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Thread: SSS Glow at Intersection of 2 Objects

  1. #1
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    SSS Glow at Intersection of 2 Objects

    Here are a couple of boxes, one with Simple Skin added. When the smaller box touches the bigger one, the area of contact immediately illuminates. If the bigger box is set to Double Sided, the problem goes away. If reflection is turned up on the smaller box, it's back again! Any idea what's going on (and more importantly, how to stop it)?

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    Thanks,

    (c:

  2. #2
    Vacant, pretty vacant pinkmouse's Avatar
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    SSS expects a closed mesh, and I suspect that interpolating other geometry confuses the shader. Have you tried booleaning the intersection out?
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  3. #3
    Goes bump in the night RebelHill's Avatar
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    Thats just how it is with SSS, penetrations/intersections cause this owing to the "internalised" shading.
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  4. #4
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    Hmm.. well that seems like somewhat of an oversight, since reflective and SSS surfaces would come into contact with one another quite commonly I'd have thought. Take humans and animals for example...

  5. #5
    Goes bump in the night RebelHill's Avatar
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    Its not an oversight... its just one of the problems inherent in SSS shading methods, you see other kinda artifacts in other renderers in the same sorta situations. The only real fix for it is to use an AO shader to "detect" proximity of geo and use that to mask the depth shading effect.
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  6. #6
    Super Member spherical's Avatar
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    So, you have a microscopic air gap between the two; instead of actually touching. Which, btw, is the case in reality. There is always some air between objects that are not actually part of one another. If there weren't, they would actually stick together.
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  7. #7
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    Quote Originally Posted by RebelHill View Post
    Its not an oversight... its just one of the problems inherent in SSS shading methods, you see other kinda artifacts in other renderers in the same sorta situations. The only real fix for it is to use an AO shader to "detect" proximity of geo and use that to mask the depth shading effect.
    Would it be safe to call it a bug then...? Seems rather odd that the reflectivity of one object would have such an effect on the SSS of another, as the two objects happily intersect otherwise without adversely affecting the SSS. That AO solution sounds tricky... I shall look into it, thanks.

    Quote Originally Posted by spherical View Post
    So, you have a microscopic air gap between the two; instead of actually touching. Which, btw, is the case in reality. There is always some air between objects that are not actually part of one another. If there weren't, they would actually stick together.
    Yes I realise this, but when you have a number of morphs, bones, effectors and things working together to slide one object over the other (as in an eyelid), maintaining a consistent, indiscernable gap is far more difficult than having a small amount of overlap.

    (c:

  8. #8
    Goes bump in the night RebelHill's Avatar
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    Quote Originally Posted by Chris Jones View Post
    Would it be safe to call it a bug then...?
    No... its just the way it is... Intersections WILL cause SSS shading errors. In some simple setups, with certain lighting conditions (which are really just special cases) then the double sided can appear to fix things, but in a lot of situations it wont.
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  9. #9

    cloning the object and use a clip map might be a way to solve it?

    not quite sure, but maybe...

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  10. #10

    could this be a solution for the close-ups...?



    If the bigger box is set to Double Sided, the problem goes away. If reflection is turned up on the smaller box, it's back again!
    seems to work here... (running LightWave 11.6)
    Last edited by erikals; 01-01-2014 at 01:16 PM.
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  11. #11
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    Unless I'm misunderstanding, I don't think clip maps would work for spherical or organic shaped objects..?

    Double sided only works if both objects are SSS unfortunately.

  12. #12
    Unless I'm misunderstanding, I don't think clip maps would work for spherical or organic shaped objects..?
    clip maps work with UV mapping, so i think it should work. (time-consuming though...)

    Double sided only works if both objects are SSS unfortunately.
    looks to work here >
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  13. #13
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    That's very weird... I tried it earlier and it definitely didn't work. Tried it again just now and it does. Is there a special practical joke version of LW? Because I think that's the one I have...

    Thanks for the tips, I'll see if I can get them to work in practice.

  14. #14

    so there is a random bug here? right?...
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  15. #15
    Registered User Lucasmorif's Avatar
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    I had this similar problem with an eye intersection once, didn't know how to solved it and ended up abandoning the SSS.
    Looking forward for a solution.

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