GCDrawKit is a Cocoa Vectror Graphic Framework from AppTree attempts to do for drawing applications what Cocoa’s text system does for text applications. It provides a set of interrelated classes which implement a complete vector-drawing framework, while trying to maximise flexibility and remaining agnostic about the final end use of the application.

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.