Documents sample

samples/motion_blend/README.md

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 ## Description
 
+Motion blending extends the concept of animation blending to root motion. It blends the motion resulting from the motion extraction process, in addition to blending animations.
+
 ## Concept
 
+This sample is built on top of the animation blending sample. It blends three animations (walk, jog and run) and their corresponding root motions according to a single "speed" coefficient.
+
+It uses animation and motion tracks converted using *2ozz tools, relying itself on `ozz::animation::offline::MotionExtractor`. It uses animation.tracks.motion settings as described in the reference configuration. See motion playback sample for more details.
+
+
+
+At runtime, the position and rotation are sampled from the motion tracks each frame. They are accumulated to move the character transform (by delta motion each frame), allowing to continue moving when the animation loops.
+The sample uses `ozz::sample::MotionAccumulator` and `ozz::sample::MotionSampler` utilities to help with the complexity of managing loops.
+
 ## Sample usage
 
 ## Implementation
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