Game Development Reference
In-Depth Information
Bone Animation
Bone animation
,or
joint animation
, as it is sometimes called, is the process of cre-
ating an internal object or character animation based on a system of bones and
joints that make up a skeleton. Bone animation is by far the most complex of the
three basic types of animation and is used for animating characters in games.
When setting up bone animation, the artist creates a skeleton for the model and
then attaches the vertices of the model to the skeleton in a process called
rigging
.
When a bone is pivoted on a joint, the attached vertices move with the bone.
Vertices can often have more than one influencing bone. When more than one
bone influences a vertex, it divides the movement between the two or more bones
based on the percentage of influence from each bone.
Game
AI
,or
artificial intelligence
, can mean a lot of things in game development,
but for this chapter we will simply use it to refer to the game code that controls
where and how environments, objects, and characters are displayed. In other
words, games are controlled by a complex system of software. This software deter-
mines what the player sees at any given time during the game. It also reacts to any
input from the player.
A lot things have to work together perfectly for even a single frame of a 3D game
to be displayed. To get some perspective, think of it in these terms. A single setting
in a game contains as many as 70,000 polygons. Each of these polygons has at least
three vertices. Even if many of these vertices are shared, there could be as many as
100,000 vertices—or, in other words, specific virtual space locations. All of these
virtual space locations have to be tracked by the game system, not just once but
several times every second. Many of the most popular games run at 60 frames per
second. That means that in one second of game play, the system is tracking six mil-
lion vertices. But it doesn't stop there.
In addition to simply keeping track of all of these vertices, the system has to apply
textures to each polygon. These textures have to be mapped to the polygons so that
they stay in place. Every polygon in the game has either a color or a texture applied
to it. Sometimes these textures have more information than just a picture. They
might have multiple layers containing information about transparency, bump,
specularity, diffusion, and other attributes. So the game is tracking complex textures
on 70,000 polygons 60 times every second. But it doesn't end there either.
