code: def forward(
      self,
      src,
      pos,
      reference_points,
      spatial_shapes,
      level_start_index,
      padding_mask=None,
  ):
      # Self attention
      src2 = self.self_attn(
          self.with_pos_embed(src, pos),
          reference_points,
          src,
          spatial_shapes,
          level_start_index,
          padding_mask,
      )
      src = src + self.dropout1(src2)
      src = self.norm1(src)
  
      # FFN
      src = self.forward_ffn(src)
  
      return src
  
imports: import copy
  import numpy
  import paddle
  import paddle.nn
  import paddle.nn.functional
  from paddleseg.cvlibs import param_init
  from paddlepanseg.models.param_init import c2_xavier_fill, THLinearInitMixin
  from .common import Conv2D, PositionEmbeddingSine
  from ._ms_deform_attn import MSDeformAttn
label_desc: Use image node_id 4 for calling the MSDeformAttnTransformerEncoderLayer obj's underlying member method code with example usage: obj.forward(src, pos, reference_points, spatial_shapes, level_start_index, padding_mask) and returns: src