title: Placing one object in front of another in Corona SDK
body: <p>I am building a platform jumper, and when the ball passes through the platform, I would like it to appear in front, not behind, the platform.  I've tried putting both objects into a new dispaly group in the proper order and sending the ball to the front using <code>toFront()</code>, but I just can't get it to work.  Any thoughts?</p>
  
  <pre><code>local ball = display.newCircle( 100, 100, 30 )
  ball.id = "ball"
  ball.x, ball.y = 160, 350
  ball.rotation = 15
  
  local gradient = {
      type="gradient",
      color1={ 1, 4, 7 }, color2={ .1, 1, 1.5}, direction="down"
                  }
  ball:setFillColor( gradient )
  
  -- add physics to the ball
  physics.addBody( ball, "dynamic", { density=1.0,
                  friction=0.9, bounce=0 } )
  
  -- create a platform w/ physics
  local bottom = display.newRect( 0, 0, 320, 100 )
  bottom.anchorX = 0
  bottom.anchorY = 1
  bottom.x, bottom.y = 0, display.contentHeight
  
  physics.addBody( bottom, "static", { friction=0.3 } )
  
  -- put plat in middle
  local platform = display.newRect( 0, 0, screenW-100, screenH-450 )
  platform.x, platform.y = 160, 200
  platform.collType = "passthru"
  physics.addBody( platform, "static", { bounce=0.0, friction=0.3 } )
  
  -- place ball in front
  local group = display.newGroup( )
  group:insert( ball )
  group:insert( platform )
  
  ball:toFront( )
  </code></pre>