// heart — generated from https://github.com/gl-transitions/gl-transitions/blob/master/transitions/heart.glsl
// Author: gre
// License: MIT
// Description: A heart shape grows 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))); }

float inHeart (vec2 p, vec2 center, float size) {
  if (size==0.0) return 0.0;
  vec2 o = (p-center)/(1.6*size);
  float a = o.x*o.x+o.y*o.y-0.3;
  return step(a*a*a, o.x*o.x*o.y*o.y*o.y);
}
vec4 transition (vec2 uv) {
  return mix(
    getFromColor(uv),
    getToColor(uv),
    inHeart(uv, vec2(0.5, 0.4), progress)
  );
}

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);
}