Add XSETTINGS support to x11 driver

Import the XSettingsClient implementation to handle the settings
selection.

Currently, we only care about the Gdk/WindowScalingFactor value used by
the windowing system to notify us of display-wide changes in the scaling
factor.

cmake/3rdparty.cmake

@@ -104,7 +104,10 @@ function(get_clang_tidy_ignored_files OUTVAR)
       "hid.m"
       "hidraw.cpp"
       "hidusb.cpp"
-      "hidapi.h")
+      "hidapi.h"
+      # XSETTINGS
+      "xsettings-client.c"
+      "xsettings-client.h")
 
   foreach(SOURCE_FILE ${3RD_PARTY_SOURCES})
     list(APPEND IGNORED_LIST "{\"name\":\"${SOURCE_FILE}\",\"lines\":[[1,1]]}")

src/video/x11/SDL_x11events.c

@@ -33,6 +33,7 @@
 #include "SDL_x11touch.h"
 #include "SDL_x11xinput2.h"
 #include "SDL_x11xfixes.h"
+#include "SDL_x11settings.h"
 #include "../SDL_clipboard_c.h"
 #include "../../core/unix/SDL_poll.h"
 #include "../../events/SDL_events_c.h"
@@ -779,6 +780,16 @@ static void X11_HandleClipboardEvent(SDL_VideoDevice *_this, const XEvent *xeven
     }
 }
 
+static void X11_HandleSettingsEvent(SDL_VideoDevice *_this, const XEvent *xevent)
+{
+    SDL_VideoData *videodata = _this->driverdata;
+
+    SDL_assert(videodata->xsettings_window != None);
+    SDL_assert(xevent->xany.window == videodata->xsettings_window);
+
+    X11_HandleXsettings(_this, xevent);
+}
+
 static Bool isMapNotify(Display *display, XEvent *ev, XPointer arg)
 {
     XUnmapEvent *unmap;
@@ -1103,6 +1114,12 @@ static void X11_DispatchEvent(SDL_VideoDevice *_this, XEvent *xevent)
         return;
     }
 
+    if ((videodata->xsettings_window != None) &&
+        (videodata->xsettings_window == xevent->xany.window)) {
+        X11_HandleSettingsEvent(_this, xevent);
+        return;
+    }
+
     data = X11_FindWindow(_this, xevent->xany.window);
 
     if (!data) {

src/video/x11/SDL_x11settings.c

@@ -0,0 +1,97 @@
+/*
+  Simple DirectMedia Layer
+  Copyright 2024 Igalia S.L.
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+*/
+
+#include "SDL_internal.h"
+
+#if defined(SDL_VIDEO_DRIVER_X11)
+
+#include "SDL_x11video.h"
+#include "SDL_x11settings.h"
+
+#define SDL_XSETTINGS_GDK_WINDOW_SCALING_FACTOR "Gdk/WindowScalingFactor"
+
+static void X11_XsettingsNotify(const char *name, XSettingsAction action, XSettingsSetting *setting, void *data)
+{
+    SDL_VideoDevice *_this = data;
+    float scale_factor = 1.0;
+    int i;
+
+    if (SDL_strcmp(name, SDL_XSETTINGS_GDK_WINDOW_SCALING_FACTOR) != 0) {
+        return;
+    }
+
+    if (setting->type != XSETTINGS_TYPE_INT) {
+        return;
+    }
+
+    switch (action) {
+    case XSETTINGS_ACTION_NEW:
+        SDL_FALLTHROUGH;
+    case XSETTINGS_ACTION_CHANGED:
+        scale_factor = setting->data.v_int;
+        break;
+    case XSETTINGS_ACTION_DELETED:
+        scale_factor = 1.0;
+        break;
+    }
+
+    if (_this) {
+        for (i = 0; i < _this->num_displays; ++i) {
+            SDL_SetDisplayContentScale(_this->displays[i], scale_factor);
+        }
+    }
+}
+
+void X11_InitXsettings(SDL_VideoDevice *_this)
+{
+    SDL_VideoData *data = _this->driverdata;
+    SDLX11_SettingsData *xsettings_data = &data->xsettings_data;
+
+    xsettings_data->xsettings = xsettings_client_new(data->display,
+        DefaultScreen(data->display), X11_XsettingsNotify, NULL, _this);
+
+}
+
+void X11_QuitXsettings(SDL_VideoDevice *_this)
+{
+    SDL_VideoData *data = _this->driverdata;
+    SDLX11_SettingsData *xsettings_data = &data->xsettings_data;
+
+    if (xsettings_data->xsettings) {
+        xsettings_client_destroy(xsettings_data->xsettings);
+        xsettings_data->xsettings = NULL;
+    }
+}
+
+void X11_HandleXsettings(SDL_VideoDevice *_this, const XEvent *xevent)
+{
+    SDL_VideoData *data = _this->driverdata;
+    SDLX11_SettingsData *xsettings_data = &data->xsettings_data;
+
+    if (xsettings_data->xsettings) {
+        if (!xsettings_client_process_event(xsettings_data->xsettings, xevent)) {
+            xsettings_client_destroy(xsettings_data->xsettings);
+            xsettings_data->xsettings = NULL;
+        }
+    }
+}
+
+#endif /* SDL_VIDEO_DRIVER_X11 */

src/video/x11/SDL_x11settings.h

@@ -0,0 +1,38 @@
+/*
+  Simple DirectMedia Layer
+  Copyright 2024 Igalia S.L.
+
+  This software is provided 'as-is', without any express or implied
+  warranty.  In no event will the authors be held liable for any damages
+  arising from the use of this software.
+
+  Permission is granted to anyone to use this software for any purpose,
+  including commercial applications, and to alter it and redistribute it
+  freely, subject to the following restrictions:
+
+  1. The origin of this software must not be misrepresented; you must not
+     claim that you wrote the original software. If you use this software
+     in a product, an acknowledgment in the product documentation would be
+     appreciated but is not required.
+  2. Altered source versions must be plainly marked as such, and must not be
+     misrepresented as being the original software.
+  3. This notice may not be removed or altered from any source distribution.
+*/
+
+#include "SDL_internal.h"
+
+#ifndef SDL_x11settings_h_
+#define SDL_x11settings_h_
+
+#include <X11/Xlib.h>
+#include "xsettings-client.h"
+
+typedef struct X11_SettingsData {
+    XSettingsClient *xsettings;
+} SDLX11_SettingsData;
+
+extern void X11_InitXsettings(SDL_VideoDevice *_this);
+extern void X11_QuitXsettings(SDL_VideoDevice *_this);
+extern void X11_HandleXsettings(SDL_VideoDevice *_this, const XEvent *xevent);
+
+#endif /* SDL_x11settings_h_ */

src/video/x11/SDL_x11video.c

@@ -443,6 +443,8 @@ int X11_VideoInit(SDL_VideoDevice *_this)
     X11_InitXfixes(_this);
 #endif /* SDL_VIDEO_DRIVER_X11_XFIXES */
 
+    X11_InitXsettings(_this);
+
 #ifndef X_HAVE_UTF8_STRING
 #warning X server does not support UTF8_STRING, a feature introduced in 2000! This is likely to become a hard error in a future libSDL3.
 #endif
@@ -469,6 +471,10 @@ void X11_VideoQuit(SDL_VideoDevice *_this)
         X11_XDestroyWindow(data->display, data->clipboard_window);
     }
 
+    if (data->xsettings_window) {
+        X11_XDestroyWindow(data->display, data->xsettings_window);
+    }
+
 #ifdef X_HAVE_UTF8_STRING
     if (data->im) {
         X11_XCloseIM(data->im);
@@ -480,6 +486,7 @@ void X11_VideoQuit(SDL_VideoDevice *_this)
     X11_QuitMouse(_this);
     X11_QuitTouch(_this);
     X11_QuitClipboard(_this);
+    X11_QuitXsettings(_this);
 }
 
 SDL_bool X11_UseDirectColorVisuals(void)

src/video/x11/SDL_x11video.h

@@ -36,6 +36,7 @@
 #include "SDL_x11modes.h"
 #include "SDL_x11mouse.h"
 #include "SDL_x11opengl.h"
+#include "SDL_x11settings.h"
 #include "SDL_x11window.h"
 #include "SDL_x11vulkan.h"
 
@@ -58,6 +59,8 @@ struct SDL_VideoData
 #ifdef SDL_VIDEO_DRIVER_X11_XFIXES
     SDL_Window *active_cursor_confined_window;
 #endif /* SDL_VIDEO_DRIVER_X11_XFIXES */
+    Window xsettings_window;
+    SDLX11_SettingsData xsettings_data;
 
     /* This is true for ICCCM2.0-compliant window managers */
     SDL_bool net_wm;

src/video/x11/xsettings-client.h

@@ -0,0 +1,153 @@
+/*
+ * Copyright © 2001, 2007 Red Hat, Inc.
+ * Copyright 2024 Igalia S.L.
+ *
+ * Permission to use, copy, modify, distribute, and sell this software and its
+ * documentation for any purpose is hereby granted without fee, provided that
+ * the above copyright notice appear in all copies and that both that
+ * copyright notice and this permission notice appear in supporting
+ * documentation, and that the name of Red Hat not be used in advertising or
+ * publicity pertaining to distribution of the software without specific,
+ * written prior permission.  Red Hat makes no representations about the
+ * suitability of this software for any purpose.  It is provided "as is"
+ * without express or implied warranty.
+ *
+ * RED HAT DISCLAIMS ALL WARRANTIES WITH REGARD TO THIS SOFTWARE, INCLUDING ALL
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS, IN NO EVENT SHALL RED HAT
+ * BE LIABLE FOR ANY SPECIAL, INDIRECT OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
+ * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
+ * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
+ * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
+ *
+ * Author:  Owen Taylor, Red Hat, Inc.
+ */
+#ifndef XSETTINGS_CLIENT_H
+#define XSETTINGS_CLIENT_H
+
+#ifdef __cplusplus
+extern "C" {
+#endif /* __cplusplus */
+
+typedef struct _XSettingsBuffer  XSettingsBuffer;
+typedef struct _XSettingsColor   XSettingsColor;
+typedef struct _XSettingsList    XSettingsList;
+typedef struct _XSettingsSetting XSettingsSetting;
+
+/* Types of settings possible. Enum values correspond to
+ * protocol values.
+ */
+typedef enum
+{
+  XSETTINGS_TYPE_INT     = 0,
+  XSETTINGS_TYPE_STRING  = 1,
+  XSETTINGS_TYPE_COLOR   = 2
+} XSettingsType;
+
+typedef enum
+{
+  XSETTINGS_SUCCESS,
+  XSETTINGS_NO_MEM,
+  XSETTINGS_ACCESS,
+  XSETTINGS_FAILED,
+  XSETTINGS_NO_ENTRY,
+  XSETTINGS_DUPLICATE_ENTRY
+} XSettingsResult;
+
+struct _XSettingsBuffer
+{
+  char byte_order;
+  size_t len;
+  unsigned char *data;
+  unsigned char *pos;
+};
+
+struct _XSettingsColor
+{
+  unsigned short red, green, blue, alpha;
+};
+
+struct _XSettingsList
+{
+  XSettingsSetting *setting;
+  XSettingsList *next;
+};
+
+struct _XSettingsSetting
+{
+  char *name;
+  XSettingsType type;
+
+  union {
+    int v_int;
+    char *v_string;
+    XSettingsColor v_color;
+  } data;
+
+  unsigned long last_change_serial;
+};
+
+XSettingsSetting *xsettings_setting_copy  (XSettingsSetting *setting);
+void              xsettings_setting_free  (XSettingsSetting *setting);
+int               xsettings_setting_equal (XSettingsSetting *setting_a,
+                                           XSettingsSetting *setting_b);
+
+void              xsettings_list_free   (XSettingsList     *list);
+XSettingsList    *xsettings_list_copy   (XSettingsList     *list);
+XSettingsResult   xsettings_list_insert (XSettingsList    **list,
+                                         XSettingsSetting  *setting);
+XSettingsSetting *xsettings_list_lookup (XSettingsList     *list,
+                                         const char        *name);
+XSettingsResult   xsettings_list_delete (XSettingsList    **list,
+                                         const char        *name);
+
+char xsettings_byte_order (void);
+
+#define XSETTINGS_PAD(n,m) ((n + m - 1) & (~(m-1)))
+
+typedef struct _XSettingsClient XSettingsClient;
+
+typedef enum
+{
+  XSETTINGS_ACTION_NEW,
+  XSETTINGS_ACTION_CHANGED,
+  XSETTINGS_ACTION_DELETED
+} XSettingsAction;
+
+typedef void (*XSettingsNotifyFunc) (const char       *name,
+                                     XSettingsAction   action,
+                                     XSettingsSetting *setting,
+                                     void             *cb_data);
+typedef Bool (*XSettingsWatchFunc)  (Window            window,
+                                     Bool              is_start,
+                                     long              mask,
+                                     void             *cb_data);
+typedef void (*XSettingsGrabFunc)   (Display          *display);
+
+XSettingsClient *xsettings_client_new             (Display             *display,
+                                                   int                  screen,
+                                                   XSettingsNotifyFunc  notify,
+                                                   XSettingsWatchFunc   watch,
+                                                   void                *cb_data);
+XSettingsClient *xsettings_client_new_with_grab_funcs (Display             *display,
+                                                       int                  screen,
+                                                       XSettingsNotifyFunc  notify,
+                                                       XSettingsWatchFunc   watch,
+                                                       void                *cb_data,
+                                                       XSettingsGrabFunc    grab,
+                                                       XSettingsGrabFunc    ungrab);
+void             xsettings_client_set_grab_func   (XSettingsClient     *client,
+                                                   XSettingsGrabFunc    grab);
+void             xsettings_client_set_ungrab_func (XSettingsClient     *client,
+                                                   XSettingsGrabFunc    ungrab);
+void             xsettings_client_destroy         (XSettingsClient     *client);
+Bool             xsettings_client_process_event   (XSettingsClient     *client,
+                                                   const XEvent        *xev);
+XSettingsResult  xsettings_client_get_setting     (XSettingsClient     *client,
+                                                   const char          *name,
+                                                   XSettingsSetting   **setting);
+
+#ifdef __cplusplus
+}
+#endif /* __cplusplus */
+
+#endif /* XSETTINGS_CLIENT_H */