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.opencode/skills/shader/references/glsl-procedural-textures-clouds-marble-wood-terrain.md

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+# Procedural Textures
+
+Practical texture recipes using fBm and noise. See `glsl-fbm-fractional-brownian-motion-turbulence-octaves.md` for core functions.
+
+## Clouds
+
+```glsl
+vec3 clouds(vec2 st, float time) {
+    float n = fbm(st * 3.0 + vec2(time * 0.1, 0.0));
+    n = smoothstep(0.4, 0.6, n);
+    return mix(vec3(0.4, 0.6, 0.9), vec3(1.0), n);
+}
+```
+
+## Marble
+
+```glsl
+float marble(vec2 st) {
+    float n = fbm(st * 4.0);
+    return sin(st.x * 10.0 + n * 20.0) * 0.5 + 0.5;
+}
+
+vec3 marbleColor(vec2 st) {
+    float v = marble(st);
+    vec3 white = vec3(0.95);
+    vec3 gray = vec3(0.3);
+    return mix(gray, white, v);
+}
+```
+
+## Wood Grain
+
+```glsl
+float wood(vec2 st) {
+    float n = fbm(st * 2.0);
+    float grain = sin((st.x + n * 0.5) * 50.0) * 0.5 + 0.5;
+    return mix(0.3, 0.6, grain);
+}
+
+vec3 woodColor(vec2 st) {
+    float v = wood(st);
+    vec3 light = vec3(0.76, 0.60, 0.42);
+    vec3 dark = vec3(0.44, 0.30, 0.18);
+    return mix(dark, light, v);
+}
+```
+
+## Terrain Height
+
+```glsl
+float terrain(vec2 st) {
+    float h = fbm(st * 2.0);
+    h += ridged(st * 4.0) * 0.5;
+    return h;
+}
+
+vec3 terrainColor(vec2 st) {
+    float h = terrain(st);
+    vec3 water = vec3(0.1, 0.3, 0.5);
+    vec3 sand = vec3(0.76, 0.70, 0.50);
+    vec3 grass = vec3(0.2, 0.5, 0.2);
+    vec3 rock = vec3(0.5, 0.5, 0.5);
+    vec3 snow = vec3(1.0);
+
+    if (h < 0.3) return mix(water, sand, h / 0.3);
+    if (h < 0.5) return mix(sand, grass, (h - 0.3) / 0.2);
+    if (h < 0.7) return mix(grass, rock, (h - 0.5) / 0.2);
+    return mix(rock, snow, (h - 0.7) / 0.3);
+}
+```
+
+## Fire / Smoke
+
+```glsl
+vec3 fire(vec2 st, float time) {
+    vec2 q = st;
+    q.y -= time * 0.5;  // Rise
+
+    float n = turbulence(q * 3.0);
+    n *= smoothstep(1.0, 0.0, st.y);  // Fade at top
+
+    vec3 col = mix(vec3(1.0, 0.0, 0.0), vec3(1.0, 1.0, 0.0), n);
+    return col * n;
+}
+
+vec3 smoke(vec2 st, float time) {
+    vec2 q = st;
+    q.y -= time * 0.2;
+
+    float n = fbm(q * 4.0);
+    n *= smoothstep(1.0, 0.0, st.y);
+
+    return vec3(0.3 + n * 0.3) * n;
+}
+```
+
+## Water Caustics
+
+```glsl
+float caustics(vec2 st, float time) {
+    vec2 p = st * 8.0;
+    float c = 0.0;
+    for (int i = 0; i < 3; i++) {
+        float t = time * (0.5 + float(i) * 0.1);
+        c += abs(sin(p.x + sin(p.y + t)) * sin(p.y + sin(p.x + t * 1.3)));
+        p *= 1.5;
+    }
+    return c / 3.0;
+}
+```
+
+## Lava
+
+```glsl
+vec3 lava(vec2 st, float time) {
+    float n = warpedFbm(st + vec2(time * 0.05));
+    vec3 cold = vec3(0.1, 0.0, 0.0);
+    vec3 hot = vec3(1.0, 0.3, 0.0);
+    vec3 bright = vec3(1.0, 0.9, 0.3);
+    return mix(cold, mix(hot, bright, n), smoothstep(0.3, 0.7, n));
+}
+```
+
+## Grass/Fur
+
+```glsl
+float grass(vec2 st) {
+    float n = fbm(st * 20.0);
+    float blade = smoothstep(0.3, 0.5, n);
+    return blade * (0.8 + fbm(st * 5.0) * 0.2);
+}
+```
+
+## Stone/Rock
+
+```glsl
+vec3 stone(vec2 st) {
+    float n1 = fbm(st * 4.0);
+    float n2 = fbm(st * 8.0 + 5.0) * 0.5;
+    float crack = smoothstep(0.48, 0.52, n1);
+    vec3 base = vec3(0.5 + n2 * 0.2);
+    return mix(base * 0.7, base, crack);
+}
+```