Game Development Reference
In-Depth Information
keyframe to keyframe. This type of animation is time consuming, but it allows
the animator to use more of the physics of animation, such as squash and
stretch and other cartoony movements.
m o c a p
Short for motion capture, mocap is the technique of capturing the
performance of an actor as an animated skeletal file. This skeletal data can then
be applied to a character in a 3D application, mimicking that performance.
The advantages of mocap compared to traditional keyframe techniques include
the speed of animating lengthy sequences and the performance fidelity. Since
its mainstream introduction in the early 1990s, mocap has become one of the
major tools for 3D character animation.
The systems currently available typically utilize either optical markers or mag-
netic sensors, although contour detection (markerless) is slowly entering the
field. The optical marker system requires multiple cameras ringing a capture
volume. 3D points are derived from the intersection of the streaming 2D high-
contrast images for the cameras. The markers are typically placed along the joints
of the performers. A connect-the-dots approach is used to define the skeletal
structure to extract rotational information. Cost of equipment and space and
preparation time make optical tracking the most expensive approach, although
it's also the most accurate.
Magnetic sensors are more easily set up and require no cameras. The person in
Figure 3.17 is wearing a mocap suit; this particular rig is used by ElektraShock
netic fields, a sensor is able to give a discreet rotational value. Nesting the sensor
data in a hierarchy, you can export an animated skeletal file. The only concession
is that magnetic data has a much lower fidelity than optical data.
Most animation for games runs in cycles. In other words, you create short
sequences that can be strung together as needed during gameplay. These cycles
may be walking, running, flying, punching, or dying—this is just a short list
of all the different types of cycles that can be created. Chapter 5, “Computer
Graphic Basics for Game Design,” provides a more in-depth discussion about
animation.
The main constraints placed on game design these days are far less techni-
cal and more financial: how much detail can you afford to have people make, to
complete the game in a reasonable amount of time? The most common techni-
cal problems tend to be related to the amount of memory available on a console
for storing textures.
