https://docs.bazel.build/versions/master/install-ubuntu.html#ubuntu
git clone https://github.com/Itseez/opencv.git
cd opencv/
mkdir build install
cd build
apt install libgtk2.0-dev pkg-config
cmake -D CMAKE_BUILD_TYPE=Release -D CMAKE_INSTALL_PREFIX=/usr/local ..
make install
bazel build main:hello-world
./bazel-bin/main/hello-world yingshaoxo.jpg
bazel test test:hello-test