CSG: co-planar faces break algorithm

[nodefish]

Godot version:
3.1.dev

OS/device including version:
Win10 64 / GTX 980 Ti

Issue description:

Using union, subtraction or intersection on CSG nodes with co-planar / overlapping faces breaks the CSG algorithm and results in either missing faces or clipping.

Adding a small jitter (e.g. translating by 0.01) resolves the issue as it makes the affected faces not co-planar, but this creates significant workflow strain that adds up.

Steps to reproduce:

• Add 2 CSGBox (or other CSG node) in the same CSGCombiner
• Place them such that 2 of their faces are co-planar, e.g. try making a staircase with union

Bugsquad edit (keywords for easier searching): coplanar

[bojidar-bg]

Can confirm, this is quite a nuisance when playing around with CSG-s.

[MikeSchulze]

this bug still occurs on 3.2.1

[Calinou]

@MikeSchulze This is because the fix wasn't cherry-picked to 3.2.1. Due to how big the pull request that fixed it was (over 1,000 modified lines), it would be difficult to cherry-pick it for a later 3.2.x release.

That said, anyone is welcome to try to backport the pull request to the 3.2 branch by rebasing the changes and opening a pull request against the 3.2 branch.

[MikeSchulze]

@Calinou thanx for this information. Me was not clear this fix was only merged into master
@madmiraal very good to you create a pull request to bring the fix in 3.2.x ;)