Godot 3D Collision Shapes Not Behaving As Expected

[gm4real]

Tested versions

-Reproducible in: v4.5.mono.stable

System information

Windows 10 - Godot v4.5.mono.stable - Vulkan (Forward+) - Ryzen 5 5600G - 768p monitor

Issue description

Collision shapes in my project started behaving erratically since Godot 4.5. Normally, collision shapes would follow the player, camera, or rigid body smoothly. In my case, they're not. For context, I am using Jolt Physics instead of the default physics engine and I've not changed things for the most part since I've migrated to 4.5. I even tried opening a 4.4.1 backup project in 4.5 and it gave the same issue.
Here is a clip of the project in Godot 4.4.1 (videos are a bit bad quality due to hardware limitations):

clip1.mp4

And here is a clip of the same project in 4.5:

clip2.mp4

As you can see, the ray casts and collision capsule shake and tremble rapidly, and the faster the more violent, whenever I'm moving in any direction. And the rigid body sphere (the dark grey ball) is showing streaks and weird blue curves when moved around.

Steps to reproduce

Give a CharacterBody3D a collision shape, make a ray cast a child of it, and add a script to move the character around. Or give a RigidBody3D (preferably a sphere) a collision shape, and then move it around. I had Jolt Physics enabled, so it's better to have that on as well. I also had Debug > Visible Collision Shapes turned on to see for myself.

Minimal reproduction project (MRP)

The following link is for a barebones copy of the project where the issue occurred:

first-person-controller.zip

(Note: The project is an edited version of another project under an MIT license. Original project: https://github.com/LegionGames/FirstPersonController)

[mihe]

Seeing as how the shaking goes away when disabling the physics/common/physics_interpolation project setting, I'm guessing it might have something to do with #104269?

I'm unfortunately not very well acquainted with the gotchas of the physics interpolation, so I'm not sure what the fix would be in this case. Maybe you have some idea, @lawnjelly?

EDIT: The regression did seem to happen between 4.5-dev3 and 4.5-dev4, so likely caused by #104269.

[lawnjelly]

I answered a question on discord about this just the other day.

We are aware, it's because the debug physics were interpolated in 4.4, and in 4.5 the debug physics are not interpolated (since SceneTreeFTI) and show the correct position of the actual physics. These will jitter as seen in the viewport as you are looking from an interpolated camera, but the physics is actually correct, 4.4 is in some sense "incorrect" as it gives you a false impression of where the physics is.

Now, if by popular opinion we decide that just "looking nicer" trumps physically correct in this case.. we need to proceed with #104518 (or a variation) and then we can tell the debug physics to use this method (as debug physics doesn't use nodes, so can't use SceneTreeFTI).

In the short term, yeah it looks a bit weird, but it's not actually incorrect (or a bug per se) but we may decide to smooth it out.