From Melchior Franz, "In KDE I switch desktops with Super-Tab, and occasionally I

get an excess Tab key report when switching back to an OSG
application (usually FlightGear :-). Although KDE has consumed
the Tab, it's sometimes still in the XKeymapEvent's key_vector,
and followed by a Tab KeyRelease event.

Avoid this artifact by
- asking for a "fresh" keymap (via XQueryKeymap()), rather than
 using the unreliable(?) XKeymapEvent's key_vector, and by
- flushing all key events on focus-in (to avoid the KeyRelease)

After Super-press, Tab-press, Super-release, Tab-release (note
the wrong release order!) I still get an extra Tab event. But
this is not surprising and not exactly wrong either. Also it's
hard to avoid, as we can't see what happened to the keyboard
before we regained focus.

Files changed:
 src/osgViewer/GraphicsWindowX11.cpp
 include/osgViewer/api/X11/GraphicsWindowX11"

include/osgViewer/api/X11/GraphicsWindowX11

@@ -169,6 +169,7 @@ class OSGVIEWER_EXPORT GraphicsWindowX11 : public osgViewer::GraphicsWindow
         void getModifierMap(char* keymap) const;
         int getModifierMask() const;
         void syncLocks();
+        void flushKeyEvents();
         
         bool            _valid;
         Display*        _display;

src/osgViewer/GraphicsWindowX11.cpp

@@ -993,6 +993,7 @@ void GraphicsWindowX11::checkEvents()
 
             case FocusIn :
                 osg::notify(osg::INFO)<<"FocusIn event received"<<std::endl;
+                flushKeyEvents();
                 break;
 
             case UnmapNotify :
@@ -1038,12 +1039,15 @@ void GraphicsWindowX11::checkEvents()
                 getModifierMap(modMap);
                 syncLocks();
 
+                char keyMap[32];
+                XQueryKeymap(_eventDisplay, keyMap);
+
                 // release normal (non-modifier) keys
                 for (unsigned int key = 8; key < 256; key++)
                 {
                     bool isModifier = keyMapGetKey(modMap, key);
                     if (isModifier) continue;
-                    bool isPressed = keyMapGetKey(ev.xkeymap.key_vector, key);
+                    bool isPressed = keyMapGetKey(keyMap, key);
                     if (!isPressed) forceKey(key, eventTime, false);
                 }
 
@@ -1052,7 +1056,7 @@ void GraphicsWindowX11::checkEvents()
                 {
                     bool isModifier = keyMapGetKey(modMap, key);
                     if (!isModifier) continue;
-                    bool isPressed = keyMapGetKey(ev.xkeymap.key_vector, key);
+                    bool isPressed = keyMapGetKey(keyMap, key);
                     forceKey(key, eventTime, isPressed);
                 }
 
@@ -1061,7 +1065,7 @@ void GraphicsWindowX11::checkEvents()
                 {
                     bool isModifier = keyMapGetKey(modMap, key);
                     if (isModifier) continue;
-                    bool isPressed = keyMapGetKey(ev.xkeymap.key_vector, key);
+                    bool isPressed = keyMapGetKey(keyMap, key);
                     if (isPressed) forceKey(key, eventTime, true);
                 }
                 break;
@@ -1385,6 +1389,13 @@ void GraphicsWindowX11::rescanModifierMapping()
     }
 }
 
+void GraphicsWindowX11::flushKeyEvents()
+{
+    XEvent e;
+    while (XCheckMaskEvent(_eventDisplay, KeyPressMask|KeyReleaseMask, &e))
+        continue;
+}
+
 // Returns char[32] keymap with bits for every modifier key set.
 void GraphicsWindowX11::getModifierMap(char* keymap) const
 {