#version 300 es

#define ITR 64

precision highp float;

uniform float iTime;
uniform vec2  iResolution;
uniform float zoom; //value=1,min=1,max=100,step=0.001
uniform float pos_x; //value=0,min=-2,max=2,step=0.001
uniform float pos_y; //value=0,min=-2,max=2,step=0.001
uniform float shadow_angle; //value=5.5,min=-0,max=6.28,step=0.001
uniform float shadow_strength; //value=0.5,min=-0,max=1,step=0.001

uniform vec3 bailout_color; //value=0,1,.7
uniform vec3 inner_color; //value=0,0,0
uniform vec3 shadow_color; //value=0,0,0

out vec4 fragColor;

vec2 vp2(vec2 v){
    return vec2(v.x * v.x - v.y * v.y, 2. * v.x * v.y);
}

int itr(vec2 c){
    vec2 z = vec2(0.);
    
    int i = 0;
    
    while(i < ITR){
        i++;
        z = vp2(z) + c;
        if(length(z) > 20.) return i;
    }
    return ITR;
}

bool shadow(vec2 c){
    vec2 d = c - vec2(3., -3.) / zoom;
    /*vec2 m = mix(c, d, .5);
    if(itr(m) == ITR) return true;
    return shadow(mix(d, m, .5), o - 1) || shadow(mix(m, c, .5), o - 1);*/
    for(float t = 0.; t < 1.; t += .015){
        if(itr(mix(d, c, t)) == ITR) return true;
    }
    return false;
}

float shadow2(vec2 c){
    float r = 0.;
    vec2 d = c - vec2(cos(shadow_angle), sin(shadow_angle)) * 3. / zoom;
    for(float t = 0.; t < 1.; t += .015){
        if(itr(mix(d, c, t)) == ITR) r += 0.015;
    }
    return r;
}

void main() {
    // Screen coordinate (from [-aspect, -1] to [aspect, 1])
    vec2 q   = (2. * gl_FragCoord.xy - iResolution) / iResolution.y;
    
    vec2 c = q * 2. / zoom + vec2(pos_x, pos_y);

    // Pixel color
    vec3 col = itr(c) == ITR ? inner_color : bailout_color;
    
    //if(shadow(c)) col *= .6;
    col = mix(col, shadow_color, shadow2(c) * shadow_strength);

    // Output
    fragColor = vec4(col, 1.);
}