This is the first white paper I implemented, by Chris Wyman
An Approximate Image-Space Approach for Interactive Refraction.
It implements glass refraction, by doing a cubemap lookup, based on the refraction of a look-at ray direction to the surface. It then bends the ray at the surface of the mesh, and again at the back faces. The scene depth is rendered twice, once with the model’s backfaces, and once with the model’s front faces. which gives us a thickness map, to calculate the refraction angles from. The index of refraction for the material is being animated over the duration of the animation above.