PROGRAM Sierpinski_GASKET     !21st April 2004 © W.Van Duyn
SET MODE "color"
SET WINDOW 0,1199,0,903
SET BACKGROUND COLOR "white"
CLEAR
CALL init
END

SUB init
OPTION ANGLE degrees
PRINT "input: x try 400, y try 400"
INPUT x,y
PRINT "input: Side try 200,level try 6, dimension try 3"
INPUT side,level,ak
CLEAR
SET COLOR "black"
FLOOD 10,10
LET k=360/ak
LET r=(1+2*(1+cos(k)))^(level-1)
LET a=0
SET COLOR 10
FOR i=1 TO ak
CALL shift(level,side,x,y,a,ak,k)
NEXT i
END SUB

SUB shift(level,side,x,y,a,ak,k)
LET lev=level
LET d=side/r
CALL moveX(d,lev,a,x,y,k,ak)
CALL turnRIGHT(a,k)
END SUB

SUB moveX(d,lev,a,x,y,k,ak)
IF lev=0 THEN
CALL moveON(d,a,x,y)
EXIT IF
ELSE
CALL moveX(d,lev-1,a,x,y,k,ak)
CALL turnLEFT(a,k)
CALL moveX(d,lev-1,a,x,y,k,ak)
CALL turnRIGHT(a,k)
CALL moveX(d,lev-1,a,x,y,k,ak)
CALL turnRIGHT(a,k)
CALL moveX(d,lev-1,a,x,y,k,ak)
CALL turnLEFT(a,k)
CALL moveX(d,lev-1,a,x,y,k,ak)
END IF
END SUB

SUB moveON(d,a,x,y)
OPTION ANGLE degrees
LET x2=x+d*cos(a)
LET y2=y+d*sin(a)
PLOT x,y;x2,y2
LET x=x2
LET y=y2
END SUB

SUB turnLEFT(a,k)
LET a=a+k
END SUB

SUB turnRIGHT(a,k)
LET a=a-k
END SUB