[3.x] Physics Interpolation - Fix 3D CPUParticle restart bug

[lawnjelly]

Particles that were being emitted were having their data copied to previous particle data too early, missing some transform changes that could result in graphical anomalies in some situations.

Before

2024-06-08.11-51-33.mp4

After

2024-06-08.11-49-57.mp4

Notes

• Fixes emitted particles being overly large for a frame in 3D platformer demo.
• In retrospect this bug is obvious, was a no brainer to fix.

[Calinou]

Tested locally, this seems to resolve the issue partially with particle interpolation. I still notice the particles teleporting on spawn in the Platformer 3D demo if I re-enable physics interpolation on the bullet scene's particles:

3d_interpolation.mp4

The particle scale wobbling is fixed now still.

Testing project: platformer.zip

[lawnjelly]

Tested locally, this seems to resolve the issue partially with particle interpolation. I still notice the particles teleporting on spawn in the Platformer 3D demo if I re-enable physics interpolation on the bullet scene's particles:

That will (most likely) be a different issue (probably the lack of Node auto-restarts, rather than individual particle restarts). The artifact in your video doesn't actually appear on my 60hz monitor (even at 20tps) but it is likely it is lack of node auto-restart, possibly the Bullet/Sphere mesh instance rather than the particle system (you could also try hiding this to confirm).

I can't say 100% from my side as I can't reproduce, but it seems likely unless it is being introduced by this fix.

If you want to test that out try #92784 , which has this fix applied as part of it.

But really wanted this independently reviewed so we can get approved and merged asap (for 3.6) as it is separable, and doesn't change anything fundamental.

I'm thinking actually given the amount of testing that is finally happening, it might be worth still trying #92784 for 3.6, as these are all bug fixes rather than new features.

[lawnjelly]

Already merged as part of #92784.