NAME

       Tk::overview - An overview of an Object Oriented Tk8 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 provide a complete interface to the
       latest production version of John Ousterhout's Tk, while providing an Object Oriented
       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 Tk8.x, 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 sub-directory contains the various perl modules 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 functions 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 keyboard/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: dropping 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 Tk8.x's "images" what Tk::Widget does for widgets.  Images are new to
           Tk8.x and the class structure is not mature either.

           There are three sub-classes Tk::Bitmap, Tk::Pixmap and Tk::Photo.

           It is possible to create dynamic or auto-loaded image types inherited from Tk::Image
           for other image types or photo formats (e.g. support for TIFF format).

       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
           composite, 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).