The SkeletonKeyFrameAnimation is an optimized KeyFrameAnimationT for character animation. A SkeletonKeyFrameAnimation instance animates the bone transforms of a SkeletonPose. It can animate a single bone (e.g. only the head), several bones (e.g. an upper body animation) or all bones of skeleton at once.

A SkeletonKeyFrameAnimation is defined by adding key frames calling the method AddKeyFrame(Int32, TimeSpan, SrtTransform) for the animated bones. The animation controls a bone if at least one key frame for the bone has been added (see also IsBoneAnimated(Int32)). After adding all key frames, Freeze must be called. Freeze optimizes the animation data for fast access at runtime.

When key frames are added after calling Freeze, the animation is automatically reset into an editable state. All internal optimizations will be discarded! Freeze needs to be called again after all key frames are added.

Bone Channel Weights:
A weight can be set for each animated bone (see SetWeight(Int32, Single)). If the weight is 0, the bone is not animated. If the weight is 1, the bone is animated and replaces all preceding animations in the animation composition chain. If the weight is less than 1, the bone animation is blended with preceding animations.

Weights can be modified before and after Freeze. For example, weights can be modified while the animation is running.

Key Frame Interpolation:
A key frame animation contains a list of key frames that define the animation values at certain points in time. When the animation is played the class automatically looks up the animation value in the list of key frames. The property EnableInterpolation defines whether interpolation between key frames is enabled. When the property is set (default), the values between two key frames are interpolated using linear interpolation.

Cyclic Animations:
A skeleton key frame animation, by default, runs until the last key frame is reached. The types TimelineClip and AnimationClipT can be used to repeat the entire key frame animation (or a certain clip) for a number of times using a certain loop-behavior (see LoopBehavior).

The first and the last key frame need to be identical to achieve a smooth cyclic interpolation.

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