gtk: Keep Firefox working in the DrawingContext world

Firefox does a bunch of interesting things with GTK.

If the top-level GtkWindow does not have a "csd" style class associated,
Firefox will happily draw the contents of the container used to render
HTML and XUL directly on the top level's GdkWindow; on the other hand,
if a "csd" style class is found, the MozContainer will create a new
child window, and draw on it.

Then, Firefox will proceed to disable double buffering on both the
top-level window and the MozContainer (unless they are backed by the
same GdkWindow, in which case only the top-level will be
single-buffered) *and* it will add a GDK_EXPOSURE_MASK flag to the
MozContainer events for good measure (even if this is only needed for
GTK+ 2.x).

After landing the GdkDrawingContext API in GdkWindow, GTK enabled
automatic double buffering on all top-level windows backed by a native
surface, ad most users of single buffering rely on child widgets instead
of top-levels, and we'd still like to have the same double buffering
behaviour for all top-levels on all backends. Obviously, with Firefox
disabling double buffering on the top-level window, the change broke
their drawing mechanism.

Ideally, Firefox could be fixed to not disable double buffering on the
top-level window when MozContainer has a separate GdkWindow — i.e. the
CSD case — but since we did introduce a slight change of behaviour in
fringe users of the GTK+ API, let's keep backwards compatibility with
the old code for a little while longer, and create an intermediate Cairo
context unbound from the GdkDrawingContext, like we used to do until
GTK+ 3.20.

diff --git a/gtk/gtkwidget.c b/gtk/gtkwidget.c
index e6dfac7ef1c61f859e44068cb4d7907df467416a..5b87a3338ea873497fdc9e4eb63c6a722b13d9ef 100644 (file)
--- a/gtk/gtkwidget.c
+++ b/gtk/gtkwidget.c
@@ -17463,15 +17463,30 @@ gtk_widget_render (GtkWidget            *widget,
       /* We only render double buffered on native windows */
       if (!gdk_window_has_native (window))
         return;
-    }
 
-  context = gdk_window_begin_draw_frame (window, region);
-  cr = gdk_drawing_context_get_cairo_context (context);
+      context = gdk_window_begin_draw_frame (window, region);
+      cr = gdk_drawing_context_get_cairo_context (context);
+    }
+  else
+    {
+      /* This is annoying, but it has to stay because Firefox
+       * disables double buffering on a top-level GdkWindow,
+       * which breaks the drawing context.
+       *
+       * Candidate for deletion in the next major API bump.
+       */
+G_GNUC_BEGIN_IGNORE_DEPRECATIONS
+      cr = gdk_cairo_create (window);
+G_GNUC_END_IGNORE_DEPRECATIONS
+    }
 
   do_clip = _gtk_widget_get_translation_to_window (widget, window, &x, &y);
   cairo_translate (cr, -x, -y);
 
   gtk_widget_draw_internal (widget, cr, do_clip);
 
-  gdk_window_end_draw_frame (window, context);
+  if (priv->double_buffered)
+    gdk_window_end_draw_frame (window, context);
+  else
+    cairo_destroy (cr);
 }