precision mediump float;
float circle_transparency(vec2 uv, vec2 center, float radius) {
    float d = length(uv - center) - radius; // if d positive, then is outside circle
    return clamp(d,0.0,1.0); // if d between 0 and 1, blend for anti-aliasing.
}

void main(void) {
    vec2 uv = gl_FragCoord.xy;
    vec2 center = iResolution.xy * 0.5;
    float radius = 0.25 * iResolution.y;

    vec3 background = vec3(.2);
    vec3 foreground = vec3(1,0,0);
    float alpha = circle_transparency(uv, center, radius);

uniform sampler2D startImage;
uniform sampler2D endImage;
uniform float progress;
uniform vec4 backColor;
uniform vec2 center;
precision mediump float;
/*{
    "CATEGORIES": [
        "Wipe"
    ],
    "CREDIT": "Automatically converted from https://www.github.com/gl-transitions/gl-transitions/tree/master/circle.glsl",
    "DESCRIPTION": "",
    "INPUTS": [
        {

precision mediump float;

uniform float u_time;
uniform vec2 u_resolution;

// https://iquilezles.org/articles/distfunctions2d/
float sdfCircle(vec2 p, float r) {
  // note: sqrt(pow(p.x, 2.0) + pow(p.y, 2.0)) - r;
  return length(p) - r;
}

void main() {
  // note: set up uv coordinates
  vec2 uv = gl_FragCoord.xy / u_resolution;