/**
   * This constructor reads animation data from the object structore. The stored data is the
   * AnimData and additional data is armature's OMA.
   *
   * @param objectStructure the structure of the object
   * @param modifierStructure the structure of the modifier
   * @param blenderContext the blender context
   * @throws BlenderFileException this exception is thrown when the blender file is somehow
   *     corrupted
   */
  public ArmatureModifier(
      Structure objectStructure, Structure modifierStructure, BlenderContext blenderContext)
      throws BlenderFileException {
    if (this.validate(modifierStructure, blenderContext)) {
      Pointer pArmatureObject = (Pointer) modifierStructure.getFieldValue("object");
      if (pArmatureObject.isNotNull()) {
        ObjectHelper objectHelper = blenderContext.getHelper(ObjectHelper.class);
        ArmatureHelper armatureHelper = blenderContext.getHelper(ArmatureHelper.class);

        Structure armatureObject =
            pArmatureObject.fetchData(blenderContext.getInputStream()).get(0);
        this.armatureObjectOMA = armatureObject.getOldMemoryAddress();

        // read skeleton
        // changing bones matrices so that they fit the current object
        Structure armatureStructure =
            ((Pointer) armatureObject.getFieldValue("data"))
                .fetchData(blenderContext.getInputStream())
                .get(0);
        Structure bonebase = (Structure) armatureStructure.getFieldValue("bonebase");
        List<Structure> bonesStructures = bonebase.evaluateListBase(blenderContext);
        for (Structure boneStructure : bonesStructures) {
          BoneTransformationData rootBoneTransformationData =
              armatureHelper.readBoneAndItsChildren(boneStructure, null, blenderContext);
          armatureHelper.addBoneDataRoot(rootBoneTransformationData);
        }
        Matrix4f armatureObjectMatrix = objectHelper.getTransformationMatrix(armatureObject);
        Matrix4f inverseMeshObjectMatrix =
            objectHelper.getTransformationMatrix(objectStructure).invert();
        Matrix4f additionalRootBoneTransformation =
            inverseMeshObjectMatrix.multLocal(armatureObjectMatrix);
        Bone[] bones =
            armatureHelper.buildBonesStructure(Long.valueOf(0L), additionalRootBoneTransformation);

        // read mesh indexes
        Structure meshStructure =
            ((Pointer) objectStructure.getFieldValue("data"))
                .fetchData(blenderContext.getInputStream())
                .get(0);
        this.meshOMA = meshStructure.getOldMemoryAddress();
        this.readVerticesWeightsData(objectStructure, meshStructure, blenderContext);

        // read animations
        ArrayList<Animation> animations = new ArrayList<Animation>();
        List<FileBlockHeader> actionHeaders =
            blenderContext.getFileBlocks(Integer.valueOf(FileBlockHeader.BLOCK_AC00));
        if (actionHeaders != null) { // it may happen that the model has armature with no actions
          for (FileBlockHeader header : actionHeaders) {
            Structure actionStructure = header.getStructure(blenderContext);
            String actionName = actionStructure.getName();

            BoneTrack[] tracks = armatureHelper.getTracks(actionStructure, blenderContext);
            // determining the animation  time
            float maximumTrackLength = 0;
            for (BoneTrack track : tracks) {
              float length = track.getLength();
              if (length > maximumTrackLength) {
                maximumTrackLength = length;
              }
            }

            Animation boneAnimation = new Animation(actionName, maximumTrackLength);
            boneAnimation.setTracks(tracks);
            animations.add(boneAnimation);
          }
        }
        animData = new AnimData(new Skeleton(bones), animations);
      }
    }
  }