13.frag

uniform float time;
uniform vec2 resolution;
out vec4 fragColor;

float random(in vec2 st) {
    return fract(sin(dot(st.xy, vec2(12.9898, 78.233))) *
        43758.5453123);
}

float noise(in vec2 st) {
    vec2 i = floor(st);
    vec2 f = fract(st);

    // Four corners in 2D of a tile
    float a = random(i);
    float b = random(i + vec2(1.0, 0.0));
    float c = random(i + vec2(0.0, 1.0));
    float d = random(i + vec2(1.0, 1.0));
    vec2 u = f * f * (3.0 - 2.0 * f);
    return mix(a, b, u.x) +
        (c - a) * u.y * (1.0 - u.x) +
        (d - b) * u.x * u.y;
}
#define OCTAVES 4
float fbm(in vec2 st) {
    float value = 0.0;
    float amplitude = .5;
    float frequency = 0.;
    for (int i = 0 ; i < OCTAVES ; i ++) {
        value += amplitude * noise(st);
        st *= 2.;
        amplitude *= .5;
    }
    return value;
}

void main() {
    vec2 st = gl_FragCoord.xy / resolution.xy;
    st.x *= resolution.x / resolution.y;
    vec3 color = vec3(0.0);
    color += fbm(st * 18.3 + vec2(time * 7.1, time * 10.3));
    color *= fbm(st * 12.2 + vec2(time * 5.2, time * 10.2));
    color *= fbm(st * 10.2 + vec2(time * 3.3, time * 10.1));
    color = mod(color * 12.0, 1.0);
    vec4 fcolor = vec4(color, 1.0);
    fragColor = TDOutputSwizzle(fcolor);
}