Add raymarched fog

res/shaders/noise.wgsl

@@ -0,0 +1,40 @@
+// Noise functions from 42yeah:
+// https://blog.42yeah.is/rendering/2023/02/11/clouds.html
+fn rand(p: vec3<f32>) -> f32 {
+    return fract(sin(dot(p, vec3<f32>(12.345, 67.89, 412.12))) * 42123.45) * 2.0 - 1.0;
+}
+
+fn value_noise(p: vec3<f32>) -> f32 {
+    let u = floor(p);
+    let v = fract(p);
+    let s = smoothstep(vec3<f32>(0.0), vec3<f32>(1.0), v);
+
+    let a = rand(u);
+    let b = rand(u + vec3<f32>(1.0, 0.0, 0.0));
+    let c = rand(u + vec3<f32>(0.0, 1.0, 0.0));
+    let d = rand(u + vec3<f32>(1.0, 1.0, 0.0));
+    let e = rand(u + vec3<f32>(0.0, 0.0, 1.0));
+    let f = rand(u + vec3<f32>(1.0, 0.0, 1.0));
+    let g = rand(u + vec3<f32>(0.0, 1.0, 1.0));
+    let h = rand(u + vec3<f32>(1.0, 1.0, 1.0));
+
+    return mix(mix(mix(a, b, s.x), mix(c, d, s.x), s.y),
+               mix(mix(e, f, s.x), mix(g, h, s.x), s.y),
+               s.z);
+}
+
+fn fbm(p: vec3<f32>) -> f32 {
+    let num_octaves = 8;
+    var weight = 0.5;
+    var q = p;
+    var ret = 0.0;
+
+    for (var i = 0; i < num_octaves; i++)
+    {
+        ret += weight * value_noise(q);
+        q *= 2.0;
+        weight *= 0.5;
+    }
+
+    return saturate(ret);
+}