[Spice-devel] [spice-gtk 3/4] gtk-deprecated: silence warn on gtk_widget_set_double_buffered()

[Frediano Ziglio]

> 
> From: Victor Toso <me at victortoso.com>
> 
> To quote documentation:
>  | gtk_widget_set_double_buffered has been deprecated since version
>  | 3.14 and should not be used in newly-written code.
>  | This function does not work under non-X11 backends or with
>  | non-native windows. It should not be used in newly written code.
> 
> So be sure to only call this function on X11 backend and silence
> warnings with G_GNUC_BEGIN/END_IGNORE_DEPRECATIONS
> 
> Warnings fixed:
>  | spice-widget.c: In function ‘spice_display_init’:
>  | spice-widget.c:643:5: warning: ‘gtk_widget_set_double_buffered’ is
>  | deprecated
>  |
>  |     gtk_widget_set_double_buffered(area, true);
>  |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>  |
>  | spice-widget.c:661:5: warning: ‘gtk_widget_set_double_buffered’ is
>  | deprecated
>  |
>  |     gtk_widget_set_double_buffered(area, true);
>  |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
>  |
>  | spice-widget.c: In function ‘set_egl_enabled’:
>  | spice-widget.c:1290:9: warning: ‘gtk_widget_set_double_buffered’ is
>  | deprecated
>  |     gtk_widget_set_double_buffered(GTK_WIDGET(area), !enabled);
>  |     ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> 
> Signed-off-by: Victor Toso <victortoso at redhat.com>
> ---
>  src/spice-widget.c | 18 ++++++++++++++++--
>  1 file changed, 16 insertions(+), 2 deletions(-)
> 
> diff --git a/src/spice-widget.c b/src/spice-widget.c
> index 6ad0865..dc8ee40 100644
> --- a/src/spice-widget.c
> +++ b/src/spice-widget.c
> @@ -640,7 +640,13 @@ static void spice_display_init(SpiceDisplay *display)
>                       "signal::realize", drawing_area_realize, display,
>                       NULL);
>      gtk_stack_add_named(d->stack, area, "draw-area");
> -    gtk_widget_set_double_buffered(area, true);
> +#ifdef GDK_WINDOWING_X11
> +    if (GDK_IS_X11_DISPLAY(gdk_display_get_default())) {
> +        G_GNUC_BEGIN_IGNORE_DEPRECATIONS
> +        gtk_widget_set_double_buffered(area, true);
> +        G_GNUC_END_IGNORE_DEPRECATIONS
> +    }
> +#endif
>      gtk_stack_set_visible_child(d->stack, area);
>  
>  #if HAVE_EGL
> @@ -658,7 +664,13 @@ G_GNUC_END_IGNORE_DEPRECATIONS
>  #endif
>      area = gtk_drawing_area_new();
>      gtk_stack_add_named(d->stack, area, "gst-area");
> -    gtk_widget_set_double_buffered(area, true);
> +#ifdef GDK_WINDOWING_X11
> +    if (GDK_IS_X11_DISPLAY(gdk_display_get_default())) {
> +        G_GNUC_BEGIN_IGNORE_DEPRECATIONS
> +        gtk_widget_set_double_buffered(area, true);
> +        G_GNUC_END_IGNORE_DEPRECATIONS
> +    }
> +#endif
>  
>      gtk_widget_show_all(widget);
>  
> @@ -1281,7 +1293,9 @@ static void set_egl_enabled(SpiceDisplay *display, bool
> enabled)
>           * only way I found to prevent glitches when the window is
>           * resized. */
>          GtkWidget *area = gtk_stack_get_child_by_name(d->stack,
>          "draw-area");
> +        G_GNUC_BEGIN_IGNORE_DEPRECATIONS
>          gtk_widget_set_double_buffered(GTK_WIDGET(area), !enabled);
> +        G_GNUC_END_IGNORE_DEPRECATIONS
>      } else
>  #endif
>      {

First time I saw this patch I though "quite ugly". Second time did not
improve much.
Maybe this function should be wrapped in a compatibility function,
something kind of suggested at https://lists.freedesktop.org/archives/spice-devel/2018-July/044590.html?
In SPICE server we already have a glib-compat.h header (slightly different usage).

There are also some scary comment on this function, see
https://developer.gnome.org/gtk3/stable/GtkWidget.html#gtk-widget-set-double-buffered, specifically
"In 3.10 GTK and GDK have been restructured for translucent drawing. Since then expose events for
double-buffered widgets are culled into a single event to the toplevel GDK window. If you now
unset double buffering, you will cause a separate rendering pass for every widget. This will
likely cause rendering problems - in particular related to stacking - and usually increases
rendering times significantly."
Which ones are the double-buffered widgets?

Frediano