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Intriguing! I was under the illusion that webGL was emit-only, and that Javascript programs can't read back any output generated by WebGL. I must be wrong or out of date :) So how does the script do it?

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With the right extensions, you can render to a texture which can be sampled from in subsequent draw calls.

The framebuffer object extensions that allow you to write to 32-bit RGBA textures are widely supported on desktops and mobiles (OpenGL ES 2). But floating point textures are not. So, shaders resort to encoding 32-bit floats in RGBA textures. This unfortunately isn't a simple cast. More here: http://aras-p.info/blog/2009/07/30/encoding-floats-to-rgba-t...

I am storing all data in textures, and you can read data from textures by binding the texture to an fbo, set that fbo to the default fbo, and then read the data with `glReadPixels`

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