Racing the Beam : the Atari Video Computer System - Index of

fi ctional world. In the textual Adventure, the player must engage in an
unusual bit of textual banter to kill the dragon: After typing “KILL
DRAGON,” the clarifying question “With your bare hands?” has to be
answered “YES.” In the VCS Adventure, you can kill the dragon, but not
with your with bare hands, and not after a repartee like this.
There were some special touches in the VCS cartridge that were
appropriate to a graphical game. Although most games of the time (and
even many of today) register a death or other consequence when the player
initially touches an enemy, Adventure’s dragon chases the player when the
latter touches it. Two small touches within a specifi c amount of time are
required to kill the avatar. Such subtle interaction between cursor and
dragon notwithstanding, text adventures often focus on riddle and puzzle
solving, such as navigating a maze or fi guring out the purpose of an item.
This practice does not carry through in action-adventure games. Instead,
rapid movement through space becomes the primary mode of play, a
characteristic of the genre that could also be seen in Robinett’s previous
game, Slot Racers.
Adventure’s sword offers an example of the curiosity of TIA collision
detection. The sword appears on the screen as a left-facing arrow. Even
though the TIA does provide a register to fl ip sprites automatically on
their horizontal axis, the sword always faces the same way, no matter how
the player moves. Moreover, the sword itself looks more like an arrow; at
best, it looks like a sword being held from the tip rather than the hilt.
Though VCS graphics could be rightly described as “blocky,” Robinett
actually had far greater resolution to work with than he ended up using for
the sword sprite. One reason for this decision might relate to the way collision
detection functions on the machine.
In today’s games, collision detection is handled in software. A computationally
cheap way to accomplish this is with bounding boxes. In this
method, boxes around each object are determined and each pair is checked
for intersections. This simple and quick method is nevertheless inaccurate,
because an object that does not fi ll its bounding box may register as
colliding with something when it actually does not.
The VCS hardware collision is performed by the TIA, which checks
for overlapping logic states on its multiple graphics registers. For this
reason, only those bits that are turned on in the graphics registers of a
sprite can register collision. In other words, the parts of a sprite that are
actually seen are the only ones subject to colliding. Thanks to a relatively
simple circuit on the TIA, the Atari VCS offers more precise collision
detection than is done using the standard technique in modern software
toolkits such as Adobe Flash (see fi gure 3.2).
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