link graphics
procedure main()
   WOpen("height=500", "width=700", "label=Curve Editor") # whm
   pts := []
   repeat case Event() of {
      &lpress: if not(i := nearpt(&x, &y, pts)) then
		   {pts |||:= [&x, &y]; draw(pts)}
      &ldrag:  if \i then
		   {pts[i] := &x; pts[i + 1] := &y; draw(pts)}
      !"Qq":   break
   }
end

procedure draw(pts)
   EraseArea()
   DrawCurve!(pts ||| [pts[1], pts[2]])
   every i := 1 to *pts by 2 do
      FillCircle(pts[i], pts[i + 1], 3)
end

procedure nearpt(x, y, pts)
   every i := 1 to *pts by 2 do
      if abs(x - pts[i]) < 4 & abs(y - pts[i + 1]) < 4 then return i
end