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    Unreal Engine 5 LUMEN

    Does anyone have any guesses as to the method core to the new GI solution? Is it related to RTGI, LPV, some kind of voxel based solution? I know that the results are accumulated over a few frames. I saw mention of shadows being pixel accurate but I am wondering if we will have to contend with any sort of GI light leakage.

    #2
    Maybe some kind of lighting probes, dynamically updated / accumulated over a couple of frames. Could be Radiance probes, tracing Rays from the surroundings and affecting only the ambient light term of the BRDF equation. They could be quite low res as the rest of the shading would still be rasterized.
    Last edited by SimSevi; 05-13-2020, 06:30 PM.

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      #3
      My guess, some kind of voxelized approach.

      If you look at the demo when Lumen is turned on, you can see in the first frame that some shadowed areas light up, only to get *darker* as the solution refines. That might indicate an initial low-rez approach that increases resolution over time. Epic says their solution has infinite bounces, which is maybe a clue?

      Whatever, their solution looks great, and I'm not seeing any of the blurryness that is evident with RTGI.

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        #4
        Turns out, it's a clever combination of methods:

        https://www.eurogamer.net/articles/d...-demo-analysis

        To achieve fully dynamic real-time GI, Lumen has a specific hierarchy. "Lumen uses a combination of different techniques to efficiently trace rays," continues Wright. "Screen-space traces handle tiny details, mesh signed distance field traces handle medium-scale light transfer and voxel traces handle large scale light transfer."
        Last edited by bioccular; 05-14-2020, 11:41 PM.

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          #5
          Looks like they are using a combination of their previous SVOGI system

          https://www.youtube.com/watch?v=MOvfn1p92_8

          an improved version of their previous distance field / height field GI they introduced in 4.8 and kite demo

          https://forums.unrealengine.com/deve...ield-gi-in-4-8

          and finally their current screen space GI.

          https://twitter.com/UnrealEngine/sta...38329202823168
          Last edited by Bladerskb; 05-15-2020, 04:13 AM.

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            #6
            Originally posted by Bladerskb View Post
            Looks like they are using a combination of their previous SVOGI system

            https://www.youtube.com/watch?v=MOvfn1p92_8

            an improved version of their previous distance field / height field GI they introduced in 4.8 and kite demo

            https://forums.unrealengine.com/deve...ield-gi-in-4-8

            and finally their current screen space GI.

            https://twitter.com/UnrealEngine/sta...38329202823168
            That is incredibly clever. These devs are kinda smart.

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              #7
              DFGI has artifacts on small, extreme details. I don't think that's it.

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                #8
                Originally posted by mariomguy View Post
                DFGI has artifacts on small, extreme details. I don't think that's it.
                It is part of it. DFGI makes up the mid-size portion of the GI. Screen space techniques seem to fill in the micro-gaps.

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                  #9
                  Originally posted by stomatogod View Post

                  It is part of it. DFGI makes up the mid-size portion of the GI. Screen space techniques seem to fill in the micro-gaps.
                  And skylighting seems to make up large distance, there's a new relatively low cost skylighting update coming in 4.26. There's also some mention of "voxels" for very large objects, but no details were given on how large or how far away.

                  Also seems expensive, 1440p 30 on a PS5 (highly overclocked 5700xtish) with a single little flashlight and one sunlight. Ohwell, looks neat and it's a big step up from UE4's current "either use lightmaps or try to hack out your own stuff with the weird assortment of random tools given/rely on our slow raytracing".
                  Last edited by Frenetic Pony; 05-16-2020, 03:59 AM.

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                    #10
                    Originally posted by Frenetic Pony View Post

                    And skylighting seems to make up large distance, there's a new relatively low cost skylighting update coming in 4.26. There's also some mention of "voxels" for very large objects, but no details were given on how large or how far away.

                    Also seems expensive, 1440p 30 on a PS5 (highly overclocked 5700xtish) with a single little flashlight and one sunlight. Ohwell, looks neat and it's a big step up from UE4's current "either use lightmaps or try to hack out your own stuff with the weird assortment of random tools given/rely on our slow raytracing".
                    I also wonder if you could claw back performance by slowing down the update rate of the GI and just cache it over a longer period of time.

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                      #11
                      Lumen is exciting, I hope the devs will share more technical details.
                      Just wrote my thoughts on it : https://www.artstation.com/simonmaja...need-for-lumen

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                        #12
                        Originally posted by User-957538098 View Post
                        Lumen is exciting, I hope the devs will share more technical details.
                        Just wrote my thoughts on it : https://www.artstation.com/simonmaja...need-for-lumen
                        Thanks for writing that out!

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                          #13
                          My guess is they are accumulating the GI into probes alike those in the nVidia DDGI presentation using a combination of tracing methods like distance fields and voxel cone tracing.

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