projector.py

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import torch
import torch.nn as nn
from torch.nn.init import trunc_normal_
from transformers.activations import ACT2FN


class FFN(nn.Module):
    """
    Feed-Forward Network module.

    Args:
        embed_dim (int): Input embedding dimension.
        ff_dim (int): Hidden dimension of the feed-forward network.
        output_dim (int): Output dimension.
    """

    def __init__(self, embed_dim, ff_dim, output_dim):
        super().__init__()
        self.linear_in = nn.Linear(embed_dim, ff_dim, bias=False)
        self.linear_out = nn.Linear(ff_dim, output_dim, bias=False)
        self.act = ACT2FN["gelu_new"]

    def forward(self, hidden_states):
        hidden_states = self.act(self.linear_in(hidden_states))
        hidden_states = self.linear_out(hidden_states)
        return hidden_states


class CrossAttention(nn.Module):
    """
    Cross-Attention module.

    Args:
        kv_dim (int): Dimension of key and value.
        embed_dim (int): Embedding dimension.
        num_heads (int): Number of attention heads.
        drop_out_rate (float): Dropout rate. Default is 0.
    """

    def __init__(self, kv_dim, embed_dim, num_heads, drop_out_rate=0):
        super().__init__()
        self.num_heads = num_heads
        self.q_proj = nn.Linear(embed_dim, embed_dim, bias=False)
        self.k_proj = nn.Linear(kv_dim, embed_dim, bias=False)
        self.v_proj = nn.Linear(kv_dim, embed_dim, bias=False)

        self.multihead_attn = nn.MultiheadAttention(embed_dim, num_heads)
        self.linear = nn.Linear(embed_dim, embed_dim)
        self.dropout = nn.Dropout(drop_out_rate)

        self.layer_norm = nn.LayerNorm(embed_dim)
        self.ln_kv = nn.LayerNorm(kv_dim)

    def forward(self, x, hidden_states, attn_mask=None, add_residual=False):
        """
        Forward pass of the CrossAttention module.

        Args:
            x (torch.Tensor): Input tensor for key and value.
            hidden_states (torch.Tensor): Input tensor for query.
            attn_mask (torch.Tensor, optional): Attention mask. Default is None.
            add_residual (bool): Whether to add residual connection. Default is False.

        Returns:
            torch.Tensor: Output tensor after cross-attention.
        """
        normed_hidden_states = self.layer_norm(hidden_states)
        query = self.q_proj(normed_hidden_states).permute(1, 0, 2)

        x = self.ln_kv(x)
        key = self.k_proj(x).permute(1, 0, 2)
        value = self.v_proj(x).permute(1, 0, 2)

        attn_output, _ = self.multihead_attn(query, key, value, attn_mask=attn_mask)

        attn_output = attn_output.permute(1, 0, 2)

        if add_residual:
            attn_output = hidden_states + self.dropout(self.linear(attn_output))
        else:
            attn_output = self.dropout(self.linear(attn_output))

        return attn_output


class AriaProjector(nn.Module):
    """
    A projection module with one cross attention layer and one FFN layer, which projects ViT's outputs into MoE's inputs.

    Args:
        patch_to_query_dict (dict): Maps patch numbers to their corresponding query numbers,
            e.g., {1225: 128, 4900: 256}. This allows for different query sizes based on image resolution.
        embed_dim (int): Embedding dimension.
        num_heads (int): Number of attention heads.
        kv_dim (int): Dimension of key and value.
        ff_dim (int): Hidden dimension of the feed-forward network.
        output_dim (int): Output dimension.
        norm_layer (nn.Module): Normalization layer. Default is nn.LayerNorm.

    Outputs:
        A tensor with the shape of (batch_size, query_number, output_dim)
    """

    def __init__(
        self,
        patch_to_query_dict,
        embed_dim,
        num_heads,
        kv_dim,
        ff_dim,
        output_dim,
        norm_layer=nn.LayerNorm,
    ):
        super().__init__()
        self.patch_to_query_dict = patch_to_query_dict
        self.embed_dim = embed_dim
        self.num_heads = num_heads

        self.query = nn.Parameter(
            torch.zeros(max(patch_to_query_dict.values()), self.embed_dim)
        )

        trunc_normal_(self.query, std=0.02)

        self.cross_attn = CrossAttention(kv_dim, embed_dim, num_heads)

        self.ln_ffn = norm_layer(embed_dim)
        self.ffn = FFN(embed_dim, ff_dim, output_dim)

        self.apply(self._init_weights)

    def _init_weights(self, m):
        if isinstance(m, nn.Linear):
            trunc_normal_(m.weight, std=0.02)
            if isinstance(m, nn.Linear) and m.bias is not None:
                nn.init.constant_(m.bias, 0)
        elif isinstance(m, nn.LayerNorm):
            nn.init.constant_(m.bias, 0)
            nn.init.constant_(m.weight, 1.0)

    def forward(self, x, attn_mask=None):
        """
        Forward pass of the Projector module.

        Args:
            x (torch.Tensor): Input tensor of shape (batch_size, num_patches, kv_dim).
            attn_mask (torch.Tensor, optional): Attention mask. Default is None.

        Returns:
            torch.Tensor: Output tensor of shape (batch_size, query_number, output_dim).
        """
        bs = x.shape[0]
        queries = self.query.unsqueeze(0).repeat(bs, 1, 1)

        query_num = self.patch_to_query_dict.get(x.shape[1], None)
        assert (
            query_num is not None
        ), f"Query number for {x.shape[1]} patches is not provided"

        queries = queries[:, :query_num, :]

        if attn_mask is not None:
            attn_mask = attn_mask.repeat_interleave(self.num_heads, 0)
            attn_mask = attn_mask.unsqueeze(1).expand(-1, queries.size(1), -1)

        attention_out = self.cross_attn(x, queries, attn_mask=attn_mask)

        out = self.ffn(self.ln_ffn(attention_out))

        return out