GtkAda User's Guide
*******************

GtkAda User's Guide

   GtkAda, the Ada graphical toolkit

   Version 2.22.0

   Date: $Date: 2010-11-23 17:58:38 +0100 (Tue, 23 Nov 2010) $

   Copyright (C) 1998-2000, Emmanuel Briot, Joel Brobecker, Arnaud
Charlet

   Copyright (C) 2000-2010, AdaCore

   Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License, Version 1.1 or
any later version published by the Free Software Foundation; with the
Invariant Sections being "GNU Free Documentation License", with the
Front-Cover Texts being "GtkAda User's Guide", and with no Back-Cover
Texts.  A copy of the license is included in the section entitled "GNU
Free Documentation License".

1 Introduction: What is GtkAda ?
********************************

GtkAda is a high-level portable graphical toolkit, based on the gtk+
toolkit, one of the official GNU toolkits. It makes it easy to create
portable user interfaces for multiple platforms, including most
platforms that have a X11 server and Win32 platforms.

   Although it is based on a C library, GtkAda uses some advanced Ada
features such as tagged types, generic packages, access to subprograms,
and exceptions to make it easier to use and design interfaces.  For
efficiency reasons, it does not use controlled types, but takes care of
all the memory management for you in other ways.

   As a result, this library provides a secure, easy to use and
extensible toolkit.

   Compared to the C library, GtkAda provides type safety (especially
in the callbacks area), and object-oriented programming. As opposed to
common knowledge, it requires less type casting than with in C.  Its
efficiency is about the same as the C library through the use of inline
subprograms.

   GtkAda comes with a complete integration to the graphical interface
builder `Glade'(1). This makes it even easier to develop interfaces,
since you just have to click to create a window and all the dialogs.
Ada code can then be generated with a single click.

   Under some platforms, GtkAda also provides a bridge to use OpenGL,
with which you can create graphical applications that display 3D
graphics, and display them in a GtkAda window, as with any other 2D
graphics.  This manual does not document OpenGL at all, see any book on
OpenGL, or the specification that came with your OpenGL library, for
more information.

   The following Internet sites will always contain the latest public
packages for `GtkAda', `gtk+', `Glade' and `Cairo'

   `http://libre.adacore.com/libre/tools/GtkAda/'

   `http://www.gtk.org/'

   `http://glade.gnome.org/'

   `http://www.cairographics.org/'

   The scheme used for GtkAda's version numbers is the following: the
major and minor version number is the same as for the underlying gtk+
library (e.g 2.18).  The micro version number depends on GtkAda's
release number.

   This toolkit was tested on the following systems:
   * GNU Linux/x86

   * GNU Linux/x86-64

   * GNU Linux/ia64

   * Solaris/sparc

   * Windows XP/Vista/2003

   with the latest version of the `GNAT' compiler, developed and
supported by Ada Core Technologies (see `http://www.adacore.com').

   This version of GtkAda is known to be compatible with `gtk+' 2.16.x
and 2.18.x.  This release may or may not be compatible with older
versions of gtk+.

   This version of GtkAda is compatible with `Glade' version 2.0.0.
Due to some modification in the output format of Glade, this release
will not work with older versions. It is also not guaranteed to work
with more recent versions.

   This document does not describe all the widgets available in GtkAda,
nor does it try to explain all the subprograms. The GtkAda Reference
Manual provides this documentation instead, as well as the GtkAda
sources spec files themselves, whose extension is `.ads'.

   No complete example is provided in this documentation. Instead,
please refer to the examples that you can find in the `testgtk/' and
`examples/' directory in the GtkAda distribution, since these are more
up-to-date (and more extensive).  They are heavily commented, and are
likely to contain a lot of information that you might find interesting.

   If you are interested in getting support for GtkAda-including
priority bug fixes, early releases, help in using the toolkit, help in
designing your interface, and on site consulting-please contact AdaCore
(`mailto:sales@adacore.com').

   ---------- Footnotes ----------

   (1) Glade was written by Damon Chaplin

2 Getting started with GtkAda
*****************************

This chapter describes how to start a new GtkAda application. It
explains the basic features of the toolkit, and shows how to compile
and run your application.

   It also gives a brief overview of the extensive widget hierarchy
available in GtkAda.

2.1 How to build and install GtkAda
===================================

This section explains how to build and install GtkAda on your machine.

   On Windows systems, we provide an automatic installer that installs
GtkAda along with dependent components like gtk+ libraries and `Glade'.
If you are a Windows user, you can skip the rest of this section which
will address installation on Unix systems.

   On Unix systems, you first need to install the glib and gtk+
libraries. Download the compatible packages from the gtk+ web site
(`http://www.gtk.org'), compile and install it.  Alternatively, if your
operating system vendor provides glib and gtk+ development packages,
you can install the libraries they provide.

   Change your PATH environment variable so that the script
`pkg-config', which indicates where gtk+ was installed and what
libraries it needs is automatically found by GtkAda. You will no longer
need this script once GtkAda is installed, unless you develop part of
your application in C.

   OpenGL support will not be activated in GtkAda unless you already
have the OpenGL libraries on your systems. You can for instance look at
Mesa, which is free implementation.

   Optionally, you can also install the `Glade' interface builder. Get
the compatible package from the Glade web site, compile and install it.
The official version already knows about Ada (at least enough to call
GtkAda's own programs), so no patch is needed.

   You can finally download the latest version of GtkAda from the web
site.  Untar and uncompress the package, then simply do the following
steps:
     $ ./configure
     $ make
     $ make tests     (this step is optional)
     $ make install

   As usual with the `configure' script, you can specify where you want
to install the GtkAda libraries by using the `--prefix' switch.

   You can specify the switch `--disable-shared' to prevent building
shared libraries, even if your system supports them (by default, both
shared and static libraries are installed). By default, your application
will be linked statically with the GtkAda libraries. You can override
this default by specifying `--enable-shared' as a switch to `configure',
although you can override it later through the LIBRARY_TYPE scenario
variable.

   If you have some OpenGL libraries installed on your system, you can
make sure that `configure' finds them by specifying the
`--with-GL-prefix' switch on the command line. `configure' should be
able to automatically detect the libraries however.

   You must then make sure that the system will be able to find the
dynamic libraries at run time if your application uses them. Typically,
you would do one of the following:
   * run `ldconfig' if you installed GtkAda in one of the standard
     location and you are super-user on your machine

   * edit `/etc/ld.conf' if you are super-user but did not install
     GtkAda in one of the standard location. Add the path that contains
      libgtkada.so (by default `/usr/local/lib' or `$prefix/lib'.

   * modify your `LD_LIBRARY_PATH' environment variable if you are
     not super-user. You should simply add the path to libgtkada.

   In addition, if you are using precompiled Gtk+ binary packages, you
will also need to set the `FONTCONFIG_FILE' environment variable to
point to the `prefix/etc/fonts/fonts.conf' file of your binary
installation.

   For example, assuming you have installed Gtk+ under `/opt/gtk' and
using bash:

     $ export FONTCONFIG_FILE=/opt/gtk/etc/fonts/fonts.conf

   If your application is using printing, on UNIX and Linux you will
need to point your environment variable GTK_EXE_PREFIX to the root
directory of your Gtk+ installation:

     $ export GTK_EXE_PREFIX=/opt/gtk/

2.2 How to distribute a GtkAda application
==========================================

Since GtkAda depends on Gtk+, you usually need to distribute some Gtk+
libraries along with your application.

   Under some OSes such as Linux, Gtk+ comes preinstalled, so in this
case, a simple solution is to rely on the preinstalled Gtk+ libraries.
See below for more information on the gtkada library itself.

   Under other unix systems, GtkAda usually comes with a precompiled
set of Gtk+ libraries that have been specifically designed to be easily
redistributed.

   In order to use the precompiled Gtk+ binaries that we distribute
with GtkAda, you need to distribute all the Gtk+ .so libraries along
with your application, and use the LD_LIBRARY_PATH environment variable
to point to these libraries.

   The list of libraries needed is `<gtkada-prefix>/lib/lib*.so.?'
along with your executable, and set LD_LIBRARY_PATH.

   You may also need the `libgtkada-xxx.so' file. This dependency is
optional since gtkada supports both static and dynamic linking, so by
e.g. using `gtkada-config --static' or by using `gtkada_static.gpr',
you will end up linking with `libgtkada.a'.

   Under Windows, you need to distribute the following files and
directories along with your application, and respect the original
directory set up:

   * `bin/*.dll'

   * `etc/'

   * `lib/gtk-2.0'

2.3 Organization of the GtkAda package
======================================

In addition to the full sources, the GtkAda package contains a lot of
heavily commented examples. If you haven't been through those examples,
we really recommend that you look at them and try to understand them,
since they contain some examples of code that you might find
interesting for your own application.

   * `testgtk/' directory:

     This directory contains the application `testgtk' that tests all
     the widgets in GtkAda. It gives you a quick overview of what can
     be found in the toolkit, as well as some detailed information on
     the widgets and their parameters.

     Each demo is associated with contextual help pointing to aspects
     worth studying.

     It also contains an OpenGL demo, if GtkAda was compiled with
     support for OpenGL.

     This program is far more extensive that its C counterpart, and the
     GtkAda team has added a lot of new examples.

     This directory also contains the application `testcairo' which
     demonstrates the use of various Cairo functions in GtkAda.

   * `examples/' directory:

     This directory contains some small examples, unrelated to
     `testgtk'.  For instance, this is where you will find some sample
     XML files for `Gate' and `Dgate', as well as some new widgets
     created directly in Ada, as examples of how to create your own
     callback marshallers.

     On the whole these examples are a little more complex than
     `testgtk' but since they focus on demonstrating a precise concept,
     they are still quite easy to understand.

   * `docs/' directory:

     It contains the html, info, text and TeX versions of the
     documentation you are currently reading. Note that the
     documentation is divided into two subdirectories, one containing
     the user guide, which you are currently reading, the other
     containing the reference manual, which gives detailed information
     on all the widgets found in GtkAda. The docs directory also
     contains a subdirectory with some slides that were used to present
     GtkAda at various shows.


2.4 How to compile an application with GtkAda
=============================================

This section explains how you can compile your own applications.

   There are several ways to use GtkAda in your applications

2.4.1 Using project files
-------------------------

A set of project files is installed along with GtkAda. If you have
installed GtkAda in the same location as GNAT itself, nothing else
needs to be done.

   Otherwise, you need to make the directory that contains these
project files visible to the compiler. This is done by adding the
directory to the `ADA_PROJECT_PATH' environment variable. Assuming you
have installed the library in `prefix', the directory you need to add is
`prefix/lib/gnat'.

   On Unix, this is done with

     csh:
        setenv ADA_PROJECT_PATH $prefix/lib/gnat:$ADA_PROJECT_PATH
     sh:
        ADA_PROJECT_PATH=$prefix/lib/gnat:$ADA_PROJECT_PATH
        export ADA_PROJECT_PATH

   To build your own application, you should then setup a project file
(see the GNAT documentation for more details on project files), which
simply contains the statement

     with "gtkada";

   This will automatically set the right compiler and linker options,
so that your application is linked with GtkAda.

   By default, the linker will use GtkAda's shared library, if it was
built.  If you would prefer to link with the static library, you can
set the environment variable     LIBRARY_TYPE=static     export
LIBRARY_TYPE before launching the compiler or linker, which will force
it to use the static library instead.

2.4.2 Using the command line
----------------------------

The procedure is system-dependent, and thus is divided into two
subsections.

2.4.2.1 Unix systems
....................

On Unix systems, a script called `gtkada-config' is automatically
created when you build GtkAda. This script is copied in a subdirectory
`bin/' in the installation directory.

   The easiest and recommended way to build a GtkAda application is to
use the `gnatmake' program distributed with GNAT, that takes care of
all the dependencies for you. Use the `gtkada-config' to specify where
GtkAda and gtk+ libraries have been installed.

     > gnatmake <main-file> `gtkada-config`

   Note the use of back-ticks around gtkada-config, which force the
shell to evaluate the script and put the output on the command line.

   However, on complex systems, gnatmake might not be enough. Users
frequently like to create `Makefile's. The script `gtkada-config'
remains useful in that case, since you can call it from your Makefile
(same syntax as above with the back-ticks) to create variables like
FLAGS and LIBS. See the switches of `gtkada-config' below for more
information.

   The script `gtkada-config' understands the following command line
switches (chosen to be compatible with the ones set by `gtk-config'):

   * `--cflags': Output only the compiler flags, i.e the  include
     directories where the GtkAda spec files are found. This should be
     used   if you only want to compile your files, but do not want to
     bind or link   them.

   * `--libs': Output only the switches for the linker. This lists
     the directories where all the GtkAda, gtk+, and dependant
     libraries are   found. For instance, if GtkAda was compiled with
     support for OpenGL,   the OpenGL libraries will automatically be
     present.

   * `--static': Forces linking with the static gtkada library. This
     option will still use the dynamic gtk+ libraries.

2.4.2.2 Windows systems
.......................

Things are somewhat easier on Windows systems. You don't have access to
the `gtkada-config' script. On the other hand you also don't have to
specify which libraries to use or where to find them.

   The only thing you should specify on the `gnatmake' command line is
where the GtkAda spec files are found, as in:

     > gnatmake <main-file> -Ic:\gtkada\include\gtkada

   if GtkAda was installed under `c:\gtkada'.

2.5 Architecture of the toolkit
===============================

The gtk+ toolkit has been designed from the beginning to be portable.
It is made of two libraries: `gtk' and `gdk'.  In addition, GtkAda
provides binding to three supporting libraries: `pango', `cairo' and
`glib'.

   `Glib' is a non-graphical library that includes support for lists,
h-tables, threads, and so on. It is a highly optimized,
platform-independent library. Since most of its contents are already
available in Ada (or in the `GNAT.*' hierarchy in the GNAT
distribution), GtkAda does not include a complete binding to it.  For
the parts of `Glib' that we do depend on, we provide `Glib.*' packages
in the GtkAda distribution.

   `Gdk' is the platform-dependent part of gtk+, and so there are
different implementations (for instance, for Win32 and X11 based
systems) that implement a common API. `Gdk' provides basic graphical
functionality to, for instance, draw lines, rectangles and pixmaps on
the screen, as well as manipulate colors. The `Gdk.*' packages provide
a full Ada interface to `Gdk'.

   `Pango' is a modern font handling system. Bindings in GtkAda gives
access to the API to manipulate font descriptions and text attributes.

   `Cairo' is the low-level 2D drawing library used by `Gdk' to render
widgets. `Cairo' provides a rich set of vector drawing features,
supporting anti-aliasing, transparency, and 2D matrix
transformations.The `Cairo.*' packages provide a complete Ada binding
to `Cairo'.

   `Gtk' is the top level library. It is platform independent, and does
all its drawing through calls to Gdk and Cairo. This is where the
high-level widgets are defined. It also includes support for callbacks.
Its equivalent in the GtkAda libraries are the `Gtk.*' packages. It is
made of a fully object-oriented hierarchy of widgets (see *Note Widgets
Hierarchy::).

   Since your application only calls GtkAda, it is fully portable, and
can be recompiled as-is on other platforms.

     +------------------------------- ----------+
     |             Your Application             |
     +------------------------------------------+
     |                 GtkAda                   |
     |              +-----------------+         |
     |              |      GTK        |         |
     |         +----+-----------------+----+    |
     |         |           GDK             |    |
     |    +----+------+         +----------+----+
     |    |   Pango   |         |     Cairo     |
     +----+-----------+----+----+---------------+
     |        GLIB         |   X-Window / Win32  |
     +---------------------+--------------------+

   Although the packages have been evolving a lot since the first
versions of GtkAda, the specs are stabilizing now. We will try as much
as possible to provide backward compatibility whenever possible.

   Since GtkAda is based on gtk+ we have tried to stay as close to it
as possible while using high-level features of the Ada language. It is
thus relatively easy to convert external examples from C to Ada.

   We have tried to adopt a consistent naming scheme for Ada
identifiers:
   * The widget names are the same as in C, except that an underscore
     sign (_) is used to separate words, e.g
          Gtk_Button   Gtk_Color_Selection_Dialog

   * Because of a clash between Ada keywords and widget names, there
     are two exceptions to the above general rule:
          Gtk.GEntry.Gtk_Entry   Gtk.GRange.Gtk_Range

   * The function names are the same as in  C, ignoring the leading
     `gtk_' and the widget name, e.g
          gtk_misc_set_padding        =>  Gtk.Misc.Set_Padding
          gtk_toggle_button_set_state =>  Gtk.Toggle_Button.Set_State

   * Most enum types have been grouped in the `gtk-enums.ads' file

   * Some features have been implemented as generic packages. These are
     the timeout functions (see `Gtk.Main.Timeout'), the idle functions
     (see `Gtk.Main.Idle'), and the data that can be attached to any
     object (see `Gtk.Object.User_Data'). Type safety is ensured
     through these generic packages.

   * Callbacks were the most difficult thing to interface with. These
     are extremely powerful and versatile, since the callbacks can have
     any number of arguments and may or may not return values. These
     are once again implemented as generic packages, that require more
     explanation (*note Signal handling::).


   WARNING: all the generic packages allocate some memory for internal
structures, and call internal functions. This memory is freed by gtk
itself, by calling some Ada functions. Therefore the generic packages
have to be instantiated at library level, not inside a subprogram, so
that the functions are still defined when gtk needs to free the memory.

   WARNING Before any other call to the GtkAda library is performed,
`Gtk.Main.Init' must be invoked first. Most of the time, this procedure
is invoked from the main procedure of the application, in which case no
use of GtkAda can be done during the application elaboration.

2.6 Widgets Hierarchy
=====================

All widgets in `GtkAda' are implemented as tagged types. They all have
a common ancestor, called `Gtk.Object.Gtk_Object'. All visual objects
have a common ancestor called `Gtk.Widget.Gtk_Widget'.

   The following table describes the list of objects and their
inheritance tree. As usual with tagged types, all the primitive
subprograms defined for a type are also known for all of its children.
This is a very powerful way to create new widgets, as will be explained
in *Note Creating new widgets in Ada::.

   Although gtk+ was written in C its design is object-oriented, and
thus GtkAda has the same structure. The following rules have been
applied to convert from C names to Ada names: a widget `Gtk_XXX' is
defined in the Ada package `Gtk.XXX', in the file `gtk-xxx.ads'. This
follows the GNAT convention for file names.  For instance, the
`Gtk_Text' widget is defined in the package `Gtk.Text', in the file
`gtk-text.ads'.

   Note also that most of the documentation for GtkAda is found in the
spec files themselves.

   It is important to be familiar with this hierarchy. It is then
easier to know how to build and organize your windows. Most widgets are
demonstrated in the `testgtk/' directory in the GtkAda distribution.

Gtk_Object
  +-- Gtk_Data
  |     +-- Gtk_Tooltips
  |     \__ Gtk_Adjustment
  \__ Gtk_Widget  @i{(Visual widgets)}
        +-- Gtk_Calendar
        +-- Gtk_Container  @i{(Widgets that have children)}
        |     +-- Gtk_Bin  @i{(Widgets that have a single child)}
        |     |     +-- Gtk_Alignment
        |     |     +-- Gtk_Button @i{(Widgets that you can click)}
        |     |     |     +-- Gtk_Option_Menu
        |     |     |     +-- Gtk_Toggle_Button
        |     |     |     |     \__ Gtk_Check_Button
        |     |     |     |           \__ Gtk_Radio_Button
        |     |     +-- Gtk_Event_Box
        |     |     +-- Gtk_Frame
        |     |     |     \__ Gtk_Aspect_Frame
        |     |     +-- Gtk_Handle_Box
        |     |     +-- Gtk_Invisible
        |     |     +-- Gtk_Item
        |     |     |     +-- Gtk_List_Item
        |     |     |     +-- Gtk_Menu_Item
        |     |     |     |     +-- Gtk_Check_Menu_Item
        |     |     |     |     |     \__ Gtk_Radio_Menu_Item
        |     |     |     |     \__ Gtk_Tearoff_Menu_Item
        |     |     |     \__ Gtk_Tree_Item
        |     |     +-- Gtk_Viewport
        |     |     \__ Gtk_Window  @i{(Have an independent window)}
        |     |           +-- Gtk_Color_Selection_Dialog
        |     |           +-- Gtk_Dialog
        |     |           |     \__ Gtk_Input_Dialog
        |     |           +-- Gtk_File_Selection
        |     |           +-- Gtk_Font_Selection_Dialog
        |     |           \__ Gtk_Plug
        |     +-- Gtk_Box  @i{(Widgets that have one or more children)}
        |     |     +-- Gtk_Button_Box
        |     |     |     +-- Gtk_Vbutton_Box
        |     |     |     \__ Gtk_Hbutton_Box
        |     |     +-- Gtk_Color_Selection
        |     |     +-- Gtk_Combo
        |     |     +-- Gtk_Gamma_Curve
        |     |     \__ Gtk_Status_Bar
        |     +-- Gtk_Clist
        |     |     \__ Gtk_Ctree
        |     +-- Gtk_Fixed
        |     +-- Gtk_Layout
        |     +-- Gtk_List
        |     +-- Gtk_Menu_Shell
        |     |     +-- Gtk_Menu
        |     |     \__ Gtk_Menu_Bar
        |     +-- Gtk_Notebook
        |     |     \__ Gtk_Font_Selection
        |     +-- Gtk_Packer
        |     +-- Gtk_Paned
        |     +-- Gtk_Scrolled_Window
        |     +-- Gtk_Socket
        |     +-- Gtk_Toolbar
        |     +-- Gtk_Table
        |     \__ Gtk_Tree
        +-- Gtk_Drawing_Area
        |     \__ Gtk_Curve
        +-- Gtk_Editable
        |     +-- Gtk_Entry
        |     |     \__ Gtk_Spin_Button
        |     \__ Gtk_Text
        +-- Gtk_Misc
        |     +-- Gtk_Arrow
        |     +-- Gtk_Image
        |     +-- Gtk_Label
        |     |     +-- Gtk_Accel_Label
        |     |     \__ Gtk_Tips_Query
        |     \__ Gtk_Pixmap
        +-- Gtk_Preview
        +-- Gtk_Progress
        |     \__ Gtk_Progress_Bar
        +-- Gtk_Range
        |     +-- Gtk_Scale
        |     \__ Gtk_Scrollbar
        +-- Gtk_Ruler
        \__ Gtk_Separator
                 *Hierarchy of widgets in GtkAda*

3 Hierarchical composition of a window
**************************************

Interfaces in GtkAda are built in layers, as in Motif.  For instance, a
typical dialog is basically a Gtk_Window, that in turn contains a
Gtk_Box, itself divided into two boxes and a Gtk_Separator, and so on.

   Altough this may seem more complicated than setting absolute
positions for children, this is the simplest way to automatically
handle the resizing of windows. Each container that creates a layer
knows how it should behave when it is resized, and how it should move
its children.  Thus almost everything is handled automatically, and you
don't have to do anything to support resizing.

   If you really insist on moving the children to a specific position,
look at the `Gtk_Fixed' widget and its demo in `testgtk/'. But you
really should not use this container, since you will then have to do
everything by hand.

   All the containers are demonstrated in `testgtk/', in the GtkAda
distribution. This should help you understand all the parameters
associated with the containers. It is very important to master these
containers, since using the appropriate containers will make building
interfaces a lot easier.

   If you look at the widget hierarchy (*note Widgets Hierarchy::), you
can see that a Gtk_Window inherits from Gtk_Bin, and thus can have only
one child. In most cases, the child of a Gtk_Window will thus be a
Gtk_Box, which can have any number of children.

   Some widgets in GtkAda itself are built using this strategy, from the
very basic `Gtk_Button' to the more advanced `Gtk_File_Selection'.

   For example, by default a Gtk_Button contains a Gtk_Label, which
displays the text of the button (like "OK" or "Cancel").

   However, it is easy to put a pixmap in a button instead. When you
create the button, do not specify any label. Thus, no child will be
added, and you can give it your own. See `testgtk/create_pixmap.adb'
for an example on how to do that.

4 Signal handling
*****************

In GtkAda, the interaction between the interface and the core
application is done via signals. Most user actions on the graphical
application trigger some signals to be `emitted'.

   A signal is a message that an object wants to broadcast. It is
identified by its name, and each one is associated with certain events
which happen during the widget's lifetime. For instance, when the user
clicks on a Gtk_Button, a "clicked" signal is emitted by that button.
More examples of signals can be found in the GtkAda reference manual.

   It is possible to cause the application to react to such events by
`connecting' to a signal a special procedure called a `handler' or
`callback'.  This handler will be called every time that signal is
emitted, giving the application a chance to do any processing it needs.
More than one handler can be connected to the same signal on the same
object; the handlers are invoked in the order they were connected.

4.1 Predefined signals
======================

Widgets, depending on their type, may define zero or more different
signals.  The signals defined for the parent widget are also
automatically inherited; thus every widget answers many signals.

   The easiest way to find out which signals can be emitted by a widget
is to look at the GtkAda reference manual. Every widget will be
documented there. The GtkAda RM explains when particular signals are
emitted, and the general form that their handlers should have (although
you can always add a `User_Data' if you wish, see below).

   You can also look directly at the C header files distributed with
the gtk+ library. Each widget is described in its own C file and has
two C structures associated with it. One of them is the "class"
structure, which contains a series of pointers to functions. Each of
these functions has the same name as the signal name.

   For instance, consider the following extract from gtkbutton.h:
     struct _GtkButtonClass
     {
       GtkBinClass        parent_class;

       void (* pressed)  (GtkButton *button);
       void (* released) (GtkButton *button);
       void (* clicked)  (GtkButton *button);
       void (* enter)    (GtkButton *button);
       void (* leave)    (GtkButton *button);
     };

   This means that the Gtk_Button widget redefines five new signals
called `pressed', `released', and so on, respectively.

   The profile of the handler can also be deduced from those pointers:
The handler has the same arguments, plus an optional `User_Data'
parameter that can be used to pass any kind of data to the handler.
When the `User_Data' parameter is used, the value of this data is
specified when connecting the handler to the signal. It is then given
back to the handler when the signal is raised.

   Therefore, the profile of a handler should look like:
     procedure Pressed_Handler
       (Button    : access Gtk_Button_Record'Class;
        User_Data : ...);

   The callback does not need to use all the arguments. It is legal to
use a procedure that "drops" some of the last arguments.  There is one
special case, however: if, at connection time, you decided to use
`User_Data', your callback must handle it.  This is checked by the
compiler.

   Any number of arguments can be dropped as long as those arguments are
the last ones in the list and you keep the first one. For instance, the
signal "button_press_event" normally can be connected to a handler with
any of the following profiles:

     --  with a user_data argument
     procedure Handler
       (Widget    : access Gtk_Widget_Record'Class;
        Event     : Gdk.Event.Gdk_Event;
        User_Data : ...);
     procedure Handler
       (Widget    : access Gtk_Widget_Record'Class;
        User_Data : ...);

     --  without a user_data argument
     procedure Handler
       (Widget : access Gtk_Widget_Record'Class;
        Event  : Gdk.Event.Gdk_Event);
     procedure Handler (Widget : access Gtk_Widget_Record'Class);

   Beware that adding new arguments is not possible, since no value
would be provided for them. When connecting a handler, GtkAda will not
always verify that your handler does not have more arguments than
expected, so caution is recommended (it only does so if you use the
`Gtk.Marshallers' package, see below).

4.2 Connecting signals
======================

All signal handling work is performed using services provided by the
`Gtk.Handlers' package. This package is self-documented, so please read
the documentation for this package either in the GtkAda Reference
Manual or in the specs themselves. The rest of this section assumes
that you have this documentation handy.

   A short, annotated example of connecting signals follows; a complete
example can be found in create_file_selection.adb (inside the `testgtk/'
directory). In our example, an application opens a file selector to
allow the user to select a file.  GtkAda provides a high-level widget
called Gtk_File_Selection which can be used in this case:

     declare
        Window : Gtk_File_Selection;
     begin
        Gtk.File_Selection.Gtk_New (Window, Title => "Select a file");
     end;

   When the "OK" button is pressed, the application needs to retrieve
the selected file and then close the dialog. The only information that
the handler for the button press needs is which widget to operate upon.
This can be achieved by the following handler:

     procedure OK (Files : access Gtk_File_Selection_Record'Class) is
     begin
        Ada.Text_IO.Put_Line ("Selected " & Get_Filename (Files));
        --  Prints the name of the selected file.
        Destroy (Files);
        --  Destroys the file selector dialog
     end Ok;

   We now need to connect the object we created in the first part with
the new callback we just defined. `Gtk.Handlers' defines four types of
generic packages, depending on the arguments one expects in the
callback and whether the callback returns a value or not. Note that you
can not use an arbitrary list of arguments; this depends on the signal,
as explained in the previous section.

   In our example, since the callback does not return any value and
does not handle any `User_Data' (that is, we don't pass it extra data,
which will be specified at connection time), the appropriate package to
use is `Gtk.Handlers.Callback'. We thus instantiate that package.

   Remember that generic package instantiations in GtkAda must be
present in memory at all times, since they take care of freeing
allocated memory when finished. GtkAda generic package instantiations
must therefore always be performed at the library level, and not inside
any inner block.

     package Files_Cb is new
       Handlers.Callback (Gtk_File_Selection_Record);

   The `Files_Cb' package now provides a set of Connect subprograms
that can be used to establish a tie between a widget and a handler.  It
also provides a set of other subprograms which you can use to emit the
signals manually, although most of the time, the signals are simply
emitted internally by GtkAda. We will not discuss the Emit_By_Name
subprograms here.

   The general form of handler, as used in `Gtk.Handlers', expects some
handlers that take two or three arguments: the widget on which the
signal was applied, an array of all the extra arguments sent internally
by GtkAda, and possibly some user data given when the connection was
made.

   This is the most general form of handler and it covers all the
possible cases. However, it also expects the user to manually extract
the needed values from the array of arguments. This is not always the
most convenient solution. This is why GtkAda provides a second package
related to signals, `Gtk.Marshallers'.

   The `Gtk.Marshallers' package provides a set of functions that can
be used as callbacks directly for GtkAda, and that will call your
application's handlers after extracting the required values from the
array of arguments. Although this might sound somewhat complicated, in
practice it simplifies the task of connecting signals. In fact, the
techniques employed are similar to what is done internally by gtk+ in
C. Because of the similarity of techniques, there is no overhead
involved in using `Gtk.Marshallers' with Ada over the C code in gtk+.

   A set of functions `To_Marshaller' is found in every generic package
in `Gtk.Handlers'. They each take a single argument, the name of the
function you want to call, and return a handler that can be used
directly in `Connect'.

   The connection is then done with the following piece of code:

     Files_Cb.Object_Connect
       (Get_Ok_Button (Window),  --  The object to connect to the handler
        "clicked",               --  The name of the signal
        Files_Cb.To_Marshaller (Ok'Access),  --  The signal handler
        Slot_Object => Window);

   Note that this can be done just after creating the widget, in the
same block. As soon as it is created, a widget is ready to accept
connections (although no signals will be emitted before the widget is
shown on the screen).

   We use `To_Marshaller' since our handler does not accept the array
of arguments as a parameter, and we use the special `Object_Connect'
procedure. This means that the parameter to our callback (Files) will
be the Slot_Object given in Object_Connect, instead of being the button
itself.

4.3 Handling user data
======================

As described above, it is possible to define some data that is that
passed to the callback when it is called. This data is called
user_data, and is passed to the `Connect' or `Object_Connect'
subprograms.

   GtkAda will automatically free any memory it has allocated internally
to store this user data. For instance, if you instantiated the generic
package `User_Callback' with a String, it means that you want to be
able to have a callback of the form:

        procedure My_Callback (Widget : access Gtk_Widget_Record'Class;
                                User_Data : String);

   and connect it with a call similar to:

        Connect (Button, "Clicked", To_Marshaller (My_Callback'Access),
                 User_Data => "any string");

   GtkAda needs to allocate some memory to store the string (an
unconstrained type). However, this memory is automatically freed when
the callback is destroyed.

   There are a few subtleties in the use of user_data, most importantly
when the user data is itself a widget.

   The following four examples do exactly the same thing: each creates
two buttons, where clicking on the first one will destroy the second
one.  They all work fine the first time, while both buttons exist.
However, some of them will fail if you press on the first button a
second time.

   Complete, compilable source code for these examples can be found in
the distribution's `examples/user_data' directory, from which the code
samples below are excerpted.

4.3.1 First case: simple user data
----------------------------------

This code will fail: even after `Button2' is destroyed, the Ada pointer
continues to reference memory that has been deallocated.  The second
call to `Destroy' will fail with a Storage_Error.

        package User_Callback is new Gtk.Handlers.User_Callback
          (Gtk_Widget_Record, Gtk_Widget);

        procedure My_Destroy2
          (Button : access Gtk_Widget_Record'Class; Data : Gtk_Widget) is
        begin
           Destroy (Data);
        end My_Destroy2;

        begin
           User_Callback.Connect
             (Button1, "clicked",
              User_Callback.To_Marshaller (My_Destroy2'Access),
              Gtk_Widget (Button2));
        end;

4.3.2 Second case: using Object_Connect instead
-----------------------------------------------

One of the solutions to fix the above problem is to use
`Object_Connect' instead of `Connect'. In that case, GtkAda
automatically takes care of disconnecting the callback when either of
the two widgets is destroyed.

        procedure My_Destroy (Button : access Gtk_Widget_Record'Class) is
        begin
           Destroy (Button);
        end My_Destroy;

        begin
           Widget_Callback.Object_Connect
             (Button1, "clicked",
              Widget_Callback.To_Marshaller (My_Destroy'Access),
              Button2);
        end;

4.3.3 Third case: manually disconnecting the callback
-----------------------------------------------------

Using `Object_Connect' is not always possible. In that case, one of the
possibilities is to store the `Id' of the callback, and properly
disconnect it when appropriate. This is the most complex method, and
very often is not applicable, since you cannot know for sure when the
callback is no longer needed.

        type My_Data3 is record
           Button, Object : Gtk_Widget;
           Id             : Handler_Id;
        end record;
        type My_Data3_Access is access My_Data3;

        package User_Callback3 is new Gtk.Handlers.User_Callback
          (Gtk_Widget_Record, My_Data3_Access);

        procedure My_Destroy3
          (Button : access Gtk_Widget_Record'Class;
           Data   : My_Data3_Access) is
        begin
           Destroy (Data.Button);
           Disconnect (Data.Object, Data.Id);
        end My_Destroy3;

           Id : Handler_Id;
        begin
           Data3 := new My_Data3' (Object => Gtk_Widget (Button1),
                                   Button => Gtk_Widget (Button2),
                                   Id     => (Null_Signal_Id, null));
           Id := User_Callback3.Connect
             (Button1, "clicked",
              User_Callback3.To_Marshaller (My_Destroy3'Access),
              Data3);
           Data3.Id := Id;
        end;

4.3.4 Fourth case: setting a watch on a specific widget
-------------------------------------------------------

GtkAda provides a function `Add_Watch', that will automatically
disconnect a callback when a given widget is destroyed. This is the
function used internally by `Object_Connect'. In the example below, the
callback is automatically disconnected whenever `Button2' is destroyed.

        procedure My_Destroy2
          (Button : access Gtk_Widget_Record'Class; Data : Gtk_Widget) is
        begin
           Destroy (Data);
        end My_Destroy2;

           Id : Handler_Id;
        begin
           Id := User_Callback.Connect
             (Button1, "clicked",
              User_Callback.To_Marshaller (My_Destroy2'Access),
              Gtk_Widget (Button2));
           Add_Watch (Id, Button2);
        end;

5 Starting an application with GtkAda
*************************************

You need to perform some initializations to start a GtkAda application:
     --  predefined units of the library
     with Gtk.Rc;
     with Gtk.Main;
     with Gtk.Enums;
     with Gtk.Window;
     ...
     --  My units
     with Callbacks;
     ...
     procedure Application is
        procedure Create_Window is ...

     begin
        --  Set the locale specific datas (e.g time and date format)
        Gtk.Main.Set_Locale;

        --  Initializes GtkAda
        Gtk.Main.Init;

        --  Load the resources. Note that this part is optional.
        Gtk.Rc.Parse ("application.rc");

        --  Create the main window
        Create_Window;

        --  Signal handling loop
        Gtk.Main.Main;
     end Application;

   the `Create_Window' procedure looks like

        procedure Create_Window is
           Main_Window : Gtk.Window.Gtk_Window;
           ...
        begin
           Gtk.Window.Gtk_New
             (Window   => Main_Window,
              The_Type => Gtk.Enums.Window_Toplevel);

           --  From Gtk.Widget:
           Gtk.Window.Set_Title (Window => Main_Window, Title  => "Editor");

           --  Construct the window and connect various callbacks

           ...
           Gtk.Window.Show_All (Main_Window);
        end Create_Window;

6 Resource files
****************

Resource files let you parametrize aspects of the widgets in a GtkAda
application without having to recompile it.

   A resource file needs to be loaded (`Gtk.Rc.Parse') BEFORE setting
the corresponding window.

   In this file, it is possible to specify visual characteristics of
widgets, such as their colors and fonts.  Under X, the `xfontsel'
command allows you to easily select a font.  The FontSelection widget
is also a simple way to select fonts.

   Here is an example of a resource file:
     # application.rc
     #
     # resource file for "Application"

     # Buttons style
     style "button"
     {
     # BackGround Colors
     #                  Red  Green  Blue
       bg[PRELIGHT] = { 0.0,  0.75, 0.0 } # Green when the mouse is on
                                          # the button
       bg[ACTIVE]   = { 0.75, 0.0,  0.0 } # Red on click
     # ForeGround Colors
     #                  Red  Green  Blue
       fg[PRELIGHT] = { 1.0,  1.0,  1.0 } # White when the mouse is on
                                          # the button
       fg[ACTIVE]   = { 1.0,  1.0,  1.0 } # White on click
     }

     # All the buttons will have the style "button"
     widget_class "*GtkButton*" style "button"

     # Text style
     style "text"
     {
       font = "-adobe-courier-medium-r-normal-*-15-*-*-*-*-*-*-*"
       text[NORMAL] = { 0.0, 0.0, 0.0 } # black
       fg[NORMAL]   = { 0.0, 0.0, 0.0 } # black
       base[NORMAL] = { 1.0, 1.0, 1.0 } # white : background color
     }

     # All Gtk_Text will have the "text" style
     widget_class "*GtkText" style "text"

7 Memory management
*******************

GtkAda takes care of almost all the memory management for you.  Here is
a brief overview of how this works, you'll have to check the sources if
you want more detailed information.  Gtk+ (the C library) does its own
memory management through reference counting, i.e. any widget is
destroyed when it is no longer referenced anywhere in the application.

   In GtkAda itself, a "user_data" is associated with each object
allocated by a `Gtk_New' procedure. A "destroy" callback is also
associated, to be called when the object to which the user_data belongs
is destroyed.  Thus, every time a C object is destroyed, the equivalent
Ada structure is also destroyed (see `Gtk.Free_User_Data').

   Concerning widgets containing children, every container holds a
reference to its children, whose reference counting is thus different
from 0 (and generally 1). When the container is destroyed, the
reference of all its children and grand-children is decremented, and
they are destroyed in turn if needed. So the deallocation of a widget
hierarchy is also performed automatically.

8 Tasking with GtkAda
*********************

Note that Gtk+ under Windows does not interact properly with threads,
so the only safe approach under this operating system is to perform all
your Gtk+ calls in the same task.

   On other platforms, the Glib library can be used in a task-safe mode
by calling `Gdk.Threads.G_Init' and `Gdk.Threads.Init' before making
any other Glib/Gdk calls.  Gdk routines may then be called
simultaneously by multiple tasks, thanks to task-safe construction of
Gdk's internal data structures. However, Gdk objects such as hash
tables are not automatically protected, so it is the application's
responsibility to prevent simultaneous access to user-defined objects
(e.g. by using protected objects).

   When Gdk is initialized to be task-safe, GtkAda becomes task aware.
There is a single global lock that you must acquire with
`Gdk.Threads.Enter' before making any Gdk/Gtk call, and which you must
release with `Gdk.Threads.Leave' afterwards.

   `Gtk.Main.Main' should be called with the lock acquired (see example
below), ensuring that all the functions executed in the task that
started the main loop do not need to protect themselves again.

   Beware that the GtkAda main loop (`Gtk.Main.Main') can only be be
run inside one specific task. In other words, you cannot call
`Gtk.Main.Main' from any task other than the one that started the outer
level main loop.

   Note that `Gdk.Threads' assumes that you are using a tasking run time
that maps Ada tasks to native threads.

   A minimal main program for a tasking GtkAda application looks like:

     with Gdk.Threads;
     with Gtk.Main;
     with Gtk.Enums; use Gtk.Enums;
     with Gtk.Window; use Gtk.Window;

     procedure GtkAda_With_Tasks is
        Window : Gtk_Window;
     begin
        Gdk.Threads.G_Init;
        Gdk.Threads.Init;
        Gtk.Main.Init;

        Gtk_New (Window, Window_Toplevel);
        Show (Window);

        Gdk.Threads.Enter;
        Gtk.Main.Main;
        Gdk.Threads.Leave;
     end GtkAda_With_Tasks;

   Callbacks require a bit of attention. Callbacks from GtkAda
(signals) are made within the GtkAda lock. However, callbacks from Glib
(timeouts, IO callbacks, and idle functions) are made outside of the
GtkAda lock. So, within a signal handler you do not need to call
`Gdk.Threads.Enter', but within the other types of callbacks, you do.

9 Processing external events
****************************

It often happens that your application, in addition to processing
graphical events through the GtkAda main loop, also needs to monitor
external events.  This is the case if, for instance, you are running
external processes and need to display their output, or if you are
listening to incoming data on a socket.  If you implement your own main
loop to poll for these external events and then invoke the GUI, the GUI
will enter its main loop and not return control back to you.

   There are several ways to handle this situation:

   * The cleanest solution, especially if you intend to make the GUI a
     major part of your application (as opposed to just popping up a
     few dialogs here and there), would be to use the gtk+ main loop as
     the  infinite loop, instead of yours.

     You can then use gtk+ "idle callbacks" (which are called  every
     time the gtk+ loop is not busy processing graphical events)  or
     "timeout callbacks" (which are called every n milliseconds), and
     in those callbacks do the work you were doing before in your own
     main loop (that assumes the check is relatively fast,  otherwise
     the GUI will be frozen during that time). Such callbacks  are
     created through packages in glib-main.ads

   * Another approach is to not start the gtk+ main loop, but to check
     periodically whether there are some events to be handled.   See
     the subprogram `Gtk.Main.Main_Iteration'.

     This second approach is not necessarily recommended, since you
     would  basically duplicate code that's already in gtk+ to manage
     the main  loop, and you also get finer control using idle and
     timeout callbacks


10 Object-oriented features
***************************

GtkAda has been designed from the beginning to provide a full object
oriented layer over gtk+. This means that features such as type
extension and dynamic dispatching are made available through the
standard Ada language.

   This section will describe how things work, how you can extend
existing widgets, and even how to create your own widgets.

10.1 General description of the tagged types
============================================

10.1.1 Why should I use object-oriented programming ?
-----------------------------------------------------

Every widget in the `Gtk.*' packages in GtkAda is a tagged type with a
number of primitive subprograms that are inherited by all of its
children.  Tagged types in Ada make it possible to perform safe,
automatic type conversions without using explicit casts (such as is
necessary when coding in C). It is also possible for the compiler to
verify whether or not these type conversions are valid. Most errors are
found at compile time, which leads to a safer and more robust
application.

   As a further example, imagine a table that has been populated by
some widgets.  It is possible to query for this table's children and
operate on these widgets without knowing details about their type,
their creator, and so on-the tagged objects that are returned contain
all the information necessary.  It becomes possible to use dynamic
dispatching without ever having to cast to a known type.

   Modifying a standard widget to draw itself differently or display
different data is easy using tagged types.  Simply create a new type
that extends the current one (see the section *Note Using tagged types
to extend Gtk widgets:: below.

   Creating a new reusable widget from scratch is also possible.
Create a new tagged type and specify properties of the widget-such as
how it is to draw itself and how it should react to events.  See the
section *Note Creating new widgets in Ada:: below.

   Object oriented programming through the use of Ada tagged types makes
GtkAda a very powerful, flexible, and safe tool for designing graphical
interfaces.

10.1.2 Type conversions from C to Ada widgets
---------------------------------------------

There are three kinds of widgets that you can use with GtkAda:
   * Ada widgets: These are widgets that are written directly in Ada,
     using the object oriented features of GtkAda

   * Standard widgets: These are the widgets that are part of the
     standard gtk+ and GtkAda distributions. This include all the basic
     widgets you need to build advanced interfaces.

   * third party C widgets These are widgets that were created in C,
     and for which you (or someone else) created an Ada binding. This
     is most probably the kind of widgets you will have if you want to
     use third party widgets.

   GtkAda will always be able to find and/or create a valid tagged type
in the first two cases, no matter if you explicitly created the widget
or if it was created automatically by gtk+. For instance, if you
created a widget in Ada, put it in a table, and later on extracted it
from the table, then you will still have the same widget.

   In the third case (third party C widgets), GtkAda is not, by
default, able to create the corresponding Ada type.

   The case of third party C widgets is a little bit trickier. Since
GtkAda does not know anything about them when it is built, it can't
magically convert the C widgets to Ada widgets. This is your job to
teach GtkAda how to do the conversion.

   We thus provide a 'hook' function which you need to modify. This
function is defined in the package Glib.Type_Conversion. This function
takes a string with the name of the C widget (ex/ "GtkButton"), and
should return a newly allocated pointer. If you don't know this type
either, simply return null.

10.2 Using tagged types to extend Gtk widgets
=============================================

With this toolkit, it's possible to associate your own data with
existing widgets simply by creating new types. This section will show
you a simple example, but you should rather read the source code in the
`testgtk/' directory where we used this feature instead of using
`user_data' as is used in the C version.

     type My_Button_Record is new Gtk_Button_Record with record
         --  whatever data you want to associate with your button
     end record;
     type My_Button is access all My_Button_Record'Class;

   With the above statements, your new type is defined. Every function
available for `Gtk_Button' is also available for `My_Button'.  Of
course, as with every tagged type in Ada, you can create your own
primitive functions with the following prototype:

     procedure My_Primitive_Func (Myb : access My_Button_Record);

   To instanciate an object of type `My_Button' in your application, do
the following:

     declare
        Myb : My_Button;
     begin
        Myb := new My_Button_Record;
        Initialize (Myb);   --  from Gtk.Button
     end;

   The first line creates the Ada type, whereas the `Initialize' call
actually creates the C widget and associates it with the Ada type.

10.3 Creating new widgets in Ada
================================

With GtkAda, you can create widgets directly in Ada. These new widgets
can be used directly, as if they were part of gtk itself.

   Creating new widgets is a way to create reuseable components. You can
apply to them the same functions as you would for any other widget,
such as `Show', `Hide', and so on.

   This section will explain how to create two types of widgets:
composite widgets and widgets created from scratch. Two examples are
provided with GtkAda, in the directories `examples/composite_widget' and
`examples/base_widget'. Please also refer to the gtk+ tutorial, which
describes the basic mechanisms that you need to know to create a widget.

10.3.1 Creating composite widgets
---------------------------------

A composite widget is a widget that does not do much by itself. Rather,
this is a collection of subwidgets grouped into a more general entity.
For instance, among the standard widgets, `Gtk_File_Selection' and
`Gtk_Font_Selection' belong to this category.

   The good news is that there is nothing special to know. Just create a
new tagged type, extending one of the standard widgets (or even another
of your own widgets), provide a `Gtk_New' function that allocates
memory for this widget, and call the `Initialize' function that does
the actual creation of the widget and the subwidgets.  There is only
one thing to do: `Initialize' should call the parent class's
`Initialize' function, to create the underlying C widget.

   The example directory `examples/composite_widget' reimplements the
`Gtk_Dialog' widget as written in C by the creators of gtk+.

10.3.2 Creating widgets from scratch
------------------------------------

Creating a working widget from scratch requires a certain level of
familiary with the GtkAda signal mechanism and entails much work with
low level signals.  This is therefore not an activity recommended for
novice GtkAda programmers.

   Creating a widget from scratch is what you want to do if your widget
should be drawn in a special way, should create and emit new signals,
or otherwise perform differently than pre-existing widgets.  The
example we give in `examples/base_widget' is a small target on which
the user can click, and that sends one of two signals: "bullseye" or
"missed", depending on where the user has clicked.

   See also the example in `examples/tutorial/gtkdial' for a more
complex widget, that implements a gauge where the user can move the
arrow to select a new value.

   Once again, the only two functions that you must create are `Gtk_New'
and `Initialize'.  This time, `Initialize' has to do two things:

     Parent_Package.Initialize (Widget);

     --  The above line calls the Initialize function from the parent.
     --  This creates the underlying C widget, which we are going to
     --  modify with the following call:

     Gtk.Object.Initialize_Class_Record
       (Widget, Signals, Class_Record);
     --  This initializes the "class record" for the widget and
     --  creates the signals.

   In the above example, the new part is the second call. It takes
three or four arguments:
   * `Widget' This is the widget that you want to initialize

   * `Signals' This is an array of string access containing the name of
     the signals you want to create. For instance, you could create
     Signals with
          Signals : Gtkada.Types.Chars_Ptr_Array := "bullseye" + "missed";
     This will create two signals, named "bullseye" and "missed", whose
     callbacks' arguments can be specified with the fourth parameter.

   * `Class_Record' Every widget in C is associated with two records.
     The first one, which exists only once per widget type, is the
     "class record". It contains the list of signals that are known by
     this widget type, the list of default callbacks for the signals,
     ...; the second record is an "instance record", which contains
     data specific to a particular instance.

     In GtkAda, the "instance record" is simply your tagged type and
     its fields.  The call to `Initialize_Class_Record' is provided to
     initialize the "class record". As we said, there should be only
     one such record per widget type. This parameter "Class_Record"
     will point to this records, once it is created, and will be reused
     for every instanciation of the widget.

   * `Parameters' This fourth argument is in fact optional, and is used
     to specify which kind of parameters each new signal is expecting.
     By default (ie if you don't give any value for this parameter),
     all the signals won't expect any argument, except of course a
     possible user_data.  However, you can decide for instance that the
     first signal ("bullseye") should in fact take a second argument
     (say a Gint), and that "missed" will take two parameters (two
     Gints).

     `Parameters' should thus contain a value of
          (1 => (1 => Gtk_Type_Int, 2 => Gtk_Type_None),
           2 => (1 => Gtk_Type_Int, 2 => Gtk_Type_Int));

     Due to the way arrays are handled in Ada, each component must have
     the same number of signals. However, if you specify a type of
     `Gtk_Type_None', this will in fact be considered as no argument.
     Thus, the first signal above has only one parameter.

     Note also that to be able to emit a signal such a the second one,
     ie with multiple arguments, you will have to extend the packages
     defined in Gtk.Handlers. By default, the provided packages can
     only emit up to one argument (and only for a few specific types).
     Creating your own `Emit_By_Name' subprograms should not be hard if
     you look at what is done in `gtk-marshallers.adb'. Basically,
     something like:

          procedure Emit_With_Two_Ints
            (Object : access Widget_Type'Class;
             Name   : String;
             Arg1   : Gint;
             Arg2   : Gint);
          pragma Import (C, Emit_With_Two_Ints,
              "gtk_signal_emit_by_name");

          Emit_With_Two_Ints (Gtk.Get_Object (Your_Widget),
              "missed" & ASCII.NUL, 1, 2);

     will emit the "missed" signal with the two parameters 1 and 2.


   Then of course `Initialize' should set up some signal handlers for
the functions you want to redefine.  Three signals are especially
useful:

   * "size_request"

     This callback is passed one parameter, as in :
          procedure Size_Request
             (Widget      : access My_Widget_Record;
              Requisition : in out Gtk.Widget.Gtk_Requisition);
     This function should modify Requisition to specify the widget's
     ideal size. This might not be the exact size that will be set,
     since some containers might decide to enlarge or to shrink it.

   * "size_allocate"

     This callback is called every time the widget is moved in its
     parent window, or it is resized. It is passed one paramater, as in
     :
          procedure Size_Allocate
             (Widget     : access My_Widget_Record;
              Allocation : in out Gtk.Widget.Gtk_Allocation)
     This function should take the responsability to move the widget,
     using for instance `Gdk.Window.Move_Resize'.

   * "expose_event"

     This callback is called every time the widget needs to be redrawn.
     It is passed one parameter, the area to be redrawn (to speed
     things up, you don't need to redraw the whole widget, just this
     area).


11 Support for Glade, the Gtk GUI builder
*****************************************

11.1 Introduction
=================

GtkAda now comes with support for the GUI builder Glade (this is not
the glade released with Gnat for distributed systems).  Using Glade
itself is straightforward: it is an intuitive point and click GUI
builder. The main difference from other builders is that, since GtkAda
builds a UI with blocks by default, you will not be asked to set the
size and position of your windows by default. If you are looking for
this kind of interaction you should consider using the Gtk_Fixed
container. However, please read the GtkAda reference manual before
considering using Gtk_Fixed.

11.2 Using Glade
================

Note that we only recommend using version 2.0.0 of Glade, as previous
versions are not compatible. Using this version you can directly create
Ada files from Glade by selecting Ada95 as the language under project
options.  Glade saves your interface in a project file whose syntax is
XML based. In the following sections, we will refer to this file as
either `the XML file' or `the project file' interchangeably.

11.2.1 Taking advantage of Glade's options
------------------------------------------

In this XML file, Glade will save various options that Gate can take
advantage of. In particular, going to the project options window, some
General Options in the `C Options' section will also be used by Gate:
Gettext support, if enabled, will generate an additional package called
<project>_intl that will use Gtkada.Intl; The `Set Widget Names' option
is also recognized and will generate additional calls to Set_Name for
each widget.

11.2.2 Associating icons with buttons
-------------------------------------

Up to now, the only way to specify an icon for a button was to
associate a pixmap file to it. As an alternative, if the name specified
in the `Icon' field does not contain any dots, Gate will consider the
name as a variable rather than a file name. It is up to you to provide
the necessary definitions in order to compile properly the generated
code.

11.2.3 Note for GNU/Linux users
-------------------------------

Some GNU/Linux systems come with a precompiled version of Glade that
will usually have support for Gnome. Gate currently does not provide
support for Gnome, which means that you should not enable Gnome support
in Glade.

11.3 Gate
=========

11.3.1 Invoking Gate
--------------------

Gate is a program that is delivered with GtkAda. Gate takes the Glade
XML file as an argument and generates a set of Ada files.  When
compiled, these files will recreate the interface you just designed with
Glade.

   Gate is generally invoked through the `Write source code' button in
Glade's menu bar.

   In addition, you can also invoke it from the command line by
providing a Glade project file. This will generate Ada files in the
directory set as the `Source Directory' project option, or otherwise in
the current working directory. Note that under Windows, the `Source
Directory' option is ignored, and the current directory is always used
instead.

11.3.2 Structure of the generated files
---------------------------------------

11.3.2.1 The main file
......................

The main file is the name of the program name specified in the XML
Glade file: `<program name>.adb'. It contains initialization and
creation code for each top level widget contained in the XML file. This
is intended as a convenient default to visualize your GUI, but you will
usually want to modify this initialization.

11.3.2.2 Top level widget files
...............................

For each top level widget, Gate will generate a package `<widget>_Pkg'
in the files `<widget>_pkg.ads' and `.adb'. These packages contain all
the GtkAda calls needed to create the widgets you designed within
Glade. You will usually not need to modify these files yourself.

11.3.2.3 Main handler file
..........................

This file, called `callbacks_<program name>.ads' contains all the
Handler package instantiations needed by your application. You will
usually not need to modify it.

11.3.2.4 Top level widget signal files
......................................

These are the most important files created by Gate. Each is called
`<widget_name>_pkg-callbacks.adb'.  They contain stubs for all the
callbacks related to a top level widget you declared in Glade. With the
main file, this the only files you should modify yourself. Note that it
is recommended that you structure your application such that the real
code is put in separate packages (i.e not generated files) as much as
possible, to avoid potential merging problems when your interface is
significantly changed within Glade. See next section for more details.

   Currently, Gate will generate callback stub procedures that can
handle the expected number of arguments for each signal. This is done
using a relatively low level mechanism explained in the reference manual
(package `Gtk.Handlers'). Basically, callbacks expecting arguments will
take a Gtk_Argument as their only parameter, and Gate will generate the
appropriate variable declaration and conversion calls to provide the
expected GtkAda arguments. You should not modify this code by hand
unless you know what you are doing.

   For example, given a signal `delete_event', Gate will generate the
following procedure body, giving access to the arguments of this
callback: a `Gtk_Window_Record' (Object) and a `Gdk_Event' (Arg1)

     function On_Main_Window_Delete_Event
       (Object : access Gtk_Window_Record'Class;
        Params : Gtk.Arguments.Gtk_Args) return Boolean
     is
        Arg1 : Gdk_Event := To_Event (Params, 1);
     begin
        return False;
     end On_Main_Window_Delete_Event;

11.3.3 Modifying generated files
--------------------------------

Note that you can easily go back to Glade any time, modify your
interface, and have Gate re-generate a set of files. All your
modifications will be kept in the new files. For that, Gate creates a
directory `.gate' in the current directory. Please do not delete it if
you want Gate to be able to keep your changes from one version to the
next.

   Also note that to keep track of your modifications, gate relies on
either `merge', or `patch' and `diff' being available on your system.
If you don't have a working set of `diff/patch', `configure' will
simply replace them by null operations, which means that regenerated
files will override the previous ones.

   Under Windows, Gate will not attempt to merge changes. Instead, it
will always regenerate and overwrite every file.

   In some cases, due to major changes in the project file, Gate may
not be able to merge all the changes. In this case, it will notify you
so, and will either keep the old and new sections in the files (if you
are using `merge'), or files with a `.rej' extension will be generated
to help you do the merge manually.

11.3.4 Adding Gate support for new widgets
------------------------------------------

This section is intended for developpers that wish to add support for
new GtkAda widgets in Gate. Note that this section is not complete yet.

11.3.4.1 Implementing the `Generate' procedure
..............................................

To provide support for a new widget, you first need to write a
`Generate' procedure that will take care of generating the piece of
code related to the widget's properties. Note that the parents
properties do not have to be handled by this function.

   * Glib.Glade API The Glib.Glade package contains a self documented
     API that will help you automate most of the work for common
     widgets.

   * Most common mapping
        * Gen_New

        * Gen_Set

        * Gen_Call_Child

        * example

   * Registering `Generate' functions   Gtk.Glade.Register_Generate
     (Widget, Func) This procedure associates a given Generate
     procedure with a given widget C name.

11.4 Dynamic loading of XML files
=================================

11.4.1 Introduction to Libglade
-------------------------------

Libglade is an external library provided by default on some systems (e.g
GNU/Linux, Gnome) that supports dynamic loading of XML files and
creation of widgets at run time. The advantage of using libglade is
that you do not need to recompile your application to change your user
interface. On the other hand, everything is done at run time, meaning
less compile checks, and also the inability to take advantage of the
object oriented features of GtkAda and Ada such as deriving from a
widget creating using the GUI builder, to add fields and properties.
See packages Glade and Glade.XML for more information.

11.5 Limitations
================

Gate currently support all Gtk+ widgets and properties available under
Glade. But, to help you identify widgets that may not be supported (e.g
Gnome widgets), Gate will generate a warning on the standard error:

     $ gate warning.glade
     Generating Ada files...

     GtkAda-WARNING **: Unsupported widget GnomeCanvas (canvas1)
     The following files have been created/updated in src:
     [...]

   and add a comment in the `<widget>_pkg.adb' file that looks like:

     --  WARNING: Unsupported widget GnomeCanvas (canvas1)

   This means that while generating the file Gate detected an
unsupported widget (in this case GnomeCanvas) whose name is canvas1.
If you get such a warning your file may or may not compile properly, but
you won't get the complete widget hierarchy at run time.

   Feel free to send us (see *Note How to report bugs::) the XML file
that causes this problem. We don't guarantee a rapid fix for each
particular problem but receiving real examples of missing
functionnalities will certainly help implementing them faster.

12 Binding new widgets
**********************

GtkAda comes with a Perl script to help you create a binding to a C
widget (this is the script we have used ourselves).  This will not fully
automate the process, although it should really speed things up. You
will probably need less than 15 min to create a new binding once you
will get used to the way GtkAda works. Note that your C file should
have the same format as is used by Gtk+ itself.

   To get started on a new binding, launch the script
`contrib/binding.pl' as follows:

     $ touch gtk-button.ads
     $ binding.pl ../include/gtk/gtkbutton.h > temporary

   This dumps several kind of information on the standard output:

   * List of subprograms defined in the `.h' file. Their
     documentation is also added, since binding.pl will parse the `.c'
     file   as appropriate.

   * List of properties and signals for the widget

   * Tentative bodies for the subprograms   These will often need
     adjustements, but provide a good start

   You can also use this script to update existing bindings:

     $ binding.pl ../include/gtk/*.h

13 Debugging GtkAda applications
********************************

This chapter presents a number of technics that can be used when
debugging GtkAda applications. First, the standard tools to debug Ada
applications can be used:

Compile with -g
     You should almost always include debugging information when
     compiling and linking your code. This gives you the possibility to
     use the debugger. See below the variable GDK_DEBUG for how to
     disable grabs.

bind with -E
     Using this argument on the `gnatbind' or `gnatmake' command line
     will force the compiler to include backtraces when an exception is
     raised. These backtraces can be converted to symbolic backtraces by
     using the `addr2line' tool.

Link with -lgmem
     Using this switch gives access to the `gnatmem' tool, that helps
     you to detect memory leaks or doubly-deallocated memory. The latter
     often results in hard-to-fix Storage_Error exceptions. See the GNAT
     User's guide for more information.


   There are also a number of technics specific to GtkAda or gtk+
applications. For most of them, you might need to recompile these
libraries with the appropriate switches to get access to the extended
debugging features.

Use the `--sync' switch
     Under unix systems, all applications compiled with gtk+
     automatically support this switch, which forces events to be
     processed synchronously, thus making it easier to detect problems
     as soon as they happen.  This switch is not relevant to Windows
     systems.

break on g_log
     In the debugger, it is often useful to put a breakpoint on the glib
     function `g_log'. When gtk+ is linked dynamically, you will need
     to first start your application with `begin', then put the
     breakpoint and continue the application with `cont'. This helps
     understand internal errors or warnings reported by gtk+ and glib

compile glib with `--disable-mem-pools'
     Glib, the underlying layer that provides system-independent
     services to gtk+, has an extensive and optimized system for memory
     allocation. Bigger chunks of Memory are allocated initially, and
     then subdivided by glib itself. Although this is extremely
     performant, this also make the debugging of memory-related
     problems (storage_error) more difficult. Compiling with the above
     switch forces glib to use the standard malloc() and free() system
     calls. On GNU/Linux systems, it might be useful to set the
     variable `MALLOC_CHECK_' to 1 to use error-detecting algorithms
     (see the man page for malloc()).

compile glib and gtk+ with `--enable-debug=yes'
     It is recommended that you specify this switch on the `configure'
     command line when compiling these two libraries.  In addition to
     compiling the libraries with debugging information for the
     debugger, additional runtime debug options (controllable via
     environment variables) become available.  Specifying
     `--enable-debug=no' is not recommended for production releases
     (see glib or gtk+ documentation for details).

     For these three variables, the possible values are given below.
     These are lists of colon-separated keywords. You can choose to
     remove any of these value from the variable

    `GOBJECT_DEBUG=objects:signals'
          This sets up the debugging output for glib. The value
          `objects' is probably the most useful, and displays, on exit
          of the application, the list of unfreed objects. This helps
          detect memory leaks. The second value `signals' will display
          all the signals emitted by the objects. Note that this
          results in a significant amount of output.

    `GDK_DEBUG=updates:nograbs:events:dnd:misc:
          xim:colormap:gdkrgb:gc:pixmap:image:input:cursor'
          This sets up the debugging output for gdk. The most useful
          value is `nograbs', which prevents the application from ever
          grabbing the mouse or keyboards. If you don't set this, it
          might happen that the debugger becomes unusable, since you
          don't have access to the mouse when the debugger stops on a
          breakpoint. Another simpler solution is to debug remotely
          from another machine, in which case the grabs won't affect
          the terminal on which the debugger is running.

    `GTK_DEBUG=misc:plugsocket:text:tree:updates:keybindings'
          This sets up the debugging output for gtk. Almost all of
          these values are mostly for internal use by gtk+ developpers,
          although `keybindings' might prove useful sometimes.


Import the C function ada_gtk_debug_get_ref_count
     This function has the following Ada profile:
          function Ref_Count (Add : System.Address) return Guint;
          pragma Import (C, Ref_Count, "ada_gtk_debug_get_ref_count");

     and should be called in a manner similar to

          declare
             Widget : Gtk_Widget;
             Count  : Guint;
          begin
             Count := Ref_Count (Get_Object (Widget));
          end;

     and returns the internal reference counter for the widget. When
     this counter reaches 0, the memory allocated for the widget is
     automatically freed.

     This is mostly a debugging aid for people writting their own
     containers, and shouldn't generally be needed. You shouldn't rely
     on the internal reference counter in your actual code, which is
     why it isn't exported by default in GtkAda.


14 How to report bugs
*********************

GtkAda is a mature, stable toolkit that is heavily and widely used on a
variety of platforms.  We test GtkAda using an Ada version of the
`testgtk.c' file found in the gtk+ distribution, as well as by
generating a significant number of interfaces using the GUI builder and
Gate.  For code examples that demonstrate the use of this toolkit, look
within the `testgtk/' directory.

   There are two kinds of problems you can encounter:
   * If the gtk library itself was compiled with warnings turned on, you
     may get some  warning messages,  mainly because of types problems.
     These warnings should not appear, as we have tried to be as type
     safe as possible  in this package. To know exactly where the
     problem is, compile your program with debug information, run gdb,
     and set a breakpoint on the function `g_log'. Then run your
     program as usual, using the `run' command. Then send us the result
     of the `where' command. Here is a summary:

          $ gnatmake -f -g <your_program_name> `gtkada-config`
          $ gdb <your_program_name>
          (gdb) break main
          (gdb) run
          (gdb) break g_log
          (gdb) continue
          ....
          (gdb) where

   * In  some  (hopefully) rare cases,   you can even get a
     segmentation fault within gtk.  That means there is definitly
     something wrong either in your program or in the toolkit.  Please
     check your program carefully and, if you think this is a problem
     in GtkAda itself, send us an e-mail.

   If you are a supported user of GNAT, send mail to
`mailto:report@gnat.com' to report errors, otherwise send mail to the
GtkAda list (`mailto:gtkada@lists.adacore.com') explaining exactly what
your are  doing,  what  is  the  expected  result  and  what  you
actually get. Please include the required sources to reproduce the
problem, in a  format usable  by `gnatchop'  (basically, insert all
the required sources at  the end of  the mail). Please  try to provide
as small as possible a  subset of your sources.

   Of course, we will  welcome any patch   you can provide, so  that
this toolkit may be as useful as possible.

15 Bibliography
***************

We recommand the following documents. Most of them were written with C
in mind, but should be easily adapted after you've read the rest of
this document.

   * [1] "Gtk+/Gome Application Development" - Havoc Pennington This
     book, by one of the main authors of the the GNOME environment,
     describes in detail some of the inner mechanisms of gtk+, including
     signal handling, and a complete description of all the widgets and
     all the events found in `Gdk.Event'.

     It is worth noting that this book has been published under the Open
     Publication License. You can get an electronic copy of it at
     `http://www.opencontent.org/'.

Appendix A GNU Free Documentation License
*****************************************

Version 1.1, March 2000

Copyright (C) 2000 Free Software Foundation, Inc.
59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

Everyone is permitted to copy and distribute verbatim copies of this
license document, but changing it is not allowed.

0. PREAMBLE
===========

The purpose of this License is to make a manual, textbook, or other
written document "free" in the sense of freedom: to assure everyone the
effective freedom to copy and redistribute it, with or without
modifying it, either commercially or noncommercially.  Secondarily,
this License preserves for the author and publisher a way to get credit
for their work, while not being considered responsible for
modifications made by others.

   This License is a kind of "copyleft", which means that derivative
works of the document must themselves be free in the same sense.  It
complements the GNU General Public License, which is a copyleft license
designed for free software.

   We have designed this License in order to use it for manuals for free
software, because free software needs free documentation: a free
program should come with manuals providing the same freedoms that the
software does.  But this License is not limited to software manuals; it
can be used for any textual work, regardless of subject matter or
whether it is published as a printed book.  We recommend this License
principally for works whose purpose is instruction or reference.

1. APPLICABILITY AND DEFINITIONS
================================

This License applies to any manual or other work that contains a notice
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======================

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================

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   If the Modified Version includes new front-matter sections or
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5. COMBINING DOCUMENTS
======================

You may combine the Document with other documents released under this
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entitled "Endorsements."

   Heading 6. COLLECTIONS OF DOCUMENTS

   You may make a collection consisting of the Document and other
documents released under this License, and replace the individual
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7. AGGREGATION WITH INDEPENDENT WORKS
=====================================

A compilation of the Document or its derivatives with other separate
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8. TRANSLATION
==============

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9. TERMINATION
==============

You may not copy, modify, sublicense, or distribute the Document except
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10. FUTURE REVISIONS OF THIS LICENSE
====================================

The Free Software Foundation may publish new, revised versions of the
GNU Free Documentation License from time to time.  Such new versions
will be similar in spirit to the present version, but may differ in
detail to address new problems or concerns.  See
http://www.gnu.org/copyleft/.

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ADDENDUM: How to use this License for your documents
====================================================

To use this License in a document you have written, include a copy of
the License in the document and put the following copyright and license
notices just after the title page:

     Copyright (c)  YEAR  YOUR NAME.
     Permission is granted to copy, distribute and/or modify this
     document under the terms of the GNU Free Documentation License,
     Version 1.1 or any later version published by the Free Software
     Foundation; with the Invariant Sections being LIST THEIR TITLES,
     with the Front-Cover Texts being LIST, and with the Back-Cover
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   If your document contains nontrivial examples of program code, we
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permit their use in free software.

Table of Contents
*****************

GtkAda User's Guide
1 Introduction: What is GtkAda ?
2 Getting started with GtkAda
  2.1 How to build and install GtkAda
  2.2 How to distribute a GtkAda application
  2.3 Organization of the GtkAda package
  2.4 How to compile an application with GtkAda
    2.4.1 Using project files
    2.4.2 Using the command line
      2.4.2.1 Unix systems
      2.4.2.2 Windows systems
  2.5 Architecture of the toolkit
  2.6 Widgets Hierarchy
3 Hierarchical composition of a window
4 Signal handling
  4.1 Predefined signals
  4.2 Connecting signals
  4.3 Handling user data
    4.3.1 First case: simple user data
    4.3.2 Second case: using Object_Connect instead
    4.3.3 Third case: manually disconnecting the callback
    4.3.4 Fourth case: setting a watch on a specific widget
5 Starting an application with GtkAda
6 Resource files
7 Memory management
8 Tasking with GtkAda
9 Processing external events
10 Object-oriented features
  10.1 General description of the tagged types
    10.1.1 Why should I use object-oriented programming ?
    10.1.2 Type conversions from C to Ada widgets
  10.2 Using tagged types to extend Gtk widgets
  10.3 Creating new widgets in Ada
    10.3.1 Creating composite widgets
    10.3.2 Creating widgets from scratch
11 Support for Glade, the Gtk GUI builder
  11.1 Introduction
  11.2 Using Glade
    11.2.1 Taking advantage of Glade's options
    11.2.2 Associating icons with buttons
    11.2.3 Note for GNU/Linux users
  11.3 Gate
    11.3.1 Invoking Gate
    11.3.2 Structure of the generated files
      11.3.2.1 The main file
      11.3.2.2 Top level widget files
      11.3.2.3 Main handler file
      11.3.2.4 Top level widget signal files
    11.3.3 Modifying generated files
    11.3.4 Adding Gate support for new widgets
      11.3.4.1 Implementing the `Generate' procedure
  11.4 Dynamic loading of XML files
    11.4.1 Introduction to Libglade
  11.5 Limitations
12 Binding new widgets
13 Debugging GtkAda applications
14 How to report bugs
15 Bibliography
Appendix A GNU Free Documentation License


