#version 100

varying highp vec2 pos;
varying highp vec2 start;

void main(){
    
    highp vec2 z = start;
    
    int i = 0;
    for (i = 0; i < 7; i++) {
        highp vec2 zsq = z*z;
        if(zsq.x + zsq.y > 16.0) break;
        
        highp float t = zsq.x - zsq.y + pos.x;
        z.y = 2.0*z.x*z.y + pos.y;
        z.x = t;
    }
    
    gl_FragColor = vec4(float(i) / 7.0);
    gl_FragColor.bg = 0.5 * sin(z) + 0.5;
}