title: ignore collisions in chipmunk cocos2d v3 but gravity still affects body?
body: <p>cocos2d v3 &amp; Chipmunk ... </p>
  
  <p>How would I specify that a chipmunk physics body be affected by gravity only but ignore all other physics objects? i.e. other object don't affect its movement or collide with the body</p>
  
  <p>I tried using collisions categories and masks (with no other objects specified) as such but I'm still getting collisions.</p>
  
  <pre><code>objOnlyGravity.physicsBody.collisionType = @"objOnlyGravityType";
  objOnlyGravity.physicsBody.collisionCategories = @[@"objOnlyGravityCat"];
  objOnlyGravity.physicsBody.collisionMask = @[@""]; ///  &lt;- I assume putting nothing here would have it ignore all collisions
  </code></pre>