proc hls2rgb {h l s} {
    # Posted by frederic.bonnet@ciril.fr
    # h, l and s are floats between 0.0 and 1.0, ditto for r, g and b
    # h = 0   => red
    # h = 1/3 => green
    # h = 2/3 => blue

    set h6 [expr {($h-floor($h))*6}]
    set r [expr {  $h6 <= 3 ? 2-$h6
                            : $h6-4}]
    set g [expr {  $h6 <= 2 ? $h6
                            : $h6 <= 5 ? 4-$h6
                            : $h6-6}]
    set b [expr {  $h6 <= 1 ? -$h6
                            : $h6 <= 4 ? $h6-2
                            : 6-$h6}]
    set r [expr {$r < 0.0 ? 0.0 : $r > 1.0 ? 1.0 : double($r)}]
    set g [expr {$g < 0.0 ? 0.0 : $g > 1.0 ? 1.0 : double($g)}]
    set b [expr {$b < 0.0 ? 0.0 : $b > 1.0 ? 1.0 : double($b)}]

    set r [expr {(($r-1)*$s+1)*$l}]
    set g [expr {(($g-1)*$s+1)*$l}]
    set b [expr {(($b-1)*$s+1)*$l}]
    return [list $r $g $b]
}