UnityEngine.Timeline.AnimationTrack.CompileTrackPlayable(UnityEngine.Playables.PlayableGraph, UnityEngine.Timeline.AnimationTrack, UnityEngine.GameObject, IntervalTree, UnityEngine.Timeline.AppliedOffsetMode)

internal override Playable OnCreateClipPlayableGraph(PlayableGraph graph, GameObject go, IntervalTree<RuntimeElement> tree)
        {
            if (isSubTrack)
                throw new InvalidOperationException("Nested animation tracks should never be asked to create a graph directly");

            List<AnimationTrack> flattenTracks = new List<AnimationTrack>();
            if (CanCompileClips())
                flattenTracks.Add(this);

            var genericRoot = GetGenericRootNode(go);
            var animatesRootTransformNoMask = AnimatesRootTransform();
            var animatesRootTransform = animatesRootTransformNoMask && !IsRootTransformDisabledByMask(go, genericRoot);
            foreach (var subTrack in GetChildTracks())
            {
                var child = subTrack as AnimationTrack;
                if (child != null && child.CanCompileClips())
                {
                    var childAnimatesRoot = child.AnimatesRootTransform();
                    animatesRootTransformNoMask |= child.AnimatesRootTransform();
                    animatesRootTransform |= (childAnimatesRoot && !child.IsRootTransformDisabledByMask(go, genericRoot));
                    flattenTracks.Add(child);
                }
            }

            // figure out which mode to apply
            AppliedOffsetMode mode = GetOffsetMode(go, animatesRootTransform);
            int defaultBlendCount = GetDefaultBlendCount();
            var layerMixer = CreateGroupMixer(graph, go, flattenTracks.Count + defaultBlendCount);
            for (int c = 0; c < flattenTracks.Count; c++)
            {
                int blendIndex = c + defaultBlendCount;
                // if the child is masking the root transform, compile it as if we are non-root mode
                var childMode = mode;
                if (mode != AppliedOffsetMode.NoRootTransform && flattenTracks[c].IsRootTransformDisabledByMask(go, genericRoot))
                    childMode = AppliedOffsetMode.NoRootTransform;

                var compiledTrackPlayable = flattenTracks[c].inClipMode ?
                    CompileTrackPlayable(graph, flattenTracks[c], go, tree, childMode) :
                    flattenTracks[c].CreateInfiniteTrackPlayable(graph, go, tree, childMode);
                graph.Connect(compiledTrackPlayable, 0, layerMixer, blendIndex);
                layerMixer.SetInputWeight(blendIndex, flattenTracks[c].inClipMode ? 0 : 1);
                if (flattenTracks[c].applyAvatarMask && flattenTracks[c].avatarMask != null)
                {
                    layerMixer.SetLayerMaskFromAvatarMask((uint)blendIndex, flattenTracks[c].avatarMask);
                }
            }

            var requiresMotionXPlayable = RequiresMotionXPlayable(mode, go);

            // In the editor, we may require the motion X playable if we are animating the root transform but it is masked out, because the default poses
            //  need to properly update root motion
            requiresMotionXPlayable |= (defaultBlendCount > 0 && RequiresMotionXPlayable(GetOffsetMode(go, animatesRootTransformNoMask), go));

            // Attach the default poses
            AttachDefaultBlend(graph, layerMixer, requiresMotionXPlayable);

            // motionX playable not required in scene offset mode, or root transform mode
            Playable mixer = layerMixer;
            if (requiresMotionXPlayable)
            {
                // If we are animating a root transform, add the motionX to delta playable as the root node
                var motionXToDelta = AnimationMotionXToDeltaPlayable.Create(graph);
                graph.Connect(mixer, 0, motionXToDelta, 0);
                motionXToDelta.SetInputWeight(0, 1.0f);
                motionXToDelta.SetAbsoluteMotion(UsesAbsoluteMotion(mode));
                mixer = (Playable)motionXToDelta;
            }


#if UNITY_EDITOR
            if (!Application.isPlaying)
            {
                var animator = GetBinding(go != null ? go.GetComponent<PlayableDirector>() : null);
                if (animator != null)
                {
                    GameObject targetGO = animator.gameObject;
                    IAnimationWindowPreview[] previewComponents = targetGO.GetComponents<IAnimationWindowPreview>();

                    m_HasPreviewComponents = previewComponents.Length > 0;
                    if (m_HasPreviewComponents)
                    {
                        foreach (var component in previewComponents)
                        {
                            mixer = component.BuildPreviewGraph(graph, mixer);
                        }
                    }
                }
            }
#endif

            return mixer;
        }