PROGRAM LSYS_SIERPINSKI_GASKET_3   !© W.van Duyn 13th May 2004
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 200, y try 100"
INPUT x,y
PRINT "input: Size try 512,level try 9, dim 6"
INPUT size,level,ak
CLEAR
SET COLOR "black"
BOX AREA 0,1199,0,903
FLOOD 1,1
SET COLOR "White"
SET background Color "black"
PRINT "Sierpinski Gasket Type 2 L-System "
PRINT "© W.van Duyn May 13th 2004"
LET lev=level
LET k=360/ak
LET a=0
LET r=2
LET d=size/r^level
FOR i=1 to ak/2
SET COLOR i+11
CALL moveX(d,lev,a,x,y,k)
CALL turnLEFT(a,k)
CALL turnLEFT(a,k)
NEXT i
END SUB

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

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

SUB travelON(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