// hexagonalize — generated from https://github.com/gl-transitions/gl-transitions/blob/master/transitions/hexagonalize.glsl
// Author: Fernando Kuteken
// License: MIT
// Description: Both images turn into hexagons, crossfade, then sharpen again

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 int steps; 

uniform float horizontalHexagons; 

struct Hexagon {
  float q;
  float r;
  float s;
};

Hexagon createHexagon(float q, float r){
  Hexagon hex;
  hex.q = q;
  hex.r = r;
  hex.s = -q - r;
  return hex;
}

Hexagon roundHexagon(Hexagon hex){
  
  float q = floor(hex.q + 0.5);
  float r = floor(hex.r + 0.5);
  float s = floor(hex.s + 0.5);

  float deltaQ = abs(q - hex.q);
  float deltaR = abs(r - hex.r);
  float deltaS = abs(s - hex.s);

  if (deltaQ > deltaR && deltaQ > deltaS)
    q = -r - s;
  else if (deltaR > deltaS)
    r = -q - s;
  else
    s = -q - r;

  return createHexagon(q, r);
}

Hexagon hexagonFromPoint(vec2 point, float size) {
  
  point.y /= ratio;
  point = (point - 0.5) / size;
  
  float q = (sqrt(3.0) / 3.0) * point.x + (-1.0 / 3.0) * point.y;
  float r = 0.0 * point.x + 2.0 / 3.0 * point.y;

  Hexagon hex = createHexagon(q, r);
  return roundHexagon(hex);
  
}

vec2 pointFromHexagon(Hexagon hex, float size) {
  
  float x = (sqrt(3.0) * hex.q + (sqrt(3.0) / 2.0) * hex.r) * size + 0.5;
  float y = (0.0 * hex.q + (3.0 / 2.0) * hex.r) * size + 0.5;
  
  return vec2(x, y * ratio);
}

vec4 transition (vec2 uv) {
  
  float dist = 2.0 * min(progress, 1.0 - progress);
  dist = steps > 0 ? ceil(dist * float(steps)) / float(steps) : dist;
  
  float size = (sqrt(3.0) / 3.0) * dist / horizontalHexagons;
  
  vec2 point = dist > 0.0 ? pointFromHexagon(hexagonFromPoint(uv, size), size) : uv;

  return mix(getFromColor(point), getToColor(point), 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);
}