Hi,
When an object is attached to the screen its initial position is in the lower left corner. Try translating it to the center of the screen:
Code:
object.translate(0.5,0.5)
Screen coordinates are in the range [0,1], where [0,0] is the lower left corner and [1,1] is the upper right corner.
Do you want the object to be occluded by all objects or just some?