#version 100
precision highp float;

uniform vec2 resolution;
uniform vec2 location;
uniform double zoom;

uniform int max;

vec2 compsquare(vec2 z) {
    float temp = z.x;
    z.x = z.x * z.x - z.y * z.y;
    z.y = 2.0 * temp * z.y;
    return z;
}

vec3 hsv2rgb(vec3 hue){
    vec4 K = vec4(1.0, 2.0/3.0, 1.0/3.0, 3.0);
    vec3 p = abs(fract(hue.xxx + K.xyz) * 6.0 - K.www);
    return hue.z * mix(K.xxx, clamp(p - K.xxx, 0.0, 1.0), hue.y);
}

vec3 mandelbort(vec2 point){
    vec2 z = vec2(0.0);
    float iters = 0.0;
    for (iters = 0.0;   iters < float(max); ++iters)
    {
        z = compsquare(z) + point;
        if(dot(z, z) > 4.0) break;
    }
    float hue = iters / float(max);
    if(hue > 0.98) return vec3(0.0);
    return hsv2rgb(vec3(hue, 1.0, 1.0));
}

void main()
{
    vec2 uv = gl_FragCoord.xy / resolution;
    uv.x *= resolution.x / resolution.y;
    uv -= vec2(0.7, 0.5);
    uv *= zoom;
    uv -= location;

    gl_FragColor = vec4(mandelbort(uv), 1.0);
}