Re: Help me about this "drawable" error

[Jonathan Irwin <jmi25 cam ac uk>]

On Fri, 10 Nov 2000, Jung-Wuk Hong wrote:

> I wrote a function to write text on popup window. However it doesn't work
> correctly.
> I met the error drawable!=NULL.
> Please help me about this problem.

Before you can use GDK functions to draw on a window, it's X window has to
exist.  You need to call gtk_widget_realize() on property_window so it's X
window (or gdk window) is created, then you can draw on it (GDK windows
are not created immediately when you gtk_widget_show() a widget).
 
Alternatively (and a better approach in this case) you could use a signal
handler connected to the "expose_event" event on the GtkDrawingArea (then 
things will get redrawn properly when the user covers up the window and
then uncovers it):

gtk_signal_connect(GTK_OBJECT(plot_area), "expose_event",  
                   GTK_SIGNAL_FUNC(expose_event), NULL);

Then do the drawing in that instead:

gint expose_event (GtkWidget *w, GdkEventExpose *ev, gpointer data) {
  gdk_draw_text(GTK_WIDGET(w)->window, font,
                GTK_WIDGET(w)->style->black_gc, 10,10, 
                "abc",15);

  return(FALSE);
}

If you are going to do a lot of drawing, then it may be a good idea to
create a pixmap, and draw on that (I would use the "realize" event to
create the pixmap and allocate colours, fonts, etc., storing them in a
struct), then draw on the pixmap as required, updating the display by
drawing the pixmap to the GtkDrawingArea: I do this in the expose_event
handler, and then call gtk_widget_draw() on the GtkDrawingArea, which
triggers the expose_event handler.  That should eliminate most of the
flickering which will be seen if you update the window directly.

Jonathan