GUI: Circular hot zone. Very simple, but not necessarily very efficient way of determining mouse presence within a circular section of GUI space.

CircleCheck.cs

// Given: Vector2 point, float radius, inside valid GUI context

if (new Vector2 (Event.current.mousePosition - point).magnitude < radius)
{
	GUILayout.Label ("Inside");
}
else
{
	GUILayout.Label ("Outside");
}