It just runs a lens mapping shader on the current texture unit. I have another version that does more advanced blending on the edges, but it runs really slow on my card, fo some reason. Anyway, here's the download link and a way too large screenshot. :)
Location of texture unit in shader:-1
Location of light position variable in shader:-1
Location of light radius variable in shader:-1
Location of Screen dimensions variable in shader:-1
Yeah, that's weird. My card complains without the f's. Replace the lens.frag text with this, if you don't mind. :)
No need to change anything now. I fixed the original download. Also, I think the reason I was getting errors without "n.nf" is because I rolled backed my driver for testing a while back and forgot to reinstall the updated one. ;)
Have you been properly unloading your textures? I haven't been able to delete the folders that you've been putting the textures in from these shader demos... Says it's in use :-/
The entire demo depends on the shader? :D Hardware accelerated functions...fancy that.