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		       -tickfont => $tickfont,
		       -tst      => $tst,
		       -width    => $width,
		       -xmin     => $xmin,
		       -xmax     => $xmax,
		       -ymin     => $ymin,
		       -ymax     => $ymax,
		      );

    #    $height  - height of the window
    #    $width   - width  ......
    #    $xmin    - lowest x value we will display
    #    $xmax    - highest .....
    #    $ymin    - lowest y value .....
    #    $ymax    - highest .....
    #    $margin  - the number of pixels used as a margin around the plot
    #    $tick    - the length (in pixels) of the tickmarks
    #    $tst     - the step size for the tick marks
    #    $tst[x|y]- step size for tick marks on the x (or y) axis
    #                (if not specified tst is used)
    #    $tickfont    - for for the lables


=head1 DESCRIPTION

This is an improved version of the axis widget. Changes with respect to the
previous version are :

=over 4

=item * 

the 'pack' has been moved out the widget. One has to do his own packing

=item * 

it is now possible to work in the coordinates of the axis. The following
piece of code draws a line between the points (2 , 3.1)  (4 , 4).

    $t->create('line',$t->plx(2),$t->ply(3.1),$t->plx(4),$t->ply(4));

=back 


=head1 AUTHOR

 Kris Boulez		(Kris.Boulez@rug.ac.be)
 Biomolecular NMR unit	<http://bionmr1.rug.ac.be/~kris>
 University of Ghent, Belgium

=cut 

use strict;
require Tk::Canvas;
use Carp;


use vars qw($VERSION @ISA);
$VERSION = substr(q$Revision: 1.5 $, 10) + 1;

@ISA = qw(Tk::Derived Tk::Canvas);

Construct Tk::Widget 'Axis';


# Added since v 0.1
# -----------------
# - plx en ply allow you to work in axis coordinates
#       (eg. $t->create('line', $t->plx(.3), $t->ply(.4), $t->plx(3.2), 
#                          $t->ply(5.3)); ) 
# - pack is moved out.
#
# This is an Axis widget. It draws an XY axis on the screen and draws 
# tickmarks. This is the first public version (v 0.2), all comments, 
# crticism, ... are welcome (kris@bionmr1.rug.ac.be).
#
# I would like to thank the following people :
# - Ton Rullmann (rull@nmr.chem.ruu.nl) who started my quest for a way to
# draw 2D plot from within Perl
# - Stephen O. Lidie (lusol@Turkey.CC.Lehigh.edu) who provided me with a 
# 2D plot script. He also asked the question "why don't you write a new
# widget for it ?"
# - Nick Ing-Simmons (nik@tiuk.ti.com) without who there would be no ptk
# and whose advice was invaluable while trying to create this widget
#
# It is used as follows
#
#   require Axis;
#

sub Populate    #using Populate from Tk::Derived
{
  my ($w,$args) = @_;
  $w->SUPER::Populate($args);
  $w->ConfigSpecs(
		  '-xmin'   => ['PASSIVE',undef,undef,0],
		  '-xmax'   => ['PASSIVE',undef,undef,100], #undef],
		  '-ymin'   => ['PASSIVE',undef,undef,0],
		  '-ymax'   => ['PASSIVE',undef,undef,100], #undef],
		  '-margin' => ['PASSIVE',undef,undef,25],
		  '-tick'   => ['PASSIVE',undef,undef,10],
		  '-tst'    => ['PASSIVE',undef,undef,5],
		  '-tstx'   => ['PASSIVE',undef,undef,undef],
		  '-tsty'   => ['PASSIVE',undef,undef,undef],
		  '-tickfont'   => ['PASSIVE',undef,undef,'fixed']
		 ); # these options are new for the widget, the last value is 
                    # the default. 
} #end of Populate


sub ConfigChanged {
  my ($w,$args)= @_;;

  my $xmin = $w->cget(-xmin);   # how expensive is a ->cget ?
  my $xmax = $w->cget(-xmax);
  my $cx = $w->cget(-width);
  my $mar = $w->cget(-margin);
  my $ymin = $w->cget(-ymin);
  my $ymax = $w->cget(-ymax);
  my $cy = $w->cget(-height);
  my $tick = $w->cget(-tick);
  my $tst = $w->cget(-tst);
  my $tstx = $w->cget(-tstx);
  my $tsty = $w->cget(-tsty);
  my $tickfont = $w->cget(-tickfont);

  if (!defined ($xmax) || !defined ($ymax)) { # at least xmax and ymax needed
    croak "Axis: `Show' method requires xmax and ymax";
  }
  if (!defined ($tstx)) {$tstx = $tst;}
  if (!defined ($tsty)) {$tsty = $tst;}
  if (!defined ($tickfont)) {$tickfont = "fixed";}

  my ($zx,$zy,$t); # zx (zy) is the value (in window coordinates) where 
                   # x (y) is 0 on the X (Y) axis
  if (abs($xmin+$xmax) > abs($xmin-$xmax)) { # both values pos/neg
    $zx=$mar;
  }
  else {
    $zx = $w->plx(0);
  }

  if (abs($ymin+$ymax) > abs($ymin-$ymax)) {
    $zy=$cy-$mar;
  }
  else {   # $cy - $mar is lowest point where we will draw
    $zy = $w->ply(0);
  }  
  
 # X-axis 
 # ------