title: Collision detection with complex shapes
body: <p>I am wanting to make a game that has each level loaded from an image.
  I want to draw up the whole level in Photoshop, and then set it as the background and allow the player to walk over it.
  I want another invisible image to go over top which will be black in all places that I want to collide with.</p>
  <p>The reason I don't want to use tiles, which are much easier with rectangle collision and such, is because there will be complex corners and not everything will be rectangle.</p>
  <p>Is this a good idea, and is it possible to do easily?
  Would this be a big CPU hog or is there a better way to do this?</p>
  <h2>Level image</h2>
  <p><img src="https://i.stack.imgur.com/XtqKD.png" alt="Level image" /></p>
  <p></p>
  <h2>Obstacles shown in red</h2>
  <p><img src="https://i.stack.imgur.com/AHVq9.png" alt="Obstacle in Red" /></p>