julia.glsl

uniform float iOvertoneVolume;
void main() {
    vec2 z = (4*gl_FragCoord.xy)/iResolution.xy-2;
    vec2 c = vec2(iOvertoneVolume * 4, iOvertoneVolume * 4);
    int iter = 30;
    int i;
    for(i=0; i<iter; i++) {
        float x = (z.x * z.x - z.y * z.y) + c.x;
        float y = (z.y * z.x + z.x * z.y) + c.y;
        if((x * x + y * y) > 4.0) break;
        z.x = x;
        z.y = y;
    }
    gl_FragColor = vec4(0.0, cos(i), -cos(i), 1.0);
}