$c = $mw->Scrolled("Canvas")->pack( );
$canvas = $c->Subwidget("canvas");
$canvas->CanvasBind("<Button-1>", [ \&print_xy, Ev('x'), Ev('y') ]);
sub print_xy {
  my ($canv, $x, $y) = @_;
  print "(x,y) = ", $canv->canvasx($x), ", ", $canv->canvasy($y), "\n";
}