Langton's Ant

GRIDSIZE = 20
SPEED = 0.01 'Lower # = Faster speed.
''''''''''''''''''''''''''''''''''''''''''''''
BCOLOR 75,75,75
TCOLOR 255,0,0
PRINT "Loading..."
tick=0
size2=GRIDSIZE
size=size2*size2
x=INT((size2+1)/2)
y=INT((size2+1)/2) 'Start in middle
d=2 'Direction. '1:Left,2:Up,3:Right,4:Dwn.
DIM grid(size)
COLOR 255,255,255
FOR i=1 TO size
    grid(i)=0 'Off/White: Background grid.
NEXT
FOR i=1 TO size2
    FOR j=1 TO size2
        RRECT (i*(ScreenWidth/size2))-(ScreenWidth/size2),(j*(ScreenHeight/size2))-(ScreenHeight/size2),i*(ScreenWidth/size2),j*(ScreenHeight/size2),5
    NEXT
NEXT
SLEEP 0.01
CLS tty
WHILE x>0 AND y>0 AND x<size2 AND y<size2
    tick=tick+1
    PRINT tick
    IF grid(x*y)=0 THEN 'If off/White.
        grid(x*y)=1 'Turn on/Black.
        COLOR 0,0,0
        d=d-1 'Turn left
    ELSE
        IF grid(x*y)=1 THEN 'If on/black
            grid(x*y)=0 'Turn off/white
            COLOR 255,255,255
            d=d+1 'Turn right
        ENDIF
    ENDIF
    IF d=0 THEN
        d=4
    ENDIF
    IF d=5 THEN
        d=1
    ENDIF
    IF d=1 THEN
        x=x-1
    ENDIF
    IF d=2 THEN
        y=y-1
    ENDIF
    IF d=3 THEN
        x=x+1
    ENDIF
    IF d=4 THEN
        y=y+1
    ENDIF
    SLEEP speed
    CLS tty
    RRECT (x*(ScreenWidth/size2))-(ScreenWidth/size2),(y*(ScreenHeight/size2))-(ScreenHeight/size2),x*(ScreenWidth/size2),y*(ScreenHeight/size2),5
WEND
PRINT tick