simplexNoise3D

fn snoise3D_permute4(x: vec4<f32>) -> vec4<f32> {
    return ((x * 34.0 + 1.0) * x) % vec4<f32>(289.0);
}

fn snoise3D_taylorInvSqrt4(r: vec4<f32>) -> vec4<f32> {
    return 1.79284291400159 - 0.85373472095314 * r;
}

fn snoise3D(v: vec3<f32>) -> f32 {
    let C = vec2<f32>(1.0 / 6.0, 1.0 / 3.0);
    let D = vec4<f32>(0.0, 0.5, 1.0, 2.0);
    
    // First corner
    var i = floor(v + dot(v, C.yyy));
    let x0 = v - i + dot(i, C.xxx);
    
    // Other corners
    let g = step(x0.yzx, x0.xyz);
    let l = 1.0 - g;
    let i1 = min(g.xyz, l.zxy);
    let i2 = max(g.xyz, l.zxy);
    
    // x0 = x0 - 0. + 0.0 * C
    let x1 = x0 - i1 + 1.0 * C.xxx;
    let x2 = x0 - i2 + 2.0 * C.xxx;
    let x3 = x0 - 1.0 + 3.0 * C.xxx;
    
    // Permutations
    i = i % vec3<f32>(289.0);
    let p = snoise3D_permute4(snoise3D_permute4(snoise3D_permute4(
        i.z + vec4<f32>(0.0, i1.z, i2.z, 1.0)) +
        i.y + vec4<f32>(0.0, i1.y, i2.y, 1.0)) +
        i.x + vec4<f32>(0.0, i1.x, i2.x, 1.0));
    
    // Gradients
    // (N*N points uniformly over a square, mapped onto an octahedron.)
    let n_ = 1.0 / 7.0; // N=7
    let ns = n_ * D.wyz - D.xzx;
    
    let j = p - 49.0 * floor(p * ns.z * ns.z); // mod(p,N*N)
    
    let x_ = floor(j * ns.z);
    let y_ = floor(j - 7.0 * x_); // mod(j,N)
    
    let x = x_ * ns.x + ns.yyyy;
    let y = y_ * ns.x + ns.yyyy;
    let h = 1.0 - abs(x) - abs(y);
    
    let b0 = vec4<f32>(x.xy, y.xy);
    let b1 = vec4<f32>(x.zw, y.zw);
    
    let s0 = floor(b0) * 2.0 + 1.0;
    let s1 = floor(b1) * 2.0 + 1.0;
    let sh = -step(h, vec4<f32>(0.0));
    
    let a0 = b0.xzyw + s0.xzyw * sh.xxyy;
    let a1 = b1.xzyw + s1.xzyw * sh.zzww;
    
    var p0 = vec3<f32>(a0.xy, h.x);
    var p1 = vec3<f32>(a0.zw, h.y);
    var p2 = vec3<f32>(a1.xy, h.z);
    var p3 = vec3<f32>(a1.zw, h.w);
    
    // Normalise gradients
    let norm = snoise3D_taylorInvSqrt4(vec4<f32>(dot(p0, p0), dot(p1, p1), dot(p2, p2), dot(p3, p3)));
    p0 *= norm.x;
    p1 *= norm.y;
    p2 *= norm.z;
    p3 *= norm.w;
    
    // Mix final noise value
    var m = max(0.6 - vec4<f32>(dot(x0, x0), dot(x1, x1), dot(x2, x2), dot(x3, x3)), vec4<f32>(0.0));
    m = m * m;
    return 42.0 * dot(m * m, vec4<f32>(dot(p0, x0), dot(p1, x1), dot(p2, x2), dot(p3, x3)));
}