if 0 {[Richard Suchenwirth] 2004-08-18 - Here's another simple [canvas]
animation, with a kind of hypnotic effect: growing ovals in
rainbow colors create the impression of moving through a psychedelic
tunnel. Ten times a second, a tiny circle is created in the center, then
all circles zoomed by 20%, and finally those circles removed which are
"out of sight" (if not doing so, the program will soon crash).

[http://mini.net/files/rainbow.png]
}

 set colors {purple blue green3 green yellow orange red magenta}
 foreach color $colors {lappend colors2 $color $color}
 proc rainbowtunnel w {
    $w create oval 99 99 101 101 -fill [lcycle ::colors2] \
        -outline {} -tag oval
    $w scale oval 100 100 1.1 1.1
    foreach item [$w find withtag oval] {
        if {[lindex [$w bbox $item] 0]<-50} {$w delete $item}
    }
 }
#-- General-use utilities:
 proc lcycle listVar {
    upvar 1 $listVar list
    set first [lindex $list 0]
    set list [linsert [lrange $list 1 end] end $first]
    set first
 }
 proc every {ms body} {eval $body; after $ms [info level 0]}
#-- "main"
 pack [canvas .c -width 200 -height 200]
 every 100 {rainbowtunnel .c}

if 0 {
----
See also [TclTrain] where the same effect is used on a railroad.
----
[Category Animation] | [Arts and crafts of Tcl-Tk programming]
}