Alex Jackson wrote: >> Neither the i830 nor 965gm actually support GL_CLAMP natively (yay >> for d3d-only hardware). The different appearance is caused by the >> 965 driver mapping GL_CLAMP to GL_CLAMP_TO_BORDER while the i830 >> maps it to GL_CLAMP_TO_EDGE. The 965 driver has a comment saying >> that glconform prefers GL_CLAMP_TO_BORDER, while the i830 has a >> comment saying that the Windows GL driver uses GL_CLAMP_TO_EDGE. >> >> Several other drivers (savage, sis, unichrome) map GL_CLAMP to >> GL_CLAMP_TO_EDGE. >> >> What should I do now? >> >> 1) Fix the 965 driver to make GL_CLAMP work correctly (icky, and >> will be slower). 2) Use GL_CLAMP_TO_EDGE in the 965 driver. 3) Use >> GL_CLAMP_TO_BORDER in the i830 driver. 4) Nothing. > > If feasible, I'd make it configurable via a .drirc option whether to > map to GL_CLAMP_TO_EDGE or to GL_CLAMP_TO_BORDER, and make the former > the default. This change should be made in both 965 and i830, and > ideally in all the other drivers where the hardware natively supports > both GL_CLAMP_TO_EDGE and GL_CLAMP_TO_BORDER but not GL_CLAMP. > > Cursory Googling suggests that it's very common for other OpenGL > implementations to map GL_CLAMP to GL_CLAMP_TO_EDGE (even if that's > less conformant), and that consequently there're likely quite a few > other OpenGL applications floating around in the wild that use > GL_CLAMP when they mean GL_CLAMP_TO_EDGE. Indeed this show up every once in a while. A driconf option might be a good idea, but it doesn't solve the problem really for the hardware which indeed does support GL_CLAMP, unless you'd also introduce an option to make it non-conformant GL_CLAMP_TO_EDGE there too (which was suggested in the past). So the only real solution is to tell the app writers to fix their code. If you'd want to fix this in the driver without requiring user intervention, you'd need app detection (ugh).
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