NAME
    CGI::Screen - Perl extension for easy creation of multi screen
    CGI-scripts

SYNOPSIS
      use CGI::Screen;
      use vars qw(@ISA);
      @ISA = qw(CGI::Screen);

      my $query = __PACKAGE__->new;

      $query->dispatch;

WARNING
    This is *alpha* software. User visible changes can happen any
    time.

DESCRIPTION
    *CGI::Screen* is a subclass of `CGI' which allows the esay(TM)
    creation of simple multi screen CGI-Scripts. By 'multi screen' I
    mean scripts which present different screens to the user when
    called with different parameters. This is the common case for
    scripts linking to themselves.

    To use *CGI::Screen*, you have to subclass it. For each screen
    you want to present to the user, you must create a method
    `screen_'_screen_name_. This method has to produce the HTML code
    for the screen. CGI::Screen does generate HTTP headers and an
    HTML framework for you. The HTML-framework already contains the
    `FORM' tags. You can customize the HTTP headers HTML framework
    by providing callback methods.

    CGI::Screen keeps track of the CGI parameters used in your
    screen and passes old parameters which are not used in the
    current screen.

    It highjacks the parameters `screen_'* to dispatch the different
    screens the script implements. The `screen_user' and
    `screen_passwd' fields are used if you enable the builtin simple
    authentication. In general you should advice your HTTP server to
    do authentication. But sometimes it is convenient to check the
    authentication at the script level. Especially if you do not
    have access to yours servers configuration.

  The constructor `new'

    If the first parameter of `new' is the string `-screen' the
    second argument must be a hash reference specifying the options
    for the subclass. Other parameters are passed to the constructor
    of `CGI'.

    `-dont_cut_loops'
        Normaly the history of pages will not extended if the
        current page is the same as the last page. So looping on a
        page will not change the result of the `last_screen' method.
        If the option `-dont_cut_loops' is provided and true, the
        page will recorded twice. A third visit will be interpreted
        as jump back to the first visit.

        _That sounds weird. Will have to figure out a way to
        recognize back jumps independent of the history._

  Adding Screens

    All applications should provide a *main* screen by defining a
    method `main_screen'. This method is called if no (existing)
    screen is specified in the parameters. The method is called with
    three arguments: The query object, the screen name and the
    screen title (More precisely the third parameter (if present) is
    the text on the button or anchor which cause the jump to this
    page).

    So the minimal application looks like this:

      use CGI::Screen;
      use vars qw(@ISA);
      @ISA = qw(CGI::Screen);
      
      my $query = __PACKAGE__->new;
      
      $query->dispatch;
      
      sub main_screen {
        my $query = shift;
      
        print $query->p('This is the Main Screen');
      }

    That is not too exiting. Let us add a second screen and allow
    navigation between the screens:

      sub main_screen {
        my $query = shift;
      
        print
          $query->p('This is the Main Screen'),
          $query->goto_screen('second', 'Another Screen');
      }
      sub second_screen {
        my $query = shift;
      
        print
          $query->p('This is the Other Screen'),
          $query->goto_screen('main', 'Back to Main Screen');

      }

  Moving between screens

    Use the method `goto_screen' to produce a button for switching
    to another screen. You can also produce an anchor instead of a
    button by calling `link_to_screen' instead of `goto_screen'. You
    may pass additional parameters to encode:

        for my $docid (keys %score) {
          print $query->link_to_screen('display', $title{$docid},
                                       'docid' => $docid,
                                       'score' => $score{$docid});
        }

    For convenience, CGI::Screen keeps track of the last screen for
    you so that you can link to the previous page. Note that only
    the last seven screens are saved:

      my $screen = $query->last_screen;
      print
        $query->p("You came from screen $screen. Press "),
        $query->goto_screen($query->last_screen),
        $query->p(" to go back");

    `last_screen' returns screen name and title in list context and
    screen name in scalar context. Do not use the CGI parameters
    `screen_last_*' since they are changed before you can get hold
    of them `;-P'

  The callbacks

    All callbacks are called with three arguments: The query object,
    the screen name and the screen title (= button/anchor text).
    Callbacks should return a string.

    `application'
    The `application' method returns a string which is used in the
    default `title' and `headline' callbacks. The Default method
    returns the string `"CGI::Screen Test"' and should definitely be
    overwritten by your application.

    `title'
    The result of the method is used in the HTTP header and in the
    default headline. It defaults to the _application_.

    `headline'
    The `headline' method should return a chunk of HTML code to
    start the Screen. It defaults to the _title_ enclosed in `H1'
    tags.

  Authentication

    To enable password authentication, define a method
    `check_auth_user'. The dispatcher will call the method with the
    user and password entered by the user. The method should return
    true if the authentication succeeded and false otherwise. The
    dispatcher will present the `login_screen' if the authentication
    failed.

      sub check_auth_user {
        my ($query, $user, $passwd) = @_;

        $user eq 'pfeifer';
      }

    For IP address based authentication define the method
    `check_auth_ip'.

      sub check_auth_ip {
        my ($query, $ipaddr) = @_;

       $ipaddr =~ /^(193\.96\.65\.|139\.4\.36\.)/;
      }

    If you do not like the default login screen, overwrite with your
    own `login_screen'. Use the CGI parameters `screen_user' and
    `screen_passwd'.

  Customizing the Title

    You may provide a custom `title' method to generate a title for
    your screens.

      sub title {
        my ($query, $screen)  = shift;
      
        $query->application . ': ' . $screen;
      }

  Customizing the Headline

    You may provide a custom `headline' method to generate a HTML
    chunk to start your screens.

      sub headline { $_[0]->h1(title(@_)) }

    You should overwrite the `application' method if you use the
    default title and headline.

      sub application { 'CGI::Screen Test' }

  Customizing the Trailer

    For a custom Trailer, define the `trailer' method.

      sub trailer {
        my ($query, $screen)  = shift;
      
        "End of Screen $screen";
      }

  Multiple Forms

    If you want to have multiple forms on one screen, call the
    method `new_form'.

      sub multi_screen {
         my $query = shift;

         print
           $query->p('This is the Main Screen'),
           $query->textfield('foo'),
           $query->goto('First'),
           $query->new_form,
           $query->textfield('foo'),
           $query->goto('Second');
      }

  Non HTML screens

    You can create non HTML screens by defining a _name_`_data'
    method instead of a <name>`_screen' method. For `data' screens
    you have to generate HTTP headers yourself.

      sub gif_data {
        my $query = shift;
        
        print $query->header(
                             -type    => 'image/gif',
                             -status  => '200 OK',
                             -expires => '+120s',
                            );
        my $font  = $query->param('font');
        my $w     = GD::Font->$font()->width;
        my $h     = GD::Font->$font()->height;
        my $im    = GD::Image->new((length($query->param('foo'))+2)*$w,$h);
        my $white = $im->colorAllocate(255,255,255);
        my $red   = $im->colorAllocate(255,0,0);
        my $black = $im->colorAllocate(0,0,0);
        $im->transparent($white);
        $im->arc(8,8,5,5,0,360,$red);
        $im->string(GD::Font->$font(),10,0,$query->param('foo'),$black);
        print $im->gif;
      }

  Keeping parameter values

    CGI::Screen keeps track of the CGI parameters used in the
    current form. It simply looks at the first parameter in any call
    to a CGI method. If the first parameter is `-name', the second
    parameter is marked as _used parameter_. CGI::Screen passed all
    current parameter values not used in hidden fields or in the
    query string of an anchor. So do not use old style CGI calls to
    bypass this mechanism or you will end up with multiple values
    for the parameters.

    If you want to get rid of a parameter, you must explicitly call
    the `delete' method of CGI.

BUGS
    Support for importing from CGI.pm is incomplete.

AUTHOR
    Ulrich Pfeifer <pfeifer@wait.de>

SEE ALSO
    The CGI(3) manual and the demo CGI script eg/screen included in
    the distribution.

ACKNOWLEDGEMENTS
    I wish to thank Andreas Koenig koenig@kulturbox.de for the
    fruitfully discussion about the design of this module.

Copyright
    The *CGI::Screen* module is Copyright (c) 1997,1998 Ulrich
    Pfeifer. Germany. All rights reserved.

    You may distribute under the terms of either the GNU General
    Public License or the Artistic License, as specified in the Perl
    README file.