Bug 1411018 - Rename shellHasCSD to drawToContainer and mark our rendering widget by gtk_widget_set_app_paintable(), r=jhorak

Rename shellHasCSD to drawToContainer for better understanding and always mark our rendering widget by gtk_widget_set_app_paintable() to make sure Gtk+ does not draw default background for it.

MozReview-Commit-ID: 4mhxrG7C34i

--HG--
extra : rebase_source : 312e956e317c85196d27213dd86bd30b73a25b02

widget/gtk/nsWindow.cpp

@@ -3601,7 +3601,7 @@ nsWindow::Create(nsIWidget* aParent,
     GtkWindow      *topLevelParent = nullptr;
     nsWindow       *parentnsWindow = nullptr;
     GtkWidget      *eventWidget = nullptr;
-    bool            shellHasCSD = false;
+    bool            drawToContainer = false;
 
     if (aParent) {
         parentnsWindow = static_cast<nsWindow*>(aParent);
@@ -3777,21 +3777,29 @@ nsWindow::Create(nsIWidget* aParent,
         // it explicitly now.
         gtk_widget_realize(mShell);
 
-        // We can't draw directly to top-level window when client side
-        // decorations are enabled. We use container with GdkWindow instead.
+        /* There are two cases here:
+         *
+         * 1) We're running on Gtk+ without client side decorations.
+         *    Content is rendered to mShell window and we listen
+         *    to the Gtk+ events on mShell
+         * 2) We're running on Gtk+ > 3.20 and client side decorations
+         *    are drawn by Gtk+ to mShell. Content is rendered to mContainer
+         *    and we listen to the Gtk+ events on mContainer.
+         */
         GtkStyleContext* style = gtk_widget_get_style_context(mShell);
-        shellHasCSD = gtk_style_context_has_class(style, "csd");
+        drawToContainer = gtk_style_context_has_class(style, "csd");
 #endif
-        if (!shellHasCSD) {
-            // Use mShell's window for drawing and events.
-            gtk_widget_set_has_window(container, FALSE);
-            // Prevent GtkWindow from painting a background to flicker.
-            gtk_widget_set_app_paintable(mShell, TRUE);
-        }
-        // Set up event widget
-        eventWidget = shellHasCSD ? container : mShell;
+        eventWidget = (drawToContainer) ? container : mShell;
+
         gtk_widget_add_events(eventWidget, kEvents);
 
+        // Prevent GtkWindow from painting a background to avoid flickering.
+        gtk_widget_set_app_paintable(eventWidget, TRUE);
+
+        // If we draw to mContainer window then configure it now because
+        // gtk_container_add() realizes the child widget.
+        gtk_widget_set_has_window(container, drawToContainer);
+
         gtk_container_add(GTK_CONTAINER(mShell), container);
         gtk_widget_realize(container);
 
@@ -3960,7 +3968,7 @@ nsWindow::Create(nsIWidget* aParent,
                          G_CALLBACK(drag_data_received_event_cb), nullptr);
 
         GtkWidget *widgets[] = { GTK_WIDGET(mContainer),
-                                 !shellHasCSD ? mShell : nullptr };
+                                 !drawToContainer ? mShell : nullptr };
         for (size_t i = 0; i < ArrayLength(widgets) && widgets[i]; ++i) {
             // Visibility events are sent to the owning widget of the relevant
             // window but do not propagate to parent widgets so connect on