This is called procedural animation, because the pose data is computed via some procedure at runtime, rather than just looked up/interpolated from a pre-baked animation timeline.
Some examples of pure procedural animation in various forms:
- Animation Bootcamp: An Indie Approach to Procedural Animation (synthesizing biped animation in Overgrowth)
- This spider can climb anywhere! (placing footsteps and animating legs to crawl over arbitrary terrain)
- Animating with Math (using vertex shaders to add complex motion to props — this is also how schools of fish are animated in Abzu)
- Giving personality to procedural animations with math (layering dynamics like anticipation and bounce to make computed animations look less stiff/robotic)
- A little experiment I made for a 3-day game jam, building a procedural dance in response to player input.
This can also be mixed with conventional, pre-authored animations in various ways:
- Using weighted/masked blends between authored poses / animations, like having "aim forward, up, up-right, right" etc. poses and blending between them to match the player's input / NPC action.
- Inverse kinematics (IK), where we calculate and override a chain of joint angles in an animation to, e.g. keep feet planted on an uneven surface, or keep a hand correctly gripping a held object.
- Layering "additive animations" on top of simple walk/idle loops, to make them look less repetitive and more natural.
- Dynamically adding leans, "smear frame" distortion, or squash & stretch scaling over-top of a conventional skeletal animation to make it look more cartoony and responsive to what's happening in the game.