As done in previous examples, we use percentages when setting the dimensions of the two viewports used in this example. The viewport in which the cirle is rendered is the upper half of the device window. Thus, we start the viewport on the left boudary of the device window

   (0.0*deviceWindowWidth)

and halfway up

   (0.5*deviceWindowHeight)

The width of the circle's viewport is that of the device window

   (1.0*deviceWindowWidth)

and its height is half of the device window

   (0.5*deviceWindowHeight)

Comparible percentages are used in setting the viewport that covers the lower half of the device window where the disk is rendered.