Improved X11 focus event filtering.

Some focus events need to be ignored to allow functionality like
Alt+Tab and volume indicators to not affect application-visible window
focus.  However, the previous filtering was too broad and missed virtual
desktop switching, Alt+Tab and programmatic iconification.

Fixes #405.

README.md

@@ -76,6 +76,7 @@ GLFW bundles a number of dependencies in the `deps/` directory.
  - [X11] Bugfix: The response to `_NET_WM_PING` was sent to the wrong window
  - [X11] Bugfix: Character input via XIM did not work in many cases
  - [X11] Bugfix: No fallback existed for missing `_NET_ACTIVE_WINDOW` support
+ - [X11] Bugfix: Some significant window focus events were ignored
  - [WGL] Removed `GLFW_USE_DWM_SWAP_INTERVAL` compile-time option
  - [WGL] Bugfix: Swap interval was ignored when DWM was enabled
  - [GLX] Added dependency on `libdl` on systems where it provides `dlopen`

src/x11_window.c

@@ -1220,8 +1220,14 @@ static void processEvent(XEvent *event)
 
         case FocusIn:
         {
-            if (event->xfocus.mode == NotifyNormal)
+            if (event->xfocus.mode == NotifyGrab ||
+                event->xfocus.mode == NotifyUngrab)
             {
+                // Ignore focus events from popup indicator windows, window menu
+                // key chords and window dragging
+                return;
+            }
+
             if (window->x11.ic)
                 XSetICFocus(window->x11.ic);
 
@@ -1229,15 +1235,20 @@ static void processEvent(XEvent *event)
 
             if (window->cursorMode == GLFW_CURSOR_DISABLED)
                 disableCursor(window);
-            }
 
             return;
         }
 
         case FocusOut:
         {
-            if (event->xfocus.mode == NotifyNormal)
+            if (event->xfocus.mode == NotifyGrab ||
+                event->xfocus.mode == NotifyUngrab)
             {
+                // Ignore focus events from popup indicator windows, window menu
+                // key chords and window dragging
+                return;
+            }
+
             if (window->x11.ic)
                 XUnsetICFocus(window->x11.ic);
 
@@ -1245,7 +1256,6 @@ static void processEvent(XEvent *event)
 
             if (window->cursorMode == GLFW_CURSOR_DISABLED)
                 restoreCursor(window);
-            }
 
             return;
         }