proc repeat {} {
set i [ expr { $::cnt % 15 } ]
if {$i > 8} { set i [ expr { 15 - $i } ] }
set tag t$i
puts $tag
.c raise bg
.c raise $tag
incr ::cnt
after $::interval repeat
}
set ::cnt 0
set ::interval 200
canvas .c -width 20 -height 20
pack .c -expand 1
.c create rect 0 0 20 20 -fill gray
.c create oval -5 -5 25 25 -fill gray -tags { bg }
.c create oval 0 0 0 0 -fill green -tags {t0 }
.c create oval 0 0 5 5 -fill green -tags { t1 }
.c create oval 0 0 10 10 -fill green -tags { t2 }
.c create oval 0 0 15 15 -fill green -tags { t3 }
.c create oval 0 0 20 20 -fill green -tags { t4 }
.c create oval 5 5 20 20 -fill green -tags { t5 }
.c create oval 10 10 20 20 -fill green -tags { t6 }
.c create oval 15 15 20 20 -fill green -tags { t7 }
.c create oval 20 20 20 20 -fill green -tags { t8 }
.c raise off
update
after 200
repeat