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Old 10-25-05, 10:52 AM   #52
Mr. Nice
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Join Date: Jul 2005
Location: UK
Posts: 43
Default Re: Quak4 - Quake 4 tuning tool for NVIDIA G70/NV40/NV30 Series GPU's

Originally Posted by pliflier
Does those numbers indicate that enable Super Ultra offset mapping will decrease performance by around 40%?
Sort of, for a start (AFK) those MP/s figures only take into account shader calculation time, and ignores memory latency, or simply lack of memory bandwidth (note the "1 cycle texture lookup" assumption, which is only true if the memory read request goes through far enough in advance for the data to be "on hand" when its needed (in CPU terms, this means the data is in the L1-cache, I don't know the exact details when it comes to GPU memory architecture)).
Also, they are only measures for the fragment in interaction.vxp, which only deals with lighting & texturing (both diffuse and specular), not everything else the GPU has to do (not least sorting out light/shadow casting, ie, which surfaces each light will fall on).
Both these factors mean that that "40%" decrease in practical terms is an upper bound for the possible impact on performance. Also note that is by comparison with no offset mapping at all (I think). I would like to see similar figures comparing it to the current "ultra" offset mapping.
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