# trace the seven segment value 
when {/counter/cout} {set ss [exa -bin {/counter/cout}]} 

# set ss "0000000" 

set flag_ss 0 

# Resize the entire canvas by a scale 
proc rescale {cvn factor} { 
   global SCALE 
    
   # rescale all the boxes 
   $cvn scale all 0 0 $factor $factor 
    
   # rescale the text widths, too 
   foreach i [$cvn find all] { 
      if {[expr ! [string compare "text" [$cvn type $i]]]} { 
         set t [$cvn itemcget $i -width] 
         set t [expr $t * $factor] 
         $cvn itemconfigure $i -width $t 
      } 
   } 
    
   # resize the canvas itself 
   set t [$cvn cget -width] 
   $cvn configure -width [expr $t * $factor] 
   set t [$cvn cget -height] 
   $cvn configure -height [expr $t * $factor] 
}    

catch {destroy .sevenseg} 
set ss_w [toplevel .sevenseg] 

set fr1 [frame $ss_w.fr1] 
set fr2 [frame $ss_w.fr2] 

set ss_cv [canvas $fr1.ss_cv -height 20 -width 10] 

$ss_cv create text 1 1 -anchor nw -fill black -text "SEVEN SEG" -width 15 

set ss_a [$ss_cv create line 3 5 7 5 -fill gray -width 0] 
set ss_b [$ss_cv create line 7 6 7 10 -fill gray -width 0] 
set ss_c [$ss_cv create line 7 12 7 16 -fill gray -width 0] 
set ss_d [$ss_cv create line 7 17 3 17 -fill gray -width 0] 
set ss_e [$ss_cv create line 3 16 3 12 -fill gray -width 0] 
set ss_f [$ss_cv create line 3 10 3 6 -fill gray -width 0] 
set ss_g [$ss_cv create line 4 11 6 11 -fill gray -width 0] 
button $fr2.close -text "Close" -command {destroy .sevenseg; set flag_ss 0} 

rescale $ss_cv 8 
# indicate the existence of seven segment window 
set flag_ss 1 

# call the ss_monitor procedure with dummy parameters 
# I am calling this function bcos if user invokes the seven segment after the value is written 
# to it, then ss_monitor procedure is not called and seven segment LEDS remain inactive 
# ss_monitor 1 2 3 

pack $ss_cv 
pack $fr2.close 
pack $fr1 
pack $fr2 


trace variable ss w ss_monitor 

proc ss_monitor {name arrayindex op} { 
   global flag_ss ss_a ss_b ss_c ss_d ss_e ss_f ss_g ss ss_cv 
   if {$flag_ss==1} { 
      if {[string index $ss 0]==1} { 
         $ss_cv itemconfigure $ss_a -fill blue -width 3 
      } else { 
         $ss_cv itemconfigure $ss_a -fill gray -width 0 
      } 
      if {[string index $ss 1]==1} { 
         $ss_cv itemconfigure $ss_b -fill blue -width 3 
      } else { 
         $ss_cv itemconfigure $ss_b -fill gray -width 0 
      } 
      if {[string index $ss 2]==1} { 
         $ss_cv itemconfigure $ss_c -fill blue -width 3 
      } else { 
         $ss_cv itemconfigure $ss_c -fill gray -width 0 
      } 
      if {[string index $ss 3]==1} { 
         $ss_cv itemconfigure $ss_d -fill blue -width 3 
      } else { 
         $ss_cv itemconfigure $ss_d -fill gray -width 0 
      } 
      if {[string index $ss 4]==1} { 
         $ss_cv itemconfigure $ss_e -fill blue -width 3 
      } else { 
         $ss_cv itemconfigure $ss_e -fill gray -width 0 
      } 
      if {[string index $ss 5]==1} { 
         $ss_cv itemconfigure $ss_f -fill blue -width 3 
      } else { 
         $ss_cv itemconfigure $ss_f -fill gray -width 0 
      } 
      if {[string index $ss 6]==1} { 
         $ss_cv itemconfigure $ss_g -fill blue -width 3 
      } else { 
         $ss_cv itemconfigure $ss_g -fill gray -width 0 
      } 
   } 
}