FindOpenGL.cmake

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#[=======================================================================[.rst:
FindOpenGL
----------

Find OpenGL headers and libraries.

Imported Targets
^^^^^^^^^^^^^^^^

``OpenGL::OpenGL``
  The main OpenGL library, if found. It must *not* be assumed that this
  library provides symbols other than the base OpenGL set.
``OpenGL::GLX``
  The library containing the GL extension for the X11 windowing system,
  if found.

Result Variables
^^^^^^^^^^^^^^^^

This will define the following variables in your project:

``OpenGL_FOUND``
  True if the OpenGL library is available.
``OpenGL_VERSION``
  The version of the found OpenGL library, if possible to determine it at
  build configuration time. The variable may be undefined.

#]=======================================================================]

# TODO:
#  - Make GLX an optional component of the find-module.
#  - Make EGL an optional component here, remove FindEGL.cmake.
#  - Consider whether FindGLES2.cmake could be moved here as well.

find_package(PkgConfig QUIET)
pkg_check_modules(PC_OPENGL IMPORTED_TARGET opengl)

if (PC_OPENGL_FOUND AND TARGET PkgConfig::PC_OPENGL)
    #
    # If the "opengl" module exists, it should be preferred; and the library
    # name will typically be libOpenGL.so; in this case if GLX support is
    # available a "glx" module will *also* be available. This is a modern
    # Unix-ish convention and expected to be always provided by pkg-config
    # modules, so there is no need to fall-back to manually using find_path()
    # and find_library().
    #
    if (NOT TARGET OpenGL::OpenGL)
        add_library(OpenGL::OpenGL INTERFACE IMPORTED GLOBAL)
        set_property(TARGET OpenGL::OpenGL PROPERTY
            INTERFACE_LINK_LIBRARIES PkgConfig::PC_OPENGL
        )
    endif ()

    get_target_property(OpenGL_LIBRARY PkgConfig::PC_OPENGL INTERFACE_LINK_LIBRARIES)

    pkg_check_modules(PC_GLX IMPORTED_TARGET glx)
    if (TARGET PkgConfig::PC_GLX AND NOT TARGET OpenGL::GLX)
        add_library(OpenGL::GLX INTERFACE IMPORTED GLOBAL)
        set_property(TARGET OpenGL::GLX PROPERTY
            INTERFACE_LINK_LIBRARIES PkgConfig::PC_GLX
        )
    endif ()
else ()
    # Otherwise, if an "opengl" pkg-config module does not exist, check for
    # the "gl" one, which may or may not be present.
    #
    pkg_check_modules(PC_OPENGL gl)
    find_path(OpenGL_INCLUDE_DIR
        NAMES GL/gl.h
        HINTS ${PC_OPENGL_INCLUDEDIR} ${PC_OPENGL_INCLUDE_DIRS}
    )

    find_library(OpenGL_LIBRARY
        NAMES ${OpenGL_NAMES} gl GL
        HINTS ${PC_OPENGL_LIBDIR} ${PC_OPENGL_LIBRARY_DIRS}
    )

    if (OpenGL_LIBRARY AND NOT TARGET OpenGL::OpenGL)
        add_library(OpenGL::OpenGL UNKNOWN IMPORTED GLOBAL)
        set_target_properties(OpenGL::OpenGL PROPERTIES
            IMPORTED_LOCATION "${OpenGL_LIBRARY}"
            INTERFACE_COMPILE_OPTIONS "${PC_OPENGL_CFLAGS_OTHER}"
            INTERFACE_INCLUDE_DIRECTORIES "${OpenGL_INCLUDE_DIR}"
        )
    endif ()

    if (TARGET OpenGL::OpenGL)
        # We don't use find_package for GLX because it is part of -lGL, unlike EGL. We need to
        # have OPENGL_INCLUDE_DIRS as part of the directories check_include_files() looks for in
        # case OpenGL is installed into a non-standard location.
        include(CMakePushCheckState)
        CMAKE_PUSH_CHECK_STATE()
        set(CMAKE_REQUIRED_INCLUDES ${CMAKE_REQUIRED_INCLUDES} ${OpenGL_INCLUDE_DIR})
        include(CheckIncludeFiles)
        check_include_files("GL/glx.h" OpenGL_GLX_FOUND)
        CMAKE_POP_CHECK_STATE()

        if (OpenGL_GLX_FOUND)
            # XXX: Should this actually check that the OpenGL library contains the GLX symbols?
            add_library(OpenGL::GLX INTERFACE IMPORTED GLOBAL)
            set_property(TARGET OpenGL::GLX PROPERTY
                INTERFACE_LINK_LIBRARIES OpenGL::OpenGL
            )
        endif ()
    endif ()
endif ()

set(OpenGL_VERSION "${PC_OPENGL_VERSION}")

include(FindPackageHandleStandardArgs)
find_package_handle_standard_args(OpenGL
    REQUIRED_VARS OpenGL_LIBRARY
    FOUND_VAR OpenGL_FOUND
)

mark_as_advanced(OpenGL_INCLUDE_DIR OpenGL_LIBRARY)

if (OpenGL_FOUND)
    set(OpenGL_LIBRARIES ${OpenGL_LIBRARY})
    set(OpenGL_INCLUDE_DIRS ${OpenGL_INCLUDE_DIR})
endif ()