When you draw a cube in one point perspective you start by drawing a perfect square. But, if I understand perspective correctly, you can only see the front plane of the cube as a perfect square when the cube is right in front of you. If the cube is to the side of the vanishing point, wee see its side plane, so we are looking at it slightly from the side. Therefore the side of the square that's farther from the vanishing point should be foreshortened? Why is it then that all tutorials I've seen tell you to start with perfect square. Is it just because it's a good enough approximation?