demoscene "shaders"

i want a framework sort of thing that let's you render images in "stages". you get to defined the stages and, like shader pipelines, you get a bit of control over how it prepares each stage (color bg, basic blend modes, previous stage sampling, etc). these stages then trigger a definable action for each pixel, much like a fragment shader.

the difference here is that this would be cpu bound probably because it's easier to write the framework for it and also i don't care about shader compilation. but yeah, each stage would get pixel coordinates and the relevant context, plus the previous stage's output.

something important would likely be to have additional buffers that operate independently to stages. they would be something you can read and write to from any stage.