Rendering to pbuffers > 512 pixels introduces clipping
as a fallback on Intel 945 GM (950GMA graphics core) chipsets I am using pbuffers for rendering to offscreen buffers, as FBOs have been introduced only with the X3100 graphics core.
I noticed that when the pbuffer dimension exceeds 512 pixels (say, a 1024x1024 buffer), I get some unwanted clipping
about 600 pixels from the top left corner. So rendering is only done to a square region on the top left part of the pbuffer and the remaining parts are not rendered to. The viewport is properly set to (0,0, 1024,1024) pixel dimension and rendering is done in orthographic projection.
Are there any known workarounds, for example by resetting or redefining the OpenGL clip planes?