Animation layering allows you to have two or more levels of animation on an object’s parameters at the same time. You usually want to layer animation when you need to add an offset to the main animation on an object, but you don’t want to change that animation.
Layering lets you add keys on top of the existing base animation, which can be either action clips or fcurves. You can easily add keys on top of the action clip is currently in the mixer without needing to actually work in the mixer, or add keys on top of existing fcurves.
Animation layers are non-destructive, meaning that they don’t alter your base animation in any way: the keys in the layers always remain a separate entity. Layering allows you to experiment with different effects on your animations and build several variations of a move, each in its own layer.
For example, let’s say that you’ve imported a mocap action clip of a character running down the flight of stairs. However, in your current scene, the stairs are shallower than those used for the mocap session, so the character steps “through” the stairs instead of on them. To fix this problem, you create an animation layer, offset the contact points for the character’s feet so that they step on the stair, adjust the body’s position, then set keys. The result is an offset animation that sits on top of the mocap data: you don’t need to touch the original mocap clip at all. You can then easily edit the fcurves for the animation layer, tweaking it as you like.
Animation Layers, the Mixer, and Models
Animation layers are actually controlled and managed in the animation mixer, but you don’t need to access the mixer for creating and setting keys in layers. Using the options in the Animation Layers panel (on the KP/L tab on the main command panel), you can create layers and then set keys with your usual workflow. While you don’t need to open the animation mixer for setting keys in layers, you do have the option of using the mixer for added control, such as setting each layer’s weight.
Because animation layers use the animation mixer, you need to create models before starting to animate. Mixers are created one per model, so if the object you’re animating isn’t in a model, its animation layers remain in the animation mixer created at the level of the scene (in the scene_root’s Mixer node). For more information, see Models and the Mixer in the Nonlinear Animation guide.
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