File size: 9,352 Bytes
d9bb75c | 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172 173 174 175 176 177 178 179 180 181 182 183 184 185 186 187 188 189 190 191 192 193 194 195 196 197 198 199 200 201 202 203 204 205 206 207 208 209 210 211 212 213 214 215 | # Copyright (c) Meta Platforms, Inc. and affiliates.
#
# This software may be used and distributed in accordance with
# the terms of the DINOv3 License Agreement.
import math
import warnings
import torch
import torch.nn.functional as F
from torch import nn
from torch.autograd import Function
from torch.amp import custom_fwd, custom_bwd
from torch.autograd.function import once_differentiable
from torch.nn.init import constant_, xavier_uniform_
try:
import MultiScaleDeformableAttention as MSDA
except ImportError:
# if we just care about inference, we don't need
# the compiled extension for multi-scale deformable attention
MSDA = None
class MSDeformAttnFunction(Function):
@staticmethod
@custom_fwd(device_type="cuda", cast_inputs=torch.float32)
def forward(
ctx, value, value_spatial_shapes, value_level_start_index, sampling_locations, attention_weights, im2col_step
):
ctx.im2col_step = im2col_step
output = ms_deform_attn_core_pytorch(
value,
value_spatial_shapes,
# value_level_start_index,
sampling_locations,
attention_weights,
)
ctx.save_for_backward(
value, value_spatial_shapes, value_level_start_index, sampling_locations, attention_weights
)
return output
@staticmethod
@once_differentiable
@custom_bwd(device_type="cuda")
def backward(ctx, grad_output):
if MSDA is None:
raise RuntimeError(
"MultiScaleDeformableAttention is not available, "
"please compile with CUDA if you want to train a "
"segmentation head with deformable attention"
)
value, value_spatial_shapes, value_level_start_index, sampling_locations, attention_weights = ctx.saved_tensors
grad_value, grad_sampling_loc, grad_attn_weight = MSDA.ms_deform_attn_backward(
value,
value_spatial_shapes,
value_level_start_index,
sampling_locations,
attention_weights,
grad_output,
ctx.im2col_step,
)
return grad_value, None, None, grad_sampling_loc, grad_attn_weight, None
def ms_deform_attn_core_pytorch(value, value_spatial_shapes, sampling_locations, attention_weights):
# for debug and test only,
# need to use cuda version instead
N_, S_, M_, D_ = value.shape
_, Lq_, M_, L_, P_, _ = sampling_locations.shape
value_list = value.split([H_ * W_ for H_, W_ in value_spatial_shapes], dim=1)
sampling_grids = 2 * sampling_locations - 1
sampling_value_list = []
for lid_, (H_, W_) in enumerate(value_spatial_shapes):
# N_, H_*W_, M_, D_ -> N_, H_*W_, M_*D_ -> N_, M_*D_, H_*W_ -> N_*M_, D_, H_, W_
value_l_ = value_list[lid_].flatten(2).transpose(1, 2).reshape(N_ * M_, D_, H_, W_)
# N_, Lq_, M_, P_, 2 -> N_, M_, Lq_, P_, 2 -> N_*M_, Lq_, P_, 2
sampling_grid_l_ = sampling_grids[:, :, :, lid_].transpose(1, 2).flatten(0, 1)
# N_*M_, D_, Lq_, P_
sampling_value_l_ = F.grid_sample(
value_l_, sampling_grid_l_, mode="bilinear", padding_mode="zeros", align_corners=False
)
sampling_value_list.append(sampling_value_l_)
# (N_, Lq_, M_, L_, P_) -> (N_, M_, Lq_, L_, P_) -> (N_, M_, 1, Lq_, L_*P_)
attention_weights = attention_weights.transpose(1, 2).reshape(N_ * M_, 1, Lq_, L_ * P_)
output = (torch.stack(sampling_value_list, dim=-2).flatten(-2) * attention_weights).sum(-1).view(N_, M_ * D_, Lq_)
return output.transpose(1, 2).contiguous()
def _is_power_of_2(n):
if (not isinstance(n, int)) or (n < 0):
raise ValueError("invalid input for _is_power_of_2: {} (type: {})".format(n, type(n)))
return (n & (n - 1) == 0) and n != 0
class MSDeformAttn(nn.Module):
def __init__(self, d_model=256, n_levels=4, n_heads=8, n_points=4, ratio=1.0):
"""Multi-Scale Deformable Attention Module.
:param d_model hidden dimension
:param n_levels number of feature levels
:param n_heads number of attention heads
:param n_points number of sampling points per attention head per feature level
"""
super().__init__()
if d_model % n_heads != 0:
raise ValueError("d_model must be divisible by n_heads, but got {} and {}".format(d_model, n_heads))
_d_per_head = d_model // n_heads
# you'd better set _d_per_head to a power of 2
# which is more efficient in our CUDA implementation
if not _is_power_of_2(_d_per_head):
warnings.warn(
"You'd better set d_model in MSDeformAttn to make "
"the dimension of each attention head a power of 2 "
"which is more efficient in our CUDA implementation."
)
self.im2col_step = 64
self.d_model = d_model
self.n_levels = n_levels
self.n_heads = n_heads
self.n_points = n_points
self.ratio = ratio
self.sampling_offsets = nn.Linear(d_model, n_heads * n_levels * n_points * 2)
self.attention_weights = nn.Linear(d_model, n_heads * n_levels * n_points)
self.value_proj = nn.Linear(d_model, int(d_model * ratio))
self.output_proj = nn.Linear(int(d_model * ratio), d_model)
self._reset_parameters()
def _reset_parameters(self):
constant_(self.sampling_offsets.weight.data, 0.0)
thetas = torch.arange(self.n_heads, dtype=torch.float32) * (2.0 * math.pi / self.n_heads)
grid_init = torch.stack([thetas.cos(), thetas.sin()], -1)
grid_init = (
(grid_init / grid_init.abs().max(-1, keepdim=True)[0])
.view(self.n_heads, 1, 1, 2)
.repeat(1, self.n_levels, self.n_points, 1)
)
for i in range(self.n_points):
grid_init[:, :, i, :] *= i + 1
with torch.no_grad():
self.sampling_offsets.bias = nn.Parameter(grid_init.view(-1))
constant_(self.attention_weights.weight.data, 0.0)
constant_(self.attention_weights.bias.data, 0.0)
xavier_uniform_(self.value_proj.weight.data)
constant_(self.value_proj.bias.data, 0.0)
xavier_uniform_(self.output_proj.weight.data)
constant_(self.output_proj.bias.data, 0.0)
def forward(
self,
query,
reference_points,
input_flatten,
input_spatial_shapes,
input_level_start_index,
input_padding_mask=None,
):
"""
:param query (N, Length_{query}, C)
:param reference_points (N, Length_{query}, n_levels, 2), range in [0, 1], top-left (0,0), bottom-right (1, 1), including padding area
or (N, Length_{query}, n_levels, 4), add additional (w, h) to form reference boxes
:param input_flatten (N, \\sum_{l=0}^{L-1} H_l \\cdot W_l, C)
:param input_spatial_shapes (n_levels, 2), [(H_0, W_0), (H_1, W_1), ..., (H_{L-1}, W_{L-1})]
:param input_level_start_index (n_levels, ), [0, H_0*W_0, H_0*W_0+H_1*W_1, H_0*W_0+H_1*W_1+H_2*W_2, ..., H_0*W_0+H_1*W_1+...+H_{L-1}*W_{L-1}]
:param input_padding_mask (N, \\sum_{l=0}^{L-1} H_l \\cdot W_l), True for padding elements, False for non-padding elements
:return output (N, Length_{query}, C)
"""
N, Len_q, _ = query.shape
N, Len_in, _ = input_flatten.shape
assert (input_spatial_shapes[:, 0] * input_spatial_shapes[:, 1]).sum() == Len_in
value = self.value_proj(input_flatten)
if input_padding_mask is not None:
value = value.masked_fill(input_padding_mask[..., None], float(0))
value = value.view(N, Len_in, self.n_heads, int(self.ratio * self.d_model) // self.n_heads)
sampling_offsets = self.sampling_offsets(query).view(N, Len_q, self.n_heads, self.n_levels, self.n_points, 2)
attention_weights = self.attention_weights(query).view(N, Len_q, self.n_heads, self.n_levels * self.n_points)
attention_weights = F.softmax(attention_weights, -1).view(N, Len_q, self.n_heads, self.n_levels, self.n_points)
if reference_points.shape[-1] == 2:
offset_normalizer = torch.stack([input_spatial_shapes[..., 1], input_spatial_shapes[..., 0]], -1)
sampling_locations = (
reference_points[:, :, None, :, None, :]
+ sampling_offsets / offset_normalizer[None, None, None, :, None, :]
)
elif reference_points.shape[-1] == 4:
sampling_locations = (
reference_points[:, :, None, :, None, :2]
+ sampling_offsets / self.n_points * reference_points[:, :, None, :, None, 2:] * 0.5
)
else:
raise ValueError(
"Last dim of reference_points must be 2 or 4, but get {} instead.".format(reference_points.shape[-1])
)
output = MSDeformAttnFunction.apply(
value,
input_spatial_shapes,
input_level_start_index,
sampling_locations,
attention_weights,
self.im2col_step,
)
output = self.output_proj(output)
return output
|