Updated 2016-05-03 19:58:51 by gold â–²

## Summary edit

Keith Vetter : 2006-08-28 : Here's a visual puzzle: count the number of children in the picture then slide the scale to the other side to swap the top halves. Now how many children are there?

uniquename 2013aug17

Here is a sequence of 3 images showing why ligaments in brains are being sprained.

The first image shows the picture of children as they appear when the GUI first comes up.

You can switch the top-left portion of the picture with the top-right by sliding the 'scale' button from left to right --- as indicated by the second image.

The completed switch is shown in the 3rd image.

For those interested in the programming to move these images around, note that the 'WhereTo' proc, in the code below, is being used to move images 'vc1' and 'vc2'.

## Code edit

``` ##+##########################################################################
#
# Vanishing Child
# by Keith Vetter, August 28, 2006

package require Tk

set S(title) "Vanishing Child"
set S(step) 0
set S(help) {
Count how many children are in the picture.
Then slide the scale to the other side to swap the top halves.
Now how many children are in the picture?}

proc Hint1 {w} {
#: Hints: number the childs

if {\$::cb == 0} {.c delete "h"; return}

\$w create text -280  -66 -text  "1" -tag "h r"
\$w create text -240  -20 -text  "2" -tag "h"
\$w create text -200   -1 -text  "3" -tag "h"

\$w create text -140  -40 -text  "4" -tag "h"
\$w create text  -90  -10 -text  "5" -tag "h"

\$w create text  -45  -70 -text  "6" -tag "h r"
\$w create text    5  -25 -text  "7" -tag "h"
\$w create text   45  -10 -text  "8" -tag "h"

\$w create text  115  -60 -text  "9" -tag "h"
\$w create text  150  -10 -text "10" -tag "h"

\$w create text  210  -66 -text "11" -tag "h r"
\$w create text  245  -38 -text "12" -tag "h"
\$w create text  290  -10 -text "13" -tag "h"

\$w create text  -25  100 -text "14" -tag "h"
\$w create text  195   95 -text "15" -tag "h"

.c itemconfig "r" -fill red
}

proc DoDisplay {} {
global P S

wm title . \$S(title)
canvas .c -width 750 -height 420 -bd 2 -relief ridge -bg green4
ShadedText .c 0 -120 deepskyblue black \
-font {Times 42 bold} -anchor s -tag title -text \$S(title)
bind .c <Configure> {ReCenter %W %h %w}
CreateImages

.c create image \$P(vc,x) \$P(vc,y) -image ::img::vc -tag vc -anchor nw
foreach {x0 y0 x1 y1} [.c bbox vc] break
.c create rect \$x0 \$y0 [incr x1 -1] [incr y1 -1] -outline black
.c create image \$P(vc1,x1) \$P(vc1,y1) -image ::img::vc1 -tag vc1 -anchor nw
.c create image \$P(vc2,x1) \$P(vc2,y1) -image ::img::vc2 -tag vc2 -anchor nw

frame .bottom
scale .sc -from 0 -to 100 -orient h -variable S(step) \
-command WhereTo -showvalue 0
button .? -text "?" -command About

#causes 'expected integer but got "bold"' error on *nix systems.
#.? config -font "[.? cget -font] bold"

checkbutton .cb -text "!" -command [list Hint1 .c]

#causes 'expected integer but got "bold"' error on *nix systems.
#.cb config -font "[.cb cget -font] bold"

pack .bottom -side bottom -fill x -expand 1
pack .sc  -in .bottom -side left -expand 1 -pady 10
place .?  -in .bottom -relx .99 -rely .5 -anchor e
place .cb -in .bottom -relx .01 -rely .5 -anchor w
pack .c -fill both -expand 1 -side top

}
proc ReCenter {W h w} {                   ;# Called by configure event
set h2 [expr {\$h / 2}] ; set w2 [expr {\$w / 2}]
\$W config -scrollregion [list -\$w2 -\$h2 \$w2 \$h2]
}
proc CreateImages {} {
global P S

image create photo ::img::vc1
image create photo ::img::vc2

::img::vc1 copy ::img::vc -from   1 1 240 136
::img::vc2 copy ::img::vc -from 240 1 619 136
::img::vc put [.c cget -bg] -to   1 1 619 136

set w  [image width  ::img::vc]
set h  [image height ::img::vc]
set w1 [image width  ::img::vc1]
set w2 [image width  ::img::vc2]

set P(vc,x)   [expr {-\$w/2}]                   ;# Where vc goes
set P(vc,y)   [expr {-\$h/2}]
set P(vc1,x0) [expr {\$P(vc,x) + 1}]            ;# Where vc1 starts
set P(vc1,y0) [expr {\$P(vc,y) + 1}]
set P(vc1,x1) [expr {\$P(vc,x) + \$w - \$w1 - 1}] ;# Where vc1 ends
set P(vc1,y1) \$P(vc1,y0)
set P(vc2,x0) [expr {\$P(vc,x) + \$w - \$w2 - 1}] ;# Where vc2 starts
set P(vc2,y0) \$P(vc1,y0)
set P(vc2,x1) [expr {\$P(vc,x) + 1}]            ;# Where vc2 ends
set P(vc2,y1) \$P(vc1,y0)
}
proc ShadedText {w x y fg bg args} {
set cbg [ \$w cget -bg ]
eval [list \$w create text \$x \$y -fill \$bg] \$args
eval [list \$w create text [incr x -2] [incr y -2] -fill \$cbg] \$args
eval [list \$w create text [incr x -1] [incr y -1] -fill  \$fg] \$args
}
set msg "\$::S(title)\nby Keith Vetter, August 2006\n\$::S(help)"
tk_messageBox -message \$msg -title "About \$::S(title)"
}

proc WhereTo {args} {
global P S
set xpos \$S(step)
set ypos [expr {\$S(step) <= 50 ? \$S(step) : 100-\$S(step)}]

set x [expr {\$P(vc1,x0) + (\$P(vc1,x1) - \$P(vc1,x0)) * \$xpos / 100.0}]
set y [expr {\$P(vc1,y0) + \$ypos}]
.c coords vc1 \$x \$y
set x [expr {\$P(vc2,x0) + (\$P(vc2,x1) - \$P(vc2,x0)) * \$xpos / 100.0}]
set y [expr {\$P(vc2,y0) - \$ypos}]
.c coords vc2 \$x \$y
}

image create photo ::img::vc -data {
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################################################################
DoDisplay

return```

AMG: Arrgh, I sprained a ligament in my brain!

HJG Added a checkbutton to show hints.

AMG: Even with the hints turned on, I still don't understand how this can be possible!

Stu 2008-11-11 Commented-out code that causes expected integer but got "bold" error on *nix systems.

HJG 2016-01-31: I found some links about the origin of this kind of puzzle (as well as other nice puzzles), with history, and more amazing 'vanishing' pictures:

• johnrausch.com
• Vanishing Leprechaun, Vanishing Egg, Doggie Doo
• archimedes-lab.org - Vanish Puzzles
• Japanese Birds, Banker nightmare, Steam train, Disappearing Egg
• theguardian.com - Vanishing Leprechaun
• Vanishing Leprechaun, Magic Egg Puzzle (1880), La MystÃ©rieuse (1907),
• pin-up girls, Color-changing satellites, Swedish gnomes / apes, blue&red pens,
• The Chinese vanish, Vanishing magician
• How to draw such puzzles - Alex Bellos' blogpost