VRS: Variable Rate Shading *spawn*

Discussion in 'Rendering Technology and APIs' started by BRiT, Jun 26, 2020.

  1. snc

    snc
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    isn't deferred now most popular in modern engines ?
     
  2. Nesh

    Nesh Double Agent
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    Well if thats the case, we are probably making a big deal of something that isnt much useful in most cases?
    So software VRS is probably the way to go?
    I still havent figured how VRS functions. To me it sounds like the same logic as LOD, applied on a shader level.
     
  3. Dural

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    I thought most engines were moving toward Forward+ as it's more flexible, I believe Doom Eternal and Modern Warfare both used it.
     
  4. function

    function None functional
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    Games can be a mixture of both, and you can use a mixture of hardware and software VRS within the same game depending on what you are doing.
     
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  5. snc

    snc
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    I think id software often has different approach then "mainstream" (like Virtual texturing in Rage)
     
  6. BRiT

    BRiT (>• •)>⌐■-■ (⌐■-■)
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    Have you looked over the Microsoft Blogs and DigitalFoundry snippets that have been posted previously on this subject?
     
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  7. cwjs

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    Deferred is still probably gonna stay the most popular, but forward (thanks to the rise of compute shaders and modern apis enabling "forward+" and clustered forward) is making a big resurgence. Deferred has huge memory/bandwidth costs and is harder to anti alias, among other drawbacks, but gives high performance for many lights and comes with stuff like a depth buffer for "free" so certain effects are much more universal in deferred renderers (good decals, some post processing, etc). Forward is (conceptually) straightforward, "easy" to produce a super clean image with, handles transparency well by default, but requires complex culling and binning setups to even kinda work fast enough in a real world case.

    There are increasingly many big AAA games based on forward renderers again. Modern Warfare and Doom Eternal are very noteworthy clustered forward games -- they look great and run amazingly fast compared to similar titles. It will continue to grow going forwards.
     
  8. snc

    snc
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    according to slide 104 from activision siggraph presentation software vrs is still better than hw even in forward + modern warfare engine
    https://research.activision.com/pub...able-rate-shading-in-call-of-duty--modern-war
    [​IMG]
     
    #48 snc, Feb 19, 2021
    Last edited: Feb 19, 2021
  9. cwjs

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    Yeah, for their renderer. Custom solutions beat hardware solutions all the time -- rendering is about tradeoffs, and when you hardware accelerate some feature you're enshrining a specific tradeoff in hardware. Much faster way to use that particular trick, but if its not the right one for your renderer then it might be faster in the end to roll your own. Same thing will happen for mesh shaders, 'geometry engine', and every other cool hardware feature on some games.
     
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  10. snc

    snc
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    but it seems this hardware vrs is better for very specific cases if in deffered rendering and even forward + in modern warfare software variation is better
     
  11. cwjs

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    That's just not a conclusion you can draw from the information we have. There's no monolithic "forward +" -- its the name of a general technique. Each renderer works differently. Renderers all butt up against bandwidth, clock speed, cus, etc, at all times, and choose how to balance what they have. Searching tech talks for gotchas isn't a productive way to have a discussion.


    One bit of further clarification: @SebAaltonen is a principle engineer at one of the wealthiest companies making game engines, which currenlty includes a clustered forward renderer (among many other paths). I don't think he would have said "hardware is good" if his actual day job was "hardware is bad, use software". Listen to the experts.
     
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  12. snc

    snc
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    My conclusion wasn't about general forward+ vrs but facts are that most popular deffered engines prefers software vrs and bigest aaa game using forward + also prefer software vrs.
     
  13. cwjs

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    yep, things are looking great for adoption of VRS of all kinds, on all platforms. The technique is definitely here to stay, and will result in better performing games across the board.
     
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  14. Jay

    Jay
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    Even the Coalition document the pros and cons of VRS when they updated Gears 5.
    They also explain the benefit of using combination of the two.
    The fact is if you have the hardware your not loosing out, it's just positives all around.
    As well as the possibility for it to be used in other ways.
     
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  15. iroboto

    iroboto Daft Funk
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    I mean, if we're going to talk about VRS, here are AMD notes on it, since this won't apply to Nvidia hardware

    Variable rate shading
    • Use VRS to reduce pixel shading when pixel shading bound.
    • Avoid using VRS when fill bound.
    • Use of the following features can cause VRS fill rate to drop to 1×1:
      • Depth export.
      • Post-depth coverage.
      • Raster Ordered Access Views.
      • 16xAA.
    • Minimize the number of times per frame the VRS Image gets bound or unbound.
      • If VRS needs to get disabled for a few draw calls while the same depth buffer is being used (for example, to render alpha-tested geometry) the best practice is to leave the VRS image bound and disable VRS by modifying the combiners.
    If you guys really want to get into the nitty gritty of things, it's best to actually go through this:
    https://gpuopen.com/performance/

    Though it's probably more an open discussion than a PS5 topic.
     
  16. dobwal

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    And thats probably driven by the fact that large pubs like Activision support a plethora of platforms that all have varying features. Software VRS can be used for a broader set of hardware.

    But that can be said for any technique or technology that's limited to a subset of platforms.

    The question becomes, "Do we want to heavily invest into a technology that is limited to this or these platforms, or do we want to heavily invest into technology that applies to all platforms we support". That goes for PS5's GE and SDD tech, MS's VRS and mesh shaders, or any console tech that's exclusive to one platform.
     
  17. chris1515

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    Unreal Engine uses deffered rendering, Cry Engine uses deffered rendering, Unity uses forward rendering by default but a deffered path exist, Frosbite uses deffered rendering, Rockstar North games uses deffered rendering. The engine at Sony use mostly deffered rendering (Decima Engine, Naughty Dog engine, Sucker Punch, Sony Santa Monica, Sony San Diego, if I remember well Insomiac engine too).

    https://imgeself.github.io/posts/2020-06-19-graphics-study-rdr2/

    EDIT:
    https://www.destructoid.com/stories...-engine-made-fallout-4-so-pretty-319051.phtml

    ID software use forward rendering but bethesda Fallout engine uses deffered rendering.

    EDIT2:
    https://aschrein.github.io/2019/08/11/metro_breakdown.html

    Metro Exodus uses deffered rendering
     
    #57 chris1515, Feb 19, 2021
    Last edited: Feb 19, 2021
  18. snc

    snc
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    looking at this list I'm not surprised Sony didn't invest into hw vrs
     
  19. Cheesestraws

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    Why are people acting like hardware VRS has no use in a deferred engine? Gears 5 is using hardware VRS and runs in Unreal Engine.
     
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  20. snc

    snc
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