10 REM Dragon curve
20 REM SIN, COS in arrays for PI/4 multipl.
30 DIM S(7),C(7)
40 QPI=ATN(1):SQ=SQR(2)
50 FOR I=0 TO 7
60 S(I)=SIN(I*QPI):C(I)=COS(I*QPI)
70 NEXT I
80 LEVEL=15
90 INSIZE=128:REM 2^WHOLE_NUM (looks better)
100 X=80:Y=70
110 ROTQPI=0:RQ=1
120 DIM R(LEVEL)
130 SCREEN 2
140 GOSUB 200
150 OPEN "GRP:" FOR OUTPUT AS #1
160 DRAW "BM 0,184":PRINT #1,"Hit any key to exit."
170 IF INKEY$="" THEN 170
180 CLOSE #1
190 END
200 REM Dragon
210 ROTQPI=ROTQPI AND 7
220 IF LEVEL>1 THEN GOTO 280
230 YN=S(ROTQPI)*INSIZE+Y
240 XN=C(ROTQPI)*INSIZE+X
250 LINE (X,Y)-(XN,YN)
260 X=XN:Y=YN
270 RETURN
280 INSIZE=INSIZE*SQ/2
290 ROTQPI=(ROTQPI+RQ)AND 7
300 LEVEL=LEVEL-1
310 R(LEVEL)=RQ:RQ=1
320 GOSUB 200
330 ROTQPI=(ROTQPI-R(LEVEL)*2)AND 7
340 RQ=-1
350 GOSUB 200
360 RQ=R(LEVEL)
370 ROTQPI=(ROTQPI+RQ)AND 7
380 LEVEL=LEVEL+1
390 INSIZE=INSIZE*SQ
400 RETURN