OpenGL 4 Shading Language Cookbook - Third Edition

Refracting through both sides of the object

It is important to note that we have simplified things by only modeling the interaction of the light with one of the boundaries of the object. In reality, the light would be bent once when entering the transparent object, and again when leaving the other side. However, this simplification generally does not result in unrealistic-looking results. As is often the case in real-time graphics, we are more interested in a result that looks good than one that models the physics accurately.