Dont render geometry inside volume of another object

Support Materials and Textures
1

Is there a simple way to NOT render parts of a mesh existing inside another?
(looking up inside a character’s mouth cavity I’m seeing unwanted eyeballs, parts where a hat & hair etc intersects the head’s interior)
Boolean-ing doesn’t seem the way to go.

Thanks

2

Hi, you need to close the cavity to not show the internal parts:
See image:

mouth
mouth564×633 260 KB

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3

Thanks for the reply & suggestion. I considered this approach, but my character has an extremely massive stylized mouth cavity (not humanoid proportions at all - closer to a pac-man), and this “double-membrane” for this huge mouth gets a little cumbersome with bone deformations. If there are no other clever tricks to “cull” the inside then I guess I’ll end up doing the suggested. Thanks

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4

Can you show us your head model?

5

troubleshoot_mouth_2024_12_11_001
troubleshoot_mouth_2024_12_11_001960×540 44.6 KB

troubleshoot_mouth_2024_12_11_002
troubleshoot_mouth_2024_12_11_002960×540 62.3 KB

So if the mouth opens fantastically wide, it would just be SOOOO much simpler if I could somehow NOT see the eyeballs inside the skull and be done with it. Also, if the cavity is closed - it complicates & dictates the teeth placement a lot too. (and of course these are toon-like & rely a lot on freedom of movement & crazy placement). Thanks :slight_smile:

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6

You can always extend/extrude the inner edge of the top lip?

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7

I have 2 versions of the same idea kicking around.

  1. assign a parameter to hide the specific geometry w/ geo-nodes when the check box is ticked. Then you can animate manually to hide it when needed with one tick.
  2. Automate the parameters to automatically tick on when mouth opens in the expected way.

Bonuses!
3. Automate what is hidden based on fancier geo-nodes that detect proximity to certain other geometry to sort out internal overlapping.

I would probably go with 2 myself.

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8

There is a top set of teeth too (not nicely shown in my screenshots I’m afraid) - which also gets animated around the inside a lot, and while the suggestion is probably the way to go… I’m honestly just hoping for a way that doesn’t require accurate skinning & weighting of the mouth interior to not have it interfere with teeth & tongue. Thanks for the help!

9

I’d just create a ‘smoke screen’ inside the mouth, sealing from lip to lip, with an AOV/Holdout masked material.
And in a separated scene, a duplicate of the mouth with just the interior (that can then have any shape), and nothing else.
Finally, some fun in the compositor.

1 Like
11

Agreed. I was very much thinking in the direction of a shader/geometry based solution… and your post just sparked an idea which Ill explore first thing tomorrow.

In short: is it possible to do geonodes raycast from the eyeballs’ face normals & whatever hits the reversed normal (inside) of the character mesh … make that the criteria/factor for mixing the eyeball shader with a tranparent bsdf??

Will try and keep you posted!