[HJG] This is an example of how to put widgets onto a canvas.
It shows a schema of a neuron, which is summing up its input-signals, 
and 'fires' when this sum exceeds a threshold.
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#!/bin/sh
 # -*- mode: tcl; tab-width: 4; coding: iso-8859-1 -*-
 # Restart with tcl:  \
 exec wish $0 ${1+"$@"}

 # neuro1.tcl - HaJo Gurt - 2006-10-16
 #: Widgets on a canvas : Sliders + Entryfields 
 # Schema of a neuron, summing its input-signal, and firing when the sum exceeds a threshold.

  package require Tk

  array set S { x1 20  w1 1   x2 50  w2  8 \
                t1 500  title "Neuronal Processing" \
                s1 0  s2 0  sum 0  out 0 }

  proc int x   { expr int($x) }

  proc Calc x {
  #: Calculate results + update display
    global S

    set S(s1)  [expr {$S(x1) * $S(w1)} ]
    set S(s2)  [expr {$S(x2) * $S(w2)} ]
    set S(sum) [expr {$S(s1) + $S(s2)} ]
    set S(out) [expr {$S(sum) >= $S(t1)} ]
    if { $S(out) } {
      .c itemconfig out -fill red
    } else {
      .c itemconfig out -fill cyan
    }
  }

  proc Init {} {
  #: Build GUI
    global S

    wm title . "Neuro1"
    canvas .c -relief raised -borderwidth 0 -height 400 -width 560 -bg white
    pack   .c

    option add *Scale.highlightThickness 0
    option add *Scale.orient vertical
    option add *Scale.relief ridge
    option add *Entry.relief sunken

    scale .sx1 -from 100 -to    0 -label "x1"  -variable S(x1) -command Calc
    scale .sx2 -from 100 -to    0 -label "x2"  -variable S(x2) -command Calc
    scale .sw1 -from  10 -to    0 -label "w1"  -variable S(w1) -command Calc
    scale .sw2 -from  10 -to    0 -label "w2"  -variable S(w2) -command Calc
    scale .st1 -from   0 -to 2000 -label "Threshold" -variable S(t1) -orient horizontal -command Calc

    entry .es1 -width 5 -textvar S(s1)  -state readonly
    entry .es2 -width 5 -textvar S(s2)  -state readonly
   #entry .es3 -width 5 -textvar S(sum) -state readonly
    scale .ss3 -from 2000 -to   0 -variable S(sum) -length 200 -sliderlength 5 -state disabled -bg green2
    entry .es4 -width 3 -textvar S(out) -state readonly

    .c create text   280  20          -text $S(title) -font {Times 24 bold}

    .c create text    15  80          -text "Input 1" -anchor w
    .c create line    30 100  310 100 -width 5 -arrow last
    .c create window  50  50          -window .sx1    -anchor nw
    .c create window  50 200          -window .sx2    -anchor nw
    .c create window 240 75           -window .es1    -anchor w

    .c create text    15 230          -text "Input 2" -anchor w
    .c create window 150  50          -window .sw1    -anchor nw
    .c create window 150 200          -window .sw2    -anchor nw
    .c create line    30 250  310 250 -width 5 -arrow last
    .c create window 240 225          -window .es2   -anchor w

    .c create text   160 315          -text "Weight" -anchor w

    .c create window 275 320          -window .st1   -anchor nw
    .c create line   350 320  350 300 -width 1 -arrow last

    .c create oval   300  50  400 300 -width 3 -fill green2
    .c create text   350  65          -text "Sum"
    .c create window 350 175          -window .ss3  ;# .es3
    .c create line   400 175  450 175 -width 5 -arrow last

    .c create oval   450 125  530 225 -width 3 -tag out
    .c create text   490 150          -text "Output"
    .c create window 490 175          -window .es4

    # Debug: show cursor-pos. :
   #bind .c <Motion>   {wm title . [int [%W canvasx %x]],[int [%W canvasy %y]]}
  }

  Init
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[Category Example] -
[Category Graphics] -
[Category GUI]