574 11. Animation Systems
Figure 11.57. The Unreal Engine 3 graphical animation editor.11.11.1.4. Example: Unreal Engine 3
Unreal Engine 3 (UE3) provides its users with a graphical interface to the ani-
mation system. As shown in Figure 11.57, an animation blend tree in Unreal
is comprised of a special root node called an AnimTree. This node takes three
kinds of inputs: animations, morphs, and special nodes known as skel controls.
The animation input can be connected to the root of an arbitrarily complex
blend tree (which happens to be drawn with poses fl owing from right to left —
opposite of the convention we use in this book). The “morph” input allows
morph-target-based animations to drive the character; this is most oft en used
for facial animation. The “skel control” inputs allow various kinds of proce-
dural post-processing, such as inverse kinematics (IK), to be performed on the
pose generated by the animation and/or morph trees.The UE3 Animation Tree
The Unreal animation tree is essentially a blend tree. Individual animation
clips (called sequences in Unreal) are represented by nodes of type Anim
Sequence. A sequence node has a single output, which may either be con-
nected directly to the “animation” input of the AnimTree node or to other
complex node types. Unreal provides a wide selection of blend node types
out of the box, including binary blends, four-way two-dimensional blends