Mandelbrot set Generator

turtles-own [x0 iteration y0 xtemp x y Zoom-factor mousex mousey]

To Startup
  ca
  create-turtles 1
  ask turtles [ht]
  ask turtles [setxy -500 500]
  ask turtles [facexy -499 500]
  ask turtles [set Zoom-factor 1
    set mousex 0
    set mousey 0]
end 

To Main
  Startup
  Draw
  loop
  [Zoom]
end 

to Draw
  ask turtles
  [while [ycor >= -499]
    [fd 1
      Calculate
      if not can-move? 1
      [setxy -500 ycor - 1]]]
end 

to Calculate
  set x0 (xcor / 250)
  set y0 (ycor / 250)
  set x (0)
  set xtemp (0)
  set y (0)
  set iteration (0)
  while [((x * x) + (y * y)) < 2 * 2 and iteration < maxiteration]
  [set xtemp ((x * x) - (y * y) + x0)
    set y ((2 * x * y) + y0)
    set x (xtemp)
    set iteration (iteration + 1)]
  set pcolor (iteration / (maxiteration / 10)) + (color-scheme * 10)
end 

to Zoom
  while [not mouse-down?]
  []
  cp
  ask turtles
    [set mousex (mouse-xcor + (mousex * zoom-factor)) / zoom-factor
      set mousey (mouse-ycor + (mousey * zoom-factor)) / zoom-factor
      set zoom-factor (zoom-factor * 4)
      Draw-Zoom
      show zoom-factor]
end 

to Calculate-Zoom
  set x0 ((xcor + (zoom-factor * mousex)) / (250 * zoom-factor))
  set y0 ((ycor + (zoom-factor * mousey)) / (250 * zoom-factor))
  set x (0)
  set xtemp (0)
  set y (0)
  set iteration 0
  while [((x * x) + (y * y)) < 2 * 2 and iteration < maxiteration]
    [set xtemp ((x * x) - (y * y) + x0)
      set y ((2 * x * y) + y0)
      set x (xtemp)
      set iteration (iteration + 1)]
  set pcolor (iteration / (maxiteration / 10)) + (color-scheme * 10)
end 

to Draw-Zoom
  setxy -500 500
  while [ycor >= -499]
    [fd 1
      Calculate-Zoom
      if not can-move? 1
      [setxy xcor - 1000 ycor - 1]]
end