The characters in a game have skeletons. Similar to our own
skeleton, this is a hidden series of objects that connect
with and move in relation to each other. Using a technique
called parenting, a target object (the child) is assigned to
another object (the parent). Every time the parent object
moves, the child object will follow according to the
attributes assigned to it. A complete hierarchy can be
created with objects that have children and parents. Here's
an example for a human character
Once the skeleton is created and all of the parenting
controls put in place, the character is animated. Probably
the most popular method of character animation relies on
inverse kinematics. This technique moves the child object to
where the animator wants it, causing the parent object and
all other attached objects to follow. Another method that is
popular for games is motion capture, which uses a suit of
sensors on a real person to transmit a series of coordinates
to a computer system. The coordinates are mapped to the
skeleton of a game character and translated into fluid,
realistic motion.
Each character's range of motion is programmed into the game.
Here's a typical sequence of events:
* You press a button on the controller to make the
character move forward.
* The button completes a circuit, and the controller
sends the resulting data to the console.
* The controller chip in the console processes the data
and forwards it to the game application logic.
* The game logic determines what the appropriate action
at that point in the game is (move the character forward).
* The game logic analyzes all factors involved in making
the movement (shadows, collision models, change of viewing
angle).
* The game logic sends the new coordinates for the
character's skeleton, and all other changes, to the rendering
engine.
* The rendering engine renders the scene with new
polygons for each affected object, redrawing the scene about
60 times each second.
* You see the character move forward.
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