$canvas->createRectangle(
int $x, int $y, int $x, int $y,
                         -outline=>undef,
                         -fill=>'white' );

#to (or any variation), you need an outline color and size

$canvas->createRectangle(
int $x, int $y, int $x+1, int $y+1,
                         -outline=>'lightgreen',
                         -fill=>'white' );



##</code><code>##

$main->Button(
    -text    => "Save",
    -command => sub {
         my @capture=();
         my ($x0,$y0,$x1,$y1)=$canvas->bbox('all');
         @capture=('-x'=>$x0,'-y'=>$y0,-height=>$y1-$y0,-width=>$x1-$x0);
         $canvas -> postscript(-colormode=>'gray',
                   -file=>$0.'.ps',@capture);
                }
    )->pack;



MainLoop;