data/shaders/terrain-noise.frag

//
// Description : Array and textureless GLSL 3D simplex noise function.
//      Author : Ian McEwan, Ashima Arts.
//  Maintainer : ijm
//     Lastmod : 20110409 (stegu)
//     License : Copyright (C) 2011 Ashima Arts. All rights reserved.
//               Distributed under the MIT License. See LICENSE file.
//

#ifdef GL_ES
#define MEDIUMP mediump
#else
#define MEDIUMP
#endif

uniform float time;
uniform MEDIUMP vec2 uvScale;
varying vec2 vUv;

vec4 permute(vec4 x)
{
    return mod(((x * 34.0) + 1.0) * x, 289.0);
}

vec4 taylorInvSqrt(vec4 r)
{
    return 1.79284291400159 - 0.85373472095314 * r;
}

float snoise(vec3 v)
{
    const vec2 C = vec2(1.0 / 6.0, 1.0 / 3.0);
    const vec4 D = vec4(0.0, 0.5, 1.0, 2.0);

    // First corner
    vec3 i  = floor(v + dot(v, C.yyy));
    vec3 x0 = v - i + dot(i, C.xxx);

    // Other corners
    vec3 g = step(x0.yzx, x0.xyz);
    vec3 l = 1.0 - g;
    vec3 i1 = min(g.xyz, l.zxy);
    vec3 i2 = max(g.xyz, l.zxy);

    vec3 x1 = x0 - i1 + 1.0 * C.xxx;
    vec3 x2 = x0 - i2 + 2.0 * C.xxx;
    vec3 x3 = x0 - 1. + 3.0 * C.xxx;

    // Permutations
    i = mod(i, 289.0);
    vec4 p = permute(permute(permute(
                    i.z + vec4(0.0, i1.z, i2.z, 1.0))
                + i.y + vec4(0.0, i1.y, i2.y, 1.0))
            + i.x + vec4(0.0, i1.x, i2.x, 1.0));

    // Gradients
    // (N*N points uniformly over a square, mapped onto an octahedron.)

    float n_ = 1.0 / 7.0; // N=7

    vec3 ns = n_ * D.wyz - D.xzx;

    vec4 j = p - 49.0 * floor(p * ns.z *ns.z);  //  mod(p,N*N)

    vec4 x_ = floor(j * ns.z);
    vec4 y_ = floor(j - 7.0 * x_);    // mod(j,N)

    vec4 x = x_ *ns.x + ns.yyyy;
    vec4 y = y_ *ns.x + ns.yyyy;
    vec4 h = 1.0 - abs(x) - abs(y);

    vec4 b0 = vec4(x.xy, y.xy);
    vec4 b1 = vec4(x.zw, y.zw);


    vec4 s0 = floor(b0) * 2.0 + 1.0;
    vec4 s1 = floor(b1) * 2.0 + 1.0;
    vec4 sh = -step(h, vec4(0.0));

    vec4 a0 = b0.xzyw + s0.xzyw * sh.xxyy;
    vec4 a1 = b1.xzyw + s1.xzyw * sh.zzww;

    vec3 p0 = vec3(a0.xy, h.x);
    vec3 p1 = vec3(a0.zw, h.y);
    vec3 p2 = vec3(a1.xy, h.z);
    vec3 p3 = vec3(a1.zw, h.w);

    // Normalise gradients

    vec4 norm = taylorInvSqrt(vec4(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

    vec4 m = max(0.6 - vec4(dot(x0, x0), dot(x1, x1), dot(x2, x2), dot(x3, x3)), 0.0);
    m = m * m;
    return 42.0 * dot(m*m, vec4(dot(p0, x0), dot(p1, x1),
                dot(p2, x2), dot(p3, x3)));
}

float surface3(vec3 coord)
{
    float n = 0.0;

    n += 1.0 * abs(snoise(coord));
    n += 0.5 * abs(snoise(coord * 2.0));
    n += 0.25 * abs(snoise(coord * 4.0));
    n += 0.125 * abs(snoise(coord * 8.0));

    return n;
}

void main(void)
{
    vec3 coord = vec3(vUv.x, uvScale.y - vUv.y, -time);
    float n = surface3(coord);

    gl_FragColor = vec4(vec3(n, n, n), 1.0);
}