proc wheel {c x y r args} {
    global g
    array set opt {-color red -spokes 24 -pivot 0 -tag {}}
    array set opt $args
    set y0 [expr $y-$r]
    $c create oval [expr $x-$r] [expr $y0-$r] [expr $x+$r] [expr $y0+$r] \
        -outline white
    set r1 [expr $r-2]
    set col $opt(-color)
    set it [$c create oval [expr $x-$r1] [expr $y0-$r1] [expr $x+$r1] [expr $y0+$r1] \
        -outline $col -width 2]
    lappend g(wheels) $it
    set g($it,spokes) $opt(-spokes)
    set g($it,r) $r1
    set g($it,x) $x
    set g($it,y) $y0
    set g(alpha) 0.
    set g(-color) $opt(-color)
    drawSpokes $c $it
    if $opt(-pivot) {
        set deg2arc [expr {atan(1.0)*8/360.}]
        set rp [expr {$r1*$opt(-pivot)}]
        set xp [expr {$x-$rp*cos($deg2arc*$::g(alpha))}]
        set yp [expr {$y0-$rp*sin($deg2arc*$::g(alpha))}]
        set pivot [$c create rect $xp $yp \
            [expr {$xp+1}] [expr {$yp+1}] -fill $opt(-color) \
            -tag  [list $opt(-tag) pivot]]
        set g($it,pivot) [list $pivot $opt(-pivot)]
        $c create arc [expr {$x-$r1}] [expr {$y0-$r1}]\
            [expr {$x+$r1}] [expr {$y0+$r1}] \
            -style chord -fill $g(-color) -start 310\
            -extent 80 -tag counterweight
    }
    set rh [expr $r/12.]
    $c create oval [expr $x-$rh] [expr $y0-$rh] [expr $x+$rh] [expr $y0+$rh] \
        -fill white -tag hub
}
proc turn {c deg} {
    global g
    set g(alpha) [expr {round($g(alpha)+360-$deg)%360}]
    foreach i [$c find withtag counterweight] {
        $c itemconfig $i -start [expr 310-$g(alpha)]
    }
    $c delete spoke
    foreach i $g(wheels) {
        drawSpokes $c $i
    }
    $c raise hub
    set xp0 [expr {105+15*sin(($g(alpha)-90)*atan(1.0)*8/360)}]
    $c delete piston
    eval $c coords p0 $xp0 120 [expr {$xp0+2}] 122 ;#CW
    $c create line 90 121 $xp0 121 -width 2 -fill white -tag piston ;#CW
    drawRod $c p0 p1 p2 p3
    $c raise p0
    foreach i [$c find withtag smoke] {
        if {[lindex [$c bbox $i] 3]<0} {
            $c delete $i
        } else {
            $c move $i [expr {rand()*$::g(speed)/3.}] [expr {rand()*2-2}]
        }
    }
    set t [eval $c create oval [$c bbox chimney] -fill white -outline white -tag smoke]
    $c move $t 0 -10
    $c lower smoke
}
proc drawSpokes {c item} {
    global g
    set nspokes $g($item,spokes)
    set delta [expr 360./$nspokes]
    set alpha $g(alpha)
    set r $g($item,r)
    set x $g($item,x)
    set y $g($item,y)
    set deg2arc [expr {atan(1.0)*8/360.}]
    for {set i 0} {$i<$nspokes} {incr i} {
        set x1 [expr {$x+cos($deg2arc*$alpha)*$r}]
        set y1 [expr {$y+sin($deg2arc*$alpha)*$r}]
        $c create line $x $y $x1 $y1 -fill $g(-color) -tag spoke
        set alpha [expr {$alpha+$delta}]
    }
    if [info exists g($item,pivot)] {
        foreach {item perc} $g($item,pivot) break
        set rp [expr {$r*$perc}]
        set xp [expr {$x-$rp*cos($deg2arc*$::g(alpha))}]
        set yp [expr {$y-$rp*sin($deg2arc*$::g(alpha))}]
        $c coords $item [expr {$xp}] [expr {$yp}] [expr {$xp+1}] [expr {$yp+1}]
    }
}
proc drawRod {c p0 p1 p2 p3} {
    $c delete rod
    eval $c create rect [$c bbox $p1 $p3] -fill white -tag rod
    eval $c create line [lrange [$c bbox $p0] 0 1] \
        [lrange [$c bbox $p2] 0 1] -width 3 -fill white -tag rod
    $c raise rod
    $c raise pivot
}

set c [canvas .c -width 600 -height 160 -background lightblue]
pack $c
bind $c <1> {incr ::g(speed) 6; speed $c} ;# throttle
bind $c <3> {
    foreach i [after info] {after cancel $i}
    set g(speed) 0 ;# emergency brake
}
proc speed {c} {
    turn $c $::g(speed)
    foreach i [after info] {after cancel $i}
    after 140 speed $c
}

$c delete all
catch {unset g}
$c create rect 32 115 360 125 -fill black ;# frame
$c create rect 22 118 32 122 -fill grey30 ;# buffer
$c create line 22 115 22 125
$c create poly 60 95 40 115 50 115 70 95 -fill black
$c create rect 60 45 310 95 -fill grey25  ;# boiler
$c create oval 55 50 65 90 -fill black ;# smokebox
$c create rect 70 32 85 50 -fill black -tag chimney
$c create rect 40 52 90 75 -fill black ;# wind diverter
$c create oval 130 36 150 52 -fill black ;# dome
$c create rect 195 35 215 50 -fill black ;# sandbox
$c create oval 260 36 280 52 -fill black ;# dome
$c create rect 65 100 90 135 -fill black ;# cylinder
$c create rect 90 120 92 122 -fill red -tag p0 ;# crossbar
$c create rect 72 87 82 100 -fill black ;# steam tube
$c create rect 310 40 370 115 -fill black ;# cab
$c create rect 310 32 390 42 -fill grey30 ;# cab roof
$c create text 338 82 -text "01 234" -fill gold -font {Times 7}
$c create rect 318 48 333 66 -fill white ;# cab window #1
$c create rect 338 48 355 66 -fill white ;# cab window #2
wheel $c 50  150 13 -spokes 12
wheel $c 105 150 13 -spokes 12
wheel $c 150 150 30 -pivot 0.5 -tag p1
wheel $c 215 150 30 -pivot 0.5 -tag p2
wheel $c 280 150 30 -pivot 0.5 -tag p3
drawRod $c p0 p1 p2 p3
wheel $c 340 150 16 -spokes 12
$c create rect 360 110 380 118 -fill black

$c create rect 380 65 560 125 -fill black -tag tender
$c create rect 560 118 570 122 -fill grey30 ;# buffer
$c create line 571 116 571 125
$c create rect 390 45 525 65 -fill black -tag tender
wheel $c 395  150 13 -spokes 12
wheel $c 440  150 13 -spokes 12
$c create rect 380 132 456 142 -fill red
wheel $c 495  150 13 -spokes 12
wheel $c 540  150 13 -spokes 12
$c create rect 480 132 556 142 -fill red -outline red
$c create rect 0 150 600 160 -fill brown ;# earth
$c create line 0 150 600 150 -fill grey -width 2 ;# rail
set ::g(speed) 4
speed $c