// PuzzleRight — generated from https://github.com/gl-transitions/gl-transitions/blob/master/transitions/PuzzleRight.glsl
// Author: JustKirillS
// License: MIT
// Description: The image splits into a grid of tiles that flip one by one to 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 ivec2 size; 
uniform float pause; 
uniform float dividerWidth; 

float rand(vec2 co) {
  return fract(sin(dot(co, vec2(12.9898, 78.233))) * 43758.5453);
}

float getDelta(vec2 p) {
  vec2 rectangleSize = 1.0 / vec2(size);
  vec2 rectanglePos = floor(vec2(size) * p);
  float top = rectangleSize.y * (rectanglePos.y + 1.0);
  float bottom = rectangleSize.y * rectanglePos.y;
  float left = rectangleSize.x * rectanglePos.x;
  float right = rectangleSize.x * (rectanglePos.x + 1.0);
  float minX = min(abs(p.x - left), abs(p.x - right));
  float minY = min(abs(p.y - top), abs(p.y - bottom));
  return min(minX, minY);
}

vec4 transition(vec2 uv) {
  if (progress < pause) {
    float currentProg = progress / pause;
    float a = 1.0;
    if (getDelta(uv) < dividerWidth) { a = 1.0 - currentProg; }
    return mix(vec4(0.0, 0.0, 0.0, 1.0), getFromColor(uv), a);
  } else if (progress < 1.0 - pause) {
    if (getDelta(uv) < dividerWidth) {
      return vec4(0.0, 0.0, 0.0, 1.0);
    }
    float currentProg = (progress - pause) / (1.0 - pause * 2.0);
    vec2 rectanglePos = floor(vec2(size) * uv);
    float r = rand(rectanglePos) - 0.1;
    float cp = smoothstep(0.0, 1.0 - r, currentProg);
    float rectangleSize = 1.0 / float(size.x);
    float delta = rectanglePos.x * rectangleSize;
    float offset = rectangleSize / 2.0 + delta;
    vec2 p = uv;
    p.x = (p.x - offset) / abs(cp - 0.5) * 0.5 + offset;
    vec4 a = getFromColor(p);
    vec4 b = getToColor(p);
    float s = step(abs(float(size.x) * (uv.x - delta) - 0.5), abs(cp - 0.5));
    return vec4(mix(b, a, step(cp, 0.5)).rgb * s, 1.0);
  } else {
    float currentProg = (progress - 1.0 + pause) / pause;
    float a = 1.0;
    if (getDelta(uv) < dividerWidth) { a = currentProg; }
    return mix(vec4(0.0, 0.0, 0.0, 1.0), getToColor(uv), a);
  }
}

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);
}