ZXASCII
AUTO -1
PROG demos:fractals/julia rings
CHANGED FALSE
10 REM Julia Rings
20 WINDOW DEPTH 0,32: CLS 0
30 dw=800,dh=480:
	DIM lx(dw) BASE 0;ly(dh) BASE 0
40 xmin=-2,xmax=2,ymin=-1.5,ymax=1.5
50 deltax=(xmax-xmin)/(dw-1),deltay=(ymax-ymin)/(dh-1)
60 FOR i=0 TO dw-1:
	   lx(i)=xmin+i*deltax:
	NEXT i:
	FOR i=0 TO dh-1:
	   ly(i)=ymin+i*deltay:
	NEXT i:
	i_last=0
70 maxiter=20,maxsize=4,fr=0
80 fr=(fr+1) & $7fffffff,theta=fr*PI/180,
	p=COS(theta)*SIN(theta*.7)*.6,q=SIN(theta)+SIN(theta)*.6
90 cmagsqr=(p*p+q*q),cmag=SQR(cmagsqr),
	drad=.04,drad_l=(cmag-drad),drad_l=drad_l*drad_l,
	drad_h=cmag+drad,drad_h=drad_h*drad_h
100 FOR py=0 TO (dh/2):
	   ty=ly(py):
				FOR px=0 TO dw-1
110       x=lx(px),y=ty,xsquare,ysquare,ztot,i=0
120       DO WHILE i<maxiter AND (xsquare+ysquare)<maxsize
130          xsquare=x*x,ysquare=y*y:
										ytemp=x*y*2,x=xsquare-ysquare+p,
										y=ytemp+q,zmag=(x*x+y*y)
140          IF zmag<drad_h AND zmag>drad_l AND i>0 THEN
										   ztot=ztot+(1-(ABS(zmag-cmagsqr)/drad)),i_last=i
150          INC i
160          IF zmag>4 THEN EXIT
170       LOOP
180       IF ztot>0 THEN
							   i=INT(SQR ztot*500)
							ELSE
							   i=0
190       IF i<256 THEN
							   r=i
							ELSE
							   r=255
200       IF i<512 AND i>255 THEN
							   g=i-256
							ELSE
							   IF i>=512 THEN
										   g=255
										ELSE
										   g=0
210       IF i<=768 AND i>511 THEN
							   b=i-512
							ELSE
							   IF i>=768 THEN
										   b=255
										ELSE
										   b=0
220       tmp=((r+g+b)*.33) & 255,
							r=((r+g+tmp)*.33) & 255,
							g=((g+b+tmp)*.33) & 255,
							b=((b+r+tmp)*.33) & 255
230       CASE i_last MOD 3
240          WHEN 1:
										   tmp=r,r=g,g=b,b=tmp
250          WHEN 2:
										   tmp=r,b=g,r=b,g=tmp
260       END CASE
270       PLOT INK (r SHL 16)+(g SHL 8)+b;px,py;dw-px-1,dh-py
280    NEXT px:
	NEXT py
290 GO TO 80