Behind the Mask with Optimization and Catalyst AI
by Derek Wilson on September 26, 2004 12:05 AM EST- Posted in
- GPUs
Doom 3 Analysis
Here, we see a performance improvement when Catalyst AI is enabled and the shader replacement is made. The replacement that they make is in Id Software's specular highlights shader. The attenuation of the specular highlight was determined by a look-up table, but ATI discovered that replacing the look-up table with math runs faster on their hardware. The method by which ATI determined the proper mathematical function was simply to compare the final images rendered with both shaders and find the ones that were the closest. The mathematical result is definitely not exactly the same as the look-up table (becuase ATI is using 24bit precision math, which no one else uses).
D3D AF Tester with Catalyst AI set to High.
Click to enlarge.
D3D AF Tester with Catalyst AI disabled.
Click to enlarge.
We feel that this is a good optimization for ATI's hardware using application detection and shader replacement. Of course, rather than trial and error, it may be safer to go to the developer and ask them for the mathematical function that they used. We are still unclear on Id's take on this, and John Carmack has vocalized previously a distaste for shader replacement in certain situations.
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861 - Tuesday, September 28, 2004 - link
a great tool!dvinnen - Tuesday, September 28, 2004 - link
That's good. Only difference I saw was a little lighting difference on the floor. Even then very slight. Good for an extra 10 frams.gordon151 - Monday, September 27, 2004 - link
They did make some general opengl improvements that helped the 8500 in doom3 and some other opengl games in recent drivers, but thats pretty much it for that class.ksherman - Sunday, September 26, 2004 - link
it too bad all the new driver enhanchments have abandoned the Radeon 8500... I could really use some of the improvements in games... :(KillaKilla - Sunday, September 26, 2004 - link
Here it is: its the third image down. Don't know if the whole .net framework could make this imposible, but I don't see how this could have affect...http://www.anandtech.com/video/showdoc.aspx?i=1931...
KillaKilla - Sunday, September 26, 2004 - link
Would it be posible to implement the old, but very, very effective trick to see difference between AI settings? I'm talking about the thing where you hover your mouse over an image and it changes to the other image. I'll look for a link in a minute, if you don't see what I'm talking about.acemcmac - Sunday, September 26, 2004 - link
my question remains...... can I finally leave Cat 3.8 and MMC 8.7 if I want MMC and multimonitor support simultaneously???coldpower27 - Sunday, September 26, 2004 - link
I am glad ATI, is giving this suite allowing user to choose to use optimized drivers or not and having the ability to disable them as well. Good for ATI, now they are on par with Nvidia in this respect.