Start all performance investigations with the profiler. Find out what is dogging your app down.
In the case you describe above, my first random guess is that you are doing too much in FixedUpdate().
This mistake can have an interesting sudden performance cliff appearance, where everything is fine and suddenly it drops down to 5 fps when you break that barrier of what can be safely done in the FixedUpdate() time window.
Do absolutely NOTHING in FixedUpdate() if possible, and when you must use FixedUpdate(), be sure it is 100% solely for transacting against the Physics or Physics2D engine and absolutely nothing else.
Here is some timing diagram help:
Two good discussions on Update() vs FixedUpdate() timing:
DO NOT OPTIMIZE “JUST BECAUSE…” If you don’t have a problem, DO NOT OPTIMIZE!
If you DO have a problem, there is only ONE way to find out. Always start by using the profiler:
Window → Analysis → Profiler
Failure to use the profiler first means you’re just guessing, making a mess of your code for no good reason.
Not only that but performance on platform A will likely be completely different than platform B. Test on the platform(s) that you care about, and test to the extent that it is worth your effort, and no more.
Remember that you are gathering information at this stage. You cannot FIX until you FIND.
Remember that optimized code is ALWAYS harder to work with and more brittle, making subsequent feature development difficult or impossible, or incurring massive technical debt on future development.
Don’t forget about the Frame Debugger either, available right near the Profiler in the menu system.
Notes on optimizing UnityEngine.UI setups:
At a minimum you want to clearly understand what performance issues you are having:
- running too slowly?
- loading too slowly?
- using too much runtime memory?
- final bundle too large?
- too much network traffic?
- something else?
If you are unable to engage the profiler, then your next solution is gross guessing changes, such as “reimport all textures as 32x32 tiny textures” or “replace some complex 3D objects with cubes/capsules” to try and figure out what is bogging you down.
Each experiment you do may give you intel about what is causing the performance issue that you identified. More importantly let you eliminate candidates for optimization. For instance if you swap out your biggest textures with 32x32 stamps and you STILL have a problem, you may be able to eliminate textures as an issue and move onto something else.
This sort of speculative optimization assumes you’re properly using source control so it takes one click to revert to the way your project was before if there is no improvement, while carefully making notes about what you have tried and more importantly what results it has had.
“Software does not run in a magic fairy aether powered by the fevered dreams of CS PhDs.” - Mike Acton