Game Engine Architecture

529

blend factors βstart and βend , because this yields a well-behaved curve for our
purposes:

start

end start

(^3) start (^2) start (^23) end end
(^32) start (^23) end
let
and 1 :
( ) ( ) (3 ) (3 ) ( )
( 3 ) (3 ).
u
t
vu
t v v u T vu T u
v v u vu u

⎛⎞−

=⎜⎟⎝⎠

−

=−

β= β + + + β

=+ β+ +β

t t

Core Poses

This is an appropriate time to mention that motion continuity can actually
be achieved without blending if the animator ensures that the last pose in any
given clip matches the fi rst pose of the clip that follows it. In practice, anima-
tors oft en decide upon a set of core poses —for example, we might have a core
pose for standing upright, one for crouching, one for lying prone, and so on.
By making sure that the character starts in one of these core poses at the begin-
ning of every clip and returns to a core pose at the end, C0 continuity can be
achieved by simply ensuring that the core poses match when animations are
spliced together. C1 or higher-order motion continuity can also be achieved
by ensuring that the character’s movement at the end of one clip smoothly
transitions into the motion at the start of the next clip. This is easily achieved
by authoring a single smooth animation and then breaking it into two or more
clips.

11.6.2.3. Directional Locomotion

LERP-based animation blending is oft en applied to character locomotion.
When a real human being walks or runs, he can change the direction in which
he is moving in two basic ways: First, he can turn his entire body to change
direction, in which case he always faces in the direction he’s moving. I’ll call

Pivotal Targeted

Path of

Movement

Figure 11.30. In pivotal movement, the character faces the direction she is moving and pivots
about her vertical axis to turn. In targeted movement, the movement direction need not
match the facing direction.

11.6. Animation Blending