Blend Space and Blend Tree
Mixing animations by a parameter such as speed
Also known as: Blend Space Unreal · Blend Tree Unity · 1D blend space · 2D blend space · Locomotion blend space · Strafe blend space
Definition
A blend space, called a blend tree in Unity, mixes several animations based on one or two parameters, so the character's movement changes smoothly. A one-dimensional blend space blends idle, walk and run by speed, and a two-dimensional one adds direction for forward, backward and strafe movement. The engine calculates the in-between pose for any parameter value, which creates many variations from a small set of clips. They are the standard way to build locomotion.
In production
Author the clips with matching foot contacts and cycle lengths, so they blend without sliding, and place them at the parameter values they were made for, such as the speeds they represent. Use sync markers or normalized time to keep the cycles in step. Blend spaces are cheap and reduce the number of transitions in a state machine, though too many samples in a 2D space cost performance.
Tools that use Blend Space and Blend Tree
See also
Foot Sliding in Game Animation
Feet glide over the ground while walking
Walk and Run Cycles
The looping base of character locomotion
Animation Blending
Interpolate poses between clips
Animation State Machine
Graph of animation states and transitions
Animation Graph
Node-based runtime animation evaluation
Root Motion
Movement driven by the animation, not the controller