title: Detect collision with line, tetris like game
body: <p>I'm doing a game like tetris. There are objects which are falling from the top to the bottom of the screen. When the pile of object reach the line, the game is over.<br>
  I tried to set a boolean to detect when the object pass 2 time in the line the game ends, but it don't work like that so I don't really know how to do this.<br>
  Maybe we can detect if the object stands on the line more than 2 seconds ?<br>
  Thanks</p>
  
  <p><img src="https://i.stack.imgur.com/1XalQ.png" alt="enter image description here"></p>
  
  <p><strong>EDIT:</strong></p>
  
  <p>To simplify the problem I put the line of the top of the screen (self.frame.height), and I spawn the objects under this line, so they never cross the line before the game is over.</p>
  
  <p>The problem now is I have to spawn the objects 40 pixels below the line, or a collision is detected at the spawn point. (It does nothing if I set usesPreciseCollisionDetection = true).</p>
  
  <p>So the 40 pixels collision detection are normal ? </p>
  
  <p><img src="https://i.stack.imgur.com/97TaM.png" alt="enter image description here"></p>