'===========================================================================
' Subject: MARTIN FRACTALS FOR BASEC         Date: 03-23-99 (08:41)       
' Author:  Jernej Simoncic                   Code: BEC                    
' Origin:  jernej.simoncic@guest.arnes.si  Packet: BASEC.ABC
'===========================================================================
' Martin fractal program, by Alan Meiss
' Converted to basic by Jernej Simoncic
' This code is designed for BASEC 0.15 by William Yu
'
'  Formula from "Dynamical Systems and Fractals",
'   by Karl-Heinz Becker and Michael D”rfler,
'   Cambridge University Press, 1990
'
DIM xmax as integer, ymax as integer, t as integer, tcmax as integer
dim tc as integer, clr as integer, cx as integer, cy as integer, code as integer
DIM sa AS DOUBLE, sav AS DOUBLE, sb AS DOUBLE, sc AS DOUBLE
DIM ch AS STRING * 1, a as double, b as double, c as double, s as double
dim x as double,y as double,tmp1 as double, tmp2 as double, tmp as double
dim xold as double, yold as double,xnew as double, ynew as double
dim xc as double, yc as double, signn as double, sign as double
dim px as double, py as double,keypressed as integer, k$ as string

   RANDOMIZE TIMER

   xmax = 639
   ymax = 479
   cx = INT(.5 + xmax / 2!)
   cy = INT(.5 + ymax / 2!)
   SCREEN 12
   tcmax=100
   sa = RND * 100! - 50!
   sb = RND * 100! - 50!
   sc = RND * 100! - 50!
   sav = (ABS(sa) + ABS(sb) + ABS(sc)) / 3!
   'martin1 sa, sb, sc, 6! - ABS(sav / 10!)
   goto martin1
   SCREEN 0

martin1:' (a AS DOUBLE, b AS DOUBLE, c AS DOUBLE, s AS DOUBLE)
a=sa 
b=sb 
c=sc 
tmp=ABS(sav / 10!)
s=6-tmp
'DIM xold AS DOUBLE, yold AS DOUBLE, xnew AS DOUBLE, ynew AS DOUBLE

   xold = 0
   yold = 0
   clr = INT(RND * 256)
   t = 0
   tc = 0
   ch = "a"
   DO
      px=xold * s
      py=yold * s
      gosub plot 
      signn=xold
      gosub getsign
      xnew = yold - sign * SQR(ABS(b * xold - c)) '{ <- This is it! These two }
      ynew = a - xold                        '  { <- lines generate the }
      xold = xnew                             ' {     entire fractal! }
      yold = ynew
      t = t + 1
      IF t > 500 THEN
         tc = tc + 1
         clr = clr + 1
         IF clr > 255 THEN clr = 1
         t = 0
      END IF
      k$ = INKEY$
      IF k$ <>"" THEN end
   LOOP UNTIL keypressed or ((tc > (tcmax - 1)) AND (tcmax > 0))
   screen 0
end
'SUB plot (x AS DOUBLE, y AS DOUBLE, clr)
plot:
xc=.5+px
xc=int(xc)
xc=xc+cx
yc=.5+py
yc=int(yc)
yc=yc+cy
PSET (xc, yc), clr
return

'FUNCTION sign (x AS DOUBLE)
getsign:
if signn= 0 then sign = 0
if signn < 0 then sign=-1
if signn>0 then sign = 1
'END FUNCTION
return