Now, I admit I'm not a shader expert. Infact, before GLSL appeared over a year back I'd pretty much avoided them as I couldnt be bothered to work it all out.

So, that given how come I can work out that fragment shaders can only read from buond textures and other programmer speicified varibles, yet for some reason others cant do the same?

I mean, its not fricken rocket science, a quick look at the pipeline should clue you into the current restrictions of fragment shaders, that they can read from textures and spit out colours. If you feel like you need it cleared up any more then look at the spec or read a book they should also give you a pretty clear hint as to what a shader can and cant do.

So, with that in mind, why do people not use a few moments of brain power, possibly less than required to make a post on the subject, to work out that you CANT read from the framebuffer/stencil/accumulation/z-buffer in a shader.

seriously, it blows my mind at times that people are looking into this kinda stuff without coving the basics of what they are looking into can do...