Editing Graphics pipeline (section)

=== Inverse ===
All matrices used are [[invertible matrix|nonsingular]] and thus invertible. Since the multiplication of two nonsingular matrices creates another nonsingular matrix, the entire transformation matrix is also invertible. The inverse is required to recalculate world coordinates from screen coordinates – for example, to determine from the mouse pointer position the clicked object. However, since the screen and the mouse have only two dimensions, the third is unknown. Therefore, a ray is projected at the cursor position into the world and then the intersection of this ray with the polygons in the world is determined.