Within my Perl/Tk application, I'd like to have a 256x256 white Canvas in the center of 4 other Canvas objects (of different colors here, while debugging).

I've tried every option I can think of, searched for a possible solution, and perused the most recent volume of "Mastering Perl/Tk" -- all to no avail.

Here is a stripped down version of my original program which still shows the problem.  When you run it, you get a white Canvas in the middle of 4 Canvas "strips" of other colors.  I'd like the Canvas objects to all be flush with one another, but there's a little space between each of them.

I know this has to be something simple and easy, but I'm just not seeing it.  It's not the enclosing Frame (at least I don't think it is), because the Frame has a blue background, and there isn't any blue showing through anywhere.

Can someone point me to a solution?  Thanks!

#!/usr/bin/perl -w

# Strict
use strict;
use warnings;

# Libraries
use Tk;


# Main program
create_gui();


# Subroutines
sub create_gui {
    my $mw = new MainWindow(-title => 'Type "Escape" to exit...');
    $mw->bind('<Escape>' => sub { $mw->destroy() });
    my $frame = $mw->Frame(-background => 'blue');
    $frame->pack(-expand => 0, -fill => 'both');

    # Note:  288 = 256 + 16 + 16
    canvas($frame, 'hotpink', 'left',   16,   256 + 16 + 16);
    canvas($frame, 'gold',    'right',  16,   256 + 16 + 16);
    canvas($frame, 'maroon',  'top',    256,  16);
    canvas($frame, 'white',   'top',    256,  256);
    canvas($frame, 'purple',  'bottom', 256,  16);
    MainLoop;
}


sub canvas {
    my ($w, $background, $side, $width, $height) = @_;
    my $canvas = $w->Canvas(-background => $background);
    $canvas->configure(-width  => $width);
    $canvas->configure(-height => $height);
    $canvas->pack(-expand => 1, -fill => 'both', -side => $side);
    return $canvas;
}

#
#  Key:  H = Hotpink,  M = Maroon, P = Purple,  G = Gold,  . = White
#
#   The GUI I'm actually getting:     The GUI I'd *LIKE* to get:
#
#  +------------------------------+  +------------------------------+
#  |Tk Type "Escape" to exit..."  |  |Tk Type "Escape" to exit..."  |
#  +------------------------------+  +------------------------------+
#  |H  MMMMMMMMMMMMMMMMMMMMMMMM  G|  |HMMMMMMMMMMMMMMMMMMMMMMMMMMMMG|
#  |H                            G|  |H............................G|
#  |H  ........................  G|  |H............................G|
#  |H  ........................  G|  |H............................G|
#  |H  ........................  G|  |H............................G|
#  |H  ........................  G|  |H............................G|
#  |H  ........................  G|  |H............................G|
#  |H  ........................  G|  |H............................G|
#  |H  ........................  G|  |H............................G|
#  |H  ........................  G|  |H............................G|
#  |H                            G|  |H............................G|
#  |H  PPPPPPPPPPPPPPPPPPPPPPPP  G|  |HPPPPPPPPPPPPPPPPPPPPPPPPPPPPG|
#  +------------------------------+  +------------------------------+
#
[download]

Update:  After Super-Searching some more, I came across this node, by the venerable zentara.  He used a Canvas option I hadn't tried:  -highlightthickness => 0.

Although I'm still not exactly sure what highlightthickness is used for, it does the trick; inserting the following line completely addresses my problem:

    $canvas->configure(-highlightthickness => 0);
[download]

Thanks, zentara -- you help me even when you're not logged in!