# Objective
Fixes#13832
## Solution
Additively blend quaternions like this:
```rust
rotation = Quat::slerp(Quat::IDENTITY, incoming_rotation, weight) * rotation;
```
## Testing
Ran `animation_masks`, which behaves the same as before. (In the context
of an animation being blended only onto the base pose, there is no
difference.)
We should create some examples that actually exercise more of the
capabilities of the `AnimationGraph` so that issues like this can become
more visible in general. (On the other hand, I'm quite certain this was
wrong before.)
## Migration Guide
This PR changes the implementation of `Quat: Animatable`, which was not
used internally by Bevy prior to this release version. If you relied on
the old behavior of additive quaternion blending in manual applications,
that code will have to be updated, as the old behavior was incorrect.