##
## Example script showing a way to add user-drawn geometry that updates
## as a trajectory is animated.
##
## To use this script: 
##  1) load your trajectory
##  2) source frameupdate.vmd
##  3) enabletrace  
##  4) do your thing :-) 
##  5) disabletrace

proc enabletrace {} {
  global vmd_frame;
  trace variable vmd_frame([molinfo top]) w drawcounter
}

proc disabletrace {} {
  global vmd_frame;
  trace vdelete vmd_frame([molinfo top]) w drawcounter
}

proc drawcounter { name element op } {
  global vmd_frame;

  draw delete all
  # puts "callback!" 
  draw color white
  set psperframe 1.03
  set time [format "%8.3f ps" [expr $vmd_frame([molinfo top]) * $psperframe]]
  draw text {10 10 0}  "$time"
}