float circ(vec2 p){
    return length(p) - .5;   
}

// http://www.iquilezles.org/www/articles/palettes/palettes.htm
// As t runs from 0 to 1 (our normalized palette index or domain), 
//the cosine oscilates c times with a phase of d. 
//The result is scaled and biased by a and b to meet the desired constrast and brightness.
vec3 cosPalette( float t, vec3 a, vec3 b, vec3 c, vec3 d )
{
    return a + b*cos( 6.28318*(c*t+d) );
}

vec3 sinPalette( float t, vec3 a, vec3 b, vec3 c, vec3 d )
{
    return a + b*sin( 6.28318*(c*t+d) );
}

vec2 lissajous(float t, float a, float b, float del){
    return vec2(sin(a*t+del),sin(b*t));
}

// Repeat around the origin by a fixed angle.
// For easier use, num of repetitions is use to specify the angle.
float pModPolar(inout vec2 p, float repetitions) {
    float angle = 6.2831/repetitions;
    float a = atan(p.y, p.x) + angle/2.;
    float r = length(p);
    float c = floor(a/angle);
    a = mod(a,angle) - angle/2.;
    p = vec2(cos(a), sin(a))*r;
    return c;
}


void main()
{
    gl_FragColor = vec4(black,1.);
    
    vec2 pos = uv();
    
    pModPolar(pos, 20.0);
    
    vec2 lisa = lissajous(pos.x*20.0, 5.0*sin(time*.01), 2.0, 3.14);
    pos += lisa;
    
    
    vec3 cosp = cosPalette(time,vec3(0.5),vec3(0.5),vec3(.3),vec3(pos.x*.2,pos.y*.2,pos.x*pos.y*.2));
    
    vec3 col = vec3(circ(pos))*cosp;
    
    // output: pixel color
    gl_FragColor = min(vec4( col, 1.0 ), vec4(.8));
    // we take the min of the output color and a very light grey color because The Force makes 
    // all of their controls white at the bottom all white without any sort of outline, which is 
    // silly, so you can make it vec4(col.rgb,1.0) in other softwares or if you dont care 
    // about seeing the controls
}