Wayland: make OPTION_USE_SYSTEM_LIBDECOR ON by default

This commit makes the default FLTK build setting use libdecor
as packaged in Linux when the build system contains packages
libdecor-0-dev and libdecor-0-plugin-1-gtk in version ≥ 0.2.0.
Otherwise, FLTK uses the bundled version of libdecor.
This includes situations where package libdecor-0-dev is
present in an earlier version.

10 files changed, 80 insertions, 70 deletions

diff --git a/CMake/options.cmake b/CMake/options.cmake
index 5dad843d0..b5150dee2 100644
--- a/CMake/options.cmake
+++ b/CMake/options.cmake
@@ -258,7 +258,7 @@ if (UNIX)
     endif (X11_FOUND)
     unset (OPTION_USE_CAIRO CACHE)
     set (OPTION_USE_CAIRO TRUE CACHE BOOL "all drawing to X11 windows uses Cairo")
-    option (OPTION_USE_SYSTEM_LIBDECOR "use libdecor from the system" OFF)
+    option (OPTION_USE_SYSTEM_LIBDECOR "use libdecor from the system" ON)
     unset (OPTION_USE_XRENDER CACHE)
     unset (OPTION_USE_XINERAMA CACHE)
     unset (OPTION_USE_XFT CACHE)
@@ -293,13 +293,25 @@ if (UNIX)
     unset (OPTION_USE_PANGO CACHE)
     set (OPTION_USE_PANGO TRUE CACHE BOOL "use lib Pango")
     if (OPTION_USE_SYSTEM_LIBDECOR)
-      pkg_check_modules(SYSTEM_LIBDECOR libdecor-0)
+      pkg_check_modules(SYSTEM_LIBDECOR libdecor-0>=0.2.0)
       if (NOT SYSTEM_LIBDECOR_FOUND)
         set (OPTION_USE_SYSTEM_LIBDECOR OFF)
+      else ()
+        pkg_get_variable(LIBDECOR_LIBDIR libdecor-0 libdir)
+        set (LIBDECOR_PLUGIN_DIR ${LIBDECOR_LIBDIR}/libdecor/plugins-1)
+        if (EXISTS ${LIBDECOR_PLUGIN_DIR} AND IS_DIRECTORY ${LIBDECOR_PLUGIN_DIR})
+          set (LIBDECOR_PLUGIN_DIR "\\\"${LIBDECOR_PLUGIN_DIR}\\\" " )
+        else ()
+          set (OPTION_USE_SYSTEM_LIBDECOR OFF)
+        endif ()
       endif (NOT SYSTEM_LIBDECOR_FOUND)
     endif (OPTION_USE_SYSTEM_LIBDECOR)
 
-    option (OPTION_ALLOW_GTK_PLUGIN "Allow to use libdecor's GTK plugin" ON)
+    if (OPTION_USE_SYSTEM_LIBDECOR)
+        set (OPTION_ALLOW_GTK_PLUGIN ON)
+    else ()
+      option (OPTION_ALLOW_GTK_PLUGIN "Allow to use libdecor's GTK plugin" ON)
+    endif (OPTION_USE_SYSTEM_LIBDECOR)
 
     if (${CMAKE_HOST_SYSTEM_NAME} STREQUAL "FreeBSD")
       CHECK_INCLUDE_FILE (linux/input.h LINUX_INPUT_H)
@@ -856,7 +868,7 @@ if ((X11_Xft_FOUND OR NOT USE_PANGOXFT) AND OPTION_USE_PANGO)
 
 endif ((X11_Xft_FOUND OR NOT USE_PANGOXFT) AND OPTION_USE_PANGO)
 
-if (OPTION_USE_WAYLAND AND NOT OPTION_USE_SYSTEM_LIBDECOR)
+if (OPTION_USE_WAYLAND)
 
   # Note: Disable OPTION_ALLOW_GTK_PLUGIN to get cairo titlebars rather than GTK
   if (OPTION_ALLOW_GTK_PLUGIN)
@@ -869,7 +881,7 @@ if (OPTION_USE_WAYLAND AND NOT OPTION_USE_SYSTEM_LIBDECOR)
     endif (GTK_FOUND)
   endif (OPTION_ALLOW_GTK_PLUGIN)
 
-endif (OPTION_USE_WAYLAND AND NOT OPTION_USE_SYSTEM_LIBDECOR)
+endif (OPTION_USE_WAYLAND)
 
 if (OPTION_USE_XFT)
   set (USE_XFT X11_Xft_FOUND)
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 21ef377d7..d2ae79f14 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -281,6 +281,11 @@ if (UNIX AND NOT (APPLE AND NOT OPTION_APPLE_X11))
 
   if (OPTION_USE_WAYLAND)
     message (STATUS "Use Wayland             : Yes (if available at run-time)")
+    if (OPTION_USE_SYSTEM_LIBDECOR)
+      message (STATUS "Use system libdecor     : Yes")
+    else ()
+      message (STATUS "Use system libdecor     : No")
+    endif ()
   else ()
     message (STATUS "Use Wayland             : No (therefore, X11 is used)")
   endif ()
diff --git a/README.CMake.txt b/README.CMake.txt
index c64c0c75c..c80832136 100644
--- a/README.CMake.txt
+++ b/README.CMake.txt
@@ -232,10 +232,12 @@ OPTION_USE_STD - default OFF
    or major (maybe 4.0.0) release which will default to use std::string
    and more modern C++ features.
 
-OPTION_USE_SYSTEM_LIBDECOR - default OFF
-   This option makes FLTK use package libdecor-0 to draw window titlebars
-   under Wayland. It's mainly meant for future use, when that package
-   and its plugins will be part of major Linux distributions.
+OPTION_USE_SYSTEM_LIBDECOR - default ON
+   This option makes FLTK use package libdecor-0-dev to draw window titlebars
+   under Wayland. When OFF or when this package has a version < 0.2.0, FLTK
+   uses its bundled copy of libdecor to draw window titlebars.
+   As of november 2023, version 0.2.0 of package libdecor-0-dev is available
+   only in testing distributions.
 
 Documentation options: these options are only available if `doxygen' is
    installed and found by CMake. PDF related options require also `latex'.
diff --git a/README.Wayland.txt b/README.Wayland.txt
index 1bd930535..497f34af9 100644
--- a/README.Wayland.txt
+++ b/README.Wayland.txt
@@ -75,10 +75,10 @@ be used to produce a Wayland-only library which can be useful, e.g., when
 cross-compiling for systems that lack X11 headers and libraries.
 
 The FLTK Wayland platform uses a library called libdecor which handles window decorations
-(i.e., titlebars, shade). Libdecor is bundled in the FLTK source code and FLTK uses by default
-this form of libdecor. CMake OPTION_USE_SYSTEM_LIBDECOR can be turned on to have FLTK
-use the system's version of libdecor which is available on recent Linux distributions (e.g.,
-Debian Bookworm or more recent in packages libdecor-0-0 and libdecor-0-plugin-1-cairo).
+(i.e., titlebars, shade). On very recent Linux distributions (e.g., Debian trixie)
+libdecor is available as Linux packages (libdecor-0-dev and libdecor-0-plugin-1-gtk).
+FLTK requires version 0.2.0 of these packages or more.
+In other situations, FLTK uses a copy of libdecor bundled in the FLTK source code.
 FLTK equipped with libdecor supports both the client-side decoration mode (CSD) and the
 server-side decoration mode (SSD) as determined by the active Wayland compositor.
 Mutter (gnome's Wayland compositor) and Weston use CSD mode, KWin and Sway use SSD mode.
@@ -145,6 +145,9 @@ in section 2.1 of file README.Unix.txt :
 These packages allow to run FLTK apps under the Gnome-Wayland desktop:
 - gnome-core
 - libgtk-3-dev   <== highly recommended, gives windows a Gnome-style titlebar
+- libdecor-0-dev and libdecor-0-plugin-1-gtk in versions ≥ 0.2.0
+                 <== Recommended if available for the Linux version in use,
+                 <== FLTK uses a bundled copy of these packages otherwise.
 
 These packages allow to run FLTK apps under the KDE/Plasma-Wayland desktop:
 - kde-plasma-desktop
@@ -169,6 +172,7 @@ package groups listed in section 2.2 of file README.Unix.txt :
 - mesa-libGLU-devel
 - dbus-devel   <== recommended to query current cursor theme
 - gtk3-devel   <== highly recommended, gives windows a GTK-style titlebar
+- libdecor-0.2.0 <== recommended, present in Fedora Rawhide, not in Fedora 39
 - glew-devel   <== necessary to use OpenGL version 3 or above
 - cmake        <== if you plan to build with CMake
 - cmake-gui    <== if you plan to use the GUI of CMake
diff --git a/configure.ac b/configure.ac
index 697945548..b2465fccf 100644
--- a/configure.ac
+++ b/configure.ac
@@ -1055,12 +1055,18 @@ AS_CASE([$host_os_gui], [cygwin* | mingw*], [
        BUILD="WAYLANDX11"
        graphics="Wayland or X11 with cairo"
        ])
-#     CFLAGS="$CFLAGS -DUSE_SYSTEM_LIBDECOR=0"
-#     CXXFLAGS="$CXXFLAGS -DUSE_SYSTEM_LIBDECOR=0"
+      AS_IF([$PKGCONFIG --exists 'libdecor-0 >= 0.2.0'],
+      [
+        plugin_dir="$($PKGCONFIG --variable=libdir libdecor-0)/libdecor/plugins-1"
+        CFLAGS="$CFLAGS -DUSE_SYSTEM_LIBDECOR"
+        CFLAGS="$CFLAGS -DLIBDECOR_PLUGIN_DIR=\\\"$plugin_dir\\\" "
+        LIBS="$LIBS $($PKGCONFIG --libs libdecor-0)"
+      ],
+      [CFLAGS="$CFLAGS -DUSE_SYSTEM_LIBDECOR=0 -DLIBDECOR_PLUGIN_DIR=\"\" "]
+      )
       LIBS="$LIBS $($PKGCONFIG --libs wayland-cursor) $($PKGCONFIG --libs wayland-client) $($PKGCONFIG --libs xkbcommon) $($PKGCONFIG --libs pangocairo) "
       AS_IF([test x$enable_x11 != xno], [LIBS="$LIBS $($PKGCONFIG --libs x11)"] )
       LIBS="$LIBS -ldl"
-#     CXXFLAGS="$CXXFLAGS -I../libdecor/src"
       DSOFLAGS="$LIBS $DSOFLAGS"
       enable_pango=yes
       LIBDECORDIR="libdecor/build"
diff --git a/documentation/src/wayland.dox b/documentation/src/wayland.dox
index 170ab10c7..f08cc74ac 100644
--- a/documentation/src/wayland.dox
+++ b/documentation/src/wayland.dox
@@ -26,7 +26,7 @@ always entirely filled with whatever resizable windows are mapped at any given
 time. Compositors follow either the
 client-side decoration (CSD) rule where client apps draw window titlebars, or the
 server-side decoration (SSD) rule where the compositor draws titlebars. FLTK supports both
-CSD and SSD compositors. It bundles a library called \c libdecor charged of determining whether
+CSD and SSD compositors. It uses a library called \c libdecor charged of determining whether
 a CSD or a SSD compositor is active, and of drawing titlebars in the first case.
 
 Wayland is divided in various protocols that a given compositor may or may not support,
@@ -92,7 +92,7 @@ Overall, and ignoring for now OpenGL usage, FLTK interacts with Wayland as follo
 - When opening the display: FLTK calls \c Fl::add_fd() in \c FL_READ mode to associate
 a  callback function to the socket connecting the client and the compositor.
 - Client to compositor: FLTK calls C functions of the \c libwayland-client.so,
-\c libwayland-cursor.so and \c libxkbcommon.so shared libraries and of the bundled
+\c libwayland-cursor.so and \c libxkbcommon.so shared libraries and of the
 libdecor library. These send suitable messages to the compositor writing to the socket.
 The names of these functions begin with \c wl_, \c xkb_ or \c libdecor_.
 - Compositor to client: the callback function runs when there are data to read in the
@@ -1061,14 +1061,25 @@ and also to draw window titlebars when in CSD mode (see \ref bundled-libdecor).
 \c Libdecor is conceived to be present in a shared library linked to the Wayland
 client application which itself, and if the running Wayland compositor uses CSD mode,
 loads another shared library intended to draw titlebars in a way that best matches the
-Desktop. As of early 2023, two titlebar-drawing \c libdecor plugins are available:
+Desktop. As of late 2023, libdecor is at version 0.2.0 and contains two titlebar-drawing
+plugins:
 - \c libdecor-gtk intended for the Gnome desktop;
 - \c libdecor-cairo for other situations.
 
-Because \c libdecor is not yet in Linux packages, or only in a preliminary state, FLTK bundles the
-most recent source code of \c libdecor and its plugins. This code is included in libfltk.
-FLTK uses \c libdecor-gtk when software package \c libgtk-3-dev is present in the
-build system, and \c libdecor-cairo otherwise.
+Because \c libdecor is not yet in major Linux packages, or only at version 0.1.x,
+FLTK bundles the most recent source code of \c libdecor and its plugins. This code
+is included in libfltk. FLTK uses \c libdecor-gtk when software package \c libgtk-3-dev
+is present in the build system, and \c libdecor-cairo otherwise.
+
+As of late 2023, libdecor version 0.2.0 is available in very recent Linux distributions
+in packages \c libdecor-0-dev and \c libdecor-0-plugin-1-gtk. If they are installed on the
+build system, preprocessor variable \c USE_SYSTEM_LIBDECOR is 1,
+and both \c libdecor and its plugin are loaded at run-time from shared libraries.
+When these packages are not available or are at an earlier version, FLTK uses the bundled
+copy of \c libdecor.
+When CMake \c OPTION_USE_SYSTEM_LIBDECOR is OFF, FLTK uses the bundled \c libdecor copy
+even if shared libraries \c libdecor.so and \c libdecor-gtk.so are installed.
+This option is ON by default.
 
 \c Libdecor uses the Wayland protocol
 <a href=https://wayland.app/protocols/xdg-decoration-unstable-v1>
@@ -1079,12 +1090,6 @@ However, if environment variable \c LIBDECOR_FORCE_CSD is defined to value \c 1
 FLTK app runs, \c libdecor instructs an SSD-able compositor to refrain from decorating its
 windows and decorates windows itself.
 
-CMake \c OPTION_USE_SYSTEM_LIBDECOR has been defined to allow FLTK in the future, when \c libdecor and
-\c libdecor-gtk will be part of Linux packages, to use these packages rather than the \c libdecor
-code bundled in FLTK. When this option is ON, preprocessor variable \c USE_SYSTEM_LIBDECOR is 1,
-and both \c libdecor and its plugin are loaded at run-time from shared libraries. This option is OFF
-by default.
-
 Whatever the value of \c OPTION_USE_SYSTEM_LIBDECOR, FLTK and \c libdecor use environment variable
 \c LIBDECOR_PLUGIN_DIR as follows: if this variable is defined and points to the name of a directory,
 this directory is searched for a potential \c libdecor plugin in the form of a shared library;
diff --git a/libdecor/build/Makefile b/libdecor/build/Makefile
index 946ec6318..c98f12ddb 100644
--- a/libdecor/build/Makefile
+++ b/libdecor/build/Makefile
@@ -27,7 +27,7 @@ FreeBSD_CFLAGS = -I/usr/local/include
 EXTRA_DECOR =  ${${UNAME}_CFLAGS}
 
 CFLAGS_DECOR =  -I. -I../.. -I../../src -I../src -I../src/plugins $(EXTRA_DECOR) -fPIC -D_GNU_SOURCE \
-  -DUSE_SYSTEM_LIBDECOR=0 -DHAVE_MEMFD_CREATE -DHAVE_MKOSTEMP -DHAVE_POSIX_FALLOCATE
+   -DHAVE_MEMFD_CREATE -DHAVE_MKOSTEMP -DHAVE_POSIX_FALLOCATE
 
 Linux_NOPIE = -no-pie
 FreeBSD_NOPIE =
@@ -39,10 +39,10 @@ depend:
 	: echo "libdecor/build: make depend..."
 
 fl_libdecor.o : fl_libdecor.c ../src/libdecor.c ../../src/xdg-shell-protocol.c ../../src/xdg-decoration-protocol.c ../../src/text-input-protocol.c ../../src/gtk-shell-protocol.c
-	$(CC) $(CFLAGS) $(CFLAGS_DECOR) -c  fl_libdecor.c -DLIBDECOR_PLUGIN_API_VERSION=1 -DLIBDECOR_PLUGIN_DIR=\"\"
+	$(CC) $(CFLAGS) $(CFLAGS_DECOR) -c  fl_libdecor.c -DLIBDECOR_PLUGIN_API_VERSION=1
 
 fl_libdecor-plugins.o : fl_libdecor-plugins.c ../src/plugins/cairo/libdecor-cairo.c
-	$(CC) $(CFLAGS) $(CFLAGS_DECOR) -c  fl_libdecor-plugins.c  -DLIBDECOR_PLUGIN_API_VERSION=1 -DLIBDECOR_PLUGIN_DIR=\"\"
+	$(CC) $(CFLAGS) $(CFLAGS_DECOR) -c  fl_libdecor-plugins.c  -DLIBDECOR_PLUGIN_API_VERSION=1
 
 libdecor-cairo-blur.o : ../src/plugins/common/libdecor-cairo-blur.c
 	$(CC) $(CFLAGS_DECOR) -c  ../src/plugins/common/libdecor-cairo-blur.c
diff --git a/libdecor/build/fl_libdecor.c b/libdecor/build/fl_libdecor.c
index ab6cee5c2..7a327f151 100644
--- a/libdecor/build/fl_libdecor.c
+++ b/libdecor/build/fl_libdecor.c
@@ -15,6 +15,7 @@
 //
 
 /* Improvements to libdecor.c without modifying libdecor.c itself */
+#if ! USE_SYSTEM_LIBDECOR
 
 #include "xdg-shell-client-protocol.h"
 #ifdef XDG_TOPLEVEL_STATE_SUSPENDED_SINCE_VERSION
@@ -126,3 +127,5 @@ LIBDECOR_EXPORT struct libdecor *libdecor_new(struct wl_display *wl_display, str
   wl_display_flush(wl_display);
   return context;
 }
+
+#endif //! USE_SYSTEM_LIBDECOR
diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index a1d52f197..d6a7a047c 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -521,10 +521,7 @@ if (OPTION_USE_WAYLAND)
   endif (DBUS_FOUND)
   if (OPTION_USE_SYSTEM_LIBDECOR)
     set (CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -DUSE_SYSTEM_LIBDECOR")
-    get_filename_component(PATH_TO_SHARED_LIBS ${HAVE_LIB_PANGO} DIRECTORY)
-    set (LIBDECOR_PLUGIN_DIR "\\\"${PATH_TO_SHARED_LIBS}/libdecor/plugins-1\\\" " )
     set (CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -DLIBDECOR_PLUGIN_DIR=${LIBDECOR_PLUGIN_DIR} ")
-    set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -DUSE_SYSTEM_LIBDECOR")
     if (GTK_FOUND)
       set (CMAKE_C_FLAGS "${CMAKE_C_FLAGS} -DHAVE_GTK")
     endif (GTK_FOUND)
@@ -690,18 +687,18 @@ if (UNIX AND OPTION_USE_WAYLAND)
     )
     list (APPEND STATIC_FILES "xdg-decoration-protocol.c")
     list (APPEND SHARED_FILES "xdg-decoration-protocol.c")
-    if (GTK_FOUND AND OPTION_ALLOW_GTK_PLUGIN)
-      add_custom_command(
-        OUTPUT gtk-shell-protocol.c gtk-shell-client-protocol.h
-        COMMAND wayland-scanner private-code ${CMAKE_CURRENT_SOURCE_DIR}/../libdecor/build/gtk-shell.xml gtk-shell-protocol.c
-        COMMAND wayland-scanner client-header ${CMAKE_CURRENT_SOURCE_DIR}/../libdecor/build/gtk-shell.xml gtk-shell-client-protocol.h
-        DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/../libdecor/build/gtk-shell.xml
-        VERBATIM
-      )
-      list (APPEND STATIC_FILES "gtk-shell-protocol.c")
-      list (APPEND SHARED_FILES "gtk-shell-protocol.c")
-    endif (GTK_FOUND AND OPTION_ALLOW_GTK_PLUGIN)
   endif (NOT OPTION_USE_SYSTEM_LIBDECOR)
+  if (GTK_FOUND AND (OPTION_USE_SYSTEM_LIBDECOR OR OPTION_ALLOW_GTK_PLUGIN))
+    add_custom_command(
+      OUTPUT gtk-shell-protocol.c gtk-shell-client-protocol.h
+      COMMAND wayland-scanner private-code ${CMAKE_CURRENT_SOURCE_DIR}/../libdecor/build/gtk-shell.xml gtk-shell-protocol.c
+      COMMAND wayland-scanner client-header ${CMAKE_CURRENT_SOURCE_DIR}/../libdecor/build/gtk-shell.xml gtk-shell-client-protocol.h
+      DEPENDS ${CMAKE_CURRENT_SOURCE_DIR}/../libdecor/build/gtk-shell.xml
+      VERBATIM
+    )
+    list (APPEND STATIC_FILES "gtk-shell-protocol.c")
+    list (APPEND SHARED_FILES "gtk-shell-protocol.c")
+  endif (GTK_FOUND AND (OPTION_USE_SYSTEM_LIBDECOR OR OPTION_ALLOW_GTK_PLUGIN))
   add_custom_command(
     OUTPUT text-input-protocol.c text-input-client-protocol.h
     COMMAND wayland-scanner private-code ${PROTOCOLS}/unstable/text-input/text-input-unstable-v3.xml text-input-protocol.c
diff --git a/src/drivers/Wayland/Fl_Wayland_Window_Driver.cxx b/src/drivers/Wayland/Fl_Wayland_Window_Driver.cxx
index 83865878a..9082acf51 100644
--- a/src/drivers/Wayland/Fl_Wayland_Window_Driver.cxx
+++ b/src/drivers/Wayland/Fl_Wayland_Window_Driver.cxx
@@ -1792,25 +1792,6 @@ int Fl_Wayland_Window_Driver::set_cursor_4args(const Fl_RGB_Image *rgb, int hotx
 }
 
 
-#if defined(USE_SYSTEM_LIBDECOR) && USE_SYSTEM_LIBDECOR
-// This is only to fix a bug in libdecor where what libdecor_frame_set_min_content_size()
-// does is often destroyed by libdecor-cairo.
-static void delayed_minsize(Fl_Window *win) {
-  struct wld_window *wl_win = fl_wl_xid(win);
-  Fl_Window_Driver *driver = Fl_Window_Driver::driver(win);
-  if (wl_win->kind == Fl_Wayland_Window_Driver::DECORATED) {
-    float f = Fl::screen_scale(win->screen_num());
-    libdecor_frame_set_min_content_size(wl_win->frame, driver->minw()*f, driver->minh()*f);
-  }
-  bool need_resize = false;
-  int W = win->w(), H = win->h();
-  if (W < driver->minw()) { W = driver->minw(); need_resize = true; }
-  if (H < driver->minh()) { H = driver->minh(); need_resize = true; }
-  if (need_resize) win->size(W, H);
-}
-#endif
-
-
 void Fl_Wayland_Window_Driver::resize(int X, int Y, int W, int H) {
   struct wld_window *fl_win = fl_wl_xid(pWindow);
   if (fl_win && fl_win->kind == DECORATED && !xdg_toplevel()) {
@@ -1890,11 +1871,6 @@ void Fl_Wayland_Window_Driver::resize(int X, int Y, int W, int H) {
         xdg_surface_set_window_geometry(fl_win->xdg_surface, 0, 0, W, H);
         //printf("xdg_surface_set_window_geometry: %dx%d\n",W, H);
       }
-#if defined(USE_SYSTEM_LIBDECOR) && USE_SYSTEM_LIBDECOR
-      if (W < minw() || H < minh()) {
-        Fl::add_timeout(0.01, (Fl_Timeout_Handler)delayed_minsize, pWindow);
-      }
-#endif
     } else {
       if (!in_handle_configure && xdg_toplevel()) {
         // Wayland doesn't seem to provide a reliable way for the app to set the