Linking against OpenGL using GLVND on Ubuntu 18.04 links wrongly against libOpenGL.so.0

[hcorion]

See the recent relevant conversation that happened over here: linuxdeploy/linuxdeploy#152
And the relevant RPCS3-side issue here: RPCS3/rpcs3#10226

Essentially, when building using the following:

set(OpenGL_GL_PREFERENCE GLVND)
find_package(OpenGL REQUIRED)

add_library(3rdparty_opengl INTERFACE)
target_include_directories(3rdparty_opengl INTERFACE GL)

target_link_libraries(3rdparty_opengl INTERFACE ${OPENGL_LIBRARIES})

target_compile_definitions(3rdparty_opengl
	INTERFACE
	-DGL_GLEXT_PROTOTYPES
	-DGLX_GLXEXT_PROTOTYPES)

on Ubuntu 18.04, it links against libOpenGL.so.0 directly rather than libGL, which causes issues, due to it's distro-dependence. This will cause issues because the option to GLVND use is the default configuration for newer CMake.

Tagging @TheAssassin

[hcorion]

The odd thing with this issue that I forgot to mention is that it it the above works fine if built on 16.04, but stops working properly in 18.04 for some reason.

[JulianGro]

I don't see how linking to libOpenGL.so.0 is wrong. You are supposed to link to libOpenGL which in turn will act as a wrapper for libGLdispatch.
Legacy behaviour would be to link libGL which will also act as a wrapper on modern systems. My understanding is that it only provides GLX compatibility and no EGL compatibility like libOpenGL does, though that might not be accurate.
Whatever the case, I am sure there is a reason for libGL being "provided for backwards-compatibility" only. (See their documentation https://github.com/NVIDIA/libglvnd)

By the way, the point of glvnd is that multiple graphics drivers can coexist on the same system. Before glvnd, an Nvidia proprietary driver for example had to provide its own libGL and libOpenGL. Then if you had another driver vendor like Mesa on the same system you ran into the conflict that they too had to provide these libraries, but Nvidias libaries were already present.