How should scripts cache a function result each frame?

Question

I'm looking for a good way to cache an expensive function's result each frame. This code looks like it will work, but it's a bit complicated and requires deriving from MonoBehavior.

It seems like this would be needed often with Unity, since update order is unknown. Is there a better way to do it?

using UnityEngine; using System.Collections;

public class MyClass : MonoBehaviour { bool enableLateLateUpdate = true; static bool myVarCachedThisFrame = false; static float myVar;

 void Start() {
     StartCoroutine(LateLateUpdate());
 }

 public static float MyVar {
     get {
         if (myVarCachedThisFrame) return myVar;

         //some expensive calculation:
         myVar = Mathf.Sqrt(Mathf.Sqrt(Mathf.Sqrt(myVar)));

         myVarCachedThisFrame = true;
         return myVar;
     }
 }

 IEnumerator LateLateUpdate() {//Coroutines update after LateUpdate.  I think.
     while (enableLateLateUpdate) {
         MyClass.myVarCachedThisFrame = false;
         yield return 0;//wait one frame
     }
 }

}

Answer 1

Best Answer

Answer by duck · May 09, 2010 at 09:51 AM

You could simplify this by using Time.frameCount.

Simply check whether the frame count has increased since last time you calculated the expensive value.

Eg:

public static float MyVar { get { if (lastCalculatedFrame == Time.frameCount) {

         // return cached value
         return myVar;

     } else {

         // some expensive calculation:
         myVar = Mathf.Sqrt(Mathf.Sqrt(Mathf.Sqrt(myVar)));

         lastCalculatedFrame = Time.frameCount;
         return myVar;
     }
 }

This removes the need for a coroutine at all, and puts the responsibility of when to recalculate within the property code itself.

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Dylan Fitterer · May 09, 2010 at 03:33 PM 0

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That's better. Thanks!

Also, it looks like I may have been wrong about coroutines updating after late update. The last post on this question shows them updating between update and lateupdate: http://answers.unity3d.com/questions/1405/is-function-update-short-for-function-start-whiletrue

Mike 3 · May 09, 2010 at 04:15 PM 0

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http://www.unifycommunity.com/wiki/index.php?title=Event_Execution_Order

read this - it gives information about the order each type of event (including coroutines) is called in

Dylan Fitterer · May 09, 2010 at 05:36 PM 0

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Thanks. So the way I posted above would work as intended if the LateLateUpdate coroutine yielded on WaitForEndOfFrame.

How should scripts cache a function result each frame?

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