This module is part of the original MMBasic library. It is reproduced here with kind permission of Hugh Buckle and Geoff Graham. Be aware it may reference functionality which has changed or is deprecated in the latest versions of MMBasic.

100 'JULIA.BAS - Draws Julia set fractal images
102 'By loki on the Back Shed   Aug 2012
103 'See topic (MM) Mandelbrot & Julia set fractals
105 'Specify initial values
120 RealOffset = -1.30
125 ImaginOffset = -1.22
126 '------------------------------------------------*
130 'Set the Julia set constant [eg C = -1.2 + 0.8i]
135 CRealVal = -0.78 
140 CImagVal = -0.20
141 '------------------------------------------------*
145 MAXIT=80 'max iterations
180 PixelWidth = MM.HRES
185 PixelHeight = MM.VRES
190 GAP = PixelHeight / PixelWidth
200 SIZE = 2.50
205 XDelta = SIZE / PixelWidth
210 YDelta = (SIZE * GAP) / PixelHeight
215 CLS
220 'Loop processing - visit every pixel
225 FOR X = 0 TO (PixelWidth - 1)
230   CX = X * Xdelta + RealOffset
235   FOR Y = 0 TO (PixelHeight - 1)
240     CY = Y * YDelta + ImaginOffset
245     Zr = CX
250     Zi = CY
255     COUNT = 0
260     'Begin Iteration loop      
265     DO WHILE (( COUNT <= MAXIT ) AND (( Zr * Zr + Zi * Zi ) < 4 ))
270       new_Zr = Zr * Zr - Zi * Zi + CRealVal 
275       new_Zi = 2 * Zr * Zi + CImagVal
280       Zr = new_Zr
285       Zi = new_Zi
290       COUNT = COUNT + 1
295     LOOP
415     PIXEL(X,Y) = COUNT MOD 2
500   NEXT Y
510 NEXT X
520 DO
530   a$ = INKEY$
540 LOOP WHILE a$ = ""
600 'End listing