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Thread: Caustic shadow wrong

  1. #1
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    Default Caustic shadow wrong

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    I have a concern with representing shadows and caustics through a glass material. This material comes from Subsctance designer with the MDL transparency preset. Why this difference when the caustics are directly seen through the camera and through other glass?

    thanks you

    frédéric
    Attached Thumbnails Attached Thumbnails 2020-02-25 14_15_27-reflection.3dm (2 Mo) - Rhino 6 Commerciale.jpg  

  2. #2
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    It would be extremely helpful if you could provide the file for this test case. I did a simple recreation here and wasn't albe to easily reproduce so we'd like to look at the exact settings in the file.

    Also, do you have the Caustic Sampler enabled in the options? I assume this is with denoising turned off (which may interfer with the accuracy).

  3. #3
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    Feb 2020
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    hi Paul,

    All options are checked, I share the .3DM file as well as the .MDL file.

    thank you

    Documents.zip

  4. #4
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    The MDL you included references another MDL material "MDL_Material", do you have this as well?

  5. #5
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    Feb 2020
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    I just saw actually that the file structure is different in export, here is the exported substance designer file.


    MDL_Material.zip

  6. #6
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    Never mind, I just replaced it with the built in thick glass and get the same result so we will investigate that.

  7. #7
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    thanks you Paul

    have a nice day

  8. #8
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    I have spoken with NVIDIA and this is a known limitation of the caustic sampler. Specular-diffuse-specular paths which happen if looking at the caustic through the glass planes are not sampled. This limitation is documented in the Iray Programmers guide stating:

    The caustic sampler only improves on directly visible caustics. Caustics seen through mirrors or windows are currently not improved by the caustic sampler.
    Turning off the caustic sampler will give consistent results for both spheres in your example but of course the additional caustics will disappear.

  9. #9
    Join Date
    Feb 2020
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    Hi Paul,

    I understand, thanks for the information.

    have a nice week end

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