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_name*`screen_'.
    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 and the 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 your server's 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 be 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 caused 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 exciting. 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:

        my %score = some_fancy_search_algorithm($self->param('query'));
        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_screen('first', 'First'),
           $query->new_form,
           $query->textfield('foo'),
           $query->goto_screen('second', '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 fruitful
    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.

