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# Copyright (c) 2021, NVIDIA CORPORATION & AFFILIATES. All rights reserved.
#
# NVIDIA CORPORATION and its licensors retain all intellectual property
# and proprietary rights in and to this software, related documentation
# and any modifications thereto. Any use, reproduction, disclosure or
# distribution of this software and related documentation without an express
# license agreement from NVIDIA CORPORATION is strictly prohibited.
"""Custom replacement for `torch.nn.functional.grid_sample` that
supports arbitrarily high order gradients between the input and output.
Only works on 2D images and assumes
`mode='bilinear'`, `padding_mode='zeros'`, `align_corners=False`."""
import torch
from pkg_resources import parse_version
# pylint: disable=redefined-builtin
# pylint: disable=arguments-differ
# pylint: disable=protected-access
#----------------------------------------------------------------------------
enabled = False # Enable the custom op by setting this to true.
_use_pytorch_1_11_api = parse_version(torch.__version__) >= parse_version(
'1.11.0a') # Allow prerelease builds of 1.11
#----------------------------------------------------------------------------
def grid_sample(input, grid):
if _should_use_custom_op():
return _GridSample2dForward.apply(input, grid)
return torch.nn.functional.grid_sample(input=input,
grid=grid,
mode='bilinear',
padding_mode='zeros',
align_corners=False)
#----------------------------------------------------------------------------
def _should_use_custom_op():
return enabled
#----------------------------------------------------------------------------
class _GridSample2dForward(torch.autograd.Function):
@staticmethod
def forward(ctx, input, grid):
assert input.ndim == 4
assert grid.ndim == 4
output = torch.nn.functional.grid_sample(input=input,
grid=grid,
mode='bilinear',
padding_mode='zeros',
align_corners=False)
ctx.save_for_backward(input, grid)
return output
@staticmethod
def backward(ctx, grad_output):
input, grid = ctx.saved_tensors
grad_input, grad_grid = _GridSample2dBackward.apply(
grad_output, input, grid)
return grad_input, grad_grid
#----------------------------------------------------------------------------
class _GridSample2dBackward(torch.autograd.Function):
@staticmethod
def forward(ctx, grad_output, input, grid):
op = torch._C._jit_get_operation('aten::grid_sampler_2d_backward')
if _use_pytorch_1_11_api:
output_mask = (ctx.needs_input_grad[1], ctx.needs_input_grad[2])
grad_input, grad_grid = op(grad_output, input, grid, 0, 0, False,
output_mask)
else:
grad_input, grad_grid = op(grad_output, input, grid, 0, 0, False)
ctx.save_for_backward(grid)
return grad_input, grad_grid
@staticmethod
def backward(ctx, grad2_grad_input, grad2_grad_grid):
_ = grad2_grad_grid # unused
grid, = ctx.saved_tensors
grad2_grad_output = None
grad2_input = None
grad2_grid = None
if ctx.needs_input_grad[0]:
grad2_grad_output = _GridSample2dForward.apply(
grad2_grad_input, grid)
# st()
# ? why
# assert not ctx.needs_input_grad[2]
return grad2_grad_output, grad2_input, grad2_grid
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