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
  Make "A 0.1*((Random 199)-99)
  Make "B 0.1*((Random 199)-99)
  Make "C (Random 19)-9
  Make "Cycle 6000
End

To Display :A :B :C :Cycle
  SetPC White
  SetPos [-190 184] Label "Hopalong
  SetXY Minus 194 Minus 196 Label (List :A :B :C)
  SetX 194-LabelLength :Cycle Label :Cycle
End

To Fit2Screen :A :B :C :Cycle
  Make "X 0 Make "Y 0
  Make "Xmax 0 Make "Xmin 0
  Make "Ymax 0 Make "Ymin 0
  Repeat :Cycle [HopAlong :A :B :C
    If :X > :Xmax [Make "Xmax :X]
    If :X < :Xmin [Make "Xmin :X]
    If :Y > :Ymax [Make "Ymax :Y]
    If :Y < :Ymin [Make "Ymin :Y] ]
  Make "Xsize :Xmax + Abs :Xmin
  Make "Scale 380/:XSize
  Make "Xcent Minus (:Xmax + :Xmin) / 2
  Make "Ycent Minus (:Ymax + :Ymin) / 2
End

To Hop :A :B :C :Cycle
  Make "X 0 Make "Y 0
  Repeat 180 [
    SetPC Hue2 RepCount
    Repeat Integer :Cycle/180 [HopAlong :A :B :C
      Dot List :Scale*(:X+:XCent) :Scale*(:Y+:YCent) ] ]
End

To HopAlong :A :B :C
  Make "Xnew :Y-((Sign :X)*Sqrt (Abs (:B*:X-:C)))
  # Make "Xnew :Y-((Sign :X)*Abs((Sine :X)*(Cos :B)+:C-:X*Sine (:A+:B+:C)))     # 3-ply fractal
  Make "Y :A-:X
  Make "X :Xnew
End

To Sign :Num
  # return sign (-1 or 1) of number
  If :Num < 0 [Output Minus 1] [Output 1]
End

To Hue2 :Theta
  # Output RGB hue list from angle :Theta
  Make "Red Abs 255*Sin :Theta
  Make "Green Abs 255*Sin (:Theta+120)
  Make "Blue Abs 255*Sin (:Theta+240)
  Output (List :Red :Green :Blue)
End

To Go
  New Repeat 100 [
  Init Fit2Screen :A :B :C :Cycle
  Wash
  Hop :A :B :C :Cycle
  Display :A :B :C :Cycle Wait 300]
End

To GoX :A :B :C :Cycle
  New
  Fit2Screen :A :B :C :Cycle
  Hop :A :B :C :Cycle
  Display :A :B :C :Cycle
End