GLSL.io Transition (v1)

cube.glsl

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

uniform float persp;
uniform float unzoom;
uniform float reflection;
uniform float floating;

vec2 project (vec2 p) {
  return p * vec2(1.0, -1.2) + vec2(0.0, -floating/100.);
}

bool inBounds (vec2 p) {
  return all(lessThan(vec2(0.0), p)) && all(lessThan(p, vec2(1.0)));
}

vec4 bgColor (vec2 p, vec2 pfr, vec2 pto) {
  vec4 c = vec4(0.0, 0.0, 0.0, 1.0);
  pfr = project(pfr);
  if (inBounds(pfr)) {
    c += mix(vec4(0.0), texture2D(from, pfr), reflection * mix(1.0, 0.0, pfr.y));
  }
  pto = project(pto);
  if (inBounds(pto)) {
    c += mix(vec4(0.0), texture2D(to, pto), reflection * mix(1.0, 0.0, pto.y));
  }
  return c;
}

// p : the position
// persp : the perspective in [ 0, 1 ]
// center : the xcenter in [0, 1] \ 0.5 excluded
vec2 xskew (vec2 p, float persp, float center) {
  float x = mix(p.x, 1.0-p.x, center);
  return (
    (
      vec2( x, (p.y - 0.5*(1.0-persp) * x) / (1.0+(persp-1.0)*x) )
      - vec2(0.5-distance(center, 0.5), 0.0)
    )
    * vec2(0.5 / distance(center, 0.5) * (center<0.5 ? 1.0 : -1.0), 1.0)
    + vec2(center<0.5 ? 0.0 : 1.0, 0.0)
  );
}

void main() {
  vec2 op = gl_FragCoord.xy / resolution.xy;
  float uz = unzoom * 2.0*(0.5-distance(0.5, progress));
  vec2 p = -uz*0.5+(1.0+uz) * op;
  vec2 fromP = xskew(
    (p - vec2(progress, 0.0)) / vec2(1.0-progress, 1.0),
    1.0-mix(progress, 0.0, persp),
    0.0
  );
  vec2 toP = xskew(
    p / vec2(progress, 1.0),
    mix(pow(progress, 2.0), 1.0, persp),
    1.0
  );
  if (inBounds(fromP)) {
    gl_FragColor = texture2D(from, fromP);
  }
  else if (inBounds(toP)) {
    gl_FragColor = texture2D(to, toP);
  }
  else {
    gl_FragColor = bgColor(op, fromP, toP);
  }
}

uniforms.default.json

{"persp":0.7,"unzoom":0.3,"reflection":0.4,"floating":3}

~LICENSE

GLSL.io Transition License (v1): 
The MIT License (MIT)

Copyright (C) 2014 contact@glsl.io

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.