2d Physics Interpolation in scenes with thousands of Nodes decreases performance a lot even when doing nothing

[MatthiasBae]

Tested versions

v4.5.stable.mono.official [876b290]

System information

Godot v4.5.stable.mono - Windows 11 (build 26100) - Multi-window, 2 monitors - Vulkan (Forward+) - dedicated NVIDIA GeForce RTX 4070 Ti (NVIDIA; 32.0.15.8129) - 13th Gen Intel(R) Core(TM) i9-13900KF (32 threads) - 31.81 GiB memory

Issue description

When having a scene with a lot of subscenes / nodes turning physics interpolation on in the project settings decreases the performance a lot.

In my case from about 500 FPS to about 100 FPS. Initially mentioned in a different issue which lacks a GDScript MRP. So I made one.

Even when nothing happens in game and nothing is moving the FPS is constantly low. I would expect higher FPS as there is no need for interpolating positions when nothing is moving.

Steps to reproduce

1. Create a scene which has about 10.000 Nodes
2. Check FPS
3. Turn on "Physics Interpolation" in the Project Settings
4. Check FPS again

Minimal reproduction project (MRP)

Physics Interpolation Test.zip

[lawnjelly]

Limited amount of time to look at this today (I'll be back after the weekend) but a quick profile shows that in 2D it does interpolation for all items, whether or not they are moving.

This is normally not a problem (providing reasonable amount of items on screen), but it can be compounded in some situations in 4.x, as it doesn't have 2D hierarchical culling (it processes items that are off screen as well as on screen) and doesn't have MultiRect, so it does a lot more per item processing than 3.x.

It's possible I can optimize this to reduce the processing on non-moving items as this seems more of an issue in 4.x.

Although no promises at this stage : 2D rendering combines the camera in the 2D xforms. I can't remember the details as it is a few years since I wrote this, and there was probably a reason why it doesn't do this already.

In 3D in contrast, there is no cost for FTI with non-moving items, but 3D processing for rendering is totally different.. there are trade-offs either way.

UPDATE:
It looks like I may have simply forgotten to check one of the flags, which should speed up performance in this case for 4.x particularly. I'll double check this is correct after the weekend and do a 4.x version. 👍

[MatthiasBae]

Thanks for looking into it!

(it processes items that are off screen as well as on screen)

This is something which is not possible to change? I am not that deep in the technical details and how engines work so this is not obvious for me but in theory it would make sense to not process the items which are offscreen?