The Skeleton class defines a skeleton in bind pose. The SkeletonPose can be used to animate the bones of a skeleton. There are two ways to animate a skeleton using the animation system:

• The skeleton pose implements the interface IAnimatableProperty<SkeletonPose>. This means that the skeleton pose can be treated as one animation value and can be animated as a whole. A skeleton pose can, for example, be animated using a SkeletonKeyFrameAnimation.
• The skeleton pose also implements the interface IAnimatableObject. The bones of the skeleton pose are animatable properties. This means that the bones can be animated individually. For example, a SrtKeyFrameAnimation can be applied directly to a single bone.

Bone Transforms:
A bone transform is a local transformation that is applied to a bone. Bones are animated by changing the bone transforms (see GetBoneTransform(Int32) and SetBoneTransform(Int32, SrtTransform)). A bone transform is defined using a SrtTransform given in bone space. If a bone transform is the identity transformation (see Identity), then the bone is not animated and rendered in its bind pose.

Bone Poses:
A bone pose transformation matrix (bone pose) defines the resulting pose of bone after the bone transforms are applied. A bone pose describes the bone's position, orientation and scale relative to another coordinate space. A relative bone pose describes the pose of a bone relative to the parent bone (see GetBonePoseRelative(Int32)). An absolute bone pose describes the pose of a bone relative to model space (GetBonePoseAbsolute(Int32)).

The bone poses are computed and updated automatically: Whenever a bone transform is changed, the relative bone pose, absolute bone pose and the skinning matrices of the affected bone needs to be updated. Additionally, the absolute bone poses and the skinning matrices of all bones attached to this bone need to be updated as well. The skeleton pose automatically keeps track of which poses and matrices need to be recomputed. The recomputation is performed automatically as soon as one of these values is required.

To update all derived transformations at once, Update can be called.

IAnimatableProperty Implementation:
The class SkeletonPose implements the interface IAnimatableProperty<SkeletonPose> (see IAnimatablePropertyT). This means the SkeletonPose itself is an animatable property. It can be animated using any animation of type IAnimation<SkeletonPose>. Typically a SkeletonKeyFrameAnimation is used to animate the SkeletonPose. This is the most efficient way to animate a skeleton.

Note: The SkeletonPose as a IAnimatableProperty does not have a base value and therefore cannot be used in some from-to-by animations and similar animations that require a base value.

IAnimatableObject Implementation (For Advanced Uses Only!):
The class SkeletonPose additionally implements the interface IAnimatableObject. This means that the bones of the skeleton can also be animated independently. The animatable properties are the bone transforms given as IAnimatableProperty<SrtTransform>. The animatable properties can be accessed by calling the method GetAnimatablePropertyT(String) passing the name of the desired bone as the parameter. (Bones need to be named if they should be animated independently.)

For example, a SrtKeyFrameAnimation (or any other animation that implements IAnimation<SrtTransform>) can be applied directly to a bone.

Or, multiple SrtKeyFrameAnimations can be grouped together in a TimelineGroup. The animations can be assigned to different bones by setting the animation's TargetProperty to the name of the bone. The TimelineGroup can then be played as one animation.

Animating the SkeletonPose this way is very flexible - but slower than animating it with a single SkeletonKeyFrameAnimation.

Note: The IAnimatablePropertys of the individual bones do not have a base value and therefore cannot be used in some from-to-by animations or similar animations that require a base value.

Tip:
When bone transforms are manipulated regularly, e.g. in an IK solver, numerical errors can accumulate. If this happens and the skeleton seems to "explode", try to normalize the rotation quaternions regularly.

Reference