gligen/ldm/modules/diffusionmodules/positionnet.py

import torch
import torch.nn as nn
from ldm.modules.attention import BasicTransformerBlock
from ldm.modules.diffusionmodules.util import checkpoint, FourierEmbedder
import torch.nn.functional as F



class PositionNet(nn.Module):
    def __init__(self,  positive_len, out_dim, fourier_freqs=8):
        super().__init__()
        self.positive_len = positive_len
        self.out_dim = out_dim 

        self.fourier_embedder = FourierEmbedder(num_freqs=fourier_freqs)
        self.position_dim = fourier_freqs*2*4 # 2 is sin&cos, 4 is xyxy 

        self.linears = nn.Sequential(
            nn.Linear( self.positive_len + self.position_dim, 512),
            nn.SiLU(),
            nn.Linear( 512, 512),
            nn.SiLU(),
            nn.Linear(512, out_dim),
        )
        
        self.null_positive_feature = torch.nn.Parameter(torch.zeros([self.positive_len]))
        self.null_position_feature = torch.nn.Parameter(torch.zeros([self.position_dim]))
  

    def forward(self, boxes, masks, positive_embeddings):
        B, N, _ = boxes.shape 
        masks = masks.unsqueeze(-1)

        # embedding position (it may includes padding as placeholder)
        xyxy_embedding = self.fourier_embedder(boxes) # B*N*4 --> B*N*C

        # learnable null embedding 
        positive_null = self.null_positive_feature.view(1,1,-1)
        xyxy_null =  self.null_position_feature.view(1,1,-1)

        # replace padding with learnable null embedding 
        positive_embeddings = positive_embeddings*masks + (1-masks)*positive_null
        xyxy_embedding = xyxy_embedding*masks + (1-masks)*xyxy_null

        objs = self.linears(  torch.cat([positive_embeddings, xyxy_embedding], dim=-1)  )
        assert objs.shape == torch.Size([B,N,self.out_dim])        
        return objs