Particle jitter on low speed scale, when the SceneTree is paused or when process mode is Disabled due to interpolation

[KoBeWi]

Godot version

cf8e9fd

System information

W10

Issue description

When you set speed_scale of particles to low value, e.g. 0.1, this happens:

Steps to reproduce

1. Add GPUParticles2D
2. Add some material etc.
3. Set time_scale to 0.1

Minimal reproduction project

No response

[Calinou]

The interpolation likely doesn't take the time scale into account. Can you reproduce this if you disable interpolation in the GPUParticles2D node?

[KoBeWi]

You mean fract_delta? It doesn't change anything.

[Calinou]

GPUParticles3D has this property:

It looks like it wasn't ported to GPUParticles2D yet: #55357

[RPicster]

This problem is not only happening on slow time scales - it's only making it more visible.
It's also extremely visible when using the orbit parameter.

[Calinou]

To work around this, disabling Interpolation and setting Fixed Fps to 0 (or a very high value such as 1000) seems to do the trick.

[Calinou]

This problem is not only happening on slow time scales - it's only making it more visible. It's also extremely visible when using the orbit parameter.

This may be due to #51318.