title: How does 3D collision / object detection work?
body: <p>I'v always wondered this. In a game like <a href="http://en.wikipedia.org/wiki/Grand_Theft_Auto_%28series%29" rel="noreferrer">GTA</a> where there are 10s of thousands of objects, how does the game know as soon as you're on a health pack?</p>
  
  <p>There can't possibly be an event listener for each object? Iterating isn't good either? I'm just wondering how it's actually done.</p>