brighten

$line brighten outline (factor): changes color by factor if not constraint

obj method line brighten {what factor} {
  if {
    ![$self constraint linecolor] &&
    $what eq "outline" &&
    [$self cget -outline] ni {{} transparent}
  } then {
    set color [::brighten [$self cget -outline] $factor]
    $self configure -outline $color
  }
}