I'm working on a Perl/Tk application, and wanted to know how popup menus (such as those created when you right-click on something in, say, Netscape) work.

There doesn't seem to be any built-in support (i.e. a specific module) for creating these -- I had to look through the Tk source distribution to find what I wanted. I basically copied their code verbatim, and it works, but relies on some sort of magic I don't understand. Here's the relevant snippet: 

# A right-click in the viewer should bring up the popup menu.
$viewer->bind("<3>", [\&post_popup_menu]);

sub post_popup_menu {
  my $w = shift; # no idea how this works.
  my $X = $w->XEvent->X;
  my $Y = $w->XEvent->Y;
  $viewer_menu->Post($X, $Y);
}

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The line that mystifies me is the first line of post_popup_menu... I'm not sending the callback any arguments, but it still manages to receive a mysterious $w variable somehow. After doing some preliminary poking with Data::Dumper, it looks like $w is the $viewer that the menu is associated with.

Beyond that, however, I'm stumped... anyone know how Tk works this magic?

In reply to How do Tk popup menus actually work? by Falkkin

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