Logo Arts

To New
  # set default screen, pen and turtle values
  ResetAll SetScreenSize [400 400] HideTurtle
  SetSC Black SetPC Green SetPS 1 PenUp
End

To Init
  # initialise starting speeds and coordinate lists
  Make "dX RanSpeed Make "dY RanSpeed
  Make "P 0 Make "Q 0
  Make "eX RanSpeed Make "eY RanSpeed
  Make "R 0 Make "S 0
  Make "Pp [ 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ]
  Make "Qp [ 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ]
  Make "Rp [ 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ]
  Make "Sp [ 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 ]
End

To DrawLine
  # move to point PQ and draw a line to point RS
  Make "P :P+:dX Make "Q :Q+:dY
  If :P > 180 [Make "dX Minus RanSpeed]
  If :P < -180 [Make "dX RanSpeed]
  If :Q > 180 [Make "dY Minus RanSpeed]
  If :Q < -180 [Make "dY RanSpeed]
  PenUp SetXY :P :Q
  Make "Pp LPut First Pos :Pp
  Make "Qp LPut Last Pos :Qp
  Make "R :R+:eX Make "S :S+:eY
  If :R > 180 [Make "eX Minus RanSpeed]
  If :R < -180 [Make "eX RanSpeed]
  If :S > 180 [Make "eY Minus RanSpeed]
  If :S < -180 [Make "eY RanSpeed]
  PenDown SetXY :R :S
  Make "Rp LPut First Pos :Rp
  Make "Sp LPut Last Pos :Sp
End

To EraseLine
  # move to point PQ and draw a black line to point RS
  PenUp
  SetXY (First :Pp) (First :Qp)
  PenDown SetPC Black
  SetXY (First :Rp) (First :Sp)
  Make "Pp ButFirst :Pp
  Make "Qp ButFirst :Qp
  Make "Rp ButFirst :Rp
  Make "Sp ButFirst :Sp
End

To RanSpeed
  # return a random speed between 4 and 13
  Output 4 + Random 10
End

To Hue :Theta
  # Output RGB hue list from angle :Theta
  Make "Red Round 127.5*(1+Sin :Theta)
  Make "Green Round 127.5*(1+Sin (:Theta+120))
  Make "Blue Round 127.5*(1+Sin (:Theta+240))
  Output (List :Red :Green :Blue)
End

To Go
  New Init
    Forever [
      SetPC Hue :P+:Q+:R+:S
      DrawLine EraseLine Wait 4]
End