Enable nvidia-optical-flow-sdk when building opencv4 with cuda

[mjlbach]

Motivation for this change

fixes #81103

This adds and enables nvidia's optical flow sdk which causes cuda 4 to fail to build when cuda is enabled.

Things done

Patched CMakeLists.txt in opencv contrib to avoid trying to download opencv headers.

• Tested using sandboxing (nix.useSandbox on NixOS, or option sandbox in nix.conf on non-NixOS linux)
• Built on platform(s)
  • NixOS
  • macOS
  • other Linux distributions
• Tested via one or more NixOS test(s) if existing and applicable for the change (look inside nixos/tests)
• Tested compilation of all pkgs that depend on this change using nix-shell -p nixpkgs-review --run "nixpkgs-review wip"
• Tested execution of all binary files (usually in ./result/bin/)
• Determined the impact on package closure size (by running nix path-info -S before and after)
• Ensured that relevant documentation is up to date
• Fits CONTRIBUTING.md.

[mjlbach]

@tbenst

[tbenst]

Thanks for the pull-request! I got an error at the end of the build:

In file included from /build/source/modules/core/include/opencv2/core.hpp:54,
                 from /build/source/modules/core/include/opencv2/core/cuda.hpp:51,
                 from /build/source/opencv_contrib/cudaoptflow/include/opencv2/cudaoptflow.hpp:50,
                 from /build/source/opencv_contrib/cudaoptflow/src/precomp.hpp:48,
                 from /build/source/opencv_contrib/cudaoptflow/src/nvidiaOpticalFlow.cpp:7:
/build/source/modules/core/include/opencv2/core/base.hpp:320:40: error: expected constructor, destructor, or type conversion before '(' token
  320 | #define CV_Error( code, msg ) cv::error( code, msg, CV_Func, __FILE__, __LINE__ )
      |                                        ^
/build/source/opencv_contrib/cudaoptflow/src/nvidiaOpticalFlow.cpp:15:1: note: in expansion of macro 'CV_Error'
   15 | CV_Error(cv::Error::HeaderIsNull, "Nvidia Optical Flow headers not found. Make sure cmake downloads it properly");
      | ^~~~~~~~
make[2]: *** [modules/cudaoptflow/CMakeFiles/opencv_cudaoptflow.dir/build.make:110: modules/cudaoptflow/CMakeFiles/opencv_cudaoptflow.dir/src/nvidiaOpticalFlow.cpp.o] Error 1
make[2]: *** Waiting for unfinished jobs....
make[1]: *** [CMakeFiles/Makefile2:5679: modules/cudaoptflow/CMakeFiles/opencv_cudaoptflow.dir/all] Error 2
make: *** [Makefile:163: all] Error 2
builder for '/nix/store/7wqh2c7wfpgwknafi114kh382z5lsfw5-opencv-4.1.2.drv' failed with exit code 2
error: build of '/nix/store/7wqh2c7wfpgwknafi114kh382z5lsfw5-opencv-4.1.2.drv' failed

Full output here: https://gist.github.com/tbenst/7d53ace5b6533d7d1225429caddcc95c.

Also, could you please split into two commits? e.g. nvidia-optical-flow-sdk: init at 79c6cee80a2df9a196f20afd6b598a9810964c32 and opencv4: Enable nvidia-optical-flow-sdk when building with cuda

[tbenst]

Build now succeeds. LGTM

[mjlbach]

@mdaiter @basvandijk would one of you be able to review? This fixes compiling opencv4 when cuda is enabled.

[nixos-discourse]

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/prs-ready-for-review-may-2019/3032/125

[veprbl]

Some minor formatting comments

[mjlbach]

@veprbl I think I fixed everything you mentioned except what is in the comments. Please see my latest commit for the diff, after which I'll squash.

[nixos-discourse]

This pull request has been mentioned on NixOS Discourse. There might be relevant details there:

https://discourse.nixos.org/t/prs-already-reviewed/2617/122

[averelld]

Could someone pick this to 20.03? The build's broken there too, and this applies cleanly and works.

[mjlbach]

@averelld done. #83733