code: public void getLocalRotation(int boneindex, Quaternionf q)
      {
          Bone bone = mBones[boneindex];
  
          if ((bone.Changed & (WORLD_POS | WORLD_ROT)) != 0)
          {
              calcLocal(bone, mSkeleton.getParentBoneIndex(boneindex));
          }
          bone.LocalMatrix.getUnnormalizedRotation(q);
          q.normalize();
      }
docs: Gets the local rotation for a bone given its index.
  @param boneindex	zero based index of bone whose rotation is wanted.
  @return local rotation for the designated bone as a quaternion.
  
  @see #setLocalRotation
  @see #setWorldRotations
  @see #setWorldMatrix
  @see GVRSkeleton#setBoneAxis