Glass brick
512 x 512 pixels

This texture, while still using the VTF format, is not so much a texture, as a set of instructions telling the Source engine how to refract the light.

To create this texture, I first used a base image of some glass bricks, from which I derive the usual normal map. However, there is an extra layer called the DUDV map (derivative map), which tells the engine how light passes through the texture.