Game Engine Architecture

504 11. Animation Systems

In general, the global pose (joint-to-model transform) of any joint j can be

writt en as follows:

0

jMpii( ),

i

→→

=

PP=∏

j

(11.1)

where it is implied that i becomes p(i) (the parent of joint i) aft er each iteration

in the product, and p(0)≡M.

11.3.3.1. Representing a Global Pose in Memory

We can extend our SkeletonPose data structure to include the global pose

as follows, where again we dynamically allocate the m_aGlobalPose array

based on the number of joints in the skeleton:

struct SkeletonPose

{

Skeleton* m_pSkeleton; // skeleton + num joints

JointPose* m_aLocalPose; // local joint poses

Matrix44* m_aGlobalPose; // global joint poses

};

11.4 Clips

In a fi lm , every aspect of each scene is carefully planned out before any anima-

tions are created. This includes the movements of every character and prop in

the scene, and even the movements of the camera. This means that an entire

scene can be animated as one long, contiguous sequence of frames. And char-

acters need not be animated at all whenever they are off -camera.

0

12

3 45

xM

yM

Figure 11.8. A global pose can be calculated by walking the hierarchy from the joint in

question towards the root and model space origin, concatenating the child-to-parent (local)

transforms of each joint as we go.