Simple fade transition

fade.glsl

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

void main() {
  vec2 p = gl_FragCoord.xy / resolution.xy;
  gl_FragColor = mix(texture2D(from, p), texture2D(to, p), progress);
}

uniforms.default.json

{}