DCenter.org tries to find out the reasons behind massive performance advantage of NVIDIA’s GeForce 6800-series hardware over competing RADEON X800 products in Doom III game. It appears that in addition to faster stencil calculations the GeForce 6 and FX graphics processors can boast with, the RADEON’s HyperZ technology works inefficiently in Doom III game, according to the web-site.
Even though the GeForce 6800 graphics cards offer extreme performance in Doom III and it does not seem that ATI’s CATALYST 4.9 beta help that much for the RADEON X800 hardware to catch-up, it seems that an ATI employee has found a yet another way to boost the speed of the X800 in Doom III, it is said over Beyond3D forums.
“When I read the shader it striked me how many texture accesses it did compared to the relatively short shader, even for stuff that could just as well be done with math for a small cost in instructions. Using a dependent texture lookup for POW evaluation makes a lot of sense for R200 level hardware due to instruction set limits, but for R300 and up it’s much better to just spend the three cycles it takes to evaluate POW with math instead of risking texture cache trashing with a dependent texture read, which may be much more costly, especially since the access pattern in this case will be far from linear. Also, using math improves the quality too, even though it may not be very noticable in this game,” said Humus, a well-known graphics specialists who now works for ATI Technologies.
While in some cases image quality after the modification suffers, the majority of observers noted that in general Doom III plays without degradation.
News source: Xbit Labs