I am making a 3D solid model of a iPhone. It was working out fine, but suddenly when I began sketching on a front plane, it was showing the sketches on the back of the model when I rotated it. I do not want that to happen. I don't want it to be transparent either since it's a part of the model. I was making a screen for the model. But when I rotated the model, the screen can still be seen. I attached a few pics to make it clear. How do I only make it view-able on that plane? Thank you.