if temp > maxTemp {
+				maxTemp = temp
+			}
+			biomesSeen[biome.GetBiomeAt(x, z, seed)] = true
+		}
+	}
+	if maxTemp-minTemp < 0.4 {
+		t.Errorf("temperature range too narrow: [%.3f, %.3f] - biome noise is not varying enough", minTemp, maxTemp)
+	}
+	if len(biomesSeen) < 3 {
+		t.Errorf("only %d biome types seen in 20k×20k area - expected at least 3", len(biomesSeen))
+	}
+}
+
 func TestGaussianBiomeWeights_SumToOne(t *testing.T) {
 // Blending weights must sum to 1.0 at every climate point.
 testPoints := [][2]float64{

wasm/biome/registry.go

@@ -30,7 +30,7 @@ var DefaultBiomes = map[BiomeType]BiomeDefinition{
 		Lacunarity:       2.2,
 		Persistence:      0.60,
 		Amplitude:        1.0,
-		HeightMultiplier: 3.0,
+		HeightMultiplier: 10.0,
 	},
 	Valley: {
 		Name:             "Valley",

wasm/biome/selector.go

@@ -23,17 +23,18 @@ func GetBiomeAt(worldX, worldZ float64, seed int) BiomeType {
 // values are used for smooth biome blending.
 func GetBiomeParams(worldX, worldZ float64, seed int) (temperature, humidity float64) {
 	// Domain warping: shift sample coordinates to create non-linear biome boundaries.
-	wx := noise.FBm(worldX*warpNoiseScale, worldZ*warpNoiseScale, seed+1001, 3, warpNoiseScale, 2.0, 0.5)
-	wz := noise.FBm((worldX+1000)*warpNoiseScale, (worldZ+1000)*warpNoiseScale, seed+1001, 3, warpNoiseScale, 2.0, 0.5)
+	// Pass raw world coords; FBm handles frequency scaling internally.
+	wx := noise.FBm(worldX, worldZ, seed+1001, 3, warpNoiseScale, 2.0, 0.5)
+	wz := noise.FBm(worldX+500000, worldZ+500000, seed+1001, 3, warpNoiseScale, 2.0, 0.5)
 	sx := worldX + wx*warpStrength
 	sz := worldZ + wz*warpStrength
 
 	// Temperature noise — seed offset to differ from terrain and humidity noise.
-	tempRaw := noise.FBm(sx*biomeNoiseScale, sz*biomeNoiseScale, seed+1000, 3, biomeNoiseScale, 2.0, 0.5)
+	tempRaw := noise.FBm(sx, sz, seed+1000, 3, biomeNoiseScale, 2.0, 0.5)
 	temperature = (tempRaw + 1.0) * 0.5
 
-	// Humidity noise — positionally offset to de-correlate from temperature.
-	humidRaw := noise.FBm((sx+5000)*biomeNoiseScale, (sz+5000)*biomeNoiseScale, seed+2000, 3, biomeNoiseScale, 2.0, 0.5)
+	// Humidity noise — large offset to de-correlate from temperature.
+	humidRaw := noise.FBm(sx+500000, sz+500000, seed+2000, 3, biomeNoiseScale, 2.0, 0.5)
 	humidity = (humidRaw + 1.0) * 0.5
 	return
 }