Pick random point inside box collider

Using this script i almost get the effect I want, but some points that get picked are a bit outside the box collider. Am I missing something?

Code (CSharp):

1. private Vector3 RandomPointInBox()
2.     {
3.         return _collider.bounds.center + new Vector3(
4.            (Random.value - 0.5f) * _collider.bounds.size.x,
5.            (Random.value - 0.5f) * _collider.bounds.size.y,
6.            (Random.value - 0.5f) * _collider.bounds.size.z
7.         );
8.     }

 

You can simply use Random.Range instead and get a random point inside a Bounds, like this:

Code (CSharp):

1. public static Vector3 RandomPointInBounds(Bounds bounds) {
2.     return new Vector3(
3.         Random.Range(bounds.min.x, bounds.max.x),
4.         Random.Range(bounds.min.y, bounds.max.y),
5.         Random.Range(bounds.min.z, bounds.max.z)
6.     );
7. }

And use the method like this:

Code (CSharp):

1. RandomPointInBounds(myCollider.bounds);

Hope this helps.
Thanks.

 

This is really nice, but do you know of a solution that takes the rotation of the transform into account? This will always act as if the rotation is 0,0,0.

 

Collider bounds always form an AABB. You'll need to cache the original bounds, without rotation, and then use TransformPoint on them to form an OBB.

 

Cool, whats an OBB?

 

AABB is Axis-Aligned. It never rotates, rather shrinks and grows to contain the entire object.

An OBB is Object-Aligned. It does not need to shrink or grow as it follows the orientation of the enclosed object. GroZZleR's point is that Unity handles the AABB but it is up to you to handle the OBB yourself.

 

So does anyone have the *complete* code to do this that works with rotation, scale and position of the box collider on a gameObject?

 

I use collider.ClosestPoint method to know if the point is inside. The point is inside if the returned vector is equal to the point, otherwise it's out of the collider:

Code (CSharp):

1. Vector3 GetRandomPointInCollider()
2.     {
3.         var point = new Vector3(
4.             Random.Range(collider.bounds.min.x, collider.bounds.max.x),
5.             Random.Range(collider.bounds.min.y, collider.bounds.max.y),
6.             Random.Range(collider.bounds.min.z, collider.bounds.max.z)
7.         );
8.  
9.         if (point != collider.ClosestPoint(point))
10.         {
11.             Debug.Log("Out of the collider! Looking for other point...");
12.             point = GetRandomPointInVolume();
13.         }
14.  
15.         return point;
16.     }

 

Came here looking for a quick copy/paste job, didn't get it

Unfortunately I'm not a huge fan of tetto_green's recursive method. While it works, it could theoretically loop infinitely (although the probability is it won't). My code mathematically gets a point within the bounds on the "first try", so to speak.

So for any future lazy programmers like me, here's the copy/paste.

First, here's the "nice way" as an extension to the BoxCollider class because I'm fancy and like things clean.

Code (CSharp):

1.  
2. public static Vector3 GetRandomPointInsideCollider( this BoxCollider boxCollider )
3. {
4.     Vector3 extents = boxCollider.size / 2f;
5.     Vector3 point = new Vector3(
6.         Random.Range( -extents.x, extents.x ),
7.         Random.Range( -extents.y, extents.y ),
8.         Random.Range( -extents.z, extents.z )
9.     );
10.  
11.     return boxCollider.transform.TransformPoint( point );
12. }
13.  

For anyone who doesn't know, make sure to place the above code inside a static class, so something like "public static MyExtensions { ...(code here) }". Then it can be used as

Code (CSharp):

1. BoxCollider b;
2. ...
3. Vector3 point = b.GetRandomPointInsideCollider();

And here's the simple method in case someone is unfamiliar with extension methods:

Code (CSharp):

1.  
2. public Vector3 GetRandomPointInsideCollider( BoxCollider boxCollider )
3. {
4.     Vector3 extents = boxCollider.size / 2f;
5.     Vector3 point = new Vector3(
6.         Random.Range( -extents.x, extents.x ),
7.         Random.Range( -extents.y, extents.y ),
8.         Random.Range( -extents.z, extents.z )
9.     );
10.  
11.     return boxCollider.transform.TransformPoint( point );
12. }
13.  

Enjoy!

 

OpticalOverride - this is great. If your boxcolliders aren't centered, you'll also want to add boxCollider.center to your point value before you transform it:

Code (CSharp):

1. public Vector3 GetRandomPointInsideCollider( BoxCollider boxCollider )
2. {
3.     Vector3 extents = boxCollider.size / 2f;
4.     Vector3 point = new Vector3(
5.         Random.Range( -extents.x, extents.x ),
6.         Random.Range( -extents.y, extents.y ),
7.         Random.Range( -extents.z, extents.z )
8.     )  + boxCollider.center;
9.     return boxCollider.transform.TransformPoint( point );
10. }

 

I had to implement these functions for the 2D physics system, so here's the code for a

BoxCollider2D

and a

CircleCollider2D

using extension methods to get a cleaner syntax:

Code (CSharp):

1.  
2. public static Vector2 GetRandomPoint(this BoxCollider2D box) {
3.  
4.         Vector2 extents = box.size * 0.5f;
5.  
6.         Vector2 localPoint = new Vector2(
7.             Random.Range(-extents.x, extents.x),
8.             Random.Range(-extents.y, extents.y)
9.         );
10.  
11.         localPoint += box.offset;
12.  
13.         return box.transform.TransformPoint(localPoint);
14.     }
15.  
16.     public static Vector2 GetRandomPoint(this CircleCollider2D circle) {
17.  
18.         float angle = Random.Range(0, Mathf.PI * 2);
19.         float distance = circle.radius * Mathf.Sqrt(Random.Range(0f, 1f)); // sqrt for even distribution
20.  
21.         Vector2 localPoint = new Vector2(distance * Mathf.Cos(angle), distance * Mathf.Sin(angle));
22.         localPoint += circle.offset;
23.  
24.         return circle.transform.TransformPoint(localPoint);
25.     }

One note: Unity's circle collider always remains a circle even under scaling transformations, but this version scales the random point according to the transform, so you can use this to generate random points in an ellipse as well.

Usage is like this:

box.GetRandomPoint()

or

circle.GetRandomPoint()

I also have one for

CapsuleCollider2D

, if anyone's interested, but its kind of a mess and it only handles local scaling correctly. It doesn't work properly if the parent has non-uniform scaling.