I am doing offscreen tiled rendering of very large output images using FBOs. In order to have the best performance, I am trying to create the largest FBO (and thus tile size) that I can. To that end, I am using GL_MAX_RENDERBUFFER_SIZE_EXT to retrieve the maximum possible size and then reducing it so that my FBO does not fill more than 1/16'th of the available VRAM.
Doing this seems to ensure that my renderer never fails on an out of memory or incomplete FBO error; however, with large enough FBOs (2002x1202 in one simple test case), I sometimes get a strange result. On my Quadro 8600M as well as on another Quadro FX 1700, I'll see bands of scan-lines in which either nothing is rendered or a few pixels are rendered of the wrong color. This does not happen if I constrain the size of the FBO to something smaller such as 500x500.
Does this ring any bells for anyone? I'm kind of stumped.
(I am using Windows XP Professional SP3)