怎么居中放置一个Tk窗口

Question

@飞觞醉月 问起这个问题。

Code: wm-center.tcl

proc wm_center {win} {
  set w  [winfo width $win]
  set h  [winfo height $win]
  set W  [winfo screenwidth  .]
  set H  [winfo screenheight .]
  
  set x [expr {($W-$w)>>1}] 
  set y [expr {($H-$h)>>1}] 

  wm geometry $win +$x+$y
}