Viewing a 3d world from an arbitrary camera position.
This program demonstrates how to use the get_camera_matrix()
function to view a 3d world from any position and angle. The
example draws a checkered floor through a viewport region
on the screen. You can use the keyboard to move around the
camera or modify the size of the viewport. The keys that can
be used with this example are displayed between brackets at
the top of the screen.