Physics Interpolation positions are incorrect when renderer set to MultiThreaded

[lawnjelly]

Godot version

3.5 beta 2, beta 3

System information

All

Issue description

Exhibits as the objects and Camera being rendered in incorrect positions.

Will add more info when I know more, but for now, recommend using the default safe single threaded renderer mode. This may be some assumption I've made about the order of operations and the interpolated lists are not getting flushed correctly / in order.

Steps to reproduce

Try 3D Platformer demo, set to low physics tick rate, turn physics interpolation on, switch to multithreaded renderer.

Minimal reproduction project

No response

[mrezai]

I have a project here that using Physics Interpolation. I tested multiple settings and these are what I found:

• When Thread Model = Multi-Threaded and Use V-Sync = ON, Engine.get_frames_per_second() returns inconsistent results that will be seen as jitters in player movement. This is unrelated to what Physics Interpolation is set to.
• When Thread Model = Multi-Threaded and camera.set_physics_interpolated(false), Physics Interpolation works correctly but if "Visible Collision Shapes" is enabled and player moves, position of debugging view of player's collision shape updated after couple of seconds and not instantly like when Thread Model = Single-Safe.
• When Thread Model = Multi-Threaded and camera.set_physics_interpolated(true), chaos happened! It seems like a bug in camera and not Physics Interpolation as a whole.

[lawnjelly]

Ah that will be useful info thank you. 👍

I'm sure this will not be too tricky, I'm just trying to finish up some work on PoolVector first, as I don't think this bug is super pressing as it is possible to just set to single-threaded renderer until it is fixed.

It could indeed be related to the Engine.get_frames_per_second() not working correctly in multithreaded, that is interesting (presumably that happens also before 3.5, I don't think I changed anything to do with this).

[mrezai]

You right, Engine.get_frames_per_second() has same behavior in Godot 3.4.2 when multithreading is enabled.

[Calinou]

When Thread Model = Multi-Threaded and Use V-Sync = ON, Engine.get_frames_per_second() returns inconsistent results that will be seen as jitters in player movement. This is unrelated to what Physics Interpolation is set to.

Remember that #52314 is not merged in master yet, and #48555 does not have a master counterpart yet.

[akien-mga]

Fixed by #60147.