Ray-Tracing, meaningful performance metrics and alternatives? *spawn*

Discussion in 'Rendering Technology and APIs' started by Scott_Arm, Aug 21, 2018.

  1. DavidGraham

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    Those scenes are filled with subtle reflections though, only noticeable up close. Barrels, metallic surfaces, glass, walls of buildings .. etc, all are bouncing rays left and right. There were also the huge amount of bugs that caused performance degradation: Destructibles, foliage, and many objects through the bounding boxes expanding bug, all caused fps drops and compounded the cost of ray tracing needlessly.

    It looks like this is an early application of the hyprid system they are planning to deploy, they are calling it "hybrid ray trace/ray march system".

    https://www.eurogamer.net/articles/digitalfoundry-2018-battlefield-5-rtx-ray-tracing-analysis
     
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  2. dobwal

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    www.cbc.ca/i/caffeine/syndicate/mediaId=839625795653
     
  3. Kaotik

    Kaotik Drunk Member
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  4. DavidGraham

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    PCGH did their testing confirming the huge performance uplift.

    EDIT: for further calrifications.

    So before the patch, small foliage like grass and flying leaves were not reflected at all with DXR, but after the patch, DICE decided to make these objects be reflected but through SSR, on top of the ray traced reflections.

    Old Post:
    PCGH had several notes regarding the hybrid ray tracing methods, it looks like this is now used to make previously non-reflected objects, become visibly reflected. So some foliage (grass, flying leaves) and fine particles were previously not visible with the DXR reflections, after the patch they are now reflected through SSR, while the rest of the environment is reflected through ray tracing, large foliage like tree tops and branches are also ray traced.

    So the patch increases the image quality in this particular aspect, but introduces some limited SSR artifacts into the mix.

    http://www.pcgameshardware.de/Battl...5-Day-1-Patch-Direct-X-12-Nvidia-RTX-1269296/
     
    #524 DavidGraham, Dec 6, 2018
    Last edited: Dec 6, 2018
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  5. eloyc

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    So, indeed, a significant part of the improvement is because RT is pared back, not just because RT is optimized, per se.
     
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  6. DavidGraham

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    No, most of the uplift comes from bug fixes and optimizations, the elements now rendered with SSR were not even originally rendered with DXR , they are now being rendered in the new patch. All originally ray traced objects remain ray traced, they didn't undergo any degradation in quality.
     
  7. Shifty Geezer

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    That's quite the leap. It could just as well be that the RT aspect is improved, and the SSR reflections are added on top to solve the non-traced aspects. Is there any evidence the raytracing has been reduced?
     
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  8. eloyc

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    Cool, then. :)
     
  9. DavidGraham

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    So far, no. And we've had testing from TPU, PCGH, Guru3D, HardwareUnboxed .. etc.
    That's exactly what's happening.
     
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  10. Voxilla

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    Maybe somebody could do some new puddle investigation (old patch looks like):


    With the old patch reflections of leaves were missing.
    https://techreport.com/review/34267/examining-the-performance-of-nvidia-rtx-effects-in-battlefield-v
    "Part of that may be because the RTX reflection algorithm doesn't seem to try to account for the leaves blowing across the puddles of water in the scene, as the default reflections do, simply because casting that many rays on fast-moving objects may be too much to ask at the moment."
     
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  11. Shifty Geezer

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    Casting rays on 'fast moving objects' is no more costly than casting them on static objects, unless they aren't updating the BVH in realtime. They make it sound like when objects are fast moving, you need to cast more rays, almost as if looking for them. ;)
     
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  12. Kaotik

    Kaotik Drunk Member
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    I'm pretty sure vegetation was raytraced before in most scenarios, though there were buggy places too where it never appeared in reflections
     
  13. troyan

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    Looks like that casting rays has still a huge penalty in BF5. The difference between "Ultra" and "Low" is a lot smaller than between "Off" and "Low".
     
  14. Malo

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    Of course, and I wouldn't expect otherwise.
     
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  15. Scott_Arm

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    Ray casting on turing for a 1080p image with 1spp sounds like it takes slightly less than 1ms, which is significant, especially as you push to higher frame rates. At 120fps you're using 12% of your frame time just casting 1 ray per pixel. But with Turing shading is still the primary cost of ray-tracing, especially because non-coherent rays are probably not friendly to gpu cache. I'd like to see gpu power measurements before and after the patch. People said the gpus drew less power with ray-tracing on before the patch. I wonder how much closer the power gap is now, as kind of a proxy for gpu utilization.
     
  16. Voxilla

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    Question is are the falling leaves now reflected and if they do are the reflections with raytracing or SSR.
     
  17. Scott_Arm

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    If the falling leaves are reflected then they're SSR, because I doubt they'd be updating the BVH for such small dynamic geometry, but that doesn't mean they're casting any less DXR rays per scene. They screen is split into 16x16 tiles, and the rays are cast where they're needed most, up to a maxium % of the screen resolution. So Ultra is supposed to be 40% of the screen resolution. So if some rays are now SSR, the may still be casting the same number of DXR rays in the cases where SSR fails, improving the overall quality. In other words, SSR is not in itself proof that DXR resolution has been compromised. You'd have to find a scene with many off-screen reflections, like one of the city levels facing a building with many windows reflecting the scene behind the camera, and see what the quality difference and performance difference is. That would probably be the best case to test DXR performance without confusing any screen-space reflections that may muddy the waters.
     
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  18. troyan

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    But there isnt 1spp in Battlefield 5. "Low" has only 13% rays per resolution. And yet the performance impact is only slighty better than with Ultra (40%)...
     
  19. DavidGraham

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    Big ones yes (tree tops and big bushes), small ones no (grass, leaves). You can see that in the TechReport video and HardwareUnboxed. PCGH stated the same too. And now ComputerBase as well.

    https://www.computerbase.de/2018-12/battlefield-v-raytracing-dxr-patch-benchmark/2/

    I don't remember seeing them in under the ray tracing section in the bug report. They were excluded on purpose.
    Yes they are, but reflected in SSR.
     
    #539 DavidGraham, Dec 6, 2018
    Last edited: Dec 6, 2018
  20. Scott_Arm

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    Which means the bottleneck is not ray casting, but somewhere in the shading. They're not hitting good utilization rates of the other parts of the gpu when ray tracing reflections.
     

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