Next gen lighting technologies - voxelised, traced, and everything else *spawn*

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

  1. Scott_Arm

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    Those results look weird. Other sites have shown dx12 to be equal, at least with intel cpus. I've been using dx12 and performance seems roughly the same but with lower input lag because you can turn future frame rendering off.
     
  2. DavidGraham

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    Rasterization performance are an important part too. I am curious to know what made you think the game is limited only by it's RT performance.
    They are using an i7 7700K. Though BFV proved to demand a 6 core CPU for ray tracing and general gameplay.
     
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  3. Kaotik

    Kaotik Drunk Member
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    If it wasn't limited by RT performance, lowering RT quality wouldn't improve performance like it does now. Also the huge performance drop when nothing else changes when you enable RT.
    There's absolutely no indications of RT performance being hindered by anything other than RT hardware and possibly developer skills and driver quality.
     
  4. Samwell

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    It seems you have a misunderstanding how ray-tracing here works. One of the biggest problems of raytracing reflections is that you increase your shading workload massively. Shading on a Turing takes more time than RT for reflections.
    This talk from remedy explains a lot about it:


    Perf numbers for reflections on a Titan V:
    RT 5-9 ms
    Shading 3-5ms
    He explains Turing is around 5x faster than TV in RT, so 1-2 ms for RT, while the 3-5ms for shading don't change. And this is already with some optimizations for faster shading in place. Before, shading was even taking 2x the ms.
     
  5. DavidGraham

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    The huge drop happens because even when you think nothing is happening, the scene is constantly being ray traced for when stuff is happening, for an explosion or fire to be reflected on your gun (for example), or metallic surfaces, or water or ice .. etc.
    Incorrect, RT acceleration is only a part of the process, a huge chunk of it is shading heavy, and is carried out by the ALUs.
     
  6. Shifty Geezer

    Shifty Geezer uber-Troll!
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    It shouldn't be. If there are no surfaces requiring rays, which is purely reflections in this case, then there is no raytracing happening. Every pixel that has a reflective shader attached casts a ray as per the shaders, with each ray that results in a surface having that surface shader evaluated. Thus each reflective pixel is equivalent to another pixel shaded, in the case of 100% rays. However, rays are undersampled, so you have something of the order of 20% of the reflective pixels being additionally shaded (reflective surface shaders evaluated).
     
  7. Kaotik

    Kaotik Drunk Member
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    Of course I know every reflection is being constantly raytraced, but I was under the impression that all those are handled by the RT hardware, which further point to it being limiting factor, and that the shading portion wouldn't be (notably) heavier RT on vs off

    Edit: small clarification
     
    #567 Kaotik, Dec 18, 2018
    Last edited: Dec 18, 2018
  8. Scott_Arm

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    Ray tracing hardware is there to accelerate bvh traversal and accelerate triangle intersection which is typically very expensive. Shading is still a very heavy cost in rt and the dedicated hardware doesn't help. The other new cost is updating the bvh.

    Edit: Fixed my "Deficated hardware" auto-correct, which was kind of awesome.
     
    #568 Scott_Arm, Dec 19, 2018
    Last edited: Dec 19, 2018
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  9. milk

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    *shading is still a very heavy cost in RT REFLECTIONS. For shadowing, AO or some other possible uses, there is barely any shading involved, excluding filtering. Shadows will deficatedly be more efficient.

    EDIT: definitely
     
  10. keldor

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    The problem is that the reflection rays land all over the scene, with very little locality. This causes warp divergence, and completely trashes instruction caches since neighboring pixels can be executing code from a multitude of different shaders. Undersampling makes locality even worse.

    Engines will have to focus on cutting overhead by using a small number of generalized shaders rather than a large number of specialized shaders. There are a number of ways to do this, with different pros and cons, and reworking your entire shader system is a nice chunk of work, so we can expect it to take a while before we see results in games.
     
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  11. Ext3h

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    Just theoretically, would it be an option to:
    • Use a generic hit-shader which is solely responsible for re-dispatch, and records actual hit sorted by actual shader in the history with hit vector, list of dispached vectors, normal and UV. Only distinguishing flags for specular, diffuse and translucent dispatch, at most based on vertex/triangle attributes. Maybe even try pessimistic energy conservation estimation for early cut-off. Need to form buckets, to avoid global atomics.
    • Delayed evaluation of all hit types, sorted by specialized shader, annotating each recorded hit as 1x3 fp16 self contribution plus list of 3×3 fp16 color twist matrices. Use as many different shaders as you want, just iterate over all of them.
    • Delayed reduction of all ray trees based on computed PBR, depth first. Single shader again, pure random access + arithmetic, hopefully very little register pressure, because needs all the latency masking it can get.
     
    #571 Ext3h, Dec 19, 2018
    Last edited: Dec 20, 2018
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  12. Pinstripe

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    Sorry for just wading in here and asking something general:

    Are these RT cores also useful for non-Raytracing tasks? Can they be exploited for any other computational tasks like sound, physics or anything else? This would make the proposition for putting RT cores onto mainstream and lower-end cards actually sensible.
     
  13. pharma

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    Side question ... Is there a relationship between RT cores and ALU's?

    Edit: Clarification.
     
    #573 pharma, Dec 20, 2018
    Last edited: Dec 20, 2018
  14. DavidGraham

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    Yes they are, some people used them in Data lookup for complex lighting, and screen space physics (that are also world aware).
    https://blog.demofox.org/2018/11/16/how-to-data-lookups-via-raytracing/


    RTX 2060 is going to have RT cores. That would perhaps make it good for 900p60 or 1080p30 low DXR.
     
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  15. Malo

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    Soon we can have entry level 2030's for DLSS upscaled 320x200! I wonder if I still have my old CGA monitor around...
     
  16. milk

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    Old is new again. From deferred rendering to deferred ray tracing...
     
    #576 milk, Dec 21, 2018
    Last edited: Dec 21, 2018
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  17. Scott_Arm

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    Yes. Its in the turing white paper. there are two rt cores per eight sm's or something like that.
     
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  18. vipa899

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    How are those tech demo's different from BFV's RT tech`?



     
  19. iroboto

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    Design.
    One is made for real time gaming. With the challenges of trying to get RT working alongside some really optimized custom code for maximum performance/quality

    The other is just showcasing the limits of the technology.

    The reason the discussion is valid, say staying on topic for BFV, is because how RT is implemented in BFV has little to do with how it’s accelerated. How it’s accelerated direct impacts performance sure, but the fact that we see bugs/artefacts and what not, showcases other issues developers could be running into. And that worth discusssing.
     
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  20. vipa899

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    Yeah was thinking that, a game tailored and coded from the ground looking like that demo, that would be nice. Not saying BFV isnt, but the possibilitys seem great.
     
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