1.) The renderer always maps the camera's view-rectangle
    onto the framebuffer's viewport.

2.) The viewport defaults to the whole framebuffer.

3.) The user has control of the shape of the framebuffer.

4.) What should we do when the aspect ration (AR) of the
    framebuffer is not the same as the AR of the view-rectangle?

5.) If we do not do anything, then the renderer will map the
    view-rectangle onto the viewport (which is all of the
    framebuffer) and the image in the framebuffer will be
    distorted (circles in the view-rectangle appear to be
    ovals in the framebuffer and squares appear to be
    rectangles).

6.) To eliminate the distortion, we need a strategy to
    make the ARs of the view-rectangle and the viewport
    agree as the user manipulates the framebuffer.

7.) We can either force the view-rectangle AR match the
    viewport AR, or we can force the viewport AR to
    match the view-rectangle AR.

8.) To change the view-rectangle's AR, we need to use
    renderer_7 which lets us change the Camera's view
    volume (and view-rectangle, which is the front face
    of the view volume).

9.) Run the program 
        renderer_7\clients_r7\InteractiveModelsAll_R7.java
    Change to the circle model. Change the shape of the
    framebuffer and distort the circle into an oval. Use
    the 'l' key to turn on letterboxing (make the viewport
    AR match the view-rectangle's AR). Turn off letterboxing
    and use the 'r/R' keys to change the AR of the Camera's
    view-rectangle and make it match the framebuffer's AR.