bio::graphics - xyplot problems

Dear All,
I'm trying to plot a line hystogram with the code:
but instead of line like this transctiptional profile  -
http://oligomers.tamu.edu/gbrowse/tutorial/figures/figure12.gif
I get boxes ?!? - http://img147.imageshack.us/img147/9137/plotpz2.png

#!/usr/bin/perl
use Bio::Graphics;
use Bio::Graphics::Panel;
use Bio::SeqFeatureI;
use Bio::SeqFeature::Generic;

 my $panel = Bio::Graphics::Panel->new(	-length		=>	1000,
						-width		=>	800,
						-gridcolor	=>	'lightcyan',
		                    		-grid		=>	1,
					);

my $track2 =  $panel->add_track(
			-glyph          => 'xyplot',
                   -graph_type   => 'line',
                   -point_symbol => 'point',
                   -max_score    => 50,
                   -min_score    => 0,
                   -scale        => 'right'
			-key        => 'Methylation profile');
# add "subfeatures"
my @met_array=(0.2,0.5,1,2,3,4,5,6,7,8,9,10);

for (my $k=0;$k<$#met_array;$k++) {

my $feature1 = Bio::SeqFeature::Generic->new(-start=>$k,-end=>$k+20,-score=>$met_array[$k]);

 $track2->add_feature($feature1);

}

#==========END==========#
#writing in the file
    open (IMAGEFILE,">plot.png");
    binmode IMAGEFILE;
    print IMAGEFILE $panel->png;	

--

-- 
------------------------------------------------
Dr. Vesselin Baev
Research Assistant Professor
University of Plovdiv
Dept. Molecular Biology
Bioinformatics Group
Tzar Assen 24
Plovdiv 4000, BULGARIA
+359 32 261 (560)
+359 89 43 80 945
Skype: vebaev
vebaev <at> gmail.com
baev <at> uni-plovdiv.bg
http://plantgene.eu/