def calc_scene_bbox(self):
        """Calculate scene bbox"""
        bbox_min, bbox_max = None, None
        for node in self.root_nodes:
            bbox_min, bbox_max = node.calc_global_bbox(
                matrix44.create_identity(),
                bbox_min,
                bbox_max
            )

        self.bbox_min = bbox_min
        self.bbox_max = bbox_max

        self.diagonal_size = vector3.length(self.bbox_max - self.bbox_min)
Calculate scene bbox