# --- GTK ---
ocv_clear_vars(HAVE_GTK HAVE_GTK2 HAVE_GTK3 HAVE_GTKGLEXT)
if(WITH_GTK)
  if(NOT WITH_GTK_2_X)
    ocv_check_modules(GTK3 gtk+-3.0)
    if(HAVE_GTK3)
      ocv_add_external_target(gtk3 "${GTK3_INCLUDE_DIRS}" "${GTK3_LIBRARIES}" "HAVE_GTK3;HAVE_GTK")
      set(HAVE_GTK TRUE)
    endif()
  endif()
  if((PROJECT_NAME STREQUAL "OpenCV" AND HIGHGUI_ENABLE_PLUGINS) OR NOT HAVE_GTK3)
    ocv_check_modules(GTK2 gtk+-2.0)
    if(HAVE_GTK2)
      set(MIN_VER_GTK "2.18.0")
      if(GTK2_VERSION VERSION_LESS MIN_VER_GTK)
        message(FATAL_ERROR "GTK support requires a minimum version of ${MIN_VER_GTK} (${GTK2_VERSION} found)")
      else()
        ocv_add_external_target(gtk2 "${GTK2_INCLUDE_DIRS}" "${GTK2_LIBRARIES}" "HAVE_GTK2;HAVE_GTK")
        set(HAVE_GTK TRUE)
      endif()
    endif()
  endif()
  if((WITH_OPENGL OR HAVE_OPENGL) AND (HAVE_GTK2 OR HAVE_GTK3))
    if(HAVE_GTK2)
      ocv_check_modules(GTKGLEXT gtkglext-1.0)
      if(HAVE_GTKGLEXT)
        # HACK for https://github.com/opencv/opencv/issues/20850
        # pkg-config reports some include directories that do not exist. Just filter them out.
        set(GTKGLEXT_INCLUDE_DIRS_EXISTS "")
        foreach(p ${GTKGLEXT_INCLUDE_DIRS})
          if (EXISTS "${p}")
            list(APPEND GTKGLEXT_INCLUDE_DIRS_EXISTS "${p}")
          endif()
        endforeach()
        ocv_add_external_target(gtkglext "${GTKGLEXT_INCLUDE_DIRS}" "${GTKGLEXT_LIBRARIES}" "HAVE_GTKGLEXT")
      endif()
    endif()
  endif()
elseif(HAVE_GTK)
  ocv_add_external_target(gtk "${GTK_INCLUDE_DIRS}" "${GTK_LIBRARIES}" "${GTK_DEFINES};HAVE_GTK")
endif()

if(WITH_OPENGL)
  find_package(OpenGL QUIET)
  if(OPENGL_FOUND)
    set(HAVE_OPENGL TRUE)
    ocv_add_external_target(gtk_opengl "${OPENGL_INCLUDE_DIRS}" "${OPENGL_LIBRARIES}" "HAVE_OPENGL")
  endif()
endif()