Re: selection rectangle

[Rok Roskar <rroskar artsci wustl edu>]

Hello... thanks for your reply to my question.... I have another quick
question for you: how exactly is the function specified for the GC
performed? is it performed on the pixels that are already in the Drawable?
For example, if I had a picture in a pixmap  drawn on a drawing_area and I
drew a rectangle over it with a GDK_INVERT function, would it then take
the pixel values from the underlying image which was already present and
invert them? I hope this isnt too confusing.... I appreciate your help.
Thanks,

Rok

On Sat, 12 Jan 2002, Patrice St-Gelais wrote:

> This is exactly what I did for drawing a selection box in the preview area of a
> scanner interface.
>
> I first initialized a "graphic context" this way:
>
>  invert_gc = gdk_gc_new(image_area->window);
>  gdk_gc_copy(invert_gc,image_area->style->black_gc);
>  gdk_gc_set_function(invert_gc,GDK_INVERT);
>
> ... then draw / undraw with something like this:
>
>  gdk_draw_rectangle(pixmap,invert_gc,FALSE,
>   last_rect.x, last_rect.y,
>   last_rect.width, last_rect.height);
>
> An other option would be to dig in the Gimp code for the "marching ants", but
> I'm not sure it's simple.
>
> Hoping this helps.
>
> Regards,
>
> Patrice St-Gelais
> ____________________________________
>
> Johan Bondeson a écrit :
>
> > I saw an example somewere were the selection rectangle was drawn just by
> > inverting the pixels that the rectangle consisted of. To erease the
> > rectangle it was only inverted once again and the original colors were back,
> > however I think this was a Windows (excuse the bad language) and I have no
> > idea how to do this using GTK.
>
> > ----Original Message Follows----
> > From: Rok Roskar <rroskar artsci wustl edu>
> > To: <gtk-app-devel-list gnome org>
> > Subject: selection rectangle
> > Date: Sat, 12 Jan 2002 13:43:16 -0600 (CST)
> >
> > is there an easy way to draw a selection rectangle (one that the user can
> > drag) onto a pixmap in drawing_area? The only way I can come up with is
> > one where I draw a rectangle each time the user movesthe mouse, but that
> > means  that Ihave to erase the one previously drawn and it's becoming
> > rather cumbersome.... any ideas?
> >
> > Rok
> >
> > _________________________________________________________________
> > Send and receive Hotmail on your mobile device: http://mobile.msn.com
> >
> > _______________________________________________
> > gtk-app-devel-list mailing list
> > gtk-app-devel-list gnome org
> > http://mail.gnome.org/mailman/listinfo/gtk-app-devel-list
>
> _______________________________________________
> gtk-app-devel-list mailing list
> gtk-app-devel-list gnome org
> http://mail.gnome.org/mailman/listinfo/gtk-app-devel-list