dots

$line dots: returns list of used dot objects
$line dots -gravity: returs nothing if constraint gravity not true
$line dots -end: returns list of ending dots (no direction dots in curves)
$line dots show yes: invokes method show on every dot

obj method line dots args {
  set options {}
  while {[string index $args 0] eq "-"} {
    set args [lassign $args option]
    lappend options $option
  }
  set dots [my dots]
  if {"-end" in $options} then {
    set dots [lreplace $dots 1 end-1]
  }
  if {"-gravity" in $options} then {
    if {[$self constraint gravity]} then {
      lmap dot $dots {$dot {*}$args}
    }
  } else {
    lmap dot $dots {$dot {*}$args}
  }
}