Post
Animating 3D characters by moving an internal skeleton of bones, with the skin mesh deforming to follow.
Skeletal animation separates a character's visual mesh from its motion system. An invisible hierarchy of bones, called a skeleton or rig, is placed inside the 3D model. Each vertex of the skin mesh is assigned weights that determine how much each bone influences its position. When an animator rotates a shoulder bone, the vertices of the upper arm, shoulder, and nearby chest deform accordingly based on their weights. This system allows a single mesh to be posed in infinite positions from a manageable set of bone transforms. Animation data is stored as keyframes, snapshots of bone positions at specific times, with the engine interpolating between them for smooth motion. Blend trees and state machines manage transitions between animations like idle, walk, run, and attack.
Example
The animation systems in The Last of Us Part II represent a pinnacle of skeletal animation, with characters having hundreds of bones including detailed facial rigs. Ellie's animations blend seamlessly between navigation, combat, and cutscenes using sophisticated state machines. Monster Hunter World's creatures each have unique skeletal rigs that drive their distinct movement patterns, with tail swings, wing flaps, and jaw snaps all controlled by bone hierarchies. Even stylized games like Ori and the Will of the Wisps use skeletal animation for fluid, expressive character movement.
Why it matters
Skeletal animation is the universal standard for character movement in 3D games. Without it, every pose would require a completely separate model, making animation prohibitively expensive. The system's elegance lies in separating the what (mesh appearance) from the how (bone movement), allowing animators and modelers to work independently and enabling features like animation retargeting, where one character's animations can drive a differently proportioned character.
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