Implement particle seek request, get rid, and seed normalization

[QbieShay]

2024-05-18.18-45-36.mp4

Works ONLY with GPUParticles3D for now.

Test project:
particles-skim-test.zip

This PR exposes the required API to then construct better particle timing tools on top of existing particles.
I implemented the seed control in this PR because otherwise any restart() would change the seed, which makes seeking impossible.

TODO

• Implement request_process_time for CPUParticles
• Implement rnadom seed for GPUParticles2D
• Implement random seed for CPUParticles2D/3D

Closes godotengine/godot-proposals#6226
Simpler approach than godotengine/godot-proposals#7085 for editor purposes

[Calinou]

Tested locally, it works as expected.

One strange thing I noticed though is that when you set particle seed mode to Random then restart particle emission, the seed is changed to a random value which you can see after changing it back to Custom. This makes sense, but this seed is always capped to 1 million due to the inspector hint:

See the second suggestion below which aims to address this.

PS: Are there any plans to expose a high-level GPUParticles3D property that allows for easy seeking, without needing a custom script? I assume this would need to force speed scale to be 0 though (like AnimationPlayer's Manual process mode).

[Calinou]

I'd document this 30 FPS fallback for particles with fixed FPS set to 0 in the class reference in the fixed_fps description, as well as RenderingServer.particles_set_request_process_time().

[QbieShay]

@Calinou yeah definitely I would like to get to something that has a slider to seek. I don't know yet what should be the design because I have a couple of ideas I want to explore. Those being:

• maybe a vfx node, that encapsulates things for all particles.
• maybe a particles track that does special things (seek) in editor
• maybe a mix of the two?

There's also the issue that CPUParticles are not managed by the rendering server so i question whether the rendering server API is the correct way to go, or if i should keep that internal and only expose it via the node with the same interface for cpu and gpuparticles.

For now I'm stuck there but I haven't really dedicated more time to this yet.

[QbieShay]

Oh and thank you for testing even in the incomplete state!!

[QbieShay]

One strange thing I noticed though is that when you set particle seed mode to Random then restart particle emission, the seed is changed to a random value which you can see after changing it back to Custom. This makes sense, but this seed is always capped to 1 million due to the inspector hint:

I noticed that as well, and I am not sure why it resets even if the seed is set manually. For what i thought i wrote in the code, it should be possible to override the seed, but it doesn't seem to be working.

[QbieShay]

add pre process on clear