Fix usage of FLTK_BACKEND_WAYLAND and FLTK_USE_WAYLAND

- Do not change or remove the cache variable FLTK_BACKEND_WAYLAND:
  this is an option set (and must only be changed) by the user.
- CMake/options.cmake: check Wayland availability if option
  FLTK_BACKEND_WAYLAND is ON and set the result variable
  FLTK_USE_WAYLAND accordingly.
- Replace FLTK_BACKEND_WAYLAND with FLTK_USE_WAYLAND everywhere
  else, except as noted above: in options.cmake.

4 files changed, 46 insertions, 33 deletions

diff --git a/CMake/options.cmake b/CMake/options.cmake
index 3ff6d06f5..1ef64aad4 100644
--- a/CMake/options.cmake
+++ b/CMake/options.cmake
@@ -276,27 +276,40 @@ set(HAVE_LIBJPEG 1)
 if(UNIX)
   option(FLTK_INSTALL_LINKS "create backwards compatibility links" OFF)
   list(APPEND FLTK_LDLIBS -lm)
+
   if(NOT APPLE)
     option(FLTK_BACKEND_WAYLAND "support the Wayland backend" ON)
   endif(NOT APPLE)
+
+  # Check Wayland requirements and set the result variable FLTK_USE_WAYLAND.
+  # FLTK_USE_WAYLAND *must* be used *everywhere* else after these checks.
+
   if(FLTK_BACKEND_WAYLAND)
+    message(STATUS "Checking Wayland requirements ...")
+    set(FLTK_USE_WAYLAND FALSE) # assume Wayland not OK ...
+
     if(NOT PKG_CONFIG_FOUND)
-      message(FATAL_ERROR "Option FLTK_BACKEND_WAYLAND requires availability of pkg-config on the build machine.")
-    endif(NOT PKG_CONFIG_FOUND)
+      message(FATAL_ERROR "Option FLTK_BACKEND_WAYLAND requires pkg-config on the build host.")
+    endif()
+
     pkg_check_modules(WLDCLIENT IMPORTED_TARGET wayland-client>=1.18)
     pkg_check_modules(WLDCURSOR IMPORTED_TARGET wayland-cursor)
     pkg_check_modules(WLDPROTO IMPORTED_TARGET wayland-protocols>=1.15)
     pkg_check_modules(XKBCOMMON IMPORTED_TARGET xkbcommon)
-    if(NOT(WLDCLIENT_FOUND AND WLDCURSOR_FOUND AND WLDPROTO_FOUND AND XKBCOMMON_FOUND))
-      message(STATUS "Not all software modules 'wayland-client>=1.18 wayland-cursor wayland-protocols>=1.15 xkbcommon' are present")
-      message(STATUS "Consequently, FLTK_BACKEND_WAYLAND is turned off.")
-      unset(FLTK_BACKEND_WAYLAND CACHE)
-      set(FLTK_BACKEND_WAYLAND 0)
-    endif(NOT(WLDCLIENT_FOUND AND WLDCURSOR_FOUND AND WLDPROTO_FOUND AND XKBCOMMON_FOUND))
+
+    if(WLDCLIENT_FOUND AND WLDCURSOR_FOUND AND WLDPROTO_FOUND AND XKBCOMMON_FOUND)
+      set(FLTK_USE_WAYLAND TRUE) # OK, Wayland can be used
+      message(STATUS "Checking Wayland requirements: OK")
+    else()
+      message(NOTICE "Checking Wayland requirements FAILED!")
+      message(NOTICE "  Not all required software modules for Wayland are present.")
+      message(NOTICE "  The Wayland backend was requested but can't be built.")
+      message(NOTICE "  Please check Wayland requirements (see above) or")
+      message(NOTICE "  set FLTK_BACKEND_WAYLAND=OFF to silence this warning.")
+    endif()
   endif(FLTK_BACKEND_WAYLAND)
 
-  if(FLTK_BACKEND_WAYLAND)
-    set(FLTK_USE_WAYLAND 1)
+  if(FLTK_USE_WAYLAND)
     if(FLTK_BACKEND_X11)
       include(FindX11)
     endif()
@@ -373,7 +386,7 @@ if(UNIX)
       endif(NOT LINUX_INPUT_H)
     endif(${CMAKE_HOST_SYSTEM_NAME} STREQUAL "FreeBSD")
 
-  endif(FLTK_BACKEND_WAYLAND)
+  endif(FLTK_USE_WAYLAND)
 endif(UNIX)
 
 if(WIN32)
@@ -625,7 +638,7 @@ if(HAVE_GL)
 endif()
 
 if(FLTK_BUILD_GL)
-  if(FLTK_BACKEND_WAYLAND)
+  if(FLTK_USE_WAYLAND)
     pkg_check_modules(WLD_EGL IMPORTED_TARGET wayland-egl)
     pkg_check_modules(PKG_EGL IMPORTED_TARGET egl)
     pkg_check_modules(PKG_GL  IMPORTED_TARGET gl)
@@ -636,7 +649,7 @@ if(FLTK_BUILD_GL)
       message(FATAL_ERROR "*** Aborting ***")
     endif()
 
-  endif(FLTK_BACKEND_WAYLAND)
+  endif(FLTK_USE_WAYLAND)
 
   if(FLTK_BACKEND_X11)
     set(OPENGL_FOUND TRUE)
@@ -689,7 +702,7 @@ if(OPENGL_FOUND)
     list(APPEND GLLIBS -lglu32 -lopengl32)
   elseif(APPLE AND NOT FLTK_BACKEND_X11)
     list(APPEND GLLIBS "-framework OpenGL")
-  elseif(FLTK_BACKEND_WAYLAND)
+  elseif(FLTK_USE_WAYLAND)
     foreach(_lib WLD_EGL PKG_EGL PKG_GLU PKG_GL)
       list(APPEND GLLIBS ${${_lib}_LDFLAGS})
     endforeach(_lib )
@@ -824,9 +837,9 @@ endif(FLTK_USE_XCURSOR)
 #######################################################################
 if(X11_Xft_FOUND)
   option(FLTK_USE_PANGO "use lib Pango" OFF)
-  if(NOT FLTK_BACKEND_WAYLAND)
+  if(NOT FLTK_USE_WAYLAND)
     option(FLTK_GRAPHICS_CAIRO "all drawing to X11 windows uses Cairo" OFF)
-  endif(NOT FLTK_BACKEND_WAYLAND)
+  endif(NOT FLTK_USE_WAYLAND)
   if(NOT FLTK_GRAPHICS_CAIRO)
     option(FLTK_USE_XFT "use lib Xft" ON)
   endif()
@@ -886,14 +899,14 @@ if((X11_Xft_FOUND OR NOT USE_PANGOXFT) AND FLTK_USE_PANGO)
 
   endif((PANGOXFT_FOUND OR NOT USE_PANGOXFT) AND PANGOCAIRO_FOUND AND CAIRO_FOUND)
 
-  if(USE_PANGO AND (FLTK_GRAPHICS_CAIRO OR FLTK_BACKEND_WAYLAND))
+  if(USE_PANGO AND (FLTK_GRAPHICS_CAIRO OR FLTK_USE_WAYLAND))
     set(FLTK_USE_CAIRO 1)
     # fl_debug_var(FLTK_USE_CAIRO)
   endif()
 
 endif((X11_Xft_FOUND OR NOT USE_PANGOXFT) AND FLTK_USE_PANGO)
 
-if(FLTK_BACKEND_WAYLAND)
+if(FLTK_USE_WAYLAND)
 
   # Note: Disable FLTK_USE_LIBDECOR_GTK to get cairo titlebars rather than GTK
   if(FLTK_USE_LIBDECOR_GTK AND NOT USE_SYSTEM_LIBDECOR)
diff --git a/CMake/variables.cmake b/CMake/variables.cmake
index 4d1be9f2d..b2993f032 100644
--- a/CMake/variables.cmake
+++ b/CMake/variables.cmake
@@ -43,7 +43,7 @@ if(WIN32)
   list(APPEND FLTK_LDLIBS -lole32 -luuid -lcomctl32 -lws2_32 -lwinspool)
 elseif(APPLE AND NOT FLTK_BACKEND_X11)
   list(APPEND FLTK_LDLIBS ${FLTK_COCOA_FRAMEWORKS})
-elseif(FLTK_BACKEND_WAYLAND)
+elseif(FLTK_USE_WAYLAND)
   foreach(_lib WLDCURSOR WLDCLIENT XKBCOMMON DBUS)
     list(APPEND FLTK_LDLIBS "${${_lib}_LDFLAGS}")
   endforeach()
diff --git a/CMakeLists.txt b/CMakeLists.txt
index aeec6dfa8..4a45b5cc1 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -114,7 +114,7 @@ endif()
 # for instance if FLTK is built as a subproject (FetchContent)
 
 set(FLTK_VERSION ${FLTK_VERSION} CACHE STRING
-    "FLTK version: generated, do not change" FORCE)
+    "FLTK version: generated by CMake, do not change" FORCE)
 
 #######################################################################
 # basic setup
@@ -405,19 +405,19 @@ fl_summary_image("Bundled Libraries" JPEG  LIB_jpeg)
 fl_summary_image(""                  PNG   LIB_png)
 fl_summary_image(""                  ZLIB  LIB_zlib)
 
-if(FLTK_BACKEND_WAYLAND)
+if(FLTK_USE_WAYLAND)
   if(USE_SYSTEM_LIBDECOR)
     fl_summary("" "Libdecor = System: ${SYSTEM_LIBDECOR_LINK_LIBRARIES}")
   else()
     fl_summary("" "Libdecor = Bundled")
   endif()
-endif(FLTK_BACKEND_WAYLAND)
+endif(FLTK_USE_WAYLAND)
 
 message("")
 
 if(UNIX AND NOT (APPLE AND NOT FLTK_BACKEND_X11))
 
-  if(FLTK_BACKEND_WAYLAND)
+  if(FLTK_USE_WAYLAND)
     if(FLTK_BACKEND_X11)
       fl_summary("Use Wayland" "Yes (can also run as X11 client)")
     else()
@@ -425,7 +425,7 @@ if(UNIX AND NOT (APPLE AND NOT FLTK_BACKEND_X11))
     endif(FLTK_BACKEND_X11)
   else()
     fl_summary("Use Wayland" "No (X11 is used)")
-  endif(FLTK_BACKEND_WAYLAND)
+  endif(FLTK_USE_WAYLAND)
 
   fl_summary_yn("All drawing uses Cairo" FLTK_USE_CAIRO)
 
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index f84d58d85..ed1cfc276 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -215,7 +215,7 @@ endif(FLTK_USE_X11 AND NOT FLTK_OPTION_PRINT_SUPPORT)
 
 set(DRIVER_FILES)
 
-if(FLTK_USE_X11 AND NOT FLTK_BACKEND_WAYLAND)
+if(FLTK_USE_X11 AND NOT FLTK_USE_WAYLAND)
 
   # X11 (including APPLE with X11)
 
@@ -290,7 +290,7 @@ if(FLTK_USE_X11 AND NOT FLTK_BACKEND_WAYLAND)
    )
  endif(FLTK_USE_CAIRO)
 
-elseif(FLTK_BACKEND_WAYLAND)
+elseif(FLTK_USE_WAYLAND)
   set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -I${CMAKE_CURRENT_BINARY_DIR}")
   set(DRIVER_FILES
     drivers/Posix/Fl_Posix_System_Driver.cxx
@@ -407,7 +407,7 @@ else()
     drivers/GDI/Fl_GDI_Image_Surface_Driver.H
   )
 
-endif(FLTK_USE_X11 AND NOT FLTK_BACKEND_WAYLAND)
+endif(FLTK_USE_X11 AND NOT FLTK_USE_WAYLAND)
 
 source_group("Header Files" FILES ${HEADER_FILES})
 source_group("Driver Source Files" FILES ${DRIVER_FILES})
@@ -457,7 +457,7 @@ set(GL_DRIVER_FILES
   drivers/OpenGL/Fl_OpenGL_Graphics_Driver_rect.cxx
   drivers/OpenGL/Fl_OpenGL_Graphics_Driver_vertex.cxx
 )
-if(FLTK_BACKEND_WAYLAND)
+if(FLTK_USE_WAYLAND)
   set(GL_DRIVER_FILES ${GL_DRIVER_FILES} drivers/Wayland/Fl_Wayland_Gl_Window_Driver.cxx)
   set(GL_DRIVER_HEADER_FILES drivers/Wayland/Fl_Wayland_Gl_Window_Driver.H)
   if(FLTK_USE_X11)
@@ -473,7 +473,7 @@ elseif(APPLE)
 elseif(WIN32)
   set(GL_DRIVER_FILES ${GL_DRIVER_FILES} drivers/WinAPI/Fl_WinAPI_Gl_Window_Driver.cxx)
   set(GL_DRIVER_HEADER_FILES drivers/WinAPI/Fl_WinAPI_Gl_Window_Driver.H)
-endif(FLTK_BACKEND_WAYLAND)
+endif(FLTK_USE_WAYLAND)
 
 set(GL_DRIVER_HEADER_FILES ${GL_DRIVER_FILES}
   drivers/OpenGL/Fl_OpenGL_Display_Device.H
@@ -531,7 +531,7 @@ if(FLTK_USE_X11)
   endif(NOT USE_XFT)
 endif(FLTK_USE_X11)
 
-if(FLTK_BACKEND_WAYLAND)
+if(FLTK_USE_WAYLAND)
   pkg_check_modules(DBUS IMPORTED_TARGET dbus-1)
   set(IDIRS "${CMAKE_CURRENT_BINARY_DIR}")
   set(CDEFS "_GNU_SOURCE;HAVE_MEMFD_CREATE;HAVE_MKOSTEMP;HAVE_POSIX_FALLOCATE")
@@ -593,7 +593,7 @@ if(FLTK_BACKEND_WAYLAND)
       ../libdecor/src/plugins/common/libdecor-cairo-blur.c
     )
   endif(NOT USE_SYSTEM_LIBDECOR)
-endif(FLTK_BACKEND_WAYLAND)
+endif(FLTK_USE_WAYLAND)
 
 if(WIN32)
   list(APPEND CFILES
@@ -734,7 +734,7 @@ if(USE_XFT)
   endif(LIB_fontconfig)
 endif(USE_XFT)
 
-if(UNIX AND FLTK_BACKEND_WAYLAND)
+if(UNIX AND FLTK_USE_WAYLAND)
   pkg_get_variable(PROTOCOLS wayland-protocols pkgdatadir)
   # replace "//" with "/"
   string(REPLACE "//" "/" PROTOCOLS ${PROTOCOLS})
@@ -813,7 +813,7 @@ if(UNIX AND FLTK_BACKEND_WAYLAND)
     append_optional_libs(PkgConfig::DBUS)
   endif()
 
-endif(UNIX AND FLTK_BACKEND_WAYLAND)
+endif(UNIX AND FLTK_USE_WAYLAND)
 
 list(REMOVE_DUPLICATES OPTIONAL_LIBS)
 list(REMOVE_DUPLICATES OPTIONAL_INCLUDES)