How to link opengl library on CMake using keyword signature - c++

Question

I am previously using Visual Studio with NuGet for all package. Now I change to CMake.
Now I am using vcpkg to manage library.
However, I need OpenGl
The command of Cmake to link freeglut, glew, glm, libpng, zlib was provide by vcpkg. But not OpenGL.
cmake_minimum_required(VERSION 3.0)
project(little_plane)
set(CMAKE_CXX_STANDARD 14)
add_executable(little_plane main.cpp)
# ./vcpkg install freeglut
find_package(GLUT REQUIRED)
target_link_libraries(little_plane PRIVATE GLUT::GLUT)
## ./vcpkg install glew
#find_package(GLEW REQUIRED)
#target_link_libraries(little_plane PRIVATE GLEW::GLEW)
#
# glm
find_package(glm CONFIG REQUIRED)
target_link_libraries(little_plane PRIVATE glm)
# ./vcpkg install libpng
find_package(PNG REQUIRED)
target_link_libraries(little_plane PRIVATE PNG::PNG)
##
find_package(ZLIB REQUIRED)
target_link_libraries(little_plane PRIVATE ZLIB::ZLIB)
find_package(OpenGL REQUIRED)
if (OPENGL_FOUND)
message("opengl found")
message("include dir: ${OPENGL_INCLUDE_DIR}")
message("link libraries: ${OPENGL_gl_LIBRARY}")
else (OPENGL_FOUND)
message("opengl not found")
endif()
target_link_libraries(little_plane ${OPENGL_gl_LIBRARY})
find_package(glfw3 CONFIG REQUIRED)
target_link_libraries(little_plane PRIVATE glfw)
With the CMakeLists.txt above, I run cmake .
opengl found
include dir: /usr/include
link libraries: /usr/lib/x86_64-linux-gnu/libGL.so
CMake Error at CMakeLists.txt:40 (target_link_libraries):
The keyword signature for target_link_libraries has already been used with
the target "little_plane". All uses of target_link_libraries with a target
must be either all-keyword or all-plain.
The uses of the keyword signature are here:
* CMakeLists.txt:10 (target_link_libraries)
* CMakeLists.txt:20 (target_link_libraries)
* CMakeLists.txt:24 (target_link_libraries)
* CMakeLists.txt:28 (target_link_libraries)
CMake Error at CMakeLists.txt:44 (target_link_libraries):
The plain signature for target_link_libraries has already been used with
the target "little_plane". All uses of target_link_libraries with a target
must be either all-keyword or all-plain.
The uses of the plain signature are here:
* CMakeLists.txt:40 (target_link_libraries)
-- Configuring incomplete, errors occurred!
Which mean opengl is installed on my system. I just don't know how to use target_link_libraries to link with my project.
Provide answer that can copy and paste into CMakeLists.txt if possible.

Answer 1

All your previous target_link_libraries contain a transitivity keyword (PRIVATE in all cases), but you have not provided any when linking OpenGL. So just add that too:
target_link_libraries(little_plane PRIVATE ${OPENGL_gl_LIBRARY})