Add align_corners option to grid_sample and affine_grid, change default to False (#23923)
Summary:
Resolves: https://github.com/pytorch/pytorch/issues/20785
Adds the `align_corners` option to `grid_sample` and `affine_grid`, paralleling the option that was added to `interpolate` in version 0.4.0.
In short, setting `align_corners` to `False` allows these functions to be resolution agnostic.
This ensures, for example, that a grid generated from a neural net trained to warp 1024x1024 images will also work to warp the same image upsampled/downsampled to other resolutions like 512x512 or 2048x2048 without producing scaling/stretching artifacts.
Refer to the documentation and https://github.com/pytorch/pytorch/issues/20785 for more details.
**Important**: BC-Breaking Change because of new default
The old functionality can still be achieved by setting `align_corners=True`, but the default is now set to `align_corners=False`, since this is the more correct setting, and since this matches the default setting of `interpolate`.
The vectorized 2D cpu version of `grid_sampler` is refactored a bit. I don’t suspect that this refactor would affect the runtime much, since it is mostly done in inlined functions, but I may be wrong, and this has to be verified by profiling.
~The tests are not yet updated to reflect the new default. New tests should probably also be added to test both settings of `align_corners`.~ _Tests are now updated._
Pull Request resolved: https://github.com/pytorch/pytorch/pull/23923
Differential Revision: D16887357
Pulled By: ailzhang
fbshipit-source-id: ea09aad7853ef16536e719a898db8ba31595daa5
