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Thread: Clip map trick does not work under glass table

  1. #1
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    Clip map trick does not work under glass table

    Hello! I followed this clip map technigue, to make animated boolean.

    http://forums.newtek.com/showthread....tive-in-Octane

    Now as I have dropped off the use of Octane ( they are very expensive on ORC rendering cloud services ) and I have to build all my surfaces on lw natural rendered again Yipeee!

    I managed to make my papers to turn invisible on table surface, thanks to MonroePoteet great example scene. But as papers travel under my glass table surface, I see some dark shape of the paers again. This must be some other thing than just the Transparency channel!

    Click image for larger version. 

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    Can anybody help me on this?

    Pekka

  2. #2
    pass:sword OFF's Avatar
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    Try a displacement node with a scale dependence on the distance to a certain object - the gradient should be sharp.

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    Thanks, what a wild idea!! I tried this but it did not yet scaled / displacemented my pile of a4 pipers. What did I miss?

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  4. #4
    pass:sword OFF's Avatar
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    You need learn these videos for a basic understanding - preferably his oldest lessons
    https://www.youtube.com/user/bryphi77/videos

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  6. #6
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    Make sure the Refraction Index on the vanishing Paper surface is 1.0 and perhaps increase the Transmittance Distance if you still see a "smudge". For a Principled BSDF surface and the new render engine, a 100% transparent surface will still refract and absorb light unless Refraction Index is 1.0 (same as air) and the Transmittance Distance is "large enough".

    mTp

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    I have the settings like that. No help. I made a text ball and no matter what I put there as refraction number, it still is visible though the glass..

    Click image for larger version. 

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    So it is not about this clip map trick, it is overall about invisible objects through glass, they are still dark shapes.

  8. #8
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    Perhaps the settings on your glass table top need to be changed. It works for me on LW2018.0.3 using a plain Dielectric surface for the glass table top and feeding a 1.0 Constant Scalar into the Ball's Transparency channel, with its Refraction Index set to 1.0 and Transmittance Distance set to 10m:

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    mTp
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    Last edited by MonroePoteet; 05-04-2018 at 12:30 PM. Reason: typo

  9. #9
    Registered User dlvphoto's Avatar
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    I've run into this with leaves on trees as well as glass objects. Increase your refraction recursion and transparency recursion limits. For transparency, the recursion limits get decremented for each object it passes through. Similarly for refraction. Each surface that with an IOR greather than 1.0 that the ray interacts with decrements the count by 1. When that count drops to zero, you get black if the ray hasn't been terminated yet.

    Scott

  10. #10
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    Quote Originally Posted by pekka varis View Post
    I have the settings like that. No help. I made a text ball and no matter what I put there as refraction number, it still is visible though the glass..

    Click image for larger version. 

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ID:	141537

    So it is not about this clip map trick, it is overall about invisible objects through glass, they are still dark shapes.
    I didn't know if you were still having the same issue, pekka, but I thought I would have a go at your problem.

    I made an experiment like yours (glass table, paper tray, stack of papers) and used the Object Properties > Render > Clip Map on my paper stack. I used a Gradient and made it Y distance to object, with the target object being my transparent table.

    Then I added an additional 100% alpha slider and a 0% alpha slider to the gradient and adjusted the distance until the papers clipped out perfectly just after passing the top of the table.

    When all of the papers have fallen into the paper tray (passed through it) there are no shadows, reflections, etc., at all on my table from the papers that are below it. The papers just look like they are settling into the paper tray, with nothing beneath the glass table and nothing showing.

    I'm not sure if that is the effect you are going for, but it seems to work quite well.

    I wish I could share my settings but I did the experiment on my work computer and I don't have an easy way to pass images from it.

    Anyway... I hope I communicated the concept and that it helps you in your situation.
    Last edited by RPSchmidt; 05-11-2018 at 10:51 AM.

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