// powerKaleido — generated from https://github.com/gl-transitions/gl-transitions/blob/master/transitions/powerKaleido.glsl
// Author: Boundless
// License: MIT
// Description: The image folds into an animated kaleidoscope before revealing the incoming one

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))); }

const float rad = 120.; 
const float deg = rad / 180. * 3.14159265358979;
uniform float scale; 
uniform float z; 
uniform float speed; 
vec2 refl(vec2 p,vec2 o,vec2 n)
{
	return 2.0*o+2.0*n*dot(p-o,n)-p;
}

vec2 rot(vec2 p, vec2 o, float a)
{
    float s = sin(a);
    float c = cos(a);
	return o + mat2(c, -s, s, c) * (p - o);
}

vec4 mainImage(vec2 uv)
{
  float dist = scale / 10.;
  vec2 uv0 = uv;
	uv -= 0.5;
  uv.x *= ratio;
  uv *= z;
  uv = rot(uv, vec2(0.0), progress*speed);
  
	float theta = progress*6.+3.14159265358979/.5;
	for(int iter = 0; iter < 10; iter++) {
    for(float i = 0.; i < 2. * 3.14159265358979; i+=deg) {
	    float ts = sign(asin(cos(i))) == 1.0 ? 1.0 : 0.0;
      if(((ts == 1.0) && (uv.y-dist*cos(i) > tan(i)*(uv.x+dist*+sin(i)))) || ((ts == 0.0) && (uv.y-dist*cos(i) < tan(i)*(uv.x+dist*+sin(i))))) {
        uv = refl(vec2(uv.x+sin(i)*dist*2.,uv.y-cos(i)*dist*2.), vec2(0.,0.), vec2(cos(i),sin(i)));
      }
    }
  }
  uv += 0.5;
  uv = rot(uv, vec2(0.5), progress*-speed);
  uv -= 0.5;
  uv.x /= ratio;
  uv += 0.5;
  uv = 2.*abs(uv/2.-floor(uv/2.+0.5));
  vec2 uvMix = mix(uv,uv0,cos(progress*3.14159265358979*2.)/2.+0.5);
  vec4 color = mix(getFromColor(uvMix),getToColor(uvMix),cos((progress-1.)*3.14159265358979)/2.+0.5);
	return color;
    
}
vec4 transition (vec2 uv) {
  vec4 color = mainImage(uv);
  return color;
}

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);
}