Question Physics Slowing Down

Hello! I am relatively new to Unity. So far it's been going great! I've been able to work on projects with consistent ease and hardly any issues. Except for this one. I'm making a project mostly oriented around physics and things like so. I have three active objects, so there shouldn't be any performance issues. In the Unity editor, the speed is how I like it, but when compiled, it slows down to unfathomably low speeds. How do I fix this?

 

By far the most likely reason is that you have written code which is framerate dependent.

In other words - your code behaves differently at different framerates. Typical reasons for this would be:

• Not using Time.deltaTime when you should be.
• Using Time.deltaTime when you should NOT be.
• Doing physics in Update rather than FixedUpdate

Without seeing your code it's hard to say exactly what's wrong, but likely something in that domain.

 

If you are doing a lot of stuff in FixedUpdate() you can reach a point where the fixed timing loops "saturate" out and frame rate will plunge.

It is a very unstable suddenly-goes-to-10fps effect, something I witnessed when I processed my own particle system pieces and inadvertently hooked them into my FixedUpdate() loop... everything ran fine until the moment that task reached 1/50th of a second, and then the actual Update() rate dropped massively, almost to a slideshow.

Generally only do things in Update(); except for directly-physics-facing stuff, which should go in FixedUpdate();

Here is some timing diagram help:

https://docs.unity3d.com/Manual/ExecutionOrder.html

Two good discussions on Update() vs FixedUpdate() timing:

https://jacksondunstan.com/articles/4824

https://johnaustin.io/articles/2019/fix-your-unity-timestep

Beyond that, break out the profiler (Window -> Analyze -> Profiler) and track down what's going on.