Allow libdecor package version ≥ 0.2.0 with FLTK_USE_SYSTEM_LIBDECOR

CMake/options.cmake

@@ -297,7 +297,7 @@ if(UNIX)
     endif()
     unset(FLTK_GRAPHICS_CAIRO CACHE)
     set(FLTK_GRAPHICS_CAIRO TRUE CACHE BOOL "all drawing to X11 windows uses Cairo")
-    option(FLTK_USE_SYSTEM_LIBDECOR "use libdecor from the system" OFF)
+    option(FLTK_USE_SYSTEM_LIBDECOR "use libdecor from the system" ON)
     set(USE_SYSTEM_LIBDECOR 1)
     unset(FLTK_USE_XRENDER CACHE)
     unset(FLTK_USE_XINERAMA CACHE)
@@ -333,9 +333,9 @@ if(UNIX)
     unset(FLTK_USE_PANGO CACHE)
     set(FLTK_USE_PANGO TRUE CACHE BOOL "use lib Pango")
     if(FLTK_USE_SYSTEM_LIBDECOR)
-      pkg_check_modules(SYSTEM_LIBDECOR IMPORTED_TARGET libdecor-0>0.2.2 QUIET)
+      pkg_check_modules(SYSTEM_LIBDECOR libdecor-0>=0.2.0 QUIET)
       if(NOT SYSTEM_LIBDECOR_FOUND)
-        message(STATUS "Warning: system libdecor doesn't satisfy version > 0.2.2,")
+        message(STATUS "Warning: system libdecor doesn't satisfy version ≥ 0.2.0,")
         message(STATUS "         using bundled libdecor library instead.")
         set(USE_SYSTEM_LIBDECOR 0)
       else()

README.CMake.txt

@@ -282,12 +282,10 @@ FLTK_USE_PTHREADS - default ON except on Windows.
     This option is ignored (switched OFF internally) on Windows except
     when using Cygwin.
 
-FLTK_USE_SYSTEM_LIBDECOR - default OFF (Wayland only)
+FLTK_USE_SYSTEM_LIBDECOR - default ON (Wayland only)
     This option makes FLTK use package libdecor-0-dev to draw window titlebars
-    under Wayland. When OFF or when this package has a version ≤ 0.2.2, FLTK
+    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 early 2024, no version > 0.2.2 of package libdecor-0-dev is available
-    yet.
 
 FLTK_USE_SYSTEM_LIBJPEG - default ON (macOS and Windows: OFF)
 FLTK_USE_SYSTEM_LIBPNG  - default ON (macOS and Windows: OFF)

README.Wayland.txt

@@ -126,8 +126,9 @@ 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). 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 a version > 0.2.2 of these packages that's not yet available.
-Therefore, FLTK uses a copy of libdecor bundled in the FLTK source code.
+FLTK requires version 0.2.0 or more recent of these packages.
+When libdecor is not available or not recent enough, 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.

configure.ac

@@ -1092,7 +1092,7 @@ AS_CASE([$host_os_gui], [cygwin* | mingw*], [
        BUILD="WAYLANDX11"
        graphics="Wayland or X11 with cairo"
        ])
-      AS_IF([$PKGCONFIG --exists 'libdecor-0 > 0.2.2'],
+      AS_IF([$PKGCONFIG --exists 'libdecor-0 >= 0.2.0'],
       [
         plugin_dir="$($PKGCONFIG --variable=libdir libdecor-0)/libdecor/plugins-1"
         CFLAGS="$CFLAGS -DUSE_SYSTEM_LIBDECOR"

documentation/src/wayland.dox

@@ -1108,16 +1108,13 @@ Desktop. As of late 2023, libdecor 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 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
+On recent Linux distributions, FLTK uses the system \c libdecor shared library
+available via packages \c libdecor-0-dev and \c libdecor-0-plugin-1-gtk.
+On earlier Linux versions, or if CMake option \c FLTK_USE_SYSTEM_LIBDECOR is set
+to OFF, 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 early 2024, libdecor version 0.2.2 is available in very recent Linux distributions.
-This version is not binary compatible with the libdecor version bundled by FLTK.
-For this reason, CMake option \c FLTK_USE_SYSTEM_LIBDECOR is OFF by default, and
-FLTK uses the bundled \c libdecor copy to draw titlebars.
-
 \c Libdecor uses the Wayland protocol
 <a href=https://wayland.app/protocols/xdg-decoration-unstable-v1>XDG decoration</a>
 to request being decorated by a supporting compositor.

libdecor/build/fl_libdecor-plugins.c

@@ -317,13 +317,34 @@ struct libdecor { // copied from libdecor.c, for libdecor versions > 0.2.2
   struct wl_list frames;
 };
 
+struct libdecor_022 { // for libdecor versions ≤ 0.2.2
+  int ref_count;
+  const struct libdecor_interface *iface;
+  struct libdecor_plugin *plugin;
+  bool plugin_ready;
+  struct wl_display *wl_display;
+  struct wl_registry *wl_registry;
+  struct xdg_wm_base *xdg_wm_base;
+  struct zxdg_decoration_manager_v1 *decoration_manager;
+  struct wl_callback *init_callback;
+  bool init_done;
+  bool has_error;
+  struct wl_list frames;
+};
+
 
 /* Returns whether surface is a GTK-titlebar created by libdecor-gtk */
-bool fl_is_surface_gtk_titlebar(struct wl_surface *surface, struct libdecor *context) {
+bool fl_is_surface_gtk_titlebar(struct wl_surface *surface, struct libdecor *context,
+                                struct wl_display *wl_display) {
   if (!context || get_plugin_kind(NULL) != GTK3) return false;
   // loop over all decorations created by libdecor-gtk
   struct libdecor_frame *frame;
-  wl_list_for_each(frame, &context->frames, link) {
+  struct wl_list *frames;
+  if (context->wl_display == wl_display) frames = &context->frames;
+  else if (((struct libdecor_022*)context)->wl_display == wl_display)
+    frames = &(((struct libdecor_022*)context)->frames);
+  else return false;
+  wl_list_for_each(frame, frames, link) {
     struct libdecor_frame_gtk *frame_gtk = (struct libdecor_frame_gtk*)frame;
     if (frame_gtk->headerbar.wl_surface == surface) return true;
   }

src/CMakeLists.txt

@@ -756,7 +756,7 @@ if(UNIX AND FLTK_BACKEND_WAYLAND)
     list(APPEND OPTIONAL_LIBS PkgConfig::WLD_EGL PkgConfig::PKG_EGL)
   endif(FLTK_USE_GL)
   if(USE_SYSTEM_LIBDECOR)
-    list(APPEND OPTIONAL_LIBS PkgConfig::SYSTEM_LIBDECOR)
+    list(APPEND OPTIONAL_LIBS ${SYSTEM_LIBDECOR_LDFLAGS})
   elseif(GTK_FOUND AND FLTK_USE_LIBDECOR_GTK)
       list(APPEND OPTIONAL_LIBS PkgConfig::GTK)
   endif(USE_SYSTEM_LIBDECOR)

src/drivers/Wayland/Fl_Wayland_Screen_Driver.cxx

@@ -47,7 +47,7 @@
 #include <string.h> // for strerror()
 extern "C" {
   bool libdecor_get_cursor_settings(char **theme, int *size);
-  bool fl_is_surface_gtk_titlebar(struct wl_surface *, struct libdecor *);
+  bool fl_is_surface_gtk_titlebar(struct wl_surface *, struct libdecor *, struct wl_display *);
 }
 
 // set this to 1 for keyboard debug output, 0 for no debug output
@@ -206,7 +206,8 @@ static void pointer_enter(void *data, struct wl_pointer *wl_pointer, uint32_t se
   Fl_Window *win = event_coords_from_surface(surface, surface_x, surface_y);
   if (!win && gtk_shell) { // check that surface is the headerbar of a GTK-decorated window
     Fl_Wayland_Screen_Driver *scr_driver = (Fl_Wayland_Screen_Driver*)Fl::screen_driver();
-    if (fl_is_surface_gtk_titlebar(surface, scr_driver->libdecor_context)) {
+    if (fl_is_surface_gtk_titlebar(surface, scr_driver->libdecor_context,
+                                   Fl_Wayland_Screen_Driver::wl_display)) {
       gtk_shell_surface = surface;
     }
   }

src/drivers/Wayland/Fl_Wayland_Window_Driver.cxx

@@ -769,6 +769,69 @@ static struct Fl_Wayland_Screen_Driver::output *screen_num_to_output(int num_scr
 }
 
 
+#define LIBDECOR_MR131 1 // this means libdecor does not include MR!131 yet
+
+#ifdef LIBDECOR_MR131
+/* === Beginning of hack that would become un-needed if libdecor accepted MR!131 === */
+
+// true while the GUI is interactively resizing a decorated window
+static bool in_decorated_window_resizing = false;
+
+
+// libdecor's configure cb function for xdg_toplevel objects
+static void (*decor_xdg_toplevel_configure)(void*, struct xdg_toplevel *, int32_t,
+                                            int32_t, struct wl_array *);
+
+
+static void fltk_xdg_toplevel_configure(void *user_data, struct xdg_toplevel *xdg_toplevel,
+                                        int32_t width, int32_t height,
+                                        struct wl_array *states) {
+  uint32_t *p;
+  in_decorated_window_resizing = false;
+  // Replace wl_array_for_each(p, states) rejected by C++
+  for (p = (uint32_t *)(states)->data;
+      (const char *) p < ((const char *) (states)->data + (states)->size);
+      (p)++) {
+    if (*p == XDG_TOPLEVEL_STATE_RESIZING) {
+      in_decorated_window_resizing = true;
+      break;
+    }
+  }
+  decor_xdg_toplevel_configure(user_data, xdg_toplevel, width, height, states);
+}
+
+
+struct wl_object { // copied from wayland-private.h
+  const struct wl_interface *interface;
+  const void *implementation;
+  uint32_t id;
+};
+
+
+// replace libdecor's toplevel configure cb by FLTK's
+static void use_FLTK_toplevel_configure_cb(struct libdecor_frame *frame) {
+  struct wl_object *object = (struct wl_object *)libdecor_frame_get_xdg_toplevel(frame);
+  static struct xdg_toplevel_listener *fltk_listener = NULL;
+  if (!fltk_listener) {
+    struct xdg_toplevel_listener *decor_listener = (struct xdg_toplevel_listener*)
+        object->implementation;
+    fltk_listener = (struct xdg_toplevel_listener*)
+        malloc(sizeof(struct xdg_toplevel_listener));
+    // initialize FLTK's listener with libdecor's values
+    *fltk_listener = *decor_listener;
+    // memorize libdecor's toplevel configure cb
+    decor_xdg_toplevel_configure = decor_listener->configure;
+    // replace libdecor's toplevel configure cb by FLTK's
+    fltk_listener->configure = fltk_xdg_toplevel_configure;
+  }
+  // replace the toplevel listener by a copy whose configure member is FLTK's
+  object->implementation = fltk_listener;
+}
+
+/* === End of hack that would become un-needed if libdecor accepted MR!131 === */
+#endif // LIBDECOR_MR131
+
+
 static void handle_configure(struct libdecor_frame *frame,
      struct libdecor_configuration *configuration, void *user_data)
 {
@@ -786,6 +849,9 @@ static void handle_configure(struct libdecor_frame *frame,
 
   if (!window->xdg_surface) window->xdg_surface = libdecor_frame_get_xdg_surface(frame);
 
+#ifdef LIBDECOR_MR131
+  if (is_1st_run) use_FLTK_toplevel_configure_cb(frame);
+#endif
   struct wl_output *wl_output = NULL;
   if (window->fl_win->fullscreen_active()) {
     if (!(window->state & LIBDECOR_WINDOW_STATE_FULLSCREEN)) {
@@ -839,7 +905,10 @@ static void handle_configure(struct libdecor_frame *frame,
     //fprintf(stderr,"handle_configure: using floating %dx%d\n",width,height);
   }
 
-  bool condition = (window->state & LIBDECOR_WINDOW_STATE_RESIZING);
+#ifndef LIBDECOR_MR131
+  bool in_decorated_window_resizing = (window->state & LIBDECOR_WINDOW_STATE_RESIZING);
+#endif
+  bool condition = in_decorated_window_resizing;
   if (condition) { // see issue #878
     condition = (window->covered ? (window->buffer && window->buffer->in_use) : (window->frame_cb != NULL));
   }