Stutter in with transform interpolation on

[vladinator1000]

Hey folks, I think I discovered a potential issue, check out this stuttering:

2025-01-11.14-21-06.mp4

Originally I thought it was caused by the tnua library (idanarye/bevy-tnua#78) but the author said tnua doesn't mutate the transform, and the velocity remains constant. This makes us think that might be an Avian bug.

I followed these steps to reproduce:
Cloned tnua from: https://github.com/idanarye/bevy-tnua

On Windows 11, ran the demo with this command (set the wgpu backend env var to prevent log noise in the terminal):

$env:WGPU_BACKEND="dx12"; cargo run --bin platformer_2d --features avian2d

I've tried to debug, following these docs:

1. Adding a TransformExtrapolation and TransformInterpolation component to the setup_player function in for_2d_platformer.rs
2. Changing the physics plugin addition fn main in platformer_2d.rs to

               app.add_plugins(
                    PhysicsPlugins::new(FixedPostUpdate)
                        .set(avian2d::interpolation::PhysicsInterpolationPlugin::interpolate_all()),
                );

But the stutter was still present.

Possibly related links:

• Bevy time jitter issue Res<Time> is unreliable / jittery bevyengine/bevy#4669
• Avian jitter issue Jitter when making the camera follow a physics object #211
• Bevy discord help thread: https://discord.com/channels/691052431525675048/1327424197298753666/1327424197298753666

[idanarye]

Hypothesis: maybe it's the debug render who stutters?