title: Why I should use QuadTree with Collision Detection
body: <p>I'm reading some about QuadTrees and how I can use them for a better collision detection. But I doesn't understand why QuadTrees brings me more performance. 
  I'm trying this on a 2D Game.</p>
  
  <p>If I'm using a QuadTree I have to clear on every frame the QuadTree and insert all my Objects and then I loop through this to get all possible collision objects. And then loop through this to get my collision object i need.
  Why this is better then loop through all my Objects instead? 
  For the QuadTree I need O(n logn) if im right. But the loop through all my objects is O(n)</p>
  
  <p>Greetz</p>