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Old 09-03-04, 11:43 AM   #13
Abba Zabba
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Default Re: Would you like to see a benchmark demo using PS3.0?

I'm noticing some awful performance loss when switching from FP16 to FP32 (without a noticeable quality degradation though).
I'mma have 2-3 modes in the next demo where we can switch in between full and half precision using NV40 capabilities, and a regular ARB 2 path for the Radeons.
Coming soon
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Old 09-03-04, 12:20 PM   #14
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Default Re: Would you like to see a benchmark demo using PS3.0?

sounds good. keep us posted...
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Old 09-04-04, 12:01 AM   #15
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Default Re: Would you like to see a benchmark demo using PS3.0?

Forget SM3.0 on the current generation of hardware; it simply ain't fast enough.
Let me explain things before I get flamed away from these forums; I wrote this Blinn shader where light is attenuated according to a radial distance from the source.
Normally pixels residing outside of the light range will be darkened by an attenuation coefficient of zero magnitude leaving a shade equal to the ambient color of the material.
Those pixels don't need to go through the entire Blinn equation, and that's where branching could step forth, help identify and discard them early through the pixel pipe.
However, according to my findings, PS 3.0 is too slow on the current GeForce 6 range of cards to bring any advantage over the conventional way of computing illumination.

Here are few snapshots taken from a demo Iím working on right now, notice that in the PS3.0 lighting model, the pixels that were discarded are colored in green.

No branching

Branching
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Old 09-04-04, 01:18 AM   #16
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Default Re: Would you like to see a benchmark demo using PS3.0?

you're gonna need a complex lighting model to take advantages of bynamic branching, or you can apply a more strict limitation on those survived pixels(i.e. cull more unlit pixel, such as using a smaller radius on the light).
IIRC, nVIDIA said there're 2 cycles penalty for each jump in the pixel shader, and according to my own test earlier, the penalty is even bigger. That is to say, if your shader isn't complex enough, the number of culled instructions may be even smaller than the penalty.
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Old 09-04-04, 11:14 AM   #17
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Default Re: Would you like to see a benchmark demo using PS3.0?

I noticed that in the case of the softshadows demo that comes with the 8th revision of NVidia SDK.
Basically we fetch 8 samples of a shadow texture, check if all of em are within the shadow area, if it's the case, our current fragment will be unlit.
However if some of those pixels are lit, that means we're on a shadow edge and hence need to fetch up to 64 jittered samples for the softshadow effect.
If done in a pure PS 2.0 fashion, we're going to have to fetch 64 samples all the time, whereas with a PS3.0 hardware we can skip a lot of sampling by determining whether we're on an edge or not through the first initial 8 samples.
According the performance counter, PS 3.0 averages 45-50 FPS whereas PS2.0 can hardly maintain a frame rate of 30 FPS.
But as you can see, 45-50 ain't too good, at least in my opinion.
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Old 09-04-04, 11:22 AM   #18
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Default Re: Would you like to see a benchmark demo using PS3.0?

hmm ((45-30) / 30) * 100 = 50% ????
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Old 09-05-04, 02:35 AM   #19
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Default Re: Would you like to see a benchmark demo using PS3.0?

Well, I think 50% faster isn't that bad.
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