Rigidbody2D jitters on FPS drops

[ural89]

Godot version: 3.3

Platforms: MacOS, Android

Issue description:
Hello there. I'm making a racing game. Player car and other cars are Rigidbody2D type objects. Gameplay is very smooth at 60 FPS. But sometimes even a little drop in FPS(50-55) causes rigidbodies to jitter. How do I fix that (except keep fps at 60. Because it will be a mobile game and maybe not everyone able to play it on 60 FPS). I tried both versiyon 3.2.3 and 3.3
Physics jitter fix: 0.5
Code looks something like this (I can send more detailed if needed):

func _physics_process(delta):
    if speed>speed_limit:           
            thrust = Vector2(0, 0)
    else:
            thrust = Vector2(engine_power, 0)
    set_applied_force(thrust.rotated(rotation))

Steps to reproduce:
Set your project FPS limit to 50. Set physics FPS to 60. Apply force to a Rigidbody2D. You will see object jitters.

Bugsquad edit: For reference, this was cross-posted on Godot forums: https://godotforums.org/discussion/26109/rigidbody2d-jitters-on-fps-drops

[Zireael07]

See https://docs.godotengine.org/en/stable/tutorials/misc/jitter_stutter.html and this addon: https://github.com/lawnjelly/smoothing-addon

[ural89]

See https://docs.godotengine.org/en/stable/tutorials/misc/jitter_stutter.html and this addon: https://github.com/lawnjelly/smoothing-addon

it only works if physics FPS is lower than screen FPS.

[Calinou]

it only works if physics FPS is lower than screen FPS.

The smoothing add-on can still do its job even if the physics FPS is equal to rendering FPS.

Out of curiosity, are you using a Camera2D node with smoothing enabled? Try changing its update mode to Process instead of Idle.

[ural89]

it only works if physics FPS is lower than screen FPS.

The smoothing add-on can still do its job even if the physics FPS is equal to rendering FPS.

Out of curiosity, are you using a Camera2D node with smoothing enabled? Try changing its update mode to Process instead of Idle.

Yes I have camera2D node smoothing on. It follows player car. I disabled it and changed mode to process. This time both camera and rigidbody jitters together (road jitters relatively).

[Calinou]

This kind of jittering fundamentally always happens whenever rendering FPS is not a multiple or divisor of physics FPS. For a physics FPS of 60, this means your rendering FPS must be one of the following values to avoid any jittering:

• …
• 10
• 12
• 15
• 20
• 30
• 60
• 120
• 180
• 240
• …

This should be resolved with the addition of fixed timestep interpolation. It's currently only available in 3D in 3.5beta1 and later, but it'll be ported to 2D eventually (after 3.5 is released).

As a workaround, you can increase Physics Fps in the Project Settings to a greater multiple of 60 (120, 180, 240, …). This will increase CPU usage, but it will offer more values for rendering to "latch on", which should help make jittering less noticeable. For example, if you set Physics FPS to 180, these are the rendering FPS values that won't suffer from jittering:

• …
• 360
• 180
• 90
• 60
• 45
• 36
• 30
• 25.7
• 22.5
• …

[Calinou]

Closing per the above comment.