[Jolt] Ghost Collisions

[yahkr]

Tested versions

• Reproducible in v4.4.beta3.mono.official [06acfcc] (with built-in jolt)
• Reproducible in v4.3.stable.mono.official [77dcf97] (with godot-jolt plugin)

System information

Godot v4.4.beta3.mono - Windows 11 (build 22631) - Single-window, 2 monitors - Vulkan (Forward+)

Issue description

Experiencing ghost collisions on Rigidbody3D to static ConcavePolygonShape3D collisions.

Related to #89458

Jolt Physics (the body gets randomly stuck, the video does not pause when the body does):

phys1.mp4

Godot Physics:

phys2.mp4

Steps to reproduce

Create a flat ConcavePolygonShape3D with dense vertex count
Make Rigidbdoy3D slide across surface
Observe ghost collisions

Minimal reproduction project (MRP)

MRP.zip

[mihe]

I simplified the MRP a bit, mainly to not require a Blender import, but also to rule out a few things: jolt-ghost-collision.zip

I have...

• Created a new ConcavePolygonShape3D based on a subdivided PlaneMesh
• Reset all the project settings
• Reset all the properties of the RigidBody3D, including the axis locks
• Set friction to zero for the RigidBody3D
• Changed it to apply only an initial linear velocity to the RigidBody3D

Despite all that, the ghost collisions seem to generally persist, albeit at different places.

This one has me scratching my head a bit, @jrouwe. As best I can tell there seems to be something odd going on with mEnhancedInternalEdgeRemoval, as disabling it using the physics/jolt_physics_3d/simulation/use_enhanced_internal_edge_removal project setting (and thus falling back on the active edge detection) resolves the ghost collisions.

I'm able to recreate the issue in Jolt's Samples application using a snapshot as well: jolt_snapshot_2025-02-07_23-47-36_4462471020544.zip

Samples.mp4

[mihe]

When tinkering with some other subdivisions, the problem does seem to be related to the size of the triangles in some way.

Here's another version of the above revised MRP, with some different triangle densities: jolt-ghost-collision.zip

... which looks like this:

godot.windows.editor.dev.x86_64_xUhlw9ypyf.mp4

Here's a snapshot of that scene (right after applying the impulses): jolt_snapshot_2025-02-08_15-53-14_4578435137536.zip

... which looks like this in Jolt's Samples application:

Samples_yUdWVZA5o3.mp4

[jrouwe]

Thanks for the investigations @mihe! I will take a look at this.

[jrouwe]

I've created a fix, see #102614.