Philips Magnavox Videogames and the Entertainment Revolution Trigger Happy - Manual (Page 210)

Trigger Happy
212
Later games, such as R-Type (1988), took
advantage of spare power to create an inventive
impression of depth with “parallax” scrolling. Imagine
the viewer inside the circular strip described above,
only now it is not one but several concentric circular
strips, revolving at decreasing speeds as they increase
in distance from the viewer. In a train, the observer
notes that trackside posts flash by in an instant, while
distant scenery rolls past in a more leisurely fashion. In
order to imitate this effect of moving perspective, the
game screen background now acquires several different
flat planes, so that objects in the foreground plane
sweep by more quickly than objects in the middle-
distance plane, which in turn pass more quickly than
objects (mountain ranges, clouds and the like) near the
horizon. The term “parallax” itself was, fittingly for a
family of games that usually featured alien worlds,
borrowed from astronomy.
It is important to emphasize again at this point that
innovations such as wraparound and scrolling did not
at once render earlier forms obsolete. The limitations
of a fixed, bounded screen, for instance, are
reimagined as positive gameplay virtues by the tense,
claustrophobic design of Robotron (1982), in which
the player’s post-apocalyptic hero must do battle in a