overview(3)
NAME
Tk - An overview of an Object Oriented Tk8.0 extension for
perl5
SYNOPSIS
use Tk; $main = MainWindow->new(); $widget = $main->Widget(...); $widget->pack(...); ... MainLoop;
DESCRIPTION
In writing the perl Tk extension, the goals were to pro
vide a complete interface to the latest production version
of John Ousterhout's Tk, while providing an Object Ori
ented interface to perl code.
CONTENTS
The package is composed of three loosely connected parts:
- pTk - Converted Tk source
- The pTk sub-directory is a copy of the C code of
Tk4.0, modified to allow use by languages other than
the original Tcl. (The pTk can be read as 'perl' Tk
or 'portable' Tk, depending on your sensibilities.) - Tk to Perl 'Glue'
- The top level directory provides Tk.xs and tkGlue.c which provide the perl-callable interfaces to pTk
- Perl code for 'Widget' Classes
- The Tk/Tk sub-directory contains the various perl mod
ules that comprise the "Classes" that are visible to
Tk applications. - The "major" widgets such as Tk::Text are actually in
separate directories at the top level (e.g. Text/* for
Tk::Text) and are dynamically loaded as needed on
platforms which support perl5's DynaLoader.
CLASS HIERARCHY
- package Tk; - the 'base class'
- All the "command names" documented in Tcl/Tk are made
to look like perl sub's and reside in the Tk package.
Their names are all lower case. Typically there are
very few commands at this level which are called
directly by applications. - package Tk::Widget; - the 'Widget class'
- There are no actual objects of the Tk::Widget class;
however all the various Tk window "widgets" inherit
from it, and it in turn inherits all the core Tk func
tions from Tk. - Tk::Widget provides various functions and interfaces which are common to all Widgets.
- A widget is represented to perl as a blessed reference
to a hash. There are some members of the hash which
are private to Tk and its tkGlue code. Keys starting
with '.' and of the form /_[A-Z][A-Za-z_]+_/ (i.e. starting and ending in _ and with first char after _
being upper case) should be considered reserved to Tk. - Tk::Button, Tk::Entry, Tk::Text ...
- There is one class for each of the "Tk" widget item
types. Some of them like Tk::Frame do very little indeed, and really only exist so that they can be
derived from or so that focus or menu traversal can
discover the "kind" of window being processed. - Other classes, Tk::Text for example, provide a lot of
methods used with Tk's "bind" to provide a rich key
board/mouse interface to the widgets' data. - These widget classes also include conversions of the
Tcl code for event bindings, keyboard focus traversal,
menu bars, and menu keyboard traversal. All the Tcl
functions have been converted, but the names have
changed (systematically) and they have been split up
between the various classes in what I hope is an
appropriate manner. Name changes are normally: drop
ping initial tk_ as the Tk-ness is implicit in the
Tk:: prefix, and similarly dropping say Menu from the
name if it has been moved the Tk::Menu class. Thus
'proc tkMenuNextEntry' becomes 'sub NextEntry' in the
Tk::Menu package. - Tk::Image
- This does for Tk4.0's "images" what Tk::Widget does
for widgets. Images are new to Tk4.0 and the class
structure is not mature either. - There are three sub-classes Tk::Bitmap, Tk::Pixmap and Tk::Photo.
- It is expected that Tk::Image hierarchy will evolve
during the "beta" phase of Tk to allow dynamic or
auto-loaded image types or photo formats (e.g. support
for JPEG format for photos). - Composite Widgets
- A composite is some kind of 'frame' with subwidgets
which give it useful behaviour. Tk::Dialog is an example of a composite widget classes built from the
basic Tk ones. It is intended that user code should
not need to be aware that a particular class is a com
posite, and create and configure such widgets in the
same manner as any other kind. The configure mechanism and the methods of the class manipulate the subwidgets
as required. - Composite widgets are implemented via Tk::Frame and
multiple inheritance. The two 'frame' base classes
Tk::Frame and Tk::Toplevel include the additional class Tk::Derived in their inheritance. Tk::Derived provides methods to allow additional configure options to be defined for a widget. - A Composite widget is typically defined as derived
from Tk::Frame or Tk::Toplevel (e.g. Tk::Dialog).