random.onUnitCircle ?

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there's random onUnitSphere, but it doesn't work as random.onUnitCircle if it's being reduced from Vector3 to Vector2.

what are there other ways of choosing a random point on a circle.(not inside it, not outside, just on the very edge)

Answer 1

Answer by Jumbo the Great · Jan 09, 2013 at 06:09 AM

THE EASIEST WAY IS THIS:

 Random.insideUnitCircle.normalized;

Just random inside unit circle first, and then normalized it. This will convert the vector to be 1 in magnitude, which is the same as random on unit circle. Hope this helps!

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semimono · Jun 01, 2018 at 06:14 AM 3

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This seems like a nice, concise solution. However, I think there is a very rare edge-case that this would fail under, which is if Random.insideUnitCircle returns (0, 0). In that case, according to this documentation, you would get a zero vector back after normalizing. If the code using this depends on getting a normalized vector, this might not be the best solution.

Yes, this case would be extremely rare, but that also makes for a bug that more than likely will never, ever be fixed. In addition, if this operation was performed many times (in a loop, or whatnot), the frequency of occurrences would go up. Given this (very rare) failure case, wrapping one of the less elegant solutions in a method might be better.

Astirian · May 26 at 02:32 PM 0

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Then why not just...

     IEnumerator TestNullVector()
     {
         var randomPointOnCircle = Random.insideUnitCircle.normalized;
 
         // Handle edge case of getting a 0f, 0f vector.
         var nullVector = false;
         if(randomPointOnCircle == new Vector2(0f, 0f)) { nullVector = true; }
 
         while(nullVector)
         {
             randomPointOnCircle = Random.insideUnitCircle.normalized;
             if(randomPointOnCircle != new Vector2(0f, 0f)) { nullVector = false; }
         }
 
         StartCoroutine(TestNullVector());
 
         yield return null;
     }

Answer 2

Answer by zannghast · Nov 08, 2010 at 01:45 AM

Similar to Peter's answer, you could get a random angle and pass that to a custom function that accepts an angle and radius.

It would be akin to something like:

 Vector2 GetUnitOnCircle(float angleDegrees, float radius) {
 
     // initialize calculation variables
     float _x = 0;
     float _y = 0;
     float angleRadians = 0;
     Vector2 _returnVector;
 
     // convert degrees to radians
     angleRadians = angleDegrees * Mathf.PI / 180.0f;
 
     // get the 2D dimensional coordinates
     _x = radius * Mathf.Cos(angleRadians);
     _y = radius * Mathf.Sin(angleRadians);
 
     // derive the 2D vector
     _returnVector = new Vector2(_x, _y);
 
     // return the vector info
     return _returnVector;
 }

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dot · Nov 08, 2010 at 05:07 AM 0

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thank you Dendro.

Peter G · Jan 10, 2011 at 03:15 AM 0

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sorry to bring back an old tread. Just happened to see it and I noticed that degrees to radians should be $$anonymous$$athf.PI / 180.0 since there are 2pi in a circle.

Answer 3

Answer by Peter G · Nov 08, 2010 at 12:36 AM

You could get a random value between 0 and 2pi radians then find the sin and cos of that and make them your values in a Vector2.

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Potter-Solutions · Mar 03, 2017 at 04:50 AM 1

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Here's the helper function I created based on your comment. It works great!

 public static Vector2 RandomPointOnUnitCircle(float radius)
 {
     float angle = Random.Range (0f, $$anonymous$$athf.PI * 2);
     float x = $$anonymous$$athf.Sin (angle) * radius;
     float y = $$anonymous$$athf.Cos (angle) * radius;

     return new Vector2 (x, y);

 }

Answer 4

Answer by avatara359 · Dec 14, 2012 at 09:20 PM

Another way: 1. Use Unity methods to get a random point. 2. Normalize the vector to be one unit long. 3. Multiply by radius to get desired length.

     public static Vector2 RandomOnUnitCircle2( float radius) 
     {
         Vector2 randomPointOnCircle = Random.insideUnitCircle;
         randomPointOnCircle.Normalize();
         randomPointOnCircle *= radius;
         return randomPointOnCircle;
     }
     public static Vector3 RandomOnUnitSphere( float radius) 
     {
         Vector3 randomPointOnCircle = Random.insideUnitSphere;
         randomPointOnCircle.Normalize();
         randomPointOnCircle *= radius;
         return randomPointOnCircle;
     }

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Answer 5

Answer by GingerLoaf · Dec 30, 2014 at 02:23 AM

I was surprised to see so much resistance to trig here. As game programmers, we should either strive to make our code optimal (not use a bunch of high-level calls that bring in extra overhead) as well as improve what we know as far as not just programming, but mathematics. Peter G deserves the answer to this thread, as he provided the answer. I can't say whether or not it is the absolute best option, but it is most certainly hard to think of something that can compete. Using Peter G's suggestion, I was able to produce this:

 float randomAngle = Random.Range(0f, Mathf.PI * 2f);
 Vector2 randomPointAround2DCircumference = new Vector2(Mathf.Sin(randomAngle), Mathf.Cos(randomAngle)).normalized;

Wrapping this in a function should now be fairly easy:

  public Vector2 GetPointOnUnitCircleCircumference()
  {
      float randomAngle = Random.Range(0f, Mathf.PI * 2f);
      return new Vector2(Mathf.Sin(randomAngle), Mathf.Cos(randomAngle)).normalized;
  }

I have tested this in Unity and I am seeing the intended results. Enjoy!

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Oscaruzzo · Sep 07, 2015 at 09:38 PM 3

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Of course you don't need to normalize that. It's already normalized ;)

random.onUnitCircle ?

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