title: How to constrain movement within the area of a circle
body: <p>This might be more a geometry related question, but I'm trying to constrain a controller within an area of a circle. I know I have to touch the Math.sin() and Math.cos() methods, but my attemps so far have been fruitless so far. </p>
  
  <p><img src="https://i.stack.imgur.com/DneKA.png" alt="enter image description here"></p>
  
  <p>Here is the jsfiddle:
  So far I've been able to constrain it to an invisible square. <a href="http://jsfiddle.net/maGVK/" rel="nofollow noreferrer">http://jsfiddle.net/maGVK/</a></p>