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// Domain-warped noise field
uniform vec2  uResolution;
uniform float uTime;
uniform vec2  uMouse;

float fbm(vec2 p) {
    float sum = 0.0;
    float amp = 0.5;
    for (int i = 0; i < 4; i++) {
        sum += amp * snoise(p);
        p   *= 2.02;
        amp *= 0.5;
    }
    return sum;
}

void main() {
    vec2 p = (gl_FragCoord.xy - 0.5 * uResolution) / uResolution.y;
    float t = uTime * 0.045;

    // Each layer displaces the next one's sample point.
    vec2 q = vec2(fbm(p * F + vec2(0.0, t)),
                  fbm(p * F + vec2(5.2, 1.3 - t)));
    vec2 r = vec2(fbm(p * F + 2.2 * q + 1.7),
                  fbm(p * F + 2.2 * q + 8.3));

    float f = fbm(p * F + 2.4 * r + uMouse * pull);
    float v = smoothstep(0.56, 1.0, f * 0.5 + 0.5);

    outColor = vec4(mix(lo, hi, v), v * vignette);
}