Game Engine Architecture

581

chine converts multiple, temporally independent blend trees (one per layer)
into a single unifi ed blend tree. This is shown in Figure 11.59.

11.11.4. Control Parameters

From a soft ware engineering perspective, it can be challenging to orchestrate
all of the blend weights, playback rates, and other control parameters of a
complex animating character. Diff erent blend weights have diff erent eff ects
on the way the character animates. For example, one weight might control
the character’s movement direction, while others control its movement speed,
horizontal and vertical weapon aim, head/eye look direction, and so on. We
need some way of exposing all of these blend weights to the code that is re-
sponsible for controlling them.

Net blend tree

at time τ

Time

H

F

B

τ

K

LERP

+

Tree

B

Tree

F

Tree

H

+

Tree

K

Figure 11.59. A layered state machine converts the blend trees from multiple states into a
single, unifi ed tree.

11.11. Action State Machines