XNA Random Point On Plane

This method generates random points in a circle with a specified radius. The circle lies on a plane defined with a position and a normal. The generated points have an uniform distribution.

Random _random = new Random();

private Vector3 RandomPointOnPlane(Vector3 position, Vector3 normal, float radius)
{
 Vector3 random = new Vector3();
 Vector3 randomPoint;

 do
 {
  random.X = 2.0f * (float)_random.NextDouble() - 1.0f;
  random.Y = 2.0f * (float)_random.NextDouble() - 1.0f;
  random.Z = 2.0f * (float)_random.NextDouble() - 1.0f;
  Vector3.Cross(ref random, ref normal, out randomPoint);
 } while (randomPoint == Vector3.Zero);

 randomPoint.Normalize();
 randomPoint *= radius * (float)Math.Sqrt(_random.NextDouble());
 randomPoint += position;

 return randomPoint;
}

XNA Random Point In Circle

The function creates a random point in a circle on the XZ plane.

Random _random = new Random();

private Vector3 RandomPointInCircle(Vector3 position, float radius)
{
 float randomRadius = radius * (float)Math.Sqrt(_random.NextDouble());

 double randomAngle = _random.NextDouble() * MathHelper.TwoPi;

 float x = randomRadius * (float)Math.Cos(randomAngle);
 float z = randomRadius * (float)Math.Sin(randomAngle);

 return new Vector3(position.X + x, position.Y, position.Z + z);
}