Re: [gtk-list] Trying to draw in a window

[Tim Janik <timj gtk org>]

On 21 Jun 1999 hubert.fauque@wanadoo.fr wrote:

> 
> I am trying to draw in a line in a window; I connect
> a function drawing the line to the expose event, and there
> is the following problem:
> if the window is (partly) behind another window and I click on it
> to bring it in the foreground, only the part of the line that
> was already in the uncovered part of the window appears;
> the other part is immediatly overwritten (by who?);

by gtk, part of a toolkits responsiveness is to redraw exposed regions which
for normal windows will just 'clear' the background. if you want to draw
you own things in such a window, you need to inform gtk about that with the
gtk_widget_set_app_paintable () function.


> #include <gdk/gdk.h>
> #include <gtk/gtk.h>
> 
> GdkGC *gc;
> GdkDrawable *ww;
> 
> gint expose_event(GtkWidget *widget, GdkEvent *event, gpointer data)
> {
>   gdk_draw_line (ww, gc, 10, 20, 100, 20);

rather than using global variables here, i'd suggest you use something like

gdk_draw_line (widget->window,
               widget->style->fg_gc[GTK_STATE_NORMAL],
               10, 20,
               100, 20);

the widget style structure (defined in gtkstyle.h) provides a bunch
of default styles already.

>   return FALSE;
> }
> 
> 
> int main (int argc, char *argv[])
> {
>   GtkWidget *w;
>   gtk_init (&argc, &argv);
>   w = gtk_window_new (GTK_WINDOW_TOPLEVEL);

insert gtk_widget_set_app_paintable (w, TRUE); here

>   gtk_widget_show (w);
>   ww = w->window;
>   gc = gdk_gc_new(ww);
>   gtk_signal_connect (GTK_OBJECT(w), "expose_event",
> 		      GTK_SIGNAL_FUNC(expose_event), NULL);
>   gdk_draw_line (ww, gc, 10, 20, 100, 20);

you don't need this draw_line call as widgets get automatically
exposed upon initial mapping.

>   gtk_main ();
>   return 0;
> }

> 
> Hubert
> 

---
ciaoTJ