Re: Generating a drawable widget

[muppet <scott asofyet org>]

On Jan 9, 2005, at 6:54 PM, Hermann Kaser wrote:

> I've spent the past few hours trying to figure out how to create a 
> drawable area, I'm trying to make a little graph area to make a 
> network usage timeline. I have the following code:
>
> -----------------------------------------------------
> $graph = Gtk2::Gdk::Pixmap->new($drawable,200,100,-1);
> $vbox->pack_start($graph,1,1,5);

a GdkPixmap isn't a widget, so it can't be packed into a container.

what you want to do is

a) use a Gtk2::DrawingArea.  This is a drawable widget; you could draw 
directly to the screen or to a Gtk2::Gdk::Pixmap and copy that to the 
screen in expose (which is how the scribble example does it).  With 
either option you can use the gdk drawing primitives.  The drawing area 
also has its own GdkWindow, so you can handle mouse events and all 
that, e.g., to make an interactive plot (see the histogramplot.pl 
example).

b) draw to a Gtk2::Gdk::Pixbuf, and display that in a Gtk2::Image.  
This is usually a pretty good option in C, but since a GdkPixbuf is a 
24-bit rgb pixel buffer and those aren't too easy to manipulate in 
perl, and you can't use the gdk drawing primitives, i tend to avoid 
this one.


> But I haven't managed to generate a drawable area using 
> Gtk::GDK::Drawable so that it goes in $drawable and therefore fits 
> Pixmap.
> The documentation for Gtk::GDK::Pixmap says that ->new accepts either 
> a Gtk2::Gdk::Drawable or a undef, but it always gives me an error when 
> trying undef.

You can use the GdkWindow of the widget as the drawable, like this:

  $pixmap = Gtk2::Gdk::Pixmap->new ($widget->window, $width, $height,
                                 -1);  # same depth as window


--
She's obviously your child.  She looks like you, she talks a lot, and 
most of it is gibberish.
  -- Elysse, to me, of Zella.