Godot: Odd triangle holes will appear in CSG subtraction

[fire]

Similiar Issues:

https://github.com/godotengine/godot/issues/18476

Godot version:
43c2868

OS/device including version:
Nvidia GTX 1080 on Windows 10

Issue description:

Steps to reproduce:

Create CSG nodes consisting of a plane of sufficient size and then use a cylinder to subtract. Odd triangle holes will appear.

Minimal reproduction project:

epoch_packet_hidden_node.zip

[Toshiwoz]

I have a very similar issue but with cubes.

As you can see from the gif, I used 3 cubes:

• external walls
  
  
  
  • internal walls (subtracts)
  
  
  • entrance (subtracts)
  
  

Depending on the position of the door it shows or not the artifacts.
Does it have to do with the snap property value?
Possibly related to #21125?

[dbenoy]

I get a lot of artifacts when I try to subtract one aggregate union from another in this project:

Edit: Oops. Messed up archiving the project. Recreated one with similar problems.
sandbox.zip

(Using 89f8b84)

[Francesco149]

same here, running 3.1-stable on linux x86_64 on a r9 270x with the amdgpu drivers

happens on both the es2 and es3 renderers

[ShyRed]

Here are the results of a debugging session using the sandbox project 😅

In the sandbox project I see 3 holes and get exactly 3 failed polygon triangulations.

One example:

0.000000000,0.000000000
0.549831629,0.725973845
0.588947773,0.687405705
0.549831629,0.725973845
0.000000000,0.000000000
0.549831629,0.725973845
0.000000000,0.000000000
0.633987665,0.642996907
1.40420127,1.42415524
1.07861471,1.42415524
0.549831629,0.725973845
0.549831629,0.725973845
0.000000000,0.000000000
0.633987665,0.642996907
0.549831629,0.725973845

which looks like

When putting the values into some online delaunay triangulation demo, I get a working triangulation.

Just use javascript console and put in the following:

demo.addAt(0.000000000*100,0.000000000*100);
demo.addAt(0.549831629*100,0.725973845*100);
demo.addAt(0.588947773*100,0.687405705*100);
demo.addAt(0.549831629*100,0.725973845*100);
demo.addAt(0.000000000*100,0.000000000*100);
demo.addAt(0.549831629*100,0.725973845*100);
demo.addAt(0.000000000*100,0.000000000*100);
demo.addAt(0.633987665*100,0.642996907*100);
demo.addAt(1.40420127*100,1.42415524*100);
demo.addAt(1.07861471*100,1.42415524*100);
demo.addAt(0.549831629*100,0.725973845*100);
demo.addAt(0.549831629*100,0.725973845*100);
demo.addAt(0.000000000*100,0.000000000*100);
demo.addAt(0.633987665*100,0.642996907*100);
demo.addAt(0.549831629*100,0.725973845*100);

which should result in the following:

So my current assumption is that either our triangulation is faulty or not tolerant enough since other implementation seem to be able to triangulate the polygon just fine?

[ShyRed]

After some more debugging and tinkering with the source code: The failed polygons do not seem to be the ones belonging to the holes / missing triangles :( I added delaunay triangulation to CSG in case polygon triangulation fails and the resulting triangles seem to belong to the shape(s) that are being subtracted with:

So I suspect it really is the CSG algorithm itself that is having trouble finding and closing all holes. Polygon triangulation seems fine and the invalid polygons should indeed not be triangulated.

[bojidar-bg]

Just a wild guess, but.. could it be that some vertices/edges/faces are assigned wrongly, thus creating the bad polygons and holes at once?

[nonoesimposible]

I'm seeing a similar issue, but with CSG union.

Edit: Moving the ramp very slightly away from the box so that their edges don't intersect at the same point (e.g. x=0.001) fixes the issue. Towards the box works also, just as long as they don't meet exactly.

[duckinator]

Encountered this with 3.1.1.stable.official. Similar to what @nonoesimposible said, fudging values by ±0.1 seems to fix things.

[ptrojahn]

I found a way to fix the holes in the example by @fire. Please retest your csg shapes. If you can please upload small example projects. Screenshots are pretty hard to debug.

[fire]

@ptrojahn There's a new approximate equal function that scales epsilon. It may be useful.

[fire]

https://github.com/godotengine/godot/blob/45be9c67ef4367b551e6c62b3f5fd246db41e825/core/math/math_funcs.h#L290

[Toshiwoz]

I found a way to fix the holes in the example by @fire. Please retest your csg shapes. If you can please upload small example projects. Screenshots are pretty hard to debug.

The issue opener seems to have done that:
https://github.com/godotengine/godot/issues/22988#issue-369814700

If you want more I can provide mine.

[fire]

My original test case is solved. Please open a new issue if you have other test cases.