Blending

Animation Guide

Problem – After playing an animation with root translation, the root joint will snap back to the initial position and orientation after playing the animation

Solution – Add a virtual joint called a “Guide” as a parent of root joint – As a result, root position and orientation transforms are now with respect to the guide frame of reference – At the end of each animation, update the guide joint position to the current position of the character in the world

Foot IK

Allows character to walk over uneven terrain

IK Targets – Update left and right foot target positions

• Lfoot_target = Lfoot + Lfoot_height
• Rfoot_target = Rfoot + Rfoot_height

Root Position

• Determine which foot is lower
• root_offset = smaller of Lfoot_height and Rfoot_height
• Update vertical position of root joint
• y_root = y_root + root_offset

Foot Position – Use Limb IK with Lfoot_target and Rfoot_target to position feet

Cross Dissolve

dissolve

stand to walk

We could have two independent animations playing (stand & walk) and then gradually ramp up the ‘u’ value from 0 to 1

If the transition is reasonably quick (say <0.5 second), it might look OK

Note: this is just a simple example of a dissolve and not necessarily the best way to make a character start walking…

walk to run

Blending from a walk to a run requires some additional consideration…

We want to make sure that the walk and run are in phase when we blend between them – That is, both should start when the left (or right foot) hits the ground

One could animate them in a consistent way so that the two clips both start at the same phase

But, let’s assume they are not in sync…

Store an offset for each animation clip that marks some synch point (say at the time when the left foot hits the ground)

Call these offsets owalk and orun

Since we want the walk and run animations to stay in phase, we need to synchronize them

$s_{walk}=Lerp(1,\frac{T_{walk}}{T_{run}},u)$

• $t'_{walk}=s_{walk}t_{walk}=s_{walk}\mod(o_{walk}+t,T_{walk})$
• $t'_{run}=s_{walk}t_{run}=s_{walk}\mod(o_{run}+t\frac{T_{run}}{T_{walk}},T_{run})$

$u=\frac{t}{T_{walk}}$

bilinear blend

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mirroring

need symmetrical or closed enough