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OPTION BASE 0
PUBLIC NUMERIC X,Y,ALPHA,KK,XX(8500),YY(8500)
DIM FR(8500),FI(8500),TX(8500),TY(8500)
CALL GINIT(800,600)
LET N=10
LET L=400
CALL JUMP(200,450)
CALL RECURSIVE(N,L)
LET LV=INT(LOG2(KK))+1
MAT TX=XX
MAT TY=YY
DO
MAT XX=TX
MAT YY=TY
FOR I=1 TO KK-1
LET FR(I+1)=XX(I+1)-XX(I)
LET FI(I+1)=YY(I+1)-YY(I)
NEXT I
CALL FFT(LV,FR,FI,1)
LOCATE VALUE ,RANGE 2 TO 2^(LV-1)-1:NCUT
LET NCUT=INT(NCUT)
FOR I=NCUT+1 TO 2^LV-NCUT-1
LET FR(I)=0
LET FI(I)=0
NEXT I
CALL FFT(LV,FR,FI,-1)
CLEAR
PLOT LINES
FOR I=1 TO KK
LET XX(I+1)=XX(I)+FR(I+1)
LET YY(I+1)=YY(I)+FI(I+1)
IF I=1 THEN PLOT LINES:XX(I),YY(I);
PLOT LINES:XX(I+1),YY(I+1);
NEXT I
LOOP
END
EXTERNAL SUB RECURSIVE(LEV,L)
IF LEV=0 THEN
CALL MOVE(L)
ELSE
CALL TURN(45)
CALL RECURSIVE(LEV-1,L/SQR(2))
CALL TURN(-90)
CALL RECURSIVE(LEV-1,L/SQR(2))
CALL TURN(45)
END IF
END SUB
EXTERNAL SUB GINIT(XSIZE,YSIZE)
SET BITMAP SIZE XSIZE,YSIZE
SET WINDOW 0,XSIZE-1,YSIZE-1,0
SET POINT STYLE 1
SET COLOR MODE "REGULAR"
SET COLOR MIX(0) 0,0,0
SET COLOR MIX(1) 0,0,1
SET COLOR MIX(2) 1,0,0
SET COLOR MIX(3) 1,0,1
SET COLOR MIX(4) 0,1,0
SET COLOR MIX(5) 0,1,1
SET COLOR MIX(6) 1,1,0
SET COLOR MIX(7) 1,1,1
CLEAR
SET COLOR 7
END SUB
EXTERNAL SUB MOVE(L)
LET X=X+L*COS(ALPHA*PI/180)
LET Y=Y-L*SIN(ALPHA*PI/180)
PLOT LINES:X,Y;
LET KK=KK+1
LET XX(KK)=X
LET YY(KK)=Y
END SUB
EXTERNAL SUB TURN(R)
LET ALPHA=MOD(ALPHA+R+360,360)
END SUB
EXTERNAL SUB JUMP(XA,YA)
LET X=XA
LET Y=YA
PLOT LINES:X,Y;
LET KK=KK+1
LET XX(KK)=X
LET YY(KK)=Y
END SUB
EXTERNAL SUB FFT(M,XR(),XI(),INVERSE)
LET N=2^M
LET L=N/2
LET J=L+1
FOR I=2 TO N-2
IF I<J THEN
SWAP XR(I),XR(J)
SWAP XI(I),XI(J)
END IF
LET K=L
DO WHILE K<J
LET J=J-K
LET K=K/2
LOOP
LET J=J+K
NEXT I
IF INVERSE=1 THEN
LET PX=-PI
ELSE
FOR I=1 TO N
LET XR(I)=XR(I)/N
LET XI(I)=XI(I)/N
NEXT I
LET PX=PI
END IF
LET L=1
FOR K=1 TO M
LET LL=L+L
LET P=PX/L
FOR J=1 TO L
LET W=(J-1)*P
LET WR=COS(W)
LET WI=SIN(W)
FOR I=J TO N STEP LL
LET IL=I+L
LET TR=XR(IL)*WR-XI(IL)*WI
LET TI=XR(IL)*WI+XI(IL)*WR
LET XR(IL)=XR(I)-TR
LET XI(IL)=XI(I)-TI
LET XR(I)=XR(I)+TR
LET XI(I)=XI(I)+TI
NEXT I
NEXT J
LET L=LL
NEXT K
END SUB
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