Re: Help requested with drawing lines in a child window.

[John Cupitt <john cupitt ng-london org uk>]

Michael John Holme wrote:
> I understand that I'm calling gtk_draw_line with a NULL first parameter, but
> why is it NULL. I've followed a similar example from the book 'Beginning
> GTK+/GNOME Programming' by Peter Wright.

Hi Michael, you need to do the paint in response to an expose signal.
Have a look at the 'scribble' example program. You want something like
this:

-- 
    window = gtk_window_new(GTK_WINDOW_TOPLEVEL);
    gtk_window_set_default_size(GTK_WINDOW(window), 200, 200);
    gtk_window_set_title(GTK_WINDOW(window), "Output window");
    drawingarea = gtk_drawing_area_new();
    gtk_container_add(GTK_CONTAINER(window), drawingarea);

    grk_signal_connect( GTK_OBJECT( drawingarea ), "expose_event",
	GTK_SIGNAL_FUNC( expose_cb ), NULL );

    gtk_widget_show_all(window);
-- 

then expose_cb needs to be something like:

-- 
static gint expose_cb( Gtkwidget *widget, GdkExposeEvent *event )
{
  GdkDrawable *drawable = widget->window;
  
  gdk_draw_line(drawable, widget->style->white_gc,
                    0, 0, 100, 100);

  return( FALSE );
}
-- 

(this is from memory, I've probably messed up the details)

HTH, John
-- 
John Cupitt, john cupitt ng-london org uk, +44 (0)20 7747 2570
VASARI Lab, The National Gallery, Trafalgar Square, London, WC2N 5DN