I was looking through the Fragment Program specs and began wondering. Is there a way to determine the color of a destination point? When using color blending, there is a source and destination, the source being the incoming color/fragment. I want to know if a fragment program can use that color, along with its alpha value and depth in calculations. The first and probably obvious reason for this is to make my own color blending routines.
Next, I have some ideas on transparency and refraction code I would like to try out, but I need to be able to know what the color “behind” an incoming fragment is. Any thoughts or suggestions? Thanks.