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New Sky/Atmosphere model in 4.24

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    SebHillaire and The Regurgitator

    I was hopeful to maintain perspective camera as opposed to orthographic. I'm interpreting an older work and thought it'd be cool if I could apply as much of a realistic setup as possible.

    I'm a Maya artist making the switch to Unreal (slowly). Currently with this short project my goal was to have the same animation/camera etc. setup up in both Maya and unreal so they are 1:1 in setup/scale. Then I was going to use Maya/Redshift as my guide for matching post process closer to my maya render.

    1. At first I tried a realistic earth/sun/moon scale/distance, then miniaturized it, which is what I posted on page 2 of this forum. Looking back it was clear the atmosphere with a ground radius of 100 looked very wrong.
    2. So, I rebuilt my scene to match the default ground radius in Unreal (which appears to be real world scale in centimeters). This is far more appealing.
    3. From there I stubbornly built the real world sun scale and distance (ignoring the fact that that is an absurd expectation of Unreal/Maya or any 3d package), but found the sun wasn't visible in viewport unless I selected it making it hard to artistically adjust bloom/flares/color etc.
    4. From that point I built a mini sun/closer to earth.
    5. The real moon distance and scale seems to work within the clipping planes of the camera so I kept it.

    With each of these steps I reanimated everything at the new scales/locations.

    6. I suppose, worst case scenario I could find a false moon distance at which the atmosphere works and find a new focal length. And then reanimate. But before I do this, I will dig a little.

    --- --- ---

    I tried playing with the atmosphere height and Mie/Rayleigh distribution (with meshes present under the atmosphere) with no luck.

    To test the theory that it's z-fighting the geometry below the atmosphere, I hid all geo and left only the initial directional light (the one tied to the atmosphere) and the sky atmosphere node.
    Looks like the atmosphere breakup still happens without any geometry present:
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    This likely isn't relevant to the cause of the breakup, but I tried it to see if it improved or not . . . it looks like the breakup changes dramatically depending on the AA. Again, not likely relevant.
    Click image for larger version

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    I will try playing with the atmosphere height and Mie/Rayleigh distribution settings with no meshes present next, but have to get ready for work and will try more tonight.


      Thanks for the investigation and nice report. So if it still breaks without geometry then it is only due to the atmosphere tracing itself. I made sure it is on the to-investigate list.

      If you try again to reduce the radius of the planet then the atmosphere setup needs to be adapted (it does not scale automatically while preserving look):
      - proportionally reduce the atmosphere height
      - proportionally reduce the height distribution for Mie and Rayleigh
      - same for the absorption tent distribution altitude and width
      - scattering and absorption coefficient will need to be made inversely less high
      It might still look at bit different I believe because earth curvature will be different (especially at the light to shadow transition). I hope it can help you.

      If you do beauty shots from space, you might want to increase r.SkyAtmosphere.SampleCountMaxused when tracing the atmosphere (see the reference page for all the settings). I'll add details on rendering the atmosphere from space to the documentation for 4.25.


        Hi all, I have a noob question, do I have to use a skydome at all? Because for new Sun Sky plugin it seems like I don't have to (at least from visual perspective). I have volumetric clouds in the scene and I'm blending different cubemaps based on day time. I'm also planning to mix one extra cubemap for overcast. But if I had no specified cubemaps there would skybox be required for captured skylight?


          SebHillaire thank you for adding it to the to-investigate list. I was overseas for work and am back now to continue my digging.
          It's apparent I have not played with many of the rendering commands in Unreal in general nor in relation to the Sky Atmosphere node.

          Playing with the r.SkyAtmosphere.AerialPerspective.StartDepth and r.SkyAtmosphere.SampleCountMax is cleaning up a bit of the noise, not completely gone but definitely cleaner:
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          I'll keep playing with the rendering values and settings and see how much I can clean up the atmosphere. Thank you for your feedback.


            GTJC Ok then. I am surprised the AP commands improves the result in this case.

            Z0DI4C.2.0 You do not have to use the sky dome shader with IsSkyTicked. That is only if you want to render a sky dome (with custom composition of clouds, planet and whatnot) as unlit opaque while not having the aerial perspective (atmosphere fog) apply on it again.


              SebHillaire To be specific, I've narrowed it down to the one render command, r.SkyAtmosphere.AerialPerspective.StartDepth
              It seems values between 10 - 100 give a cleaner look (the look you see in my last images). If I put a value of 1, it gives the look I initially see (or if I close and reopen the project).
              I'm finding a value of 100 crushes a bit of the transition area between the light/dark side so I'm playing with values between 10 - 75 currently.

              I'll post more soon.


                anyone test 4.25?
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                  Tried last night. Won't install for me.


                    4.25 Preview 3 installs for me, in case anyone on this thread wanted an update.

                    Nice to see the atmosphere now renders behind the moon and not in front of it


                      Hey there. Concerning relations between the new Sky Atmosphere and the old Atmospheric Fog...

                      Firstly, what is the fate of the latter, will it be removed, supported independently, or somehow merged with Sky Atmosphere in the future? I am using Atmospheric Fog, I'm not satisfied with all colors it makes, especially too dark evenings (the sky must be still blue right after sunset, not black or grey with a greenish tint) but I would be upset if it's gone.

                      Secondly, I'm a bit worried about performance of Sky Atmosphere compared to Atmospheric Fog. I am using Atmospheric Fog with stars skydome and at least two layers of translucent cloud meshes (cumulus/cirrus). My clouds shader is lightweight enough, even multiple cloud layers yield dark green shader complexity. But if I use Sky Atmosphere expressions with materials, numbers of instructions dramatically rise. Just a blue skydome with custom clouds, but shaders go dark red, while the colors are hardly better, and evenings are still too dark. Even the example material with poor 90x-games-like cirrus clouds has as much as 296 ps instructions! I really don't understand why I need this all, so the first question is more important.


                        Hello Alakuloinen ,
                        A few answers:
                        • AtmosphericFog will simply be removed at some point.
                        • Shader complexity: instruction count doe not do everything: texture fetch, scheduling and more also influence performance. You have to measure the actual GPU performance for your use case. usually the sky is not full screen and when it is, a lot of the world is not visible so it balances. There is also some smart pixel work culling happening on GPU. Cost of the sky is usually tiny as compared to the rest. Fortnite has very complex sky and has shipped on ps4, xb1, switch and mobile, some of them being at 60fps.
                        • Dark evenings: SkyAtmosphere can render beautiful evening with blue sky even when the sun is way below the horizon at sunset. Just make sure you have an exposure setup to see something. If it is too dark you can do the following: add a moon because on earth it is a high contributor at night. You can also use the more expensive (just a bit more) but more accurate multiple scattering evaluation by setting r.SkyAtmosphere.MultiScatteringLUT.HighQuality 1 (just noticed a name error in the documentation, we will fix).
                        Last edited by SebHillaire; 05-06-2020, 02:55 AM.


                          Originally posted by SebHillaire View Post
                          Hello Alakuloinen ,
                          A few answers:
                          • AtmosphericFog will simply be removed at some point.
                          Looking forward to that. It will hopefully remove tons of ambiguity and confusion. Right now, there are just too many wrong combinations possible


                            AMEN to that, too much confusion indeed, so we should use one over the other NOW ? Anyway , I am using Dynamic lights, takes too long to compile static till I upgrade a little, BUT as player moves, or even as camera moves, I get these nasty circular ( I guess) shadows to move along as player does one REMOVE those, they are a real realism killer, and ya I have a world comp world 4 tiles (atm) just to verify this is on topic and I"m using Sun & Sky .

                            Solo but Seismic - feel free to apply


                              I am quite worried about usability. Unreal's keyboard shortcut mapping was never very strong, but skylight gizmo takes this to a whole new level. Ctrl and L keys are about 20 centimeters from each other on an average keyboard, making them borderline impossible to press at once with one hand. At the very same time, the light direction gizmo can NOT be operated using the mouse without the combination pressed together, so it's absolutely necessary to press those extremely distant buttons together using just one hand, and keep the hand in this very uncomfortable position during the manipulation.

                              This really needs to be done better. Right now, it's a bit of UX failure
                              Last edited by Rawalanche; 05-08-2020, 04:00 AM.



                                new sky in 426 , look great!
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