ButterflyWaveScrawler

Code

// Author: mandubian
// License: MIT
uniform float amplitude; // = 1.0
uniform float waves; // = 30.0
uniform float colorSeparation; // = 0.3
const float PI = 3.14159265358979323846264;
float compute(vec2 p, float progress, vec2 center) {
vec2 o = p*sin(progress * amplitude)-center;
// horizontal vector
vec2 h = vec2(1., 0.);
// butterfly polar function (don't ask me why this one :))
float theta = acos(dot(o, h)) * waves;
float s = sin((2.*theta - PI) / 24.);
float s2 = s * s;
return (exp(cos(theta)) - 2.*cos(4.*theta) + s2 * s2 * s) / 10.;
}
vec4 transition(vec2 uv) {
  if (progress <= 0.0) return getFromColor(uv);
  if (progress >= 1.0) return getToColor(uv);
  vec2 p = uv;
  float inv = 1. - progress;
  float disp = compute(p, progress, vec2(0.5, 0.5));
  vec4 texTo = getToColor(p + inv*disp);
  vec4 texFrom = vec4(
    getFromColor(p + progress*disp*(1.0 - colorSeparation)).r,
    getFromColor(p + progress*disp).g,
    getFromColor(p + progress*disp*(1.0 + colorSeparation)).b,
    1.0);
  return texTo*progress + texFrom*inv;
}