I’m using ARB_vertex_program and I need to get a color of a pixel which was previously on the place where a new pixel would be set. Can I somehow get a color of a previous pixel in a fragment program (for example, to make blending or something like this)?
I can use standard OpenGL functions to make blending, but these functions do not exactly apply to my task. The other way is to get a pixel color from a color buffer and to pass it to a fragment program as a parameter, but it is too slow.
If I can get a color of a previous pixel in some other ways, please, tell me how.