Access 2 of the 3 components of Vector3 (Vector3.xy?)

Question

Hey guys,

I need to do something like the following

 function Main()
 {
     Vector3 vector = arrayOfVerts[0];
 
     calculationFunc(vector.xy);
 }
 function calculationFunc(Vector2 theVector2)
 {
     //Use only those components to calculate something
 }

The problem is at the vector.xy. Unlike in GLSL, you can't access components like that (apparently). What would be the most performance-wise way of doing this?

Answer 1

Best Answer

Answer by Bunny83 · Jun 11, 2013 at 03:09 PM

I just want to sum up some ways:

 // our vector3
 var vec = new Vector3(1,2,3);
 
 // #1 The usual way
 var tmp = new Vector2(vec.x, vec.z);
 
 // #2 Your way
 var tmp = getAxis(vec, Axis.x, Axis.z);
 
 // #3 My way ;)
 var tmp = vec.xz();

My way requires you to add this extension class to your Standard Assets folder:

 // Vector3Extensions.cs
 // C#
 using UnityEngine;
 
 public static class Vector3Extensions
 {
     public static Vector2 xy(this Vector3 aVector)
     {
         return new Vector2(aVector.x,aVector.y);
     }
     public static Vector2 xz(this Vector3 aVector)
     {
         return new Vector2(aVector.x,aVector.z);
     }
     public static Vector2 yz(this Vector3 aVector)
     {
         return new Vector2(aVector.y,aVector.z);
     }
     public static Vector2 yx(this Vector3 aVector)
     {
         return new Vector2(aVector.y,aVector.x);
     }
     public static Vector2 zx(this Vector3 aVector)
     {
         return new Vector2(aVector.z,aVector.x);
     }
     public static Vector2 zy(this Vector3 aVector)
     {
         return new Vector2(aVector.z,aVector.y);
     }
 }

It will also work from UnityScript, but Monodevelop doesn't seem to provide intellisens for the extension methods, however it works ;)

edit

Just to have it complete:

1 is the fastest and most efficient way
2 is the most inefficient way of the 3 because it uses the indexer of vector3 two times and involves a function call
3 in the middle since it also requires an additional function call but it has the shortest syntax.

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Sequence · Jun 11, 2013 at 07:28 PM 0

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Thank you for your great post! In my actual code I'm using the indexer as a way of making a function dynamic. So ins$$anonymous$$d of having calculateUsingXY and calculateUsingZY I pass two integers that serve as the lookup indexes. The get axis was just an example (sorry about that). Are lookup indexes less efficient than Vector3.x?

Bunny83 · Jun 12, 2013 at 12:30 AM 0

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Well, indexers are just special properties, so reading them is also a function call. Besides that the indexer is implemented like this:

 public float this[int index]
 {
     get
     {
         switch (index)
         {
         case 0:
             return this.x;
         case 1:
             return this.y;
         case 2:
             return this.z;
         default:
             throw new IndexOutOfRangeException("Invalid Vector3 index!");
         }
     }
     set
     {
         switch (index)
         {
         case 0:
             this.x = value;
             break;
         case 1:
             this.y = value;
             break;
         case 2:
             this.z = value;
             break;
         default:
             throw new IndexOutOfRangeException("Invalid Vector3 index!");
         }
     }
 }

That means each look up will cause 1 to 3 comparisons

Sequence · Jun 15, 2013 at 04:01 PM 0

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Excellent in-depth knowledge! Thanks!

Fattie · Jan 21, 2015 at 05:25 AM 0

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FTR bud, you forgot the UnityEngine. on the declaration line of the functions, or, the "using" ! :)

Answer 2

Answer by Sequence · Jun 11, 2013 at 02:40 PM

EDIT: See accepted answer and explanations that go with it, much better than mine.

Future reference for anyone coming across this in the future. This is what I did. Vector3s' components can be accessed like an array.

 Vector3 bobTheVector = new Vector3(1, 2, 3);
 
 float oneAxis = bobTheVector[0];

Here's the way I implemented it.

 enum Axis : int {x = 0, y = 1, z = 2}
 
 function getAxis(Vector3 theVector, int a, int b)
 {
      return Vector2(theVector[a], theVector[b]);
 }

The enum is just incase you want to do something like Axis.x instead of remembering that 0 is the x axis.

 getAxis(new Vector3(1, 2, 3), Axis.x, Axis.z);

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Access 2 of the 3 components of Vector3 (Vector3.xy?)

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