Re: GnomeCanvas

["Chris Garrett" <garrett91 hotmail com>]

Hi,

Thank you for your reply. That was basically how I thought I could do it 
with the drawing area, but the problem is that a scaled pixbuf would take up 
a heck of a lot more memory than the original one.

I was hoping that there would be a way of rendering the pixbuf to the 
drawing area (or gnomecanvas) at a particular scale, whilst not actually 
increasing the amount of memory used for storing the pixbuf exponentially 
(as I suspect gdk_pixbuf_scale_simple would do sinbce it basically creates a 
larger pixbuf).

The scaling need only be performed for the rendering.

Best regards,

Chris.


> From: Tristan Van Berkom <vantr touchtunes com>
> To: Chris Garrett <garrett91 hotmail com>
> CC: gtk-app-devel-list gnome org
> Subject: Re: GnomeCanvas
> Date: Tue, 17 Dec 2002 15:54:18 -0500
>
>         I dont know about gnomecanvas
> but if you want to use the drawing area;
> you'll have to implement a couple of
> signal handlers (I think its "expose" and
> "configure" that you need). you might also
> need to call gdk_add_events(...event_mask...)
> on your instance.
>
> This is quite simple because there are a few
> examples of theese (to say the least) in the
> gtk source.
>
> essentially afterwards you'll need to use
> gtk_widget_set_size_request, (resulting
> in your handlers getting called in the
> next mainloop iteration) and then you
> should have a new size of drawing area.
>
> ofcourse you can use the usual
> gdk_pixbuf_scale_simple to scale
> what you want to "draw" to the
> newly sized widget.
>
>
> Cheers,
>                 -Tristan
>
> NOTE:
>         Theese signal handlers are
> treated as class methods. the most
> consistant way to do it would be
> to inherit from GtkDrawingArea
> and polymorph
>
> class->configure = my_configure;
>
> seeing as that way you get your
> handler in as the base class handler.
>
>         I'm not even sure if the
> signals will be emmited to "user"
> handlers if the "class" handlers
> dont exist.
> i.e. the GtkWidgetClass is basicly
> a briefcase of declared but untreated
> signals.
>
>
>
>
>
> Chris Garrett wrote:
> >
> > Hi,
> >
> > I am coding a program using GTK2.0.  Up until now, I have been using a
> > GtkDrawingArea, with a pixbuf on it.
> >
> > I am considering changing to the use of a GnomeCanvas, since it appears 
> to
> > allow relatively easy scaling.  I have the API reference, but it does 
> not
> > really explain how the whole thing hangs together.  Can I do the 
> following?
> >
> > 1. Display a GdkPixbuf on a GnomeCanvas, whilst still retaining the 
> ability
> > to poke directly at the pixel data within the pixbuf.
> >
> > 2. Zoom the canvas with gnome_canvas_set_pixels_per_unit(), and see the
> > pixbuf on the canvas scale as a result (This would simply scale the 
> rendered
> > view of the pixbuf.  The pixbuf data itself would be unchanged)
> >
> > I would also like to know how to actually add a pixbuf to the 
> gnomecanvas in
> > the first place.  For instance, do I have to use a GnomeCanvasGroup? Is
> > there a code sample I can look at or a tutorial for the GTK2.0 
> GnomeCanvas I
> > can follow?  The scribble app in the GTK tutorial uses the drawing area.
> >
> > Alternatively, if anyone can tell me how to scale a drawingarea and its
> > contents I can stick with my current code base.  I cant see anything 
> about
> > this in the drawingarea documentation.
> >
> > Best regards,
> >
> > Chris.
> >
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