GPUParticles interpolation does not affect property curves such as scale, color and rotation

[Calinou]

Godot version

4.0.dev (85186bc)

System information

Fedora 34, GeForce GTX 1080 (NVIDIA 465.31)

Issue description

The new GPUParticles3D interpolation feature smoothes out particle movement, but not property updates such as scale, color and rotation. This is important to fix as particle systems now run at 30 Hz (interpolated) by default, instead of running every frame like they did in 3.x.

This is with Fixed Fps set to 10 to make the issue more obvious:

gpuparticles3d-missing-interpolation.mp4

As a workaround, disable Fixed Fps or set it to a higher value like 60.

Steps to reproduce

• Create a GPUParticles3D node.
• Set up a particle system with color and scale changes using curves.
• Set Fixed Fps to 10, keep interpolation enabled.
• Movement is smooth, but curve changes are locked to 10 FPS.

Minimal reproduction project

test_gpuparticles_interpolation.zip

[QbieShay]

Since proposed fix has been bumped to 4.1, this should be bumped to 4.1 too.