Update snap value for precision in small scale models.

[fire]

Subtracting two CSG box nodes from a box can generate a floating triangle.

Not sure if this is the proper fix, so putting it out for testing.

Seems to resolve:

• Holes in CSG meshes with coplanar faces and engine freeze when moving them #58637
• CSG box and sphere subtract displays cracking from missing triangle  #41140
• Subtracting two CSG box nodes from a box can generate a floating triangle #86567

[fire]

godot-csg-mesh-repro.zip

[Calinou]

How well does this behave when a few thousand units away from the world origin (between 4096 and 8192 units)? I believe this is why the default is 0.001.

[fire]

@Calinou can send me a test case where this errors. I am not sure if it exists.

As far as I know this snapping value was because of a bug that used to cause an infinite loop.

#76521

I am imagining reusing that double precision tester where we have a scene at the origin and another one a million units away.

https://github.com/godotengine/godot/files/8137344/TestDoubles.zip From #58516

[fire]

@Calinou I made a video of the double precision test with https://github.com/V-Sekai/godot-double-precision-test. How did you expect it to break because it doesn't seem to be breaking on a CSG box subtractions at the top left.

https://youtu.be/VD0_45cvXaU

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I'll file a bug later, but @Zylann double precision has broken triplanar again.

[lyuma]

This change is going to make CSG appear to have a precision issue without an obvious explanation why.

I would rather keep the current behavior which is obviously incorrect for some uses and have users change snap to a value appropriate for their application, than have a non obviously bad default that users won't notice or understand

[fire]

I disagree because ordinary csg cases will be broken as in the bug reports which are human scale.

We discussed setting it to 0 and deprecating.

Edited: I refreshed manifold..

[fire]

Closing due lack of agreement on this method.

[fire]

#91748 is a better theoretical fix for this.