skins2(Linux): fix fullscreen for some Window Managers like Gnome3

   Some Window Managers (Gnome3, Unity) will keep the task bar displayed
   and limit the fullscreen display to the subarea outside the task bar
   if the window type is not set.
   Setting the Window type to normal ensures a clean 100% fullscreen.

   This fixes an issue reported on the forum at
   https://forum.videolan.org/viewtopic.php?f=13&t=127840

modules/gui/skins2/x11/x11_display.cpp

@@ -330,6 +330,9 @@ void X11Display::testEWMH()
         msg_Dbg( getIntf(), "%s support: yes", value );\
 }
 
+    TEST_EWMH( m_net_wm_window_type, "_NET_WM_WINDOW_TYPE" )
+    TEST_EWMH( m_net_wm_window_type_normal, "_NET_WM_WINDOW_TYPE_NORMAL" )
+
     TEST_EWMH( m_net_wm_state, "_NET_WM_STATE" )
     TEST_EWMH( m_net_wm_state_fullscreen, "_NET_WM_STATE_FULLSCREEN" )
     TEST_EWMH( m_net_wm_stays_on_top, "_NET_WM_STATE_STAYS_ON_TOP" )

modules/gui/skins2/x11/x11_display.hpp

@@ -36,6 +36,8 @@
 #define XGC m_rDisplay.getGC()
 
 #define NET_WM_SUPPORTED          m_rDisplay.m_net_wm_supported
+#define NET_WM_WINDOW_TYPE        m_rDisplay.m_net_wm_window_type
+#define NET_WM_WINDOW_TYPE_NORMAL m_rDisplay.m_net_wm_window_type_normal
 #define NET_WM_STATE              m_rDisplay.m_net_wm_state
 #define NET_WM_STATE_FULLSCREEN   m_rDisplay.m_net_wm_state_fullscreen
 #define NET_WM_STATE_ABOVE        m_rDisplay.m_net_wm_state_above
@@ -85,6 +87,10 @@ public:
 
     /// EWMH spec
     Atom m_net_wm_supported;
+
+    Atom m_net_wm_window_type;
+    Atom m_net_wm_window_type_normal;
+
     Atom m_net_wm_state;
     Atom m_net_wm_state_above;
     Atom m_net_wm_state_fullscreen;

modules/gui/skins2/x11/x11_window.cpp

@@ -221,6 +221,19 @@ X11Window::X11Window( intf_thread_t *pIntf, GenericWindow &rWindow,
     XChangeProperty( XDISPLAY, m_wnd, NET_WM_PID, XA_CARDINAL, 32,
                      PropModeReplace, (unsigned char *)&pid, 1 );
 
+    if( NET_WM_WINDOW_TYPE != None )
+    {
+        if( type == GenericWindow::FullscreenWindow )
+        {
+            // Some Window Managers like Gnome3 limit fullscreen to the
+            // subarea outside the task bar if no window type is provided.
+            // For those WMs, setting type window to normal ensures a clean
+            // 100% fullscreen
+            XChangeProperty( XDISPLAY, m_wnd, NET_WM_WINDOW_TYPE,
+                         XA_ATOM, 32, PropModeReplace,
+                         (unsigned char *)&NET_WM_WINDOW_TYPE_NORMAL, 1 );
+        }
+    }
 }