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Thread: So what's up with the Cook Torrance shader?

  1. #16
    I remember shaving off about 6 hours from a render because I switched out from Oren Nayer.. I couldn't actually see what it was doing!

  2. #17
    That must've been a long freakin render!
    Oren nayer is like, more diffuse than diffuse.
    Almost makes lambert (right) look silvery
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    Confirmed -
    No Weapons of Mass Destruction
    or links to Al Queda or 9/11. (Sep. 2003)

  3. #18
    Haha all my renders take forever these days, since I use radiosity and reflection/refraction blur in all of them Yeah you can see the difference there, but sometimes it's really hard to see the difference if you add in ambient occlusion and environmental radiosity to the mix.

  4. #19
    It's only good for a few things, and the difference is probably even less noticeable with gi since it's a difference in falloff; soft light sources won't really show it.
    Confirmed -
    No Weapons of Mass Destruction
    or links to Al Queda or 9/11. (Sep. 2003)

  5. #20
    Super Member Captain Obvious's Avatar
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    Actually, it makes no difference at all. None of the diffuse shaders in Lightwave respect GI. Unless you have normal lights in your scene, all the diffuse shaders will look exactly the same.
    Are my spline guides showing?

  6. #21
    I was hoping that wasn't the case, but after finding out that bump doesn't show up either... come on NT... why would they leave that out??
    Confirmed -
    No Weapons of Mass Destruction
    or links to Al Queda or 9/11. (Sep. 2003)

  7. #22
    Quote Originally Posted by Captain Obvious View Post
    I've noticed that the Cook Torrance specular shader in Lightwave's node system, isn't actually a Cook Torrance shader. One of the neat things about the real CT shading method is that it produces really bright hotspots, as if it were an actual reflection of the light source. Lightwave's does not. Lightwave's CT shader seems to be clamped at 1.0 intensity, and then further modulated by the light's intensity and falloff. Compare this with a real Cook Torrance, where the middle of the hotspot can be in the 10-20 even when it's fairly soft, and higher still for small sharp highlights.

    The same applies to certain materials, too. Delta, Conductor and Dielectric all use the same clamped Cook Torrance function.

    I was wondering why I couldn't get as good specular highlights in Lightwave's materials as I could using my custom shaders or using other renderers, but I guess this would explain it.

    Or have I just missed a setting? Is there a checkbox for "make specular highlights good"?




    Gerardo

  8. #23
    NewTek Social Media Chuck's Avatar
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    Folks, if you have entered a Fogbugz report for any of the problems described, please post the bug number - not the link version please, just the case number itself.

    If you have not entered a report, please do so, and post back the case number. We'll review the issues.

    Edit: I did find one for the clamping in specular shaders. I've upped the priority on that and will make sure Antti looks at it for the maintenance update.
    Last edited by Chuck; 07-15-2009 at 12:55 PM.
    Chuck Baker
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  9. #24
    Excellent! Thank you!



    Gerardo

    P.D. Just for people whom want to try the previous workaround - the multiplicative value for the normal input in CookTorrance node should be higher than 1.0 when the specular intensity diminishes.

  10. #25
    Super Member Captain Obvious's Avatar
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    Wait what? You're increase the amplitude of the normal of the surface? That should screw up the specular shading. Specular shaders generally require all vectors to be normalized.
    Are my spline guides showing?

  11. #26
    Don't ask me why, but it works in this case. Do make a test.



    Gerardo

  12. #27
    Ok. Normals in CookTorrance specular model reacts in reverse way. When we multiply the normal surface we are, in fact, dividing the normals values. Intensity in other specular models increases, while in CookTorrance decreases. That's the reason why the above workaround works. Maybe the problem is an incorrect normalization (-1 to 1 instead of 0 to 1).



    Gerardo

  13. #28
    Super Member Captain Obvious's Avatar
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    Well, i'm currently lw-less, so i can't try it.
    Are my spline guides showing?

  14. #29
    Master of the Yard!
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    Yes, please, report all these, bugs! I've been spending most of my time modeling and I've only used one or two of the material nodes in small areas, so I've not noticed these issues yet. But I know I'll be really frustrated when I do.
    Less clicking!

    /.\\
    Al Mejias


    I don't care if the glass is half full or half empty. Fill it up cause I'm still thirsty.

    If I order pizza and I get filet mignon, I'll still want pizza.

  15. #30
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    Um, stupid question above my pay grade, but ... do any of these issues change with FPrime or other renderers (Kray?).

    I'm digging thru the LW v9 Lighting book, and trying to think ahead.

    And will Radiosity get faster with 64 bit - or do you just have to throw more cores at it?

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