HSVfade.glsl

#ifdef GL_ES
precision highp float;
#endif
uniform sampler2D from, to;
uniform float progress;
uniform vec2 resolution;

void main() {
  vec2 p = gl_FragCoord.xy / resolution.xy;
  vec3 a = texture2D(from, p).rgb;
  vec3 b = texture2D(to, p).rgb;
  vec3 m = mix(a, b, progress);
  gl_FragColor = vec4(m, 1.0);
}