cmake c++ library with opencv addexternal - opencv

Question

I would like to build a C++ library using cmake.
The library would require a on-the-fly opencv download and build then this library will be used in an other cmake project as a library.
The project structure is like that:
template_matching_project
|
|-- build
|-- template_matching_project
| |
| |-- template_matching_library
| |
| | -- src
| | -- include
| | -- CMakeLists.txt
|-- main.cpp
|-- CMakeLists.txt
The template_matching_library performs some image processing using opencv, there is the content of its cmake file in template_matching_project/template_matching_library/CMakeLists.txt:
cmake_minimum_required(VERSION 3.0)
set(CMAKE_CXX_STANDARD 11)
project(template_matching)
# third party
include(ExternalProject)
set(EXTERNAL_INSTALL_LOCATION ${CMAKE_BINARY_DIR}/3rdparty)
set(EXTERNAL_DOWNLOAD_LOCATION ${CMAKE_BINARY_DIR}/Download)
# OpenCV
ExternalProject_Add(opencv-contrib
GIT_REPOSITORY https://github.com/opencv/opencv_contrib.git
GIT_TAG e6f32c6
SOURCE_DIR "${EXTERNAL_DOWNLOAD_LOCATION}/opencv-contrib"
CONFIGURE_COMMAND ""
BUILD_COMMAND ""
INSTALL_COMMAND ""
)
ExternalProject_Add(opencv
GIT_REPOSITORY https://github.com/opencv/opencv.git
GIT_TAG 01b2c5a
SOURCE_DIR "${EXTERNAL_DOWNLOAD_LOCATION}/opencv"
CMAKE_ARGS
-DBUILD_DOCS:BOOL=OFF
...
)
add_dependencies(opencv opencv-contrib)
# set source directories
set(PROJECT_SOURCE_DIR source)
set(INCLUDE_DIR include)
# set source files
file(GLOB_RECURSE SRCS ${PROJECT_SOURCE_DIR}/*)
file(GLOB_RECURSE HEADERS ${INCLUDE_DIR}/*)
# build library
link_directories(${EXTERNAL_INSTALL_LOCATION}/opencv/lib)
include_directories(${EXTERNAL_INSTALL_LOCATION}/opencv/include/opencv4)
include_directories(${INCLUDE_DIR})
add_library(${PROJECT_NAME} SHARED ${SRCS} ${HEADERS})
add_dependencies(${PROJECT_NAME} opencv)
target_link_libraries(${PROJECT_NAME} opencv_core opencv_highgui opencv_imgproc)
target_include_directories(${PROJECT_NAME} PUBLIC ${INCLUDE_DIR})
The template_matching_library is correctly build with this cmake, but the build of the main.cpp executable fails
Here is the template_matching_project/CMakeLists.txt:
cmake_minimum_required(VERSION 3.0)
set(CMAKE_CXX_STANDARD 11)
project(markers)
# include library
add_subdirectory(template_matching_library)
set(EXTERNAL_INSTALL_LOCATION ${CMAKE_BINARY_DIR}/3rdparty)
include_directories(${EXTERNAL_INSTALL_LOCATION}/opencv/include/opencv4)
# add file to compile
set(SRCS main.cpp)
# add executable
add_executable(${PROJECT_NAME} ${SRCS})
# add dependencies
target_link_libraries(${PROJECT_NAME} template_matching)
Then trying the build with the convetional
cd build
cmake .. -G "Unix Makefiles" -DCMAKE_BUILD_TYPE=Debug
make
I have the following error
[ 95%] Building CXX object CMakeFiles/markers.dir/main.cpp.o
[100%] Linking CXX executable markers
/usr/bin/ld: cannot find -lopencv_core
/usr/bin/ld: cannot find -lopencv_highgui
/usr/bin/ld: cannot find -lopencv_imgproc
collect2: error: ld returned 1 exit status
Any suggestion to solve my problem? Should I change one/both of those CMakeLists.txt.
Thanks.

Answer 1

I have it worked with those two CMakeLists.txt, if some have any suggestions or better solution.
template_matching_project/CMakeLists.txt:
cmake_minimum_required(VERSION 3.0)
set(CMAKE_CXX_STANDARD 11)
project(markers)
add_subdirectory(template_matching_library)
set(SRCS main.cpp)
add_executable(${PROJECT_NAME} ${SRCS})
target_link_libraries(${PROJECT_NAME} template_matching ${OpenCV_LIBS})
template_matching_project/template_matching_library/CMakeLists.txt:
cmake_minimum_required(VERSION 3.0)
set(CMAKE_CXX_STANDARD 11)
project(template_matching)
# third party
include(ExternalProject)
set(EXTERNAL_INSTALL_LOCATION ${CMAKE_BINARY_DIR}/3rdparty)
set(EXTERNAL_DOWNLOAD_LOCATION ${CMAKE_BINARY_DIR}/Download)
# OpenCV
ExternalProject_Add(opencv-contrib
GIT_REPOSITORY https://github.com/opencv/opencv_contrib.git
GIT_TAG e6f32c6
SOURCE_DIR "${EXTERNAL_DOWNLOAD_LOCATION}/opencv-contrib"
...
)
ExternalProject_Add(opencv
GIT_REPOSITORY https://github.com/opencv/opencv.git
GIT_TAG 01b2c5a
SOURCE_DIR "${EXTERNAL_DOWNLOAD_LOCATION}/opencv"
CMAKE_ARGS
-DBUILD_DOCS:BOOL=OFF
...
-DOPENCV_EXTRA_MODULES_PATH:PATH=${EXTERNAL_DOWNLOAD_LOCATION}/opencv-contrib/modules
)
add_dependencies(opencv opencv-contrib)
set(OpenCV_DIR ${EXTERNAL_INSTALL_LOCATION}/opencv/lib/cmake/opencv4)
find_package(OpenCV REQUIRED PATHS ${EXTERNAL_INSTALL_LOCATION}/opencv)
# set source directories
set(PROJECT_SOURCE_DIR source)
set(INCLUDE_DIR include)
# set source files
file(GLOB_RECURSE SRCS ${PROJECT_SOURCE_DIR}/*)
file(GLOB_RECURSE HEADERS ${INCLUDE_DIR}/*)
# build library
include_directories(${EXTERNAL_INSTALL_LOCATION}/opencv/include/opencv4)
include_directories(${INCLUDE_DIR})
add_library(${PROJECT_NAME} SHARED ${SRCS} ${HEADERS})
add_dependencies(${PROJECT_NAME} opencv)
target_link_libraries(${PROJECT_NAME} ${OpenCV_LIBS})
target_include_directories(${PROJECT_NAME} PUBLIC ${INCLUDE_DIR})
Nevertheless, using my two CMakeLists.txt, I do have to run twice cmake and make commands, unless I have a links errors with opencv, like the following:
cd build
cmake .. -G "Unix Makefiles
make
cmake .. -G "Unix Makefiles
make
Is there a way to have work with a single run cmake/make?
I try some FetchContent but was not able to make it worked. My cmake version is 3.5.1