Re: Gtk2::Gdk::Atom questions

On Fri, Jun 06, 2003 at 02:19:17PM -0400, muppet wrote:

René Seindal said:
I'm rather blank when it comes to XS code, but I an see the basic type is
defined, but there are no methods.

I stumbled over this when working with dnd callbacks where there are several
possible types of data in play.  The types are given by Atoms, but I cannot
even compare two to see if they are the same.

hmm.  you aren't good at XS, but you know how to use Atoms.

i can churn out XS like nobody's business, but i know anothing about using Atoms.


if you'll tell me what's expected of the interface and give me some example
code to port and make work, i think we can get what you want and need.  that
goes for  anybody who wants to chime in.

You create an atom with:

    GdkAtom gdk_atom_intern (const gchar *atom_name,
                             gboolean only_if_exists);

which could be mapped like

    $atom = intern Gtk2::Gdk::Atom($name, $only_if_exists);
    $atom = intern Gtk2::Gdk::Atom($name); # $only_if_exists=0

The usual terminology is intern(), but maybe there should be a new()
alias to maintain that convention.  I'd prefer writing "new

If you have a GdkAtom, you use

    gchar *gdk_atom_name (GdkAtom atom);

to get the name.  If the Gtk2::Gdk::Atom can be made as a real blessed
object, then it could be mapped as

    $name = $atom->name;

An X11 atom is simply a numeric id.  In Gtk2 an GdkAtom is an integer
X11 atom id cast to a pointer, using

   GdkAtom atom = GDK_ATOM_TO_POINTER(numeric_atom);

The definition is:

   #define GDK_ATOM_TO_POINTER(atom) (atom)

The reverse is

   guint numeric_atom = GDK_POINTER_TO_ATOM(atom);

The definition is

   #define GDK_POINTER_TO_ATOM(ptr)  ((GdkAtom)(ptr))

If possible I think Gtk2::Gdk::Atom should have an id() method that
returns that number, since it is perfect for comparisons.

There is a number of predefined GdkAtom made with a macro

#define _GDK_MAKE_ATOM(val) ((GdkAtom)GUINT_TO_POINTER(val))
#define GDK_NONE            _GDK_MAKE_ATOM (0)

I don't know if it is worth it reproducing that in gtk2-perl-xs, since
you can simply do

    $type_string_atom = new Gtk2::Gdk::Atom('STRING');

though the Gdk way saves a round-trip to the X server.  The numbers are
well-defined by X11.  On my system the list is in
/usr/X11R6/include/X11/Xatom.h, but not all are equally interesting.

The documentation for the above is at

(including predefined atoms)

Here is a small example using atoms in gtk-perl 0.78, though I think
this interface is a bit clumsier.  I like the OO approach better, but I
don't know if it is possible given the way Gdk implements the GtkAtom as
an integer cast to a pointer.

Gtk-perl seems to implement the atom as a scalar with an integer value,
thus ruling out the OO approach.  Gtk2-perl-xs already has the atom as a
blessed reference where the value of the reference is the numeric atom

Anyway, you're the expert and you decide.

Gtk 1.2 perl code:
use Gtk;
init Gtk;

use Data::Dumper;

my $a = intern Gtk::Gdk::Atom('STRING');
print "Atom a is ", Gtk::Gdk::Atom->name($a), "\n";

my $b = Gtk::Gdk::Atom->intern('New Atom to be created');
print "Atom a is ", Gtk::Gdk::Atom->name($b), "\n";

print Dumper($a, $b);

Afterwards you can run xlsatoms(1) to verify that there is a new atom
with the name 'New Atom to be created' at the end of the list.

I hope this explains it.

René Seindal (rene seindal dk)        

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