Center a Tk window under mouse cursor

[repellent]

How do I center a Tk window under the mouse cursor?

That is, upon invoking MainLoop(), I would like the main window to be centered where the cursor is at.

Update: Thanks, zentara! This is good enough for me:

use Tk;

my $main_w = MainWindow->new();
$main_w->title("Test");

my $xpos = $main_w->pointerx;
my $ypos = $main_w->pointery;
$main_w->geometry("+$xpos+$ypos");

MainLoop();

[zentara]

The position of a new window, is usually controlled by an option in your WindowManager. Look thru your WindowManager options for things like "new window at pointer", or similar things. Usually they either center new windows, or try to put it in an empty space.

About the only thing you can do is drag the window after creation.

#!/usr/bin/perl
use Tk;

my $mw = tkinit;
$mw->geometry('200x200+200+200');
#$mw->overrideredirect(1);

$mw->bind('<ButtonPress-1>', sub{ 
   my $xe = $mw->XEvent;
   $wdragiinfo{xoff} = $mw->pointerx - $mw->rootx;
   $wdragiinfo{yoff} = $mw->pointery - $mw->rooty;
    });

        
$mw->bind('<B1-Motion>', sub{ 
  my ($x,$y);
  $x=$mw->pointerx-$wdragiinfo{xoff};
  $y=$mw->pointery-$wdragiinfo{yoff};
        
  $mw->geometry($mw->width."x".$mw->height."+$x+$y");
         });

MainLoop;

[Erez]

I might be 100% wrong here, but the way I understand things, the location of the mouse can only be reported to the GUI after it has been rendered, i.e. after MainLoop is running. What most GUI do to achieve this, is actually move the mouse to the center of the window after it loads. To get it otherwise means you need to ask the OS/WM to tell you where the mouse is at loading time.