Implemented Chris' double surface refraction...
Refraction
I would like to say, people’s (as least for people who did not see that before 🙂) eyes are really forgiving. I originally planned to do some research on RenderMonkey’s ToolSuite SDK to precompute normal distance Wyman [2005]. Now, without any precomputation, but crude and direct approximation. These pictures are only beautiful in pictures and too ugly in theory🙂. I think it could be used in game.
Since there are no work worth mentioning, just show some pictures.
Single Refraction


Double Refraction


More pictures:


References
[2005] C Wyman. An approximate image-space approach for interactive refraction. pages 1050–1053. ACM, 2005.