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The last caustics implementation I looked at (not this one) did the refraction stuff per-pixel in shaders based on a CPU-computed mesh deformation.

The more general answer to your question is that in fragment shaders, you can get "non-locality" via texture lookups inside the shader code.

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> you can get "non-locality" via texture lookups inside the shader code.

So you define a way to encode arbitrary non-local data as texture data, correct? That is, you're hacking textures as a store for arbitrary data instead of the image data that textures were originally designed to store?

Yep, exactly. There are a number of techniques that take advantage of this. Most notable are bump mapping and normal mapping.

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