code: def _bbox_loss(
      self,
      pred_angle,
      pred_bboxes,
      anchor_points,
      assigned_labels,
      assigned_bboxes,
      assigned_scores,
      assigned_scores_sum,
      stride_tensor,
  ):
      # select positive samples mask
      mask_positive = assigned_labels != self.num_classes
      num_pos = mask_positive.sum()
      # pos/neg loss
      if num_pos > 0:
          # iou
          bbox_mask = mask_positive.unsqueeze(-1).tile([1, 1, 5])
          pred_bboxes_pos = paddle.masked_select(
              pred_bboxes, bbox_mask
          ).reshape([-1, 5])
          assigned_bboxes_pos = paddle.masked_select(
              assigned_bboxes, bbox_mask
          ).reshape([-1, 5])
          bbox_weight = paddle.masked_select(
              assigned_scores.sum(-1), mask_positive
          ).reshape([-1])
  
          loss_iou = (
              self.iou_loss(pred_bboxes_pos, assigned_bboxes_pos)
              * bbox_weight
          )
          loss_iou = loss_iou.sum() / assigned_scores_sum
  
          # dfl
          angle_mask = mask_positive.unsqueeze(-1).tile(
              [1, 1, self.angle_max + 1]
          )
          pred_angle_pos = paddle.masked_select(
              pred_angle, angle_mask
          ).reshape([-1, self.angle_max + 1])
          assigned_angle_pos = (
              assigned_bboxes_pos[:, 4] / self.half_pi_bin
          ).clip(0, self.angle_max - 0.01)
          loss_dfl = self._df_loss(pred_angle_pos, assigned_angle_pos)
      else:
          loss_iou = pred_bboxes.sum() * 0.0
          loss_dfl = paddle.zeros([1])
  
      return loss_iou, loss_dfl
  
imports: import paddle
  import paddle.nn
  import paddle.nn.functional
  from ppdet.core.workspace import register
  from ..losses import ProbIoULoss
  from ..initializer import bias_init_with_prob, constant_, normal_, vector_
  from ppdet.modeling.backbones.cspresnet import ConvBNLayer
  from ppdet.modeling.ops import get_static_shape, get_act_fn, anchor_generator
  from ppdet.modeling.layers import MultiClassNMS
label_desc: Use image node_id 13 for calling the PPYOLOERHead obj's underlying member method code with example usage: obj._bbox_loss(pred_angle, pred_bboxes, anchor_points, assigned_labels, assigned_bboxes, assigned_scores, assigned_scores_sum, stride_tensor) and returns: loss_iou,  loss_dfl