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Thread: Erase on collision

  1. #1
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    Erase on collision

    I have a semi-transparent toroid growing over time that represents emissions from a dipole antenna. I want part of the toroid to disappear (be absorbed) when it collides with a radar dish. I am over my head here... I have tried many configurations for both the toroid and the radar dish; collision object in erase mode, static body, rigid body, nothing seems to be interacting. Can someone suggest the best way to approach this problem. I do not have a lot of experience with these features.

    thanks!

  2. #2
    Registered User Oldcode's Avatar
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    You could try a Gradient texture on the transparency channel and use "Distance to X" or something to control when the torrid goes completely transparent.

    Good Luck,

  3. #3
    Vacant, pretty vacant pinkmouse's Avatar
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    You could try setting the toroid to be lit only by a point light situated at your dipole, (that is set to only illuminate the toroid), then when it passes the dish it will be shadowed and disappear.
    Al
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  4. #4
    Vacant, pretty vacant pinkmouse's Avatar
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    This sort of thing?

    Al
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  5. #5
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    [QUOTE=pinkmouse;1494934]This sort of thing?

    Yes, that is the general idea. You did that with the point light? My scene is a bit more complex, so my results were not good. The toroid is shaped like a bicycle tire with curvature of the leading edges, plus I have luminosity and transparency settings, so I think that might be interfering with the point lights effectiveness???

  6. #6
    Super Member spherical's Avatar
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    While that does work appearancewise in that particular situation, you can still see the portion behind the dish. It's just no longer lit. If there is a background or objects behind the torus, it won't have disappeared. It will still block those distant rays.
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  7. #7
    Axes grinder- Dongle #99
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    Quote Originally Posted by spherical View Post
    While that does work appearancewise in that particular situation, you can still see the portion behind the dish. It's just no longer lit. If there is a background or objects behind the torus, it won't have disappeared. It will still block those distant rays.
    I suspect that's just a non-zero ambient.

    Possibly some GI, but that seems unlikely.
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  8. #8
    Super Member spherical's Avatar
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    You're not getting the point. The section after passing the dish needs to actually disappear, not just be non-lit. Making it "go dark" can work in specific situations, like the test shown, but it isn't the solution that the OP asked about. IF the OP's situation is a limbo set, then it can be faked this way. If in any other environment, nada.
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  9. #9
    Axes grinder- Dongle #99
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    Oh right, hmmm..... well, one way would be to use a global-coords clip map. I've used such things to cut off a cable that was supposedly winding around a capstan. You can even reference it to the occluding object so that object an be moved (but usually not rotated).

    EG:
    Click image for larger version. 

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  10. #10
    Vacant, pretty vacant pinkmouse's Avatar
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    Indeed, it's not perfect, it uses a texture rather than geometry as it was just a quick test. But it produces a result that could be comp-ed in if the OP was in a rush to get things done. I may revisit this if I get the time later today.
    Al
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  11. #11
    Vacant, pretty vacant pinkmouse's Avatar
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    This one took a bit longer, but still uses a point light on a plane to generate a (hidden from camera), shadow map, then the raytrace node projects that on the geo. Would be easier in LW12 as you could use the clip input in nodes, (as suggested above! ), but I only run 11.3 so had to bodge it a bit.

    Attached Thumbnails Attached Thumbnails Click image for larger version. 

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    Last edited by pinkmouse; 01-15-2017 at 05:50 AM. Reason: added screenshot
    Al
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