title: Asking Box2d if a collision happened
body: <p>I'm using Box2dx (ported to C#; optimized for XNA). It handles collision resolution, but how can I tell if two objects are currently colliding?</p>
  
  <p>This is the function I'm trying to write:</p>
  
  <pre><code>public bool IsColliding(GameObjectController collider1, GameObjectController collider2)
  </code></pre>
  
  <p>Where <code>collider1.Model.Body</code> is the Box2d <code>Body</code>, and <code>collider1.Model.BodyDef</code> is the Box2d <code>BodyDef</code>. (The same goes for <code>collider2</code>, of course.)</p>
  
  <p><strong>UPDATE:</strong> Looks like contact listeners or this could be useful:</p>
  
  <pre><code>        AABB collisionBox;
          model.Body.GetFixtureList().GetAABB(out collisionBox);
  </code></pre>
  
  <p>Why does <code>GetFixtureList()</code> return one fixture?</p>