text: # Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved
  """
  DETR model and criterion classes.
  """
  import torch
  import torch.nn.functional as F
  from torch import nn
  
  from util import box_ops
  from util.misc import (NestedTensor, nested_tensor_from_tensor_list,
                         accuracy, get_world_size, interpolate,
                         is_dist_avail_and_initialized)
  
  from .backbone import build_backbone
  from .matcher import build_matcher
  from .segmentation import (DETRsegm, PostProcessPanoptic, PostProcessSegm,
                             dice_loss, sigmoid_focal_loss)
  from .transformer import build_transformer
  
  
  class DETR(nn.Module):
      """ This is the DETR module that performs object detection """
      def __init__(self, backbone, transformer, num_classes, num_queries, aux_loss=False):
          """ Initializes the model.
          Parameters:
              backbone: torch module of the backbone to be used. See backbone.py
              transformer: torch module of the transformer architecture. See transformer.py
              num_classes: number of object classes
              num_queries: number of object queries, ie detection slot. This is the maximal number of objects
                           DETR can detect in a single image. For COCO, we recommend 100 queries.
              aux_loss: True if auxiliary decoding losses (loss at each decoder layer) are to be used.
          """
          super().__init__()
          self.num_queries = num_queries
          self.transformer = transformer
          hidden_dim = transformer.d_model
          self.class_embed = nn.Linear(hidden_dim, num_classes + 1)
          self.bbox_embed = MLP(hidden_dim, hidden_dim, 4, 3)
          self.query_embed = nn.Embedding(num_queries, hidden_dim)
          self.input_proj = nn.Conv2d(backbone.num_channels, hidden_dim, kernel_size=1)
          self.backbone = backbone
          self.aux_loss = aux_loss
  
      def forward(self, samples: NestedTensor):
          """ The forward expects a NestedTensor, which consists of:
                 - samples.tensor: batched images, of shape [batch_size x 3 x H x W]
                 - samples.mask: a binary mask of shape [batch_size x H x W], containing 1 on padded pixels
  
              It returns a dict with the following elements:
                 - "pred_logits": the classification logits (including no-object) for all queries.
                                  Shape= [batch_size x num_queries x (num_classes + 1)]
                 - "pred_boxes": The normalized boxes coordinates for all queries, represented as
                                 (center_x, center_y, height, width). These values are normalized in [0, 1],
                                 relative to the size of each individual image (disregarding possible padding).
                                 See PostProcess for information on how to retrieve the unnormalized bounding box.
                 - "aux_outputs": Optional, only returned when auxilary losses are activated. It is a list of
                                  dictionnaries containing the two above keys for each decoder layer.
          """
          if isinstance(samples, (list, torch.Tensor)):
              samples = nested_tensor_from_tensor_list(samples)
          features, pos = self.backbone(samples)
  
          src, mask = features[-1].decompose()
          assert mask is not None
          hs = self.transformer(self.input_proj(src), mask, self.query_embed.weight, pos[-1])[0]
  
          outputs_class = self.class_embed(hs)
          outputs_coord = self.bbox_embed(hs).sigmoid()
          out = {'pred_logits': outputs_class[-1], 'pred_boxes': outputs_coord[-1]}
          if self.aux_loss:
              out['aux_outputs'] = self._set_aux_loss(outputs_class, outputs_coord)
          return out
  
      @torch.jit.unused
      def _set_aux_loss(self, outputs_class, outputs_coord):
          # this is a workaround to make torchscript happy, as torchscript
          # doesn't support dictionary with non-homogeneous values, such
          # as a dict having both a Tensor and a list.
          return [{'pred_logits': a, 'pred_boxes': b}
                  for a, b in zip(outputs_class[:-1], outputs_coord[:-1])]
  
  
  class SetCriterion(nn.Module):
      """ This class computes the loss for DETR.
      The process happens in two steps:
          1) we compute hungarian assignment between ground truth boxes and the outputs of the model
          2) we supervise each pair of matched ground-truth / prediction (supervise class and box)
      """
      def __init__(self, num_classes, matcher, weight_dict, eos_coef, losses):
          """ Create the criterion.
          Parameters:
              num_classes: number of object categories, omitting the special no-object category
              matcher: module able to compute a matching between targets and proposals
              weight_dict: dict containing as key the names of the losses and as values their relative weight.
              eos_coef: relative classification weight applied to the no-object category
              losses: list of all the losses to be applied. See get_loss for list of available losses.
          """
          super().__init__()
          self.num_classes = num_classes
          self.matcher = matcher
          self.weight_dict = weight_dict
          self.eos_coef = eos_coef
          self.losses = losses
          empty_weight = torch.ones(self.num_classes + 1)
          empty_weight[-1] = self.eos_coef
          self.register_buffer('empty_weight', empty_weight)
  
      def loss_labels(self, outputs, targets, indices, num_boxes, log=True):
          """Classification loss (NLL)
          targets dicts must contain the key "labels" containing a tensor of dim [nb_target_boxes]
          """
          assert 'pred_logits' in outputs
          src_logits = outputs['pred_logits']
  
          idx = self._get_src_permutation_idx(indices)
          target_classes_o = torch.cat([t["labels"][J] for t, (_, J) in zip(targets, indices)])
          target_classes = torch.full(src_logits.shape[:2], self.num_classes,
                                      dtype=torch.int64, device=src_logits.device)
          target_classes[idx] = target_classes_o
  
          loss_ce = F.cross_entropy(src_logits.transpose(1, 2), target_classes, self.empty_weight)
          losses = {'loss_ce': loss_ce}
  
          if log:
              # TODO this should probably be a separate loss, not hacked in this one here
              losses['class_error'] = 100 - accuracy(src_logits[idx], target_classes_o)[0]
          return losses
  
      @torch.no_grad()
      def loss_cardinality(self, outputs, targets, indices, num_boxes):
          """ Compute the cardinality error, ie the absolute error in the number of predicted non-empty boxes
          This is not really a loss, it is intended for logging purposes only. It doesn't propagate gradients
          """
          pred_logits = outputs['pred_logits']
          device = pred_logits.device
          tgt_lengths = torch.as_tensor([len(v["labels"]) for v in targets], device=device)
          # Count the number of predictions that are NOT "no-object" (which is the last class)
          card_pred = (pred_logits.argmax(-1) != pred_logits.shape[-1] - 1).sum(1)
          card_err = F.l1_loss(card_pred.float(), tgt_lengths.float())
          losses = {'cardinality_error': card_err}
          return losses
  
      def loss_boxes(self, outputs, targets, indices, num_boxes):
          """Compute the losses related to the bounding boxes, the L1 regression loss and the GIoU loss
             targets dicts must contain the key "boxes" containing a tensor of dim [nb_target_boxes, 4]
             The target boxes are expected in format (center_x, center_y, w, h), normalized by the image size.
          """
          assert 'pred_boxes' in outputs
          idx = self._get_src_permutation_idx(indices)
          src_boxes = outputs['pred_boxes'][idx]
          target_boxes = torch.cat([t['boxes'][i] for t, (_, i) in zip(targets, indices)], dim=0)
  
          loss_bbox = F.l1_loss(src_boxes, target_boxes, reduction='none')
  
          losses = {}
          losses['loss_bbox'] = loss_bbox.sum() / num_boxes
  
          loss_giou = 1 - torch.diag(box_ops.generalized_box_iou(
              box_ops.box_cxcywh_to_xyxy(src_boxes),
              box_ops.box_cxcywh_to_xyxy(target_boxes)))
          losses['loss_giou'] = loss_giou.sum() / num_boxes
          return losses
  
      def loss_masks(self, outputs, targets, indices, num_boxes):
          """Compute the losses related to the masks: the focal loss and the dice loss.
             targets dicts must contain the key "masks" containing a tensor of dim [nb_target_boxes, h, w]
          """
          assert "pred_masks" in outputs
  
          src_idx = self._get_src_permutation_idx(indices)
          tgt_idx = self._get_tgt_permutation_idx(indices)
  
          src_masks = outputs["pred_masks"]
  
          # TODO use valid to mask invalid areas due to padding in loss
          target_masks, valid = nested_tensor_from_tensor_list([t["masks"] for t in targets]).decompose()
          target_masks = target_masks.to(src_masks)
  
          src_masks = src_masks[src_idx]
          # upsample predictions to the target size
          src_masks = interpolate(src_masks[:, None], size=target_masks.shape[-2:],
                                  mode="bilinear", align_corners=False)
          src_masks = src_masks[:, 0].flatten(1)
  
          target_masks = target_masks[tgt_idx].flatten(1)
  
          losses = {
              "loss_mask": sigmoid_focal_loss(src_masks, target_masks, num_boxes),
              "loss_dice": dice_loss(src_masks, target_masks, num_boxes),
          }
          return losses
  
      def _get_src_permutation_idx(self, indices):
          # permute predictions following indices
          batch_idx = torch.cat([torch.full_like(src, i) for i, (src, _) in enumerate(indices)])
          src_idx = torch.cat([src for (src, _) in indices])
          return batch_idx, src_idx
  
      def _get_tgt_permutation_idx(self, indices):
          # permute targets following indices
          batch_idx = torch.cat([torch.full_like(tgt, i) for i, (_, tgt) in enumerate(indices)])
          tgt_idx = torch.cat([tgt for (_, tgt) in indices])
          return batch_idx, tgt_idx
  
      def get_loss(self, loss, outputs, targets, indices, num_boxes, **kwargs):
          loss_map = {
              'labels': self.loss_labels,
              'cardinality': self.loss_cardinality,
              'boxes': self.loss_boxes,
              'masks': self.loss_masks
          }
          assert loss in loss_map, f'do you really want to compute {loss} loss?'
          return loss_map[loss](outputs, targets, indices, num_boxes, **kwargs)
  
      def forward(self, outputs, targets):
          """ This performs the loss computation.
          Parameters:
               outputs: dict of tensors, see the output specification of the model for the format
               targets: list of dicts, such that len(targets) == batch_size.
                        The expected keys in each dict depends on the losses applied, see each loss' doc
          """
          outputs_without_aux = {k: v for k, v in outputs.items() if k != 'aux_outputs'}
  
          # Retrieve the matching between the outputs of the last layer and the targets
          indices = self.matcher(outputs_without_aux, targets)
  
          # Compute the average number of target boxes accross all nodes, for normalization purposes
          num_boxes = sum(len(t["labels"]) for t in targets)
          num_boxes = torch.as_tensor([num_boxes], dtype=torch.float, device=next(iter(outputs.values())).device)
          if is_dist_avail_and_initialized():
              torch.distributed.all_reduce(num_boxes)
          num_boxes = torch.clamp(num_boxes / get_world_size(), min=1).item()
  
          # Compute all the requested losses
          losses = {}
          for loss in self.losses:
              losses.update(self.get_loss(loss, outputs, targets, indices, num_boxes))
  
          # In case of auxiliary losses, we repeat this process with the output of each intermediate layer.
          if 'aux_outputs' in outputs:
              for i, aux_outputs in enumerate(outputs['aux_outputs']):
                  indices = self.matcher(aux_outputs, targets)
                  for loss in self.losses:
                      if loss == 'masks':
                          # Intermediate masks losses are too costly to compute, we ignore them.
                          continue
                      kwargs = {}
                      if loss == 'labels':
                          # Logging is enabled only for the last layer
                          kwargs = {'log': False}
                      l_dict = self.get_loss(loss, aux_outputs, targets, indices, num_boxes, **kwargs)
                      l_dict = {k + f'_{i}': v for k, v in l_dict.items()}
                      losses.update(l_dict)
  
          return losses
  
  
  class PostProcess(nn.Module):
      """ This module converts the model's output into the format expected by the coco api"""
      @torch.no_grad()
      def forward(self, outputs, target_sizes):
          """ Perform the computation
          Parameters:
              outputs: raw outputs of the model
              target_sizes: tensor of dimension [batch_size x 2] containing the size of each images of the batch
                            For evaluation, this must be the original image size (before any data augmentation)
                            For visualization, this should be the image size after data augment, but before padding
          """
          out_logits, out_bbox = outputs['pred_logits'], outputs['pred_boxes']
  
          assert len(out_logits) == len(target_sizes)
          assert target_sizes.shape[1] == 2
  
          prob = F.softmax(out_logits, -1)
          scores, labels = prob[..., :-1].max(-1)
  
          # convert to [x0, y0, x1, y1] format
          boxes = box_ops.box_cxcywh_to_xyxy(out_bbox)
          # and from relative [0, 1] to absolute [0, height] coordinates
          img_h, img_w = target_sizes.unbind(1)
          scale_fct = torch.stack([img_w, img_h, img_w, img_h], dim=1)
          boxes = boxes * scale_fct[:, None, :]
  
          results = [{'scores': s, 'labels': l, 'boxes': b} for s, l, b in zip(scores, labels, boxes)]
  
          return results
  
  
  class MLP(nn.Module):
      """ Very simple multi-layer perceptron (also called FFN)"""
  
      def __init__(self, input_dim, hidden_dim, output_dim, num_layers):
          super().__init__()
          self.num_layers = num_layers
          h = [hidden_dim] * (num_layers - 1)
          self.layers = nn.ModuleList(nn.Linear(n, k) for n, k in zip([input_dim] + h, h + [output_dim]))
  
      def forward(self, x):
          for i, layer in enumerate(self.layers):
              x = F.relu(layer(x)) if i < self.num_layers - 1 else layer(x)
          return x
  
  
  def build(args):
      num_classes = 20 if args.dataset_file != 'coco' else 91
      if args.dataset_file == "coco_panoptic":
          num_classes = 250
      device = torch.device(args.device)
  
      backbone = build_backbone(args)
  
      transformer = build_transformer(args)
  
      model = DETR(
          backbone,
          transformer,
          num_classes=num_classes,
          num_queries=args.num_queries,
          aux_loss=args.aux_loss,
      )
      if args.masks:
          model = DETRsegm(model, freeze_detr=(args.frozen_weights is not None))
      matcher = build_matcher(args)
      weight_dict = {'loss_ce': 1, 'loss_bbox': args.bbox_loss_coef}
      weight_dict['loss_giou'] = args.giou_loss_coef
      if args.masks:
          weight_dict["loss_mask"] = args.mask_loss_coef
          weight_dict["loss_dice"] = args.dice_loss_coef
      # TODO this is a hack
      if args.aux_loss:
          aux_weight_dict = {}
          for i in range(args.dec_layers - 1):
              aux_weight_dict.update({k + f'_{i}': v for k, v in weight_dict.items()})
          weight_dict.update(aux_weight_dict)
  
      losses = ['labels', 'boxes', 'cardinality']
      if args.masks:
          losses += ["masks"]
      criterion = SetCriterion(num_classes, matcher=matcher, weight_dict=weight_dict,
                               eos_coef=args.eos_coef, losses=losses)
      criterion.to(device)
      postprocessors = {'bbox': PostProcess()}
      if args.masks:
          postprocessors['segm'] = PostProcessSegm()
          if args.dataset_file == "coco_panoptic":
              is_thing_map = {i: i <= 90 for i in range(201)}
              postprocessors["panoptic"] = PostProcessPanoptic(is_thing_map, threshold=0.85)
  
      return model, criterion, postprocessors
  