A blend group is a collection of animations (timelines). It automatically blends the animations based on a blend weight, which can be set using SetWeight(ITimeline, Single). The blend weight indicates the importance of the corresponding animation. For example, if one animation has a blend weight of 1 and another animation has a blend weight of 0.5 then the second has less influence on the animation result. A blend weight can be set to 0 to disable the animation.

The blend weights are internally normalized, meaning that the blend weights do not need be in the range [0, 1] when they are set. Blend weights can have any value equal to or greater than 0. The sum of all blend weights should be greater than 0 - i.e. at least one animation should to be active!

A blend group can contain TimelineGroups. In this case the animations within one TimelineGroup are blended with the matching animations in the other TimelineGroups. The animations are matched by comparing the TargetProperty properties.

Synchronization: Most animations have different durations. When blending cyclic animations, for example, a "Walk" cycle and a "Run" cycle of a character, then it is important to synchronize the durations of the animations. When a "Walk" cycle and a "Run" cycle are blended with equal blend weights then the result should be the average of "Walk" and "Run". The duration of the blended animation should be the average both cycles. A key frame of the "Walk" cycle needs to be interpolated with the matching key frame of the "Run" cycle. In order to synchronize the animations the method SynchronizeDurations needs to be called when all animations have been set.

Note that synchronization is optional. The methods SynchronizeDurations does not need to be called if the contained animations do not need to be synchronized.

Limitations: A blend group has certain limitations.

• The timelines within a blend group must be of type TimelineGroup or implement IAnimationT.
• If a TimelineGroup is added to a blend group, it should only contain animations (IAnimationT). Nested timelines, such as TimelineGroup within a TimelineGroup, are not supported and will be ignored.
• If a TimelineGroups is added to a blend group, the TargetProperty must be set for all animations in the TimelineGroup. This is necessary because the blend group matches the animations of one TimelineGroup with those of the other TimelineGroups by comparing the TargetProperty. A TimelineGroup should not contain multiple animations that target the same property.
• The TargetObject of the animations within a blend group will be ignored. Only the property TargetObject of the blend group itself will be read.
• Animations must not be added to or removed from the blend group if the animation is already playing. (However, if all playing animation instances of the blend group are stopped and the associated AnimationControllers are recycled, then animations can be added or removed, and the blend group can be restarted.)
• A blend group does not support additive animations. The property IsAdditive of contained animations will be ignored.

Animating Blend Weights: The blend weights in a blend group can be animated. The method GetWeightAsAnimatable(ITimeline) returns an IAnimatablePropertyT that represent the blend weight of the specified timeline and can be animated.

A blend group also implements the interface IAnimatableObject. The blend weights can also be retrieved using GetAnimatablePropertyT(String) where the blend weights are identified using the strings "Weight0", Weight1", etc. The suffix is the index of the associated timeline.

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