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TwinFan / LiveTraffic

LiveTraffic is an X-Plane multiplayer plugin, which fills your sky with live air traffic based on public flight tracking data.
https://twinfan.gitbook.io/livetraffic/
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CMakeLists.txt: find_package(OpenGL) is not plattform independent #198

Closed HellGL closed 3 years ago

HellGL commented 3 years ago

Not really a bug as LiveTraffic works anyway. FindOpenGL works different on different systems: https://github.com/TwinFan/LiveTraffic/blob/44f2cfd47843ff891cf2c58343bc80700946ec8c/CMakeLists.txt#L197-L203 On my Linux system (OpenSuSE 15.1) it sets OPENGL_INCLUDE_DIR and OPENGL_opengl_LIBRARY and on Windows (mingw64) it sets only OPENGL_gl_LIBRARY and no include path.

As openGL is loaded dynamically during runtime LiveTraffic compiles and runs without these definitions. For completeness during compilation they should be included however. I usually test for undefined references (beyond the XPLM ones) by running the linker command without "-shared". Adding 2>&1 |grep undefined | grep -v XPLM to the the command line should only show "main" or "WinMain" as it is a shared library. Very useful to find object files that are compiled and referenced, but not linked...

BTW: pthread is also not in the linker command.

TwinFan commented 3 years ago

I test missing symbols, too, using ldd -r on Linux in the Docker environment as I don't have a Linux computer. And I got used to seeing the OpenGL symbols as missing. I don't see pthread missing. It is either covered by other libraries or another thread solution is included.

I don't build LiveTraffic on Windows with CMake but with the separately provided VC++ project. I haven't found a mingw setup in Docker that includes all required C++ 17 libraries and headers in a workable way.

Googling a bit I changed to using the import targets:

# Link OpenGL and OpenAL related libraries.
set (OpenGL_GL_PREFERENCE GLVND)
find_package(OpenGL REQUIRED COMPONENTS OpenGL)  # apt install freeglut3-dev
if ( OpenGL_FOUND )
    add_dependencies( LiveTraffic OpenGL::OpenGL )
    include_directories( ${OpenGL_INCLUDE_DIRS} )
    target_link_libraries( LiveTraffic OpenGL::OpenGL )
endif( OpenGL_FOUND )

This does indeed no longer list the OpenGL symbols as missing in the ldd -r output.

TwinFan commented 3 years ago

The above way causes startup issues, apparently the old way of leaving library resolution to runtime was a better idea.

Never touch a running system...change to be rolled back: