1 files changed, 48 insertions, 9 deletions

diff --git a/vncviewer/DesktopWindow.cxx b/vncviewer/DesktopWindow.cxx
index e86e90e6..e8750b4e 100644
--- a/vncviewer/DesktopWindow.cxx
+++ b/vncviewer/DesktopWindow.cxx
@@ -684,23 +684,18 @@ int DesktopWindow::fltkHandle(int event, Fl_Window *win)
 
   if (dw) {
     switch (event) {
+    // Focus might not stay with us just because we have grabbed the
+    // keyboard. E.g. we might have sub windows, or we're not using
+    // all monitors and the user clicked on another application.
+    // Make sure we update our grabs with the focus changes.
     case FL_FOCUS:
       if (fullscreenSystemKeys) {
-        // FIXME: We reassert the keyboard grabbing on focus as FLTK there are
-        //        some issues we need to work around:
-        //        a) Fl::grab(0) on X11 will release the keyboard grab for us.
-        //        b) Gaining focus on the system level causes FLTK to switch
-        //           window level on OS X.
         if (dw->fullscreen_active())
           dw->grabKeyboard();
       }
       break;
-
     case FL_UNFOCUS:
       if (fullscreenSystemKeys) {
-        // FIXME: We need to relinquish control when the entire window loses
-        //        focus as it is very tied to this specific window on some
-        //        platforms and we want to be able to open subwindows.
         dw->ungrabKeyboard();
       }
       break;
@@ -766,6 +761,23 @@ void DesktopWindow::fullscreen_on()
     fullscreen();
 }
 
+#if !defined(WIN32) && !defined(__APPLE__)
+Bool eventIsFocusWithSerial(Display *display, XEvent *event, XPointer arg)
+{
+  unsigned long serial;
+
+  serial = *(unsigned long*)arg;
+
+  if (event->xany.serial != serial)
+    return False;
+
+  if ((event->type != FocusIn) && (event->type != FocusOut))
+    return False;
+
+  return True;
+}
+#endif
+
 void DesktopWindow::grabKeyboard()
 {
   // Grabbing the keyboard is fairly safe as FLTK reroutes events to the
@@ -793,6 +805,11 @@ void DesktopWindow::grabKeyboard()
 #else
   int ret;
 
+  XEvent xev;
+  unsigned long serial;
+
+  serial = XNextRequest(fl_display);
+
   ret = XGrabKeyboard(fl_display, fl_xid(this), True,
                       GrabModeAsync, GrabModeAsync, CurrentTime);
   if (ret) {
@@ -806,6 +823,16 @@ void DesktopWindow::grabKeyboard()
     }
     return;
   }
+
+  // Xorg 1.20+ generates FocusIn/FocusOut even when there is no actual
+  // change of focus. This causes us to get stuck in an endless loop
+  // grabbing and ungrabbing the keyboard. Avoid this by filtering out
+  // any focus events generated by XGrabKeyboard().
+  XSync(fl_display, False);
+  while (XCheckIfEvent(fl_display, &xev, &eventIsFocusWithSerial,
+                       (XPointer)&serial) == True) {
+    vlog.debug("Ignored synthetic focus event cause by grab change");
+  }
 #endif
 
   keyboardGrabbed = true;
@@ -832,7 +859,19 @@ void DesktopWindow::ungrabKeyboard()
   if (Fl::grab())
     return;
 
+  XEvent xev;
+  unsigned long serial;
+
+  serial = XNextRequest(fl_display);
+
   XUngrabKeyboard(fl_display, CurrentTime);
+
+  // See grabKeyboard()
+  XSync(fl_display, False);
+  while (XCheckIfEvent(fl_display, &xev, &eventIsFocusWithSerial,
+                       (XPointer)&serial) == True) {
+    vlog.debug("Ignored synthetic focus event cause by grab change");
+  }
 #endif
 }