Get Tk::FontDialog, it has a real nice FontDialog, and a way to apply the font to your whole window.

#!/usr/bin/perl
use Tk;
use Tk::FontDialog;

$top=new MainWindow;

my $fd;

$b = $top->Button(-text => 'Choose Font',
                  -command => sub {
                      $font = $fd->Show;
                      apply_font($font);
                  })->pack;

$f = $top->Frame->pack;
$f->Label(-text => 'Test RefontTree 1')->pack;

$f2 = $f->Frame->pack;
$f2->Label(-text => 'Test RefontTree 2')->pack;

$c = $f2->Canvas(-width => 100, -height => 30)->pack;
$c->createText(0,0,-anchor => 'nw', -text => 'Canvas Text');

$fd = $top->FontDialog(-nicefont => 0,
                       -title => 'Select Font',
                       -applycmd => \&apply_font,
                       -familylabel => 'Schrift~familie',
                       -fixedfontsbutton => 1,
                       -nicefontsbutton => 1,
                      );


$bf = $top->Frame->pack;
$bf->Button(-text => 'OK',
            -command => sub { print "ok $ok\n";
                              $top->destroy;})->pack(-side => 'left');
$bf->Button(-text => 'Not OK',
            -command => sub { print "not ok $ok\n";
                              $top->destroy;})->pack(-side => 'left');

MainLoop;

sub apply_font {
    my $font = shift;
    if (defined $font) {
        $b->configure(-font => $font);
        $f->RefontTree(-font => $font, -canvas => 1);
    }
}
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