X11: Add support for MIT XSS

Related to #854.

README.md

@@ -220,6 +220,7 @@ information on what to include when reporting a bug.
 - [Win32] Bugfix: `glfwCreateWindow` activated window even with `GLFW_FOCUSED`
                   hint set to false (#1179,#1180)
 - [X11] Added support for `org.freedesktop.ScreenSaver` (#854)
+- [X11] Added support for the MIT screensaver extension (#854)
 - [X11] Moved to XI2 `XI_RawMotion` for disable cursor mode motion input (#125)
 - [X11] Replaced `_GLFW_HAS_XF86VM` compile-time option with dynamic loading
 - [X11] Bugfix: `glfwGetVideoMode` would segfault on Cygwin/X

src/x11_init.c

@@ -623,6 +623,23 @@ static GLFWbool initExtensions(void)
         }
     }
 
+    _glfw.x11.xss.handle = _glfw_dlopen("libXss.so.1");
+    if (_glfw.x11.xss.handle)
+    {
+        _glfw.x11.xss.QueryExtension = (PFN_XScreenSaverQueryExtension)
+            dlsym(_glfw.x11.xss.handle, "XScreenSaverQueryExtension");
+        _glfw.x11.xss.Suspend = (PFN_XScreenSaverSuspend)
+            dlsym(_glfw.x11.xss.handle, "XScreenSaverSuspend");
+
+        if (XScreenSaverQueryExtension(_glfw.x11.display,
+                                       &_glfw.x11.xss.eventBase,
+                                       &_glfw.x11.xss.errorBase))
+        {
+            _glfw.x11.xss.available = GLFW_TRUE;
+        }
+    }
+
+    // Check if Xkb is supported on this display
     _glfw.x11.xkb.major = 1;
     _glfw.x11.xkb.minor = 0;
     _glfw.x11.xkb.available =

src/x11_platform.h

@@ -126,6 +126,11 @@ typedef XRenderPictFormat* (* PFN_XRenderFindVisualFormat)(Display*,Visual const
 #define XRenderQueryVersion _glfw.x11.xrender.QueryVersion
 #define XRenderFindVisualFormat _glfw.x11.xrender.FindVisualFormat
 
+typedef Bool (* PFN_XScreenSaverQueryExtension)(Display*,int*,int*);
+typedef void (* PFN_XScreenSaverSuspend)(Display*,Bool);
+#define XScreenSaverQueryExtension _glfw.x11.xss.QueryExtension
+#define XScreenSaverSuspend _glfw.x11.xss.Suspend
+
 typedef void (*PFN_dbus_error_init)(DBusError*);
 typedef dbus_bool_t (*PFN_dbus_error_is_set)(const DBusError*);
 typedef DBusConnection* (*PFN_dbus_bus_get_private)(DBusBusType,DBusError*);
@@ -263,6 +268,8 @@ typedef struct _GLFWlibraryX11
     double          restoreCursorPosX, restoreCursorPosY;
     // The window whose disabled cursor mode is active
     _GLFWwindow*    disabledCursorWindow;
+    // The number of full screen windows active on their monitors
+    int             acquiredMonitorCount;
 
     // Window manager atoms
     Atom            WM_PROTOCOLS;
@@ -355,7 +362,6 @@ typedef struct _GLFWlibraryX11
     } xkb;
 
     struct {
-        int         count;
         int         timeout;
         int         interval;
         int         blanking;
@@ -385,6 +391,15 @@ typedef struct _GLFWlibraryX11
         PFN_XineramaQueryScreens QueryScreens;
     } xinerama;
 
+    struct {
+        GLFWbool    available;
+        void*       handle;
+        int         eventBase;
+        int         errorBase;
+        PFN_XScreenSaverQueryExtension QueryExtension;
+        PFN_XScreenSaverSuspend Suspend;
+    } xss;
+
     struct {
         void*       handle;
         PFN_XGetXCBConnection GetXCBConnection;

src/x11_window.c

@@ -1078,18 +1078,20 @@ static const char* getSelectionString(Atom selection)
 //
 static void acquireMonitor(_GLFWwindow* window)
 {
-    if (_glfw.x11.saver.count == 0)
+    if (_glfw.x11.acquiredMonitorCount == 0)
+    {
+        if (_glfw.x11.xss.available)
+	        XScreenSaverSuspend(_glfw.x11.display, True);
+        else
         {
-        // Remember old screen saver settings
             XGetScreenSaver(_glfw.x11.display,
                             &_glfw.x11.saver.timeout,
                             &_glfw.x11.saver.interval,
                             &_glfw.x11.saver.blanking,
                             &_glfw.x11.saver.exposure);
-
-        // Disable screen saver
             XSetScreenSaver(_glfw.x11.display, 0, 0, DontPreferBlanking,
                             DefaultExposures);
+        }
 
         if (_glfw.x11.dbus.session)
         {
@@ -1124,7 +1126,7 @@ static void acquireMonitor(_GLFWwindow* window)
     }
 
     if (!window->monitor->window)
-        _glfw.x11.saver.count++;
+        _glfw.x11.acquiredMonitorCount++;
 
     _glfwSetVideoModeX11(window->monitor, &window->videoMode);
 
@@ -1154,16 +1156,19 @@ static void releaseMonitor(_GLFWwindow* window)
     _glfwInputMonitorWindow(window->monitor, NULL);
     _glfwRestoreVideoModeX11(window->monitor);
 
-    _glfw.x11.saver.count--;
+    _glfw.x11.acquiredMonitorCount--;
-
+    if (_glfw.x11.acquiredMonitorCount == 0)
-    if (_glfw.x11.saver.count == 0)
+    {
+        if (_glfw.x11.xss.available)
+	        XScreenSaverSuspend(_glfw.x11.display, False);
+        else
         {
-        // Restore old screen saver settings
             XSetScreenSaver(_glfw.x11.display,
                             _glfw.x11.saver.timeout,
                             _glfw.x11.saver.interval,
                             _glfw.x11.saver.blanking,
                             _glfw.x11.saver.exposure);
+        }
 
         if (_glfw.x11.dbus.session)
         {