Yes. It's possible, but it's a lot of work. Here's an example of a transparent window with a cyan-colored circle by zentara. Reverse it and see what you can come up with.

#!/usr/bin/perl

use warnings;
use strict;
use Tk;
use Tk::Zinc; 

my $width = 100;
my $height = 100;

my $mw = MainWindow->new(-background => 'cyan' ); 

#$mw->geometry($width.'x'.$height.'+300+300');

$mw->geometry('500x500+300+300');


#$mw->overrideredirect(1);
my $zinc = $mw->Zinc(-width => $width, 
                     -height => $height,
                     -reshape => 1,     #clips zinc
                     -fullreshape => 1,  #clips $mw and xterm
             -backcolor => 'blue',
                       )->pack; 

my $petal = $zinc->add('curve',1,[[$width/2,0], 
                                          [2*$width,0, 'c'], 
                                          [2*$width,$height, 'c'],
                  [$width/2,$height],
                                          [-$width,$height, 'c'], 
                                          [-$width,0, 'c'],
                               [$width/2,0]],

                   -tags => ['bezier1'],
                   -filled => 1,
                   #-fillcolor => 'cyan',
                   #attempt at semi-transparency
           -fillcolor => "=radial 0 0 |yellow;40|black;40 50|cyan;40",
+ 
           -closed => 1,
                   -linewidth => 0,
           -priority => 1,
           -visible => 1,
           );

# using the triangulaire curve to reshape both TkZinc and Mainwindow w
+idgets 
$zinc->itemconfigure(1, -clip => $petal); 

MainLoop;
[download]

See Re: Perl TK window transparency / opacity for more information.

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