Add portal interface to support `SDL_GetSystemTheme` in linux

CMakeLists.txt

@@ -1552,6 +1552,7 @@ elseif(UNIX AND NOT APPLE AND NOT RISCOS AND NOT HAIKU)
 
     if(HAVE_DBUS_DBUS_H)
       list(APPEND SOURCE_FILES "${SDL3_SOURCE_DIR}/src/core/linux/SDL_dbus.c")
+      list(APPEND SOURCE_FILES "${SDL3_SOURCE_DIR}/src/core/linux/SDL_system_theme.c")
     endif()
 
     if(SDL_USE_IME)

src/core/linux/SDL_system_theme.c

@@ -0,0 +1,175 @@
+/*
+  Simple DirectMedia Layer
+  Copyright (C) 1997-2023 Sam Lantinga <slouken@libsdl.org>
+
+  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"
+
+#include "SDL_dbus.h"
+#include "SDL_system_theme.h"
+#include "../SDL_sysvideo.h"
+
+#include <unistd.h>
+
+#define PORTAL_DESTINATION "org.freedesktop.portal.Desktop"
+#define PORTAL_PATH "/org/freedesktop/portal/desktop"
+#define PORTAL_INTERFACE "org.freedesktop.portal.Settings"
+#define PORTAL_METHOD "Read"
+
+#define SIGNAL_INTERFACE "org.freedesktop.portal.Settings"
+#define SIGNAL_NAMESPACE "org.freedesktop.appearance"
+#define SIGNAL_NAME "SettingChanged"
+#define SIGNAL_KEY "color-scheme"
+
+typedef struct SystemThemeData
+{
+    SDL_DBusContext *dbus;
+    SDL_SystemTheme theme;
+} SystemThemeData;
+
+static SystemThemeData system_theme_data;
+
+static SDL_bool
+DBus_ExtractThemeVariant(DBusMessageIter *iter, SDL_SystemTheme *theme) {
+    SDL_DBusContext *dbus = system_theme_data.dbus;
+    Uint32 color_scheme;
+    DBusMessageIter variant_iter;
+
+    if (dbus->message_iter_get_arg_type(iter) != DBUS_TYPE_VARIANT)
+        return SDL_FALSE;
+    dbus->message_iter_recurse(iter, &variant_iter);
+    if (dbus->message_iter_get_arg_type(&variant_iter) != DBUS_TYPE_UINT32)
+        return SDL_FALSE;
+    dbus->message_iter_get_basic(&variant_iter, &color_scheme);
+    switch (color_scheme) {
+        case 0:
+            *theme = SDL_SYSTEM_THEME_UNKNOWN;
+            break;
+        case 1:
+            *theme = SDL_SYSTEM_THEME_DARK;
+            break;
+        case 2:
+            *theme = SDL_SYSTEM_THEME_LIGHT;
+            break;
+    }
+    return SDL_TRUE;
+}
+
+static DBusHandlerResult
+DBus_MessageFilter(DBusConnection *conn, DBusMessage *msg, void *data) {
+    SDL_DBusContext *dbus = (SDL_DBusContext *)data;
+
+    if (dbus->message_is_signal(msg, SIGNAL_INTERFACE, SIGNAL_NAME)) {
+        DBusMessageIter signal_iter;
+        const char *namespace, *key;
+
+        dbus->message_iter_init(msg, &signal_iter);
+        /* Check if the parameters are what we expect */
+        if (dbus->message_iter_get_arg_type(&signal_iter) != DBUS_TYPE_STRING)
+            goto not_our_signal;
+        dbus->message_iter_get_basic(&signal_iter, &namespace);
+        if (SDL_strcmp(SIGNAL_NAMESPACE, namespace) != 0)
+            goto not_our_signal;
+
+        if (!dbus->message_iter_next(&signal_iter))
+            goto not_our_signal;
+
+        if (dbus->message_iter_get_arg_type(&signal_iter) != DBUS_TYPE_STRING)
+            goto not_our_signal;
+        dbus->message_iter_get_basic(&signal_iter, &key);
+        if (SDL_strcmp(SIGNAL_KEY, key) != 0)
+            goto not_our_signal;
+
+        if (!dbus->message_iter_next(&signal_iter))
+            goto not_our_signal;
+
+        if (!DBus_ExtractThemeVariant(&signal_iter, &system_theme_data.theme))
+            goto not_our_signal;
+
+        SDL_SetSystemTheme(system_theme_data.theme);
+        return DBUS_HANDLER_RESULT_HANDLED;
+    }
+not_our_signal:
+    return DBUS_HANDLER_RESULT_NOT_YET_HANDLED;
+}
+
+SDL_bool
+SDL_SystemTheme_Init(void)
+{
+    SDL_DBusContext *dbus = SDL_DBus_GetContext();
+    DBusMessage *msg;
+    static const char *namespace = SIGNAL_NAMESPACE;
+    static const char *key = SIGNAL_KEY;
+    
+    system_theme_data.theme = SDL_SYSTEM_THEME_UNKNOWN;
+    system_theme_data.dbus = dbus;
+    if (dbus == NULL) {
+        return SDL_FALSE;
+    }
+
+    msg = dbus->message_new_method_call(PORTAL_DESTINATION, PORTAL_PATH, PORTAL_INTERFACE, PORTAL_METHOD);
+    if (msg != NULL) {
+        if (dbus->message_append_args(msg, DBUS_TYPE_STRING, &namespace, DBUS_TYPE_STRING, &key, DBUS_TYPE_INVALID)) {
+            DBusMessage *reply = dbus->connection_send_with_reply_and_block(dbus->session_conn, msg, 300, NULL);
+            if (reply) {
+                DBusMessageIter reply_iter, variant_outer_iter;
+
+                dbus->message_iter_init(reply, &reply_iter);
+                /* The response has signature <<u>> */
+                if (dbus->message_iter_get_arg_type(&reply_iter) != DBUS_TYPE_VARIANT)
+                    goto incorrect_type;
+                dbus->message_iter_recurse(&reply_iter, &variant_outer_iter);
+                if (!DBus_ExtractThemeVariant(&variant_outer_iter, &system_theme_data.theme))
+                    goto incorrect_type;
+incorrect_type:
+                dbus->message_unref(reply);
+            }
+        }
+        dbus->message_unref(msg);
+    }
+
+    dbus->bus_add_match(dbus->session_conn,
+                        "type='signal', interface='"SIGNAL_INTERFACE"',"
+                        "member='"SIGNAL_NAME"', arg0='"SIGNAL_NAMESPACE"',"
+                        "arg1='"SIGNAL_KEY"'", NULL);
+    dbus->connection_add_filter(dbus->session_conn,
+                                &DBus_MessageFilter, dbus, NULL);
+    dbus->connection_flush(dbus->session_conn);
+    return SDL_TRUE;
+}
+
+SDL_SystemTheme
+SDL_SystemTheme_Get(void)
+{
+    return system_theme_data.theme;
+}
+
+void
+SDL_SystemTheme_PumpEvents(void)
+{
+    SDL_DBusContext *dbus = system_theme_data.dbus;
+    DBusConnection *conn;
+    if (dbus == NULL) return;
+    conn = dbus->session_conn;
+    dbus->connection_read_write(conn, 0);
+
+    while (dbus->connection_dispatch(conn) == DBUS_DISPATCH_DATA_REMAINS) {
+        /* Do nothing, actual work happens in DBus_MessageFilter */
+        usleep(10);
+    }
+}

src/core/linux/SDL_system_theme.h

@@ -0,0 +1,31 @@
+/*
+  Simple DirectMedia Layer
+  Copyright (C) 1997-2023 Sam Lantinga <slouken@libsdl.org>
+
+  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.
+*/
+
+#ifndef SDL_system_theme_h_
+#define SDL_system_theme_h_
+
+#include "SDL_internal.h"
+
+extern SDL_bool SDL_SystemTheme_Init(void);
+extern SDL_SystemTheme SDL_SystemTheme_Get(void);
+extern void SDL_SystemTheme_PumpEvents(void);
+
+#endif /* SDL_system_theme_h_ */

src/video/wayland/SDL_waylandevents.c

@@ -26,6 +26,7 @@
 #include "../../core/unix/SDL_poll.h"
 #include "../../events/SDL_events_c.h"
 #include "../../events/SDL_scancode_tables_c.h"
+#include "../../core/linux/SDL_system_theme.h"
 #include "../SDL_sysvideo.h"
 
 #include "SDL_waylandvideo.h"
@@ -386,6 +387,10 @@ int Wayland_WaitEventTimeout(_THIS, Sint64 timeoutNS)
     }
 #endif
 
+#ifdef SDL_USE_LIBDBUS
+    SDL_SystemTheme_PumpEvents();
+#endif
+
     /* If key repeat is active, we'll need to cap our maximum wait time to handle repeats */
     if (input && keyboard_repeat_is_set(&input->keyboard_repeat)) {
         const Uint64 elapsed = SDL_GetTicksNS() - input->keyboard_repeat.sdl_press_time_ns;
@@ -455,6 +460,10 @@ void Wayland_PumpEvents(_THIS)
     }
 #endif
 
+#ifdef SDL_USE_LIBDBUS
+    SDL_SystemTheme_PumpEvents();
+#endif
+
 #ifdef HAVE_LIBDECOR_H
     if (d->shell.libdecor) {
         libdecor_dispatch(d->shell.libdecor, 0);

src/video/wayland/SDL_waylandvideo.c

@@ -24,6 +24,7 @@
 #if SDL_VIDEO_DRIVER_WAYLAND
 
 #include "../../events/SDL_events_c.h"
+#include "../../core/linux/SDL_system_theme.h"
 
 #include "SDL_waylandvideo.h"
 #include "SDL_waylandevents_c.h"
@@ -249,6 +250,11 @@ static SDL_VideoDevice *Wayland_CreateDevice(void)
     device->FlashWindow = Wayland_FlashWindow;
     device->HasScreenKeyboardSupport = Wayland_HasScreenKeyboardSupport;
 
+#ifdef SDL_USE_LIBDBUS
+    if (SDL_SystemTheme_Init())
+        device->system_theme = SDL_SystemTheme_Get();
+#endif
+
     device->SetClipboardText = Wayland_SetClipboardText;
     device->GetClipboardText = Wayland_GetClipboardText;
     device->HasClipboardText = Wayland_HasClipboardText;

src/video/x11/SDL_x11events.c

@@ -36,6 +36,7 @@
 #include "../../events/SDL_events_c.h"
 #include "../../events/SDL_mouse_c.h"
 #include "../../events/SDL_touch_c.h"
+#include "../../core/linux/SDL_system_theme.h"
 
 #include <SDL3/SDL_syswm.h>
 
@@ -1683,6 +1684,10 @@ int X11_WaitEventTimeout(_THIS, Sint64 timeoutNS)
         SDL_IME_PumpEvents();
     }
 #endif
+
+#ifdef SDL_USE_LIBDBUS
+    SDL_SystemTheme_PumpEvents();
+#endif
     return 1;
 }
 
@@ -1725,6 +1730,10 @@ void X11_PumpEvents(_THIS)
     }
 #endif
 
+#ifdef SDL_USE_LIBDBUS
+    SDL_SystemTheme_PumpEvents();
+#endif
+
     /* FIXME: Only need to do this when there are pending focus changes */
     X11_HandleFocusChanges(_this);
 

src/video/x11/SDL_x11video.c

@@ -26,6 +26,7 @@
 
 #include "../SDL_sysvideo.h"
 #include "../SDL_pixels_c.h"
+#include "../../core/linux/SDL_system_theme.h"
 
 #include "SDL_x11video.h"
 #include "SDL_x11framebuffer.h"
@@ -315,6 +316,11 @@ static SDL_VideoDevice *X11_CreateDevice(void)
     device->Vulkan_CreateSurface = X11_Vulkan_CreateSurface;
 #endif
 
+#ifdef SDL_USE_LIBDBUS
+    if (SDL_SystemTheme_Init())
+        device->system_theme = SDL_SystemTheme_Get();
+#endif
+
     return device;
 }