// circleopen — generated from https://github.com/gl-transitions/gl-transitions/blob/master/transitions/circleopen.glsl
// Author: gre
// License: MIT
// Description: A soft-edged circle opens from the center to reveal the incoming image

uniform shader _from;
uniform shader _to;
uniform float2 _resolution;
uniform float progress;
uniform float ratio;

vec4 getFromColor(vec2 uv) { return vec4(unpremul(_from.eval(vec2(uv.x, 1.0 - uv.y) * _resolution))); }
vec4 getToColor(vec2 uv) { return vec4(unpremul(_to.eval(vec2(uv.x, 1.0 - uv.y) * _resolution))); }

uniform float smoothness; 

uniform int opening; 

const vec2 center = vec2(0.5, 0.5);
const float SQRT_2 = 1.414213562373;

vec4 transition (vec2 uv) {
  float x = (opening != 0) ? progress : 1.-progress;
  float m = smoothstep(-smoothness, 0.0, SQRT_2*distance(center, uv) - x*(1.+smoothness));
  return mix(getFromColor(uv), getToColor(uv), (opening != 0) ? 1.-m : m);
}

half4 main(float2 _coord) {
  vec2 _uv = _coord / _resolution;
  vec4 _c = clamp(transition(vec2(_uv.x, 1.0 - _uv.y)), 0.0, 1.0);
  return half4(_c.rgb * _c.a, _c.a);
}