WaylandBackend: Re-map toplevel upon becoming visible

When becoming invisible, a NULL buffer is attached to the toplevel's
surface which unmaps it. The compositor resets their state and the
surface may also be considered unconfigured. Upon becoming visible, the
surface must be re-mapped using the same process during initialization
(commit without a buffer and wait for configure) before we begin
attaching an actual buffer. The default properties should also be
recovered.

Fixes: #1456
Fixes: #1451 (probably)
Fixes: #1488 (probably)
Fixes: #1533

src/Backends/WaylandBackend.cpp

@@ -1925,6 +1925,29 @@ namespace gamescope
             return;
 
         m_bVisible = bVisible;
+
+        // Surface must be re-mapped before using it again, and default
+        // properties should be recovered as the compositor resets the state
+        if (m_bVisible)
+        {
+            assert( !m_Planes[0].GetCurrentState() );
+            wl_surface_commit( m_Planes[0].GetSurface() );
+            wl_display_roundtrip( m_pDisplay );
+
+            libdecor_frame_set_title( m_Planes[0].GetFrame(), "Gamescope" );
+            libdecor_frame_set_app_id( m_Planes[0].GetFrame(), "gamescope" );
+
+            g_nOutputWidth = g_nPreferredOutputWidth;
+            g_nOutputHeight = g_nPreferredOutputHeight;
+            if ( g_nOutputHeight == 0 )
+                g_nOutputHeight = 720;
+            if ( g_nOutputWidth == 0 )
+                g_nOutputWidth = g_nOutputHeight * 16 / 9;
+
+            m_Planes[0].CommitLibDecor( nullptr );
+            wl_display_roundtrip( m_pDisplay );
+        }
+
         force_repaint();
     }
     void CWaylandBackend::SetTitle( std::shared_ptr<std::string> pAppTitle )