I recently found this cool shader app on the Appstore called “Shaderific” and it uses GLSL, which can be used in Codea Here’s a video demonstrating its capabilities. (Sorry if this sounds like spam, but it isn’t)
http://m.youtube.com/watch?feature=youtube_gdata_player&v=WbQTN4i6uEs&rdm=xj4d24hl&hl=en&gl=CA&guid=&client=mv-google
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@CodeaNoob not spam actually very helpful, I think its been posted before though