if 0 {Richard Suchenwirth 2003-03-12 - Here's a cute little application for the iPAQ: a signal light. Dirt simple: fill the display in a single color, controlled by the "cursor keys" (navigation button up/down/left/right, back to white when hit a second time). But when background lighting is on, you can use this for signalling in the dark - or, with the default white, as a mild pocket lamp... or to test whether the display's pixels are all working... Yellow looks pretty beige, though. A cheap thrill at less than 900 bytes, this documentation included ;-) }

 proc sigbind {w color} {
    if {[$w cget -background] == $color} {set color white}
    $w config -background $color
 }
 pack [canvas .c -background white -height 320]
 wm geometry . +0+0
 wm title . "Signal lamp: use cursor-keys to change color"
 foreach {key color} {Up red Down green Left yellow Right blue} {
    bind . <$key>    "sigbind .c $color"
 }

if 0 {

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Arts and crafts of Tcl-Tk programming }