Error "Manifold creation from mesh failed" with CSGMesh3D causing Plane and Quad meshes not to get rendered.

[TCROC]

Tested versions

I bisected and can confirm it was introduced by pr: #94321

I suspect issue #99888 was also introduced by the same PR.

Versions of Godot before this PR work fine. Versions of Godot after this PR error ranging from crashing to error messages depending on if you use a commit before the crash fix. The crash fix only fixed the crash though. The meshes still error and do not render which is what this issue is for.

System information

Godot v4.4.dev.mono (01b508724) - Pop!_OS 22.04 LTS on Wayland - X11 display driver, Multi-window, 3 monitors - Vulkan (Forward+) - dedicated Intel(R) Arc(tm) A750 Graphics (DG2) - AMD Ryzen 7 5800X 8-Core Processor (16 threads)

Issue description

Certain CSGMesh3Ds error and do not render. The ones I have discovered so far are planes, quads, and ribbon trail meshes. Here are some screenshots demonstrating.

Before #94321

After #94321

Crash with log:

Manifold creation from mesh failed:2
Manifold creation from mesh failed:2
Manifold creation from mesh failed:2

Master + #99959 that improves error messages

NOTE: Error messages without a crash are in current master. They just aren't as detailed as #99959 improves them to be

As you can see in the third one, the first three meshes do not draw and instead error in the console.

Steps to reproduce

1. Download the attached MRP
2. Open up main.tscn
3. See the error messages and meshes not being drawn
4. I use double precision + mono support. I do not know if this is required.

Minimal reproduction project (MRP)

mrp.zip

[elalish]

From the Manifold perspective, this is working as intended - we only operate on manifold meshes (e.g. watertight, containing volume), because those are the only kind of meshes for which Boolean operations like CSG are well-defined. If you take two quads and partially-intersect them and then try to subtract one from the other, what would you expect for a result?

[TCROC]

@elalish I'm confused. So its intended that Godot no longer renders planes and quads?

[fire]

Planes and quads that have volume are thin wedges and rectangular prisms. These can be CSG'd geometrically, but not perfectly thin quads or planes since they have no volume.

[fire]

We have this quote in the original design of CSG.

https://godotengine.org/article/godot-gets-csg-support/

Any mesh can be used for CSG, this makes it easier to implement some types of custom shapes. Even multiple materials will be properly supported. There are some restrictions for geometry, though:

It must be closed
It must not self-intersect
Is must not contain internal faces
Every edge must connect to only two other faces

This disallows planes and quads, as everything in CSG is now a CSGMesh3D.

[TCROC]

I'm still confused. Prior to pr #94321 , planes and quads rendered fine. Now Godot pushes errors and doesn't render planes and quads. This is expected behavior?

I'm personally not familiar with anything related to manifolds. But the behavior that I am visibly seeing feels like an error. And if it's not an error, I feel like it's a significant breaking change that we should reconsider as many (likely most) games such as ours rely on planes and quads as meshes in 3d space. The heaviest usages being particles and foliage.

But again, I'm not familiar with manifolds. If you guys are agreeing that this is an issue while simultaneously offering an explanation as to why this issue is happening, that explanation was entirely lost on me due to my ignorance of manifolds 😅

[TCROC]

Okay I just read that article on csg. Thanks @fire :) I noticed that is from 2018. So planes and quads have worked with csg since then. What changed? Maybe I should be using a different node for planes and quads? Are planes and quads no longer supported for csg?

[fire]

From a technical point of view, supporting planes and quads with the CSG nodes is impossible. We noticed they used to work, and many have used them in their games. Still, a significant reason the CSG nodes were having corruption issues is that we needed to be more consistent with manifold definitions and apply them consistently in code.

I want to help draft a release note for the next release including this CSG feature. Help wanted.

[TCROC]

Ah I see. What node should be used instead for planes and quads?

Also, should planes, quads, and ribbon trails be removed as options in csg? You can presently pick them.

[fire]

Adding depth to them will work in a mathematical sense.

[TCROC]

But how about without depth. With foliage and such. Does Godot just have a plane or quad node?

I don't need the csg. Prior to this I didn't even know what csg was. But it's really cool and I'll find a usage for it. For now tho, I and many (if not most) of Godot's user base need quads and planes without depth. Does Godot have a node for this?

[fire]

Are you aware of the MeshInstance3D node with a Mesh of type PlaneMesh, RibbonTrailMesh or QuadMesh?

new-game-project.zip