modeling_vitdet.py

# coding=utf-8
# Copyright 2023 Meta AI and The HuggingFace Inc. team. All rights reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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""" PyTorch ViTDet backbone."""


import collections.abc
import math
from typing import Dict, List, Optional, Tuple, Union

import torch
import torch.utils.checkpoint
from torch import nn

from ...activations import ACT2FN
from ...modeling_outputs import BackboneOutput, BaseModelOutput
from ...modeling_utils import PreTrainedModel
from ...utils import (
    add_start_docstrings,
    add_start_docstrings_to_model_forward,
    logging,
    replace_return_docstrings,
)
from ...utils.backbone_utils import BackboneMixin
from .configuration_vitdet import VitDetConfig


logger = logging.get_logger(__name__)

# General docstring
_CONFIG_FOR_DOC = "VitDetConfig"


from ..deprecated._archive_maps import VITDET_PRETRAINED_MODEL_ARCHIVE_LIST  # noqa: F401, E402


class VitDetEmbeddings(nn.Module):
    """
    This class turns `pixel_values` of shape `(batch_size, num_channels, height, width)` into the initial
    `hidden_states` (patch embeddings) to be consumed by a Transformer.
    """

    def __init__(self, config):
        super().__init__()
        image_size, patch_size = config.pretrain_image_size, config.patch_size
        num_channels, hidden_size = config.num_channels, config.hidden_size

        image_size = image_size if isinstance(image_size, collections.abc.Iterable) else (image_size, image_size)
        patch_size = patch_size if isinstance(patch_size, collections.abc.Iterable) else (patch_size, patch_size)
        num_patches = (image_size[1] // patch_size[1]) * (image_size[0] // patch_size[0])
        self.image_size = image_size
        self.patch_size = patch_size
        self.num_channels = num_channels
        self.num_patches = num_patches

        if config.use_absolute_position_embeddings:
            # Initialize absolute positional embedding with pretrain image size.
            num_positions = num_patches + 1
            self.position_embeddings = nn.Parameter(torch.zeros(1, num_positions, config.hidden_size))
        else:
            self.position_embeddings = None

        self.projection = nn.Conv2d(num_channels, hidden_size, kernel_size=patch_size, stride=patch_size)

    def get_absolute_positions(self, abs_pos_embeddings, has_cls_token, height, width):
        """
        Calculate absolute positional embeddings. If needed, resize embeddings and remove cls_token dimension for the
        original embeddings.

        Args:
            abs_pos_embeddings (`torch.Tensor`):
                Absolute positional embeddings with (1, num_position, num_channels).
            has_cls_token (`bool`):
                If true, has 1 embedding in abs_pos_embeddings for cls token.
            height (`int`):
                Height of input image tokens.
            width (`int`):
                Width of input image tokens.

        Returns:
            Absolute positional embeddings after processing with shape (1, height, width, num_channels)
        """
        if has_cls_token:
            abs_pos_embeddings = abs_pos_embeddings[:, 1:]
        num_position = abs_pos_embeddings.shape[1]
        size = int(math.sqrt(num_position))  # This is a constant and can be recorded as such in the ONNX export.
        if size * size != num_position:
            raise ValueError("Absolute position embeddings must be a square number.")

        if torch.jit.is_tracing() or (size != height or size != width):
            # nn.functional.interpolate is a noop in case size == height and size == width - we need to always capture this path with jit.trace.
            new_abs_pos_embeddings = nn.functional.interpolate(
                abs_pos_embeddings.reshape(1, size, size, -1).permute(0, 3, 1, 2),
                size=(height, width),
                mode="bicubic",
                align_corners=False,
            )

            return new_abs_pos_embeddings.permute(0, 2, 3, 1)
        else:
            return abs_pos_embeddings.reshape(1, height, width, -1)

    def forward(self, pixel_values: torch.Tensor) -> torch.Tensor:
        num_channels = pixel_values.shape[1]
        if num_channels != self.num_channels:
            raise ValueError(
                "Make sure that the channel dimension of the pixel values match with the one set in the configuration."
                f" Expected {self.num_channels} but got {num_channels}."
            )
        embeddings = self.projection(pixel_values)

        if self.position_embeddings is not None:
            # (batch_size, num_channels, height, width) -> (batch_size, height, width, num_channels)
            embeddings = embeddings.permute(0, 2, 3, 1)
            # add position embeddings
            embeddings = embeddings + self.get_absolute_positions(
                self.position_embeddings, True, embeddings.shape[1], embeddings.shape[2]
            )
            # (batch_size, height, width, num_channels) -> (batch_size, num_channels, height, width)
            embeddings = embeddings.permute(0, 3, 1, 2)

        return embeddings


@torch.jit.script_if_tracing  # nn.functional.interpolate's `size` needs to be dynamic.
def get_rel_pos(q_size, k_size, rel_pos):
    """
    Get relative positional embeddings according to the relative positions of query and key sizes.

    Args:
        q_size (`int`):
            Size of query q.
        k_size (`int`):
            Size of key k.
        rel_pos (`torch.Tensor`):
            Relative position embeddings (num_embeddings, num_channels).

    Returns:
        Extracted positional embeddings according to relative positions.
    """
    max_rel_dist = int(2 * max(q_size, k_size) - 1)
    # Interpolate rel pos if needed.
    if rel_pos.shape[0] != max_rel_dist:
        # Interpolate rel position embeddings.
        rel_pos_resized = nn.functional.interpolate(
            rel_pos.reshape(1, rel_pos.shape[0], -1).permute(0, 2, 1),
            size=max_rel_dist,
            mode="linear",
        )
        rel_pos_resized = rel_pos_resized.reshape(-1, max_rel_dist).permute(1, 0)
    else:
        rel_pos_resized = rel_pos

    # Scale the coords with short length if shapes for q and k are different.
    q_coords = torch.arange(q_size)[:, None] * max(k_size / q_size, 1.0)
    k_coords = torch.arange(k_size)[None, :] * max(q_size / k_size, 1.0)
    relative_coords = (q_coords - k_coords) + (k_size - 1) * max(q_size / k_size, 1.0)

    return rel_pos_resized[relative_coords.long()]


def add_decomposed_relative_positions(attn, queries, rel_pos_h, rel_pos_w, q_size, k_size):
    """
    Calculate decomposed Relative Positional Embeddings as introduced in
    [MViT2](https://github.com/facebookresearch/mvit/blob/19786631e330df9f3622e5402b4a419a263a2c80/mvit/models/attention.py).

    Args:
        attn (`torch.Tensor`):
            Attention map.
        queries (`torch.Tensor`):
            Query q in the attention layer with shape (batch_size, queries_height * queries_width, num_channels).
        rel_pos_h (`torch.Tensor`):
            Relative position embeddings (Lh, num_channels) for height axis.
        rel_pos_w (`torch.Tensor`):
            Relative position embeddings (Lw, num_channels) for width axis.
        q_size (`Tuple[int]`):
            Spatial sequence size of query q with (queries_height, queries_width).
        k_size (`Tuple[int]`]):
            Spatial sequence size of key k with (keys_height, keys_width).

    Returns:
        attn (Tensor): attention map with added relative positional embeddings.
    """
    queries_height, queries_width = q_size
    keys_height, keys_width = k_size
    relative_height = get_rel_pos(queries_height, keys_height, rel_pos_h)
    relative_width = get_rel_pos(queries_width, keys_width, rel_pos_w)

    batch_size, _, dim = queries.shape
    r_q = queries.reshape(batch_size, queries_height, queries_width, dim)
    relative_height = torch.einsum("bhwc,hkc->bhwk", r_q, relative_height)
    relative_weight = torch.einsum("bhwc,wkc->bhwk", r_q, relative_width)

    attn = (
        attn.view(batch_size, queries_height, queries_width, keys_height, keys_width)
        + relative_height[:, :, :, :, None]
        + relative_weight[:, :, :, None, :]
    ).view(batch_size, queries_height * queries_width, keys_height * keys_width)

    return attn


class VitDetAttention(nn.Module):
    """Multi-head Attention block with relative position embeddings."""

    def __init__(self, config, input_size=None):
        """
        Args:
            config (`VitDetConfig`):
                Model configuration.
            input_size (`Tuple[int]`, *optional*):
                Input resolution, only required in case relative position embeddings are added.
        """
        super().__init__()

        dim = config.hidden_size
        num_heads = config.num_attention_heads

        self.num_heads = num_heads
        head_dim = dim // num_heads
        self.scale = head_dim**-0.5

        self.qkv = nn.Linear(dim, dim * 3, bias=config.qkv_bias)
        self.proj = nn.Linear(dim, dim)

        self.use_relative_position_embeddings = config.use_relative_position_embeddings
        if self.use_relative_position_embeddings:
            # initialize relative positional embeddings
            self.rel_pos_h = nn.Parameter(torch.zeros(2 * input_size[0] - 1, head_dim))
            self.rel_pos_w = nn.Parameter(torch.zeros(2 * input_size[1] - 1, head_dim))

    def forward(self, hidden_state, output_attentions=False):
        batch_size, height, width, _ = hidden_state.shape
        # qkv with shape (3, batch_size, num_heads, height * width, num_channels)
        qkv = self.qkv(hidden_state).reshape(batch_size, height * width, 3, self.num_heads, -1).permute(2, 0, 3, 1, 4)
        # queries, keys and values have shape (batch_size * num_heads, height * width, num_channels)
        queries, keys, values = qkv.reshape(3, batch_size * self.num_heads, height * width, -1).unbind(0)

        attention_scores = (queries * self.scale) @ keys.transpose(-2, -1)

        if self.use_relative_position_embeddings:
            attention_scores = add_decomposed_relative_positions(
                attention_scores, queries, self.rel_pos_h, self.rel_pos_w, (height, width), (height, width)
            )

        attention_probs = attention_scores.softmax(dim=-1)

        hidden_state = attention_probs @ values
        hidden_state = hidden_state.view(batch_size, self.num_heads, height, width, -1)
        hidden_state = hidden_state.permute(0, 2, 3, 1, 4)
        hidden_state = hidden_state.reshape(batch_size, height, width, -1)
        hidden_state = self.proj(hidden_state)

        if output_attentions:
            attention_probs = attention_probs.reshape(
                batch_size, self.num_heads, attention_probs.shape[-2], attention_probs.shape[-1]
            )
            outputs = (hidden_state, attention_probs)
        else:
            outputs = (hidden_state,)

        return outputs


# Copied from transformers.models.beit.modeling_beit.drop_path
def drop_path(input: torch.Tensor, drop_prob: float = 0.0, training: bool = False) -> torch.Tensor:
    """
    Drop paths (Stochastic Depth) per sample (when applied in main path of residual blocks).

    Comment by Ross Wightman: This is the same as the DropConnect impl I created for EfficientNet, etc networks,
    however, the original name is misleading as 'Drop Connect' is a different form of dropout in a separate paper...
    See discussion: https://github.com/tensorflow/tpu/issues/494#issuecomment-532968956 ... I've opted for changing the
    layer and argument names to 'drop path' rather than mix DropConnect as a layer name and use 'survival rate' as the
    argument.
    """
    if drop_prob == 0.0 or not training:
        return input
    keep_prob = 1 - drop_prob
    shape = (input.shape[0],) + (1,) * (input.ndim - 1)  # work with diff dim tensors, not just 2D ConvNets
    random_tensor = keep_prob + torch.rand(shape, dtype=input.dtype, device=input.device)
    random_tensor.floor_()  # binarize
    output = input.div(keep_prob) * random_tensor
    return output


# Copied from transformers.models.beit.modeling_beit.BeitDropPath
class VitDetDropPath(nn.Module):
    """Drop paths (Stochastic Depth) per sample (when applied in main path of residual blocks)."""

    def __init__(self, drop_prob: Optional[float] = None) -> None:
        super().__init__()
        self.drop_prob = drop_prob

    def forward(self, hidden_states: torch.Tensor) -> torch.Tensor:
        return drop_path(hidden_states, self.drop_prob, self.training)

    def extra_repr(self) -> str:
        return "p={}".format(self.drop_prob)


class VitDetLayerNorm(nn.Module):
    """
    A LayerNorm variant, popularized by Transformers, that performs point-wise mean and variance normalization over the
    channel dimension for inputs that have shape (batch_size, channels, height, width).
    https://github.com/facebookresearch/ConvNeXt/blob/d1fa8f6fef0a165b27399986cc2bdacc92777e40/models/convnext.py#L119
    """

    def __init__(self, normalized_shape, eps=1e-6):
        super().__init__()
        self.weight = nn.Parameter(torch.ones(normalized_shape))
        self.bias = nn.Parameter(torch.zeros(normalized_shape))
        self.eps = eps
        self.normalized_shape = (normalized_shape,)

    def forward(self, x):
        u = x.mean(1, keepdim=True)
        s = (x - u).pow(2).mean(1, keepdim=True)
        x = (x - u) / torch.sqrt(s + self.eps)
        x = self.weight[:, None, None] * x + self.bias[:, None, None]
        return x


class VitDetResBottleneckBlock(nn.Module):
    """
    The standard bottleneck residual block without the last activation layer. It contains 3 conv layers with kernels
    1x1, 3x3, 1x1.
    """

    def __init__(self, config, in_channels, out_channels, bottleneck_channels):
        """
        Args:
            config (`VitDetConfig`):
                Model configuration.
            in_channels (`int`):
                Number of input channels.
            out_channels (`int`):
                Number of output channels.
            bottleneck_channels (`int`):
                Number of output channels for the 3x3 "bottleneck" conv layers.
        """
        super().__init__()
        self.conv1 = nn.Conv2d(in_channels, bottleneck_channels, 1, bias=False)
        self.norm1 = VitDetLayerNorm(bottleneck_channels)
        self.act1 = ACT2FN[config.hidden_act]

        self.conv2 = nn.Conv2d(bottleneck_channels, bottleneck_channels, 3, padding=1, bias=False)
        self.norm2 = VitDetLayerNorm(bottleneck_channels)
        self.act2 = ACT2FN[config.hidden_act]

        self.conv3 = nn.Conv2d(bottleneck_channels, out_channels, 1, bias=False)
        self.norm3 = VitDetLayerNorm(out_channels)

    def forward(self, x):
        out = x
        for layer in self.children():
            out = layer(out)

        out = x + out
        return out


class VitDetMlp(nn.Module):
    def __init__(self, config, in_features: int, hidden_features: int) -> None:
        super().__init__()
        self.fc1 = nn.Linear(in_features, hidden_features)
        self.act = ACT2FN[config.hidden_act]
        self.fc2 = nn.Linear(hidden_features, in_features)
        self.drop = nn.Dropout(config.dropout_prob)

    def forward(self, x: torch.Tensor) -> torch.Tensor:
        x = self.fc1(x)
        x = self.act(x)
        x = self.drop(x)
        x = self.fc2(x)
        x = self.drop(x)

        return x


def window_partition(hidden_state, window_size):
    """
    Partition into non-overlapping windows with padding if needed.

    Args:
        hidden_state (`torch.Tensor`):
            Input tokens with [batch_size, height, width, num_channels].
        window_size (`int`):
            Window size.

    Returns:
        `tuple(torch.FloatTensor)` comprising various elements:
        - windows: windows after partition with [batch_size * num_windows, window_size, window_size, num_channels].
        - (padded_height, padded_width): padded height and width before partition
    """
    batch_size, height, width, num_channels = hidden_state.shape

    pad_height = (window_size - height % window_size) % window_size
    pad_width = (window_size - width % window_size) % window_size

    # Noop in case pad_width == 0 and pad_height == 0.
    hidden_state = nn.functional.pad(hidden_state, (0, 0, 0, pad_width, 0, pad_height))

    padded_height, padded_width = height + pad_height, width + pad_width

    hidden_state = hidden_state.view(
        batch_size, padded_height // window_size, window_size, padded_width // window_size, window_size, num_channels
    )
    windows = hidden_state.permute(0, 1, 3, 2, 4, 5).contiguous().view(-1, window_size, window_size, num_channels)
    return windows, (padded_height, padded_width)


def window_unpartition(windows, window_size, pad_height_width, height_width):
    """
    Window unpartition into original sequences and removing padding.

    Args:
        windows (`torch.Tensor`):
            Input tokens with [batch_size * num_windows, window_size, window_size, num_channels].
        window_size (`int`):
            Window size.
        pad_height_width (`Tuple[int]`):
            Padded height and width (padded_height, padded_width).
        height_width (`Tuple[int]`):
            Original height and width before padding.

    Returns:
        hidden_state: unpartitioned sequences with [batch_size, height, width, num_channels].
    """
    padded_height, padded_width = pad_height_width
    height, width = height_width
    batch_size = windows.shape[0] // (padded_height * padded_width // window_size // window_size)
    hidden_state = windows.view(
        batch_size, padded_height // window_size, padded_width // window_size, window_size, window_size, -1
    )
    hidden_state = hidden_state.permute(0, 1, 3, 2, 4, 5).contiguous()
    hidden_state = hidden_state.view(batch_size, padded_height, padded_width, -1)

    # We always have height <= padded_height and width <= padded_width
    hidden_state = hidden_state[:, :height, :width, :].contiguous()
    return hidden_state


class VitDetLayer(nn.Module):
    """This corresponds to the Block class in the original implementation."""

    def __init__(
        self, config: VitDetConfig, drop_path_rate: float = 0, window_size: int = 0, use_residual_block: bool = False
    ) -> None:
        super().__init__()

        dim = config.hidden_size
        input_size = (config.image_size // config.patch_size, config.image_size // config.patch_size)

        self.norm1 = nn.LayerNorm(dim, eps=config.layer_norm_eps)
        self.attention = VitDetAttention(
            config, input_size=input_size if window_size == 0 else (window_size, window_size)
        )

        self.drop_path = VitDetDropPath(drop_path_rate) if drop_path_rate > 0.0 else nn.Identity()
        self.norm2 = nn.LayerNorm(dim, eps=config.layer_norm_eps)
        self.mlp = VitDetMlp(config=config, in_features=dim, hidden_features=int(dim * config.mlp_ratio))

        self.window_size = window_size

        self.use_residual_block = use_residual_block
        if self.use_residual_block:
            # Use a residual block with bottleneck channel as dim // 2
            self.residual = VitDetResBottleneckBlock(
                config=config,
                in_channels=dim,
                out_channels=dim,
                bottleneck_channels=dim // 2,
            )

    def forward(
        self,
        hidden_states: torch.Tensor,
        head_mask: Optional[torch.Tensor] = None,
        output_attentions: bool = False,
    ) -> Union[Tuple[torch.Tensor, torch.Tensor], Tuple[torch.Tensor]]:
        hidden_states = hidden_states.permute(0, 2, 3, 1)

        shortcut = hidden_states

        hidden_states = self.norm1(hidden_states)

        # Window partition
        if self.window_size > 0:
            height, width = hidden_states.shape[1], hidden_states.shape[2]
            hidden_states, pad_height_width = window_partition(hidden_states, self.window_size)

        self_attention_outputs = self.attention(
            hidden_states,
            output_attentions=output_attentions,
        )
        hidden_states = self_attention_outputs[0]
        outputs = self_attention_outputs[1:]  # add self attentions if we output attention weights

        # Reverse window partition
        if self.window_size > 0:
            hidden_states = window_unpartition(hidden_states, self.window_size, pad_height_width, (height, width))

        # first residual connection
        hidden_states = shortcut + self.drop_path(hidden_states)

        hidden_states = hidden_states + self.drop_path(self.mlp(self.norm2(hidden_states)))

        hidden_states = hidden_states.permute(0, 3, 1, 2)

        if self.use_residual_block:
            hidden_states = self.residual(hidden_states)

        outputs = (hidden_states,) + outputs

        return outputs


class VitDetEncoder(nn.Module):
    def __init__(self, config: VitDetConfig) -> None:
        super().__init__()
        self.config = config
        depth = config.num_hidden_layers

        # stochastic depth decay rule
        drop_path_rate = [x.item() for x in torch.linspace(0, config.drop_path_rate, depth)]

        layers = []
        for i in range(depth):
            layers.append(
                VitDetLayer(
                    config,
                    drop_path_rate=drop_path_rate[i],
                    window_size=config.window_size if i in config.window_block_indices else 0,
                    use_residual_block=i in config.residual_block_indices,
                )
            )

        self.layer = nn.ModuleList(layers)
        self.gradient_checkpointing = False

    def forward(
        self,
        hidden_states: torch.Tensor,
        head_mask: Optional[torch.Tensor] = None,
        output_attentions: bool = False,
        output_hidden_states: bool = False,
        return_dict: bool = True,
    ) -> Union[tuple, BaseModelOutput]:
        all_hidden_states = () if output_hidden_states else None
        all_self_attentions = () if output_attentions else None

        for i, layer_module in enumerate(self.layer):
            if output_hidden_states:
                all_hidden_states = all_hidden_states + (hidden_states,)

            layer_head_mask = head_mask[i] if head_mask is not None else None

            if self.gradient_checkpointing and self.training:
                layer_outputs = self._gradient_checkpointing_func(
                    layer_module.__call__,
                    hidden_states,
                    layer_head_mask,
                    output_attentions,
                )
            else:
                layer_outputs = layer_module(hidden_states, layer_head_mask, output_attentions)

            hidden_states = layer_outputs[0]

            if output_attentions:
                all_self_attentions = all_self_attentions + (layer_outputs[1],)

        if output_hidden_states:
            all_hidden_states = all_hidden_states + (hidden_states,)

        if not return_dict:
            return tuple(v for v in [hidden_states, all_hidden_states, all_self_attentions] if v is not None)
        return BaseModelOutput(
            last_hidden_state=hidden_states,
            hidden_states=all_hidden_states,
            attentions=all_self_attentions,
        )


def caffe2_msra_fill(module: nn.Module) -> None:
    """
    Initialize `module.weight` using the "MSRAFill" implemented in Caffe2. Also initializes `module.bias` to 0.

    Source: https://detectron2.readthedocs.io/en/latest/_modules/fvcore/nn/weight_init.html.

    Args:
        module (torch.nn.Module): module to initialize.
    """
    nn.init.kaiming_normal_(module.weight, mode="fan_out", nonlinearity="relu")
    if module.bias is not None:
        nn.init.constant_(module.bias, 0)


class VitDetPreTrainedModel(PreTrainedModel):
    """
    An abstract class to handle weights initialization and a simple interface for downloading and loading pretrained
    models.
    """

    config_class = VitDetConfig
    base_model_prefix = "vitdet"
    main_input_name = "pixel_values"
    supports_gradient_checkpointing = True
    _no_split_modules = []

    def _init_weights(self, module: Union[nn.Linear, nn.Conv2d, nn.LayerNorm]) -> None:
        """Initialize the weights"""
        if isinstance(module, (nn.Linear, nn.Conv2d)):
            # Upcast the input in `fp32` and cast it back to desired `dtype` to avoid
            # `trunc_normal_cpu` not implemented in `half` issues
            module.weight.data = nn.init.trunc_normal_(
                module.weight.data.to(torch.float32), mean=0.0, std=self.config.initializer_range
            ).to(module.weight.dtype)
            if module.bias is not None:
                module.bias.data.zero_()
        elif isinstance(module, nn.LayerNorm):
            module.bias.data.zero_()
            module.weight.data.fill_(1.0)

        elif isinstance(module, VitDetEmbeddings):
            module.position_embeddings.data = nn.init.trunc_normal_(
                module.position_embeddings.data.to(torch.float32),
                mean=0.0,
                std=self.config.initializer_range,
            ).to(module.position_embeddings.dtype)

        elif isinstance(module, VitDetAttention) and self.config.use_relative_position_embeddings:
            module.rel_pos_h.data = nn.init.trunc_normal_(
                module.rel_pos_h.data.to(torch.float32),
                mean=0.0,
                std=self.config.initializer_range,
            )
            module.rel_pos_w.data = nn.init.trunc_normal_(
                module.rel_pos_w.data.to(torch.float32),
                mean=0.0,
                std=self.config.initializer_range,
            )

        elif isinstance(module, VitDetResBottleneckBlock):
            for layer in [module.conv1, module.conv2, module.conv3]:
                caffe2_msra_fill(layer)
            for layer in [module.norm1, module.norm2]:
                layer.weight.data.fill_(1.0)
                layer.bias.data.zero_()
            # zero init last norm layer.
            module.norm3.weight.data.zero_()
            module.norm3.bias.data.zero_()


VITDET_START_DOCSTRING = r"""
    This model is a PyTorch [torch.nn.Module](https://pytorch.org/docs/stable/nn.html#torch.nn.Module) subclass. Use it
    as a regular PyTorch Module and refer to the PyTorch documentation for all matter related to general usage and
    behavior.

    Parameters:
        config ([`VitDetConfig`]): Model configuration class with all the parameters of the model.
            Initializing with a config file does not load the weights associated with the model, only the
            configuration. Check out the [`~PreTrainedModel.from_pretrained`] method to load the model weights.
"""

VITDET_INPUTS_DOCSTRING = r"""
    Args:
        pixel_values (`torch.FloatTensor` of shape `(batch_size, num_channels, height, width)`):
            Pixel values. Pixel values can be obtained using [`AutoImageProcessor`]. See [`ViTImageProcessor.__call__`]
            for details.

        head_mask (`torch.FloatTensor` of shape `(num_heads,)` or `(num_layers, num_heads)`, *optional*):
            Mask to nullify selected heads of the self-attention modules. Mask values selected in `[0, 1]`:

            - 1 indicates the head is **not masked**,
            - 0 indicates the head is **masked**.

        output_attentions (`bool`, *optional*):
            Whether or not to return the attentions tensors of all attention layers. See `attentions` under returned
            tensors for more detail.
        output_hidden_states (`bool`, *optional*):
            Whether or not to return the hidden states of all layers. See `hidden_states` under returned tensors for
            more detail.
        return_dict (`bool`, *optional*):
            Whether or not to return a [`~utils.ModelOutput`] instead of a plain tuple.
"""


@add_start_docstrings(
    "The bare VitDet Transformer model outputting raw hidden-states without any specific head on top.",
    VITDET_START_DOCSTRING,
)
class VitDetModel(VitDetPreTrainedModel):
    def __init__(self, config: VitDetConfig):
        super().__init__(config)
        self.config = config

        self.embeddings = VitDetEmbeddings(config)
        self.encoder = VitDetEncoder(config)

        # Initialize weights and apply final processing
        self.post_init()

    def get_input_embeddings(self) -> VitDetEmbeddings:
        return self.embeddings.projection

    def _prune_heads(self, heads_to_prune: Dict[int, List[int]]) -> None:
        """
        Prunes heads of the model. heads_to_prune: dict of {layer_num: list of heads to prune in this layer} See base
        class PreTrainedModel
        """
        for layer, heads in heads_to_prune.items():
            self.encoder.layer[layer].attention.prune_heads(heads)

    @add_start_docstrings_to_model_forward(VITDET_INPUTS_DOCSTRING)
    @replace_return_docstrings(output_type=BaseModelOutput, config_class=_CONFIG_FOR_DOC)
    def forward(
        self,
        pixel_values: Optional[torch.Tensor] = None,
        head_mask: Optional[torch.Tensor] = None,
        output_attentions: Optional[bool] = None,
        output_hidden_states: Optional[bool] = None,
        return_dict: Optional[bool] = None,
    ) -> Union[Tuple, BaseModelOutput]:
        """
        Returns:

        Examples:

        ```python
        >>> from transformers import VitDetConfig, VitDetModel
        >>> import torch

        >>> config = VitDetConfig()
        >>> model = VitDetModel(config)

        >>> pixel_values = torch.randn(1, 3, 224, 224)

        >>> with torch.no_grad():
        ...     outputs = model(pixel_values)

        >>> last_hidden_states = outputs.last_hidden_state
        >>> list(last_hidden_states.shape)
        [1, 768, 14, 14]
        ```"""
        output_attentions = output_attentions if output_attentions is not None else self.config.output_attentions
        output_hidden_states = (
            output_hidden_states if output_hidden_states is not None else self.config.output_hidden_states
        )
        return_dict = return_dict if return_dict is not None else self.config.use_return_dict

        if pixel_values is None:
            raise ValueError("You have to specify pixel_values")

        # Prepare head mask if needed
        # 1.0 in head_mask indicate we keep the head
        # attention_probs has shape bsz x n_heads x N x N
        # input head_mask has shape [num_heads] or [num_hidden_layers x num_heads]
        # and head_mask is converted to shape [num_hidden_layers x batch x num_heads x seq_length x seq_length]
        head_mask = self.get_head_mask(head_mask, self.config.num_hidden_layers)

        embedding_output = self.embeddings(pixel_values)

        encoder_outputs = self.encoder(
            embedding_output,
            head_mask=head_mask,
            output_attentions=output_attentions,
            output_hidden_states=output_hidden_states,
            return_dict=return_dict,
        )
        sequence_output = encoder_outputs[0]

        if not return_dict:
            return (sequence_output,) + encoder_outputs[1:]

        return BaseModelOutput(
            last_hidden_state=sequence_output,
            hidden_states=encoder_outputs.hidden_states,
            attentions=encoder_outputs.attentions,
        )


@add_start_docstrings(
    """
    ViTDet backbone, to be used with frameworks like Mask R-CNN.
    """,
    VITDET_START_DOCSTRING,
)
class VitDetBackbone(VitDetPreTrainedModel, BackboneMixin):
    def __init__(self, config):
        super().__init__(config)
        super()._init_backbone(config)

        self.embeddings = VitDetEmbeddings(config)
        self.encoder = VitDetEncoder(config)
        self.num_features = [config.hidden_size for _ in range(config.num_hidden_layers + 1)]

        # initialize weights and apply final processing
        self.post_init()

    def get_input_embeddings(self) -> VitDetEmbeddings:
        return self.embeddings.projection

    @add_start_docstrings_to_model_forward(VITDET_INPUTS_DOCSTRING)
    @replace_return_docstrings(output_type=BackboneOutput, config_class=_CONFIG_FOR_DOC)
    def forward(
        self,
        pixel_values: torch.Tensor,
        output_hidden_states: Optional[bool] = None,
        output_attentions: Optional[bool] = None,
        return_dict: Optional[bool] = None,
    ) -> BackboneOutput:
        """
        Returns:

        Examples:

        ```python
        >>> from transformers import VitDetConfig, VitDetBackbone
        >>> import torch

        >>> config = VitDetConfig()
        >>> model = VitDetBackbone(config)

        >>> pixel_values = torch.randn(1, 3, 224, 224)

        >>> with torch.no_grad():
        ...     outputs = model(pixel_values)

        >>> feature_maps = outputs.feature_maps
        >>> list(feature_maps[-1].shape)
        [1, 768, 14, 14]
        ```"""
        return_dict = return_dict if return_dict is not None else self.config.use_return_dict
        output_hidden_states = (
            output_hidden_states if output_hidden_states is not None else self.config.output_hidden_states
        )
        output_attentions = output_attentions if output_attentions is not None else self.config.output_attentions

        embedding_output = self.embeddings(pixel_values)

        outputs = self.encoder(
            embedding_output,
            output_hidden_states=True,
            output_attentions=output_attentions,
            return_dict=return_dict,
        )

        hidden_states = outputs.hidden_states if return_dict else outputs[1]

        feature_maps = ()
        for stage, hidden_state in zip(self.stage_names, hidden_states):
            if stage in self.out_features:
                feature_maps += (hidden_state,)

        if not return_dict:
            if output_hidden_states:
                output = (feature_maps,) + outputs[1:]
            else:
                output = (feature_maps,) + outputs[2:]
            return output

        return BackboneOutput(
            feature_maps=feature_maps,
            hidden_states=outputs.hidden_states if output_hidden_states else None,
            attentions=outputs.attentions,
        )