[cairo] warning while executing gtk_widget_draw

[Uli Schlachter]

Hi,

On 12.08.2014 09:54, Lokesh Chakka wrote:
> I have written one program and I am seeing the following warning:
> 
> Gtk-CRITICAL **: gtk_widget_draw: assertion '!widget->priv->alloc_needed'
> failed

This is GTK+ and has not much to do with Cairo. Let's take a look anyway.

> program is as follows:

Missing "#include <gtk/gtk.h>

> main()
> {
>     GtkDrawingArea *statistics;
>     cairo_surface_t *surface;
>     cairo_t *cr;
>     GtkWindow *main_window;
> 
> 
>     gtk_init( NULL, NULL );
>     statistics = (GtkDrawingArea*)gtk_drawing_area_new();
>     surface = cairo_image_surface_create (CAIRO_FORMAT_ARGB32, 120, 120);
>     cr = cairo_create ( surface );
>     gtk_widget_draw( (GtkWidget*)statistics, cr );

This line is what causes that warning. Let's quote the API docs:

 widget: the widget to draw. It must be drawable (see gtk_widget_is_drawable())
and a size must have been allocated

https://developer.gnome.org/gtk3/3.2/GtkWidget.html#gtk-widget-draw

Adding this code tells us that the widget isn't drawable, but I bet that it
doesn't have a size allocated yet, too.

   puts(gtk_widget_is_drawable((GtkWidget*)statistics) ? "yes" : "no");

>     cairo_surface_write_to_png( surface, "one.png" );
>     main_window = (GtkWindow*)gtk_window_new(GTK_WINDOW_TOPLEVEL);
> 
> g_signal_connect(G_OBJECT(main_window),"destroy",G_CALLBACK(gtk_main_quit),NULL);
>     gtk_container_add (GTK_CONTAINER (main_window),(GtkWidget*)statistics);
>     gtk_widget_show_all((GtkWidget*)main_window);
> 
>     gtk_main();
> }

Cheers,
Uli
-- 
- He made himself, me nothing, you nothing out of the dust
- Er machte sich mir nichts, dir nichts aus dem Staub