Animation Blending
Interpolate poses between clips
Also known as: Blend space · Animation blend
Definition
Animation blending interpolates between two or more poses (usually weighted by gameplay variables like speed and direction) to produce a single output pose. A 1D blend space transitions between walk and run by speed; a 2D blend space adds strafing by direction. Additive blends layer a partial pose (an aim offset, a reload) on top of a base. Smooth blending is what separates a "stiff" character from a "responsive" one.
In production
Unity's Blend Tree node supports 1D blends (a single float like speed driving walk-to-run interpolation) and 2D blends (Freeform Directional or Simple Directional) for adding strafing and turning without authoring every combination as a discrete clip. Unreal's Blend Space assets work the same way, plotting clips on a 1D or 2D axis and using barycentric interpolation between the three nearest samples in a 2D blend space. Additive animation — where a partial clip is layered on top of a base pose using "Layered blend per bone" (Unreal) or additive layers with avatar masks (Unity) — is what lets a character aim up and down while running without authoring aim variants for every locomotion clip. Poor blending shows up as foot-sliding during a walk-to-run transition, which technical animators fix by matching stride timing across clips or adding root motion-aware blend synchronization (Unreal's "Sync Groups" or Unity's "Motion Time" parameter) so both clips share a normalized phase.
