How does a game character bend without being redrawn?

A game character can wave, crouch and turn while keeping the same face and clothes. Many characters are built around a hidden digital skeleton called a rig. Its bones are mathematical controls, not actual bones, and moving them changes the visible character’s shape.

The controls form a hierarchy. A forearm belongs to an upper arm, which belongs to the shoulder and body. Turning the upper arm carries the elbow, forearm and hand with it. Turning the forearm changes the bend at the elbow without needing to move the shoulder. Each control has a position and orientation relative to the control above it.

The visible surface is usually a mesh: small connected shapes, often triangles. Its points are linked to nearby bones using weights that specify each bone’s influence. A point near an elbow may follow both the upper arm and forearm. Combining their influences helps the surface bend between them instead of breaking into separate rigid pieces.

An animator can save important poses called keyframes. The game calculates intermediate positions and rotations between those poses, a process called interpolation. A walking cycle can repeat, and a transition can blend walking into running. The program still needs carefully designed timing and joint limits; automatic in-between poses do not guarantee a natural-looking movement.

This gives designers a reusable character rather than a new drawing for every possible action. It also explains some familiar glitches. A badly weighted surface can stretch oddly at a joint, and a walking animation can play at the wrong speed for the character’s travel, making feet slide. Convincing movement comes from coordinating the hidden controls, the visible surface and the character’s motion through the world.