1. Defining the space – Defining the 2D space
From Picture 1 and definition of 2D spaces you may notice that projection space is always square, while
screen space may be any rectangular form possible. That creates a problem when transforming an image
from projection space to screen space (and believe me, we will be doing that a lot). To illustrate the problem, look at Picture 2. In it we try to transform a square from projection space to screen space. Since in our
example screen space is a rectangle, a square becomes a rectangle too, because width > height. To fix the
problem we can use aspect ratio which is the ratio of the screen’s width and height: