Is the result of ExtrudeGeometry always Manifold? ~ Given necessary properties for being so

Questions
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1

Assume we have a 2D Shape with the following properties:

  • Non Overlapping edges
  • No duplicate points in shape
  • Non Overlapping Holes with other holes / boundary
  • May or May not have co-linear points

Note: Unsure about the orientation. Possibly the holes may or may not have same orientation as the other holes / boundary. Wondering if this could cause any issues in the result of the Extrusion

Assume the following properties, rest properties are default values, for ExtrudeGeometry:

  • depth
  • bevelEnabled is false

Considering the above properties, is it guaranteed that the Extrusion Result would be:

  • Water tight
  • Manifold

The issue that I am currently facing is. A Certain few meshes created using the above workflow tend to result in an error “NotManifold” when using the CSG Library “manifold-3d”, but again it’s the same workflow and it works for other cases. Not able to understand where i might be going wrong

Thank You!

2

No, it is not guaranteed to be manifold. The three.js “cap” triangulation is based on Mapbox’s earcut library which has some known cases where triangulation fails to be correctly connected.

3

Got it, A follow up question: Usually, Converting geometry from Non - Manifold to Manifold requires human assistance ( atleast in some cases, to get a visually correct output ).

Is there currently any way through which we can have a manifold output from extrude geometry? or a post processing solution which can remove the above triangulation artifact?

Thank You!

4

A solution for generating manifold output through extrusion of a cross section shape is to use manifold-3d’s extrude function

I believe that should resolve the original issue that I had mentioned