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Thread: SSS bug in 4.15.1

  1. #1

    SSS bug in 4.15.1


    I'm on 4.15.1 (But I think this bug is present in older versions too).

    Subsurface Scattering usually shows when it's hit with direct light. I.E:

    In UE4 However, I've setup a scene using only a skylight, with flat lighting or ambient lighting, you should only see the diffuse color, not SSS. BUT:

    SSS Intensity = 1

    SSS Intensity = 10

    Skylight influences the SSS way too much!

    Engine version: 4.15.1
    Repro Steps:
    1. Create a new map.
    2. Remove pre-baked lighting.
    3. Remove directional light.
    4. Add Skylight.
    5. Add PPV, disable auto exposure (just so you see the issue easier).
    6. Add a SSS material to a mesh and change the SSS multiplier.

    SSS shouldn't make a visible difference while in flat ambient lighting condition.

    Last edited by Maximum-Dev; 04-22-2017 at 11:05 AM.

  2. #2
    Another test.


    Direct + Skylight:

    Skylight only. Since Skylight has Lower Hemisphere being black, it's only casting light from above hence you see red on the bottom, but it should have been grey all the way since skylight is not a directional light source but is an ambient light.

    Lower Hemisphere is not solid black in this one, should have been grey all the way here too but it's not.

    Please fix this asap. All foliage look wrong in shadows.
    Last edited by Maximum-Dev; 04-25-2017 at 06:18 AM.

  3. #3
    Unreal Engine Developer
    Join Date
    Mar 2014
    Thank you for logging the report on the Answerhub. We will follow up there.
    Stephen Ellis | Lead Engine Support Technician | Epic Games | @TheEpicStephen
    How to report a bug | >>Click here to report a bug<<

  4. #4
    Seriously, why should fixing SSS be backlogged?

    How SSS looked under Skylight in old builds (correct):

    How it looks like in newer builds (wrong):

    It's unfortunately too amateur to require votes for fixing something as important as SSS. Literally no new features can be a priority over broken SSS.
    Last edited by Maximum-Dev; 05-19-2017 at 09:55 AM.

  5. #5
    This is definitely a bug.

    I would urge Epic to please have someone other than Andrew Hurley evaluate the AnswerHub post, as he has a track record of telling people that obvious bugs are in fact working as intended. More often than not he does not understand the repro steps and misses the point of an AnswerHub post. Definitely need a second opinion on this one.
    Last edited by DamirH; 05-19-2017 at 10:16 AM.
    Ph'nglui mglw'nafh Cthulhu R'lyeh wgah'nagl fhtagn

  6. #6
    Not sure if is a bug or intentional but:
    1) SSS was not affected by movable skylight in earlier versions and it was fine.

    2) SSS should be affected by skylight, but as to its practical dynamic implementation, unlike for actual lights, object thickness is not considered, so in the essence it looks a bit fake. I think it is better to leave up to artist to crank base color instead, for you can always make up for lack of skylight SSS with basecolor, but you can't otherwise compensate overly strong SSS with a diffuse
    3) If SSS is to be affected by movable skylight, it at least needs to weighted by material's opacity, which seems not be the case. This is actually the part that can be deemed as a bug.

  7. #7
    Has Epic followed up on this? It's a little disconcerting that something that affects every piece of foliage in UE4 could be this broken and ignored

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