Re: adding widgets to guile-gtk

[Marius Vollmer <mvo@zagadka.ping.de>]

Jules Gosnell <Julian.Gosnell@nomura.co.uk> writes:

> I am looking at guile-gtk-19980504 with an eye to adding a couple of new
> widgets to it.

Yes, that's probably the most visible new feature of guile-gtk, that
you now should be able to use it for third-party widgets.  I have
never really tested it, tho, except for gnome-guile.  So I'm happy
that you are trying this out!

You could simply hack your new definitions into gtk.def, add your
widget libraries to the link stage of guile-gtk and be done with it.
Of course, this is suboptimal, and rightly, you want to actually make
new widgets available to Guile, *without* changing guile-gtk or even
recompiling it.  It should be fairly easy to do this, but you are the
first to try it, so there might be some rough edges.

> I would like to package my widgets and the guile-mywidget glue file into
> a library that can be dynamically loaded into a guile interpreter on
> demand and used just like the gtk widgets (but in a different package).

This is the ideal thing.

> I managed to persuade Guile to compile with dynamic loading supported.

Congrats! ;-) I think there are some problems with the Guile configure
checks for dynamc-linking, right now.

> I had to relink libguilegtk.so with -R<some path> -lgtk -lgdk -lglib
> -R<another path> -lXext -lX11, so that when it is dynamically loaded
> into guile the symbols it references may be resolved.

This is a well known libtool problem, or to put it into more fair
words, a problem of several losing shared library implementations that
libtool does not currently know how to address in a winning way.

The next guile-gtk snapshot will include a slightly patched libtool
that should reenable inter-library dependencies at least for GNU ld
ELF systems.  This is not a real fix and might actually give problems
with static libraries, tho.

> I have managed to compile my widgets into a new library, but was put off
> when I tried to figure out how guile-gtk is configured to do :
> 
> ./build-guile-gtk.in glue gtk.defs >tmpt && mv tmpt gtk-glue.c
> 
> Am I following the correct path ?

Yes, absolutely.

You need to do the following to make guile-gtk glue code for your
widgets.  Let's assume you want to wrap the new GtkFoo widget, and its
accompanying function gtk_foo_new.  

The following has not been tested!

- compile and install guile-gtk

- write your foo.defs file:

    ;; this imports the basic Gtk types, like GtkWidget

    (import "gtk.defs")

    (define-object GtkFoo (GtkWidget))
    
    (define-func gtk_foo_new
      GtkFoo
      ())

- write your foo.defs.guile file:

    (options
     ;; all includes that the glue code needs
     (includes "#include <gtk/gtk.h>"
               "#include "gtkfoo.h")
     ;; the name of your init function
     (init-func "sgtk_init_foo_defs")
     ;; the name of the x-file with the snarfed initialization actions
     (snarf-file "foo-glue.x"))

- generate the glue code from it with the installed build-guile-gtk

    % build-guile-gtk glue foo.defs >foo-glue.c

- snarf it

    % guile-snarf foo-glue.c >foo-glue.x

- write a module initialization function in guile-foo.c or something

    void
    scm_init_toolkits_gtkfoo_module ()
    {
       scm_register_module_xxx ("toolkits gtkfoo", sgtk_init_foo_defs);
    }

[This should actually be done by build-guile-gtk, don't you think?]

- compile and link the glue code into a shared library

    % gcc -shared -o libguilefoo.so -fPIC foo-glue.c guile-foo.c -lguilegtk \
      -lyourfoolib -lgtk -lX11 ...

- install that library

    % cp libguilefoo.so /usr/local/lib

- make a magic symlink

    % cd /usr/local/share/guile/toolkits
    % ln -s /usr/local/lib/libguilefoo.so libgtkfoo.so

- Run Guile

    & guile
    guile> (use-modules (toolkits gtkfoo))
    guile> gtk-foo-new
    #<primitive-procedure gtk-foo-new>

That's the theory, at least.  Please tell me how it goes.

Marius