The Book of Shaders is a nice introduction to fragment shaders. Like Toby Schachman’s Pixel Shaders book, it isn’t complete, but it has promise. And the accompanying shader editor has breakpoints.
Blog: #shaders
Shadershop
Shadershop is very cool. It’s Photoshop for shaders, letting you visually manipulate and compose functions in a way that’s easy and accessible.
