#/usr/bin/tcl

# set up some variables
set nrclick 0
set selstr ""
global nrclick selstr 

# define function to react to clicks
proc do_clickme {args} {
    # import gloval variables
    global nrclick selstr sel
    global vmd_pick_atom vmd_pick_mol
    # count click
    incr nrclick
    # add picked atom to selection. 
    set selstr "$selstr $vmd_pick_atom"

    # stop after the second atom.
    if {$nrclick  > 1} {
      trace vdelete vmd_pick_atom w do_clickme
      set sel [atomselect $vmd_pick_mol $selstr]
      set nrclick 0
      # XXX error? XXX
      mouse mode 0 
    }
}

# start selection string
set selstr "index "
# hook up function to callback
trace variable vmd_pick_atom w do_clickme
# turn on atom picking
mouse mode 4 2