P.S. :Whatever I say is regarding mobile platform but may apply to other platforms as well.
I have read that to make a game frame rate independent, one must multiply all calculations with Time.deltaTime which is basically the time required to complete the last frame. However, when the system slows down or when relatively heavy background applications pop-up,(which I have experienced first hand) the game also starts lagging.
However when I multiply the same calculations with Time.fixedDeltaTime, the game runs exactly at a specific rate or “speed” no matter how many background applications pop-up mid game play.
So this would be the best way to do it right? Well actually, NO!
When I run the same game on another system(phone), the speed or rate of the game is altered. Case in point, when I play the game on my SGS4 it runs faster than on another slightly lower end device.
THE QUESTION: THE LAG THAT I EXPERIENCE WITH Time.deltaTime, is that lag natural? Is it acceptable? I mean, a lot of games made by professional developers DO LAG!
Also,any reason why my game runs so jerky on the other device but runs so smooth on my SGS4? It’s a relatively simple game, not very heavy.Neither GPU intensive,nor RAM intensive.
I don’t know the reason your game lags but the use you are giving to Time.deltaTime and Time.fixedDeltaTime is possibly wrong.
Time.deltaTime is the time interval between current frame and the last one, which is the same than the time interval between two call to the Update() method. This means that Update() is going to be called a different number of times depending on the performance of your game.
On the other hand you have the method FixedUpdate() which works essentially as Update() but with the difference that it is going to be called a fixed amount of times per second. Naturally Time.fixedDeltaTime is the difference between two calls of FixedUpdate() and it always holds the same value.
As you see, it would make no sense using Time.fixedDeltaTime in the Update() method, if you do so you should move the logic that uses Time.fixedDeltaTime to the FixedUpdate() method. Same goes for Time.deltaTime, it is wrong (or at least very wierd) to use it in FixedUpdate().
Personally I use Update() for input recognition, since it is more likely to catch a key because it gets called more often. I use FixedUpdate() for everything else.
You should use Time.deltaTime whether you’re in FixedUpdate or Update. It will return the actual amount of time that has elapsed between calls of the method you use it in (it automatically detects whether its in FixedUpdate or Update and returns the correct value).
Time.fixedDeltaTime is the target update rate for FixedUpdates. The actual time elapsed between FixedUpdate calls may not match it.
Time.deltaTime is the amount of time between frames – the inverse of which would be your frames per second. It is a value you READ. It cannot be set.
Time.fixedDeltaTime relates to physics, and is the same interval. However, it is a value you SET. You can also read it. One use is to modify it when you do slow down, so your physics works: “Note that the fixedDeltaTime interval is with respect to the in-game time affected by timeScale.”