Guy English has posted the source code to a basic implementation of the Cocoa Shaders he talked about here. There’s code for conditional shaders, shader lists, clip shaders, and affine transform shaders. As far as shaders that actually draw there’s a solid color shader and one for drawing an image. The image shader lets you tweak the compositing operation, source rect, and set a drawing scale.

In Episode 18 we look at Core Image Filters with Andy Finnell.