opencv 4.2 and support for cuda

[grzegorzk]

Hi, this is not a bug report but rather a question. I'm sorry to ask this again (question was already asked in #201 and #71) but the OpenCV modules page mentions cuda modules.

Am I correct to understand that opencv-python should now support cv2.dnn.DNN_BACKEND_CUDA and cv2.dnn.DNN_TARGET_CUDA? On my dev machine I'm getting [ WARN:0] global /io/opencv/modules/dnn/src/dnn.cpp (1363) setUpNet DNN module was not built with CUDA backend; switching to CPU so I guess there are some extra steps needed.

I'm looking through travis.yml and also what @alsrgv suggested within #71 - I understand I need to build the package myself with CUDA enabled.

This is how I build it (running within archlinux docker container):

pacman -Sy base-devel python python-pip git cmake
git clone https://github.com/skvark/opencv-python
cd opencv-python
ENABLE_CONTRIB=1 python setup.py bdist_wheel -- \
    -MB_PYTHON_VERSION=3.8 \
    -ENABLE_HEADLESS=0 \
    -DWITH_CUDA=ON \
    -DENABLE_FAST_MATH=1 \
    -DCUDA_FAST_MATH=1 \
    -DWITH_CUBLAS=1 \
    -DCUDA_ARCH_BIN=7.5 -- \
    -j8

Above fails:

CMake Error at /usr/share/cmake-3.16/Modules/FindQt4.cmake:1314 (message):
Found unsuitable Qt version "" from NOTFOUND, this code requires Qt 4.x
Call Stack (most recent call first):
cmake/OpenCVFindLibsGUI.cmake:30 (find_package)
CMakeLists.txt:672 (include)


-- Configuring incomplete, errors occurred!
See also "/python-opencv-cuda/opencv-python/_skbuild/linux-x86_64-3.8/cmake-build/CMakeFiles/CMakeOutput.log".
See also "/python-opencv-cuda/opencv-python/_skbuild/linux-x86_64-3.8/cmake-build/CMakeFiles/CMakeError.log".
Traceback (most recent call last):
File "/usr/lib/python3.8/site-packages/skbuild/setuptools_wrap.py", line 570, in setup
env = cmkr.configure(cmake_args,
File "/usr/lib/python3.8/site-packages/skbuild/cmaker.py", line 221, in configure
raise SKBuildError(

An error occurred while configuring with CMake.
Command:
"cmake" "/python-opencv-cuda/opencv-python/opencv" "-G" "Unix Makefiles" "-DCMAKE_INSTALL_PREFIX:PATH=/python-opencv-cuda/opencv-python/_skbuild/linux-x86_64-3.8/cmake-install" "-DPYTHON_EXECUTABLE:FILEPATH=/usr/sbin/python" "-DPYTHON_VERSION_STRING:STRING=3.8.1" "-DPYTHON_INCLUDE_DIR:PATH=/usr/include/python3.8" "-DPYTHON_LIBRARY:FILEPATH=/usr/lib/libpython3.8.so" "-DSKBUILD:BOOL=TRUE" "-DCMAKE_MODULE_PATH:PATH=/usr/lib/python3.8/site-packages/skbuild/resources/cmake" "-DPYTHON3_EXECUTABLE=/usr/sbin/python" "-DBUILD_opencv_python3=ON" "-DOPENCV_SKIP_PYTHON_LOADER=ON" "-DOPENCV_PYTHON3_INSTALL_PATH=python" "-DINSTALL_CREATE_DISTRIB=ON" "-DBUILD_opencv_apps=OFF" "-DBUILD_SHARED_LIBS=OFF" "-DBUILD_TESTS=OFF" "-DBUILD_PERF_TESTS=OFF" "-DBUILD_DOCS=OFF" "-DOPENCV_EXTRA_MODULES_PATH=/python-opencv-cuda/opencv-python/opencv_contrib/modules" "-DWITH_QT=4" "-DWITH_V4L=ON" "-DENABLE_PRECOMPILED_HEADERS=OFF" "-DWITH_IPP=OFF" "-DWITH_CUDA=ON" "-DENABLE_FAST_MATH=1" "-DCUDA_FAST_MATH=1" "-DWITH_CUBLAS=1" "-DCUDA_ARCH_BIN=7.5" "-DCMAKE_BUILD_TYPE:STRING=Release"
Source directory:
/python-opencv-cuda/opencv-python/opencv
Working directory:
/python-opencv-cuda/opencv-python/_skbuild/linux-x86_64-3.8/cmake-build
Please see CMake's output for more information.

I have not used cmake before, I'm guessing I'm missing some dependencies.

[grzegorzk]

I was missing qt4 on my system. After installing qt4 and also following some extra steps from here: opencv/opencv#14827 (comment) I managed to build the package.