Re: [gtk-list] Re: Is Gtk_DrawingArea in gtk-- usable?

[Tero Pulkkinen <terop students cc tut fi>]

> Jon Trowbridge <trow@emccta.com> writes:
> > It is possible to construct a drawing area widget in gtk--, but
> > how do I go about actually drawing into it?  I'm an X/gtk/gtk--
> > programming newbie, so going to the source just confused me further...

You'll need to use the C interface for this. I hope eventually we get the
C++ interface for gdk ready to help make this easier, but currently
the C interface is fine and works.

Rob Browning <rlb@cs.utexas.edu> writes:
> I'm completely unfamiliar with gtk--, but assuming plain gtk, and
> assuming that you can get a drawing area widget created (see the
> tutorial and the testgtk program for general widget info), you just
> need to put the drawing calls you want in the expose function.  Here's
> some trivial (and untested) bits:
> 
>     static gint
>     my_expose (GtkWidget *widget, GdkEventExpose *event, gpointer my_data)
>     {
>       gdk_draw_arc(GTK_WIDGET(widget)->window, my_gc, TRUE,
>                    my_x, my_y, my_width, my_height,
>                    my_start_angle, my_sweep_angle);
>       return TRUE;
>     }

In gtk-- you can just override the expose_event_impl virtual function - just
like the gtk's builtin widgets does:

class foo : public Gtk_Drawing_Area {
public:
   ...
   gint expose_event_impl(GdkEventExpose *e) {
      Gtk_Drawing_Area::expose_event_impl(e); // call base class expose
      GdkWindow *win=GTK_WIDGET(gtkobject)->window;
      /* use drawing functions here from the C interface */
      gdk_draw_arc(win,my_gc,TRUE,my_x,my_y,my_width,my_height,my_start_angle,my_sweep_angle);
   }
   ...
};

> then assuming you have a drawing area widget assigned to drawing_area:
>     gtk_signal_connect (GTK_OBJECT (drawing_area), "expose_event",
>                         GTK_SIGNAL_FUNC (my_expose), my_data);
> Note that this leaves off a bunch of smarts like only drawing the area
> that needs it by checking the expose event in my_expose, but it shows
> you the general idea.

Can use the connect() too, but IMHO its inconvinient. :)

-- 
-- Tero Pulkkinen -- terop@modeemi.cs.tut.fi --