Z-culling before T&L or...

Discussion in 'Architecture and Products' started by Bcnu, Apr 12, 2002.

  1. Bcnu

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    Investigating a frame rate problem with ATI Radeon cards and Everquest, I found that the observed problem *appears* to revolve around the engine drawing everything regardless of occlusion when T&L is enabled; frame rate is good except when in crowded areas (many figures or terrain objects)

    If T&L is turned off in the registry there is a dramatic improvement in frame rates in scenes with significant overdraw. Peak frame rates are down but overall frame rates are improved.

    So my hypothesis is (for this game engine at least) T&L and "HyperZ" optimizations are incompatible.

    Is this possible? If so, is it something that potentially could be resolved in software (either game engine or driver) or no? And why would it not be the case for a competing chip maker's T&L?
     
  2. Randell

    Randell Senior Daddy
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    hmm I had heard someone say that Operation Flashpoint works better on the 8500 with TnL turned off. I tried to compare this using FRAPS, but it appears FRAPS is now incompatible with Op. Flash (everything turns green). Playing the game didnt feel that different either way though.

    I Wonder if its a similar issue (TnL on/off not the FRAPs incompatibility).
     
  3. Xmas

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    No. T&L is geometry processing, HyperZ is part of the rendering pipeline. One does not affect the other.
    BTW, you always need T(&L), whether in hardware or in software. So it cannot be "incompatible" to anything.
     
  4. Bcnu

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    Sorry, I should try and be very clear instead of assuming that when I say T&L I meant GPU-based T&L instead of CPU-based T&L.

    Nonetheless I get your point. I can't think of any reason why one should affect the other either; but the observed behavior is that in scenes with large overdraw, frame rates are better with GPU-T&L off.

    Can anyone think of any reasons why this might be the case?
     
  5. 3dcgi

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    Maybe the 8500 is being inefficient when clipping to the viewport. When the cpu is used for t&l the app might be sending a lot less info, but depending on how the 8500 clips following t&l they might be slowing down. The setup engine might clip here and it could be the bottleneck. This is just speculation. Anyone else have another idea, agree, or disagree?
     
  6. Sharkfood

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    I play a LOT of Everquest, and do so on both a GF3 and a Radeon 8500.

    You must be specifically meaning under WinXP, as with both under Win98se, the 8500 just absolutely tears up the GF3 with or without UseTnL=TRUE/FALSE.

    Yes, the new DX8.0 Umbra engine is absurdly high in overdraw. It does not occlude at all and seems to pick back to front scene sorting more than any other sort order. HyperZ-II helps this game tremendously as the larger zones with the fattest textures absolutely fly on the 8500 (and the Kyro-II as well). It's a slideshow of 2-4 staggering fps on my GF3.

    If you are talking about WinXP, you might have simply uncovered another 8500 driver issue. My experience with EQ + WinXP lasted all of about 4 days and quickly reverted back to Win98se. The XP performance was substantially and remarkably poor, but this was back with the 6037 drivers. No idea if the issue has since been rectified with the 6048s or 6058s, but simply reverting to 98se and the 7206->9021 drivers, framerates more than doubled on the same hardware (both fresh installs). Nothing else I tried followed this trend as pronounced as EQ.

    For now, all variation of UseUmbra and UseTnL follow the *exact* same performance trends on my GF3 and my 8500, with the 8500 having a bit higher fillrate and HyperZ-II to help dramatically improve indoor towns (especially new Luclin towns like Shar Vahl and Shadow Haven). Disabling TnL be it in the registry or through EQ INI yields no noticeable improvement or detriment in overdraw heavy, town areas, and only has a marginal impact on outdoor zones. My GF3 follows the exact same trend with this switch.
     
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