ExtudeGeometry BevelOffset negative cause edges self intersection

[googincheng]

Description

ExtudeGeometry BevelOffset negative cause edges self intersection

Reproduction steps

1. ExtudeGeometry from a arbitrary shape
   2.set beveloffset to -50 (or some bigger number)

Code

null

Live example

null

Screenshots

Version

r169

Device

Desktop

Browser

Chrome

OS

No response

[googincheng]

Relate to:
#20317

[googincheng]

Guess this should help, but I don't know how to integrate it into threejs.
https://github.com/glenzli/paperjs-offset

[Mugen87]

Merging into #20317. Negative bevel offsets are not supported in ExtrudeGeometry.

[stanch]

I have just run into the same exact issue (on r175). It is not necessary to use a negative bevel offset to make things weird. More specifically, the issue occurs with small radius corners.

Convex corner and negative offset:

Concave corner and 0 offset:

It’s true that the first case produces a more broken geometry, but I would argue the underlying problem is the same.

@Mugen87

Negative bevel offsets are not supported in ExtrudeGeometry.

My reading of #20317 and the associated fix is that negative offsets are supported, as long as the shape is wide enough to accommodate them (e.g. not a very thin doughnut).

[Mugen87]

Indeed, my comment is outdated. There are some limitations (see #20317 (comment)) but in general negative offsets are supported now.

Can you demonstrate your issue with a fiddle?

[stanch]

Here are the fiddles:

• Negative offset https://jsfiddle.net/uf6t4b0v/6/
• Zero offset https://jsfiddle.net/mL4pukrz/1/

Edit: I should mention that the shapes are procedurally generated. I’ve just exported them in JSON but I could provide the code if that helps. They start out as a square and a half-octagon respectively and then get a small arc in each corner. I am mainly interested in the one with the negative offset — the other one is just to demonstrate that the issue is not isolated to it.

[stanch]

And another one for negative offset, this time a corner between a line and an arc: https://jsfiddle.net/36c9bjz8/2/

[stanch]

@Mugen87 Could the issue be reopened given the reproductions? Or should I create a new one?