opencv on termux.sh

git clone -b 4.10.0 https://github.com/opencv/opencv.git
git clone -b 4.10.0 https://github.com/opencv/opencv_contrib.git   # optional
cd ./opencv
mkdir build && cd build

cmake -D CMAKE_BUILD_TYPE=Release \
      -D CMAKE_INSTALL_PREFIX=$PREFIX \
      -D CMAKE_OPENCV_VERBOSE=OFF \
      -D BUILD_SHARED_LIBS=ON \
      -D BUILD_TESTS=OFF -D BUILD_PERF_TESTS=OFF -D BUILD_EXAMPLES=OFF \
      -D WITH_QT=OFF -D WITH_GTK=OFF -D WITH_OPENGL=OFF \
      -D WITH_VTK=OFF -D WITH_IPP=OFF \
      -D WITH_TBB=OFF -D WITH_OPENMP=ON \
      -D WITH_FFMPEG=ON -D WITH_GSTREAMER=OFF \
      -D BUILD_OPENCV_PYTHON3=ON \
      -D OPENCV_ENABLE_NONFREE=ON \ 
      -D OPENCV_EXTRA_MODULES_PATH=~/src/opencv_contrib/modules .. 
      
      
make -j$(nproc)   # use all CPU cores to speed up compilation
make install      # install OpenCV to $PREFIX (Termux's usr directory)

export LD_LIBRARY_PATH=$PREFIX/lib:$LD_LIBRARY_PATH
export PKG_CONFIG_PATH=$PREFIX/lib/pkgconfig:$PKG_CONFIG_PATH