Performance Question: function parameters vs points and multiplication vs checks

Unity Engine
,
1

Hi, I couldn’t find the answer to this and I’m hoping someone knows off the top of their head.

I heard that pointers are kind of slow on iPhone… but I don’t know if passing parameters would be faster (unless I suppose they are used many times).

I want to know if it is more efficient (in iPhone development) to pass parameters from a object to a function… or to reference the object’s variables through a pointer from the method.

Also I want to know whether doing a radius check, which would allow for fewer calculations, would be faster than doing a nested if with single dimensional checks… eg:

Doing a couple single dimension checks first to avoid multiplication 99% of the time:

float xDiff = 0;
float zDiff = 0;
float sqrDist = 0;
float minCollisionDistance = 2;
float minSqrCollisionDistance = 4;

for (int i = 0; i < enemies.Count; i++) {       
     xDiff = enemies[i].x - x;
                    
     if (Mathf.Abs(xDiff) < minCollisionDistance) {

           zDiff = enemies[i].z - z;

           if (Mathf.Abs(zDiff) < minCollisionDistance) {
                        
                sqrDist = xDiff * xDiff + zDiff * zDiff;
                           
                if (sqrDist < minSqrCollisionDistance) {                               
                    PerformSomething(); 
                }
          }
     }   
}

or would this be faster to cut out the extra checks:

float xDiff = 0;
float zDiff = 0;
float sqrDist = 0;

for (int i = 0; i < enemies.Count; i++) {       
     xDiff = enemies[i].x - x;
     zDiff = enemies[i].z - z;      
     sqrDist = xDiff * xDiff + zDiff * zDiff;
                           
      if (sqrDist < minSqrCollisionDistance) {                               
            PerformSomething(); 
      }
         
}

The first one will 90 percent of the time not need to check further than the first check ( if (Mathf.Abs(xDiff) < minCollisionDistance) )… but if the Mathf.Abs is about the same speed as the multiplications in the second one then it would be less efficient.

Also… should I be iterating through a List using a “(for int i = 0 ; i < list.Count; i++)” or would it be better to use a iterator.

Also, and maybe this is what I should have asked, is there anywhere good documentation to scripting for the iPhone hardware. I’ve only ever come across bits and pieces.

2

Generally calling square roots for an early out is bad practise. Simple if (x>y) stuff is usually the way to go… Also enemies.Count could be evaluated every loop. Try stuffing that in a variable which has been pre allocated.

You’re doing a full distance check when you should just check a rectangle which is fastr as you can check x, and if that passes, check y and if that passes finally call your sqr then performsomething. It will discard a lot more and run faster with more objects.

3

The best thing you can always do is just make a benchmark test and see for yourself. Although it’s probably better to think of higher-level optimizations, such as is this in Update, and could it be less often instead? Like use InvokeRepeating a few times per second or whatever.

–Eric

4

That’s true, I’ve been lazy about that.

Someone told me today that (for Lists anyway) it will be still faster to use a iterator than a integer for running through the List…

foreach (Enemy enemy in enemies) {  
   // Do Calculations
}

Because that way it doesn’t have to travel through the List each time to access the contents (because Lists are not stored continuously, or so I hear).