Drawing a fractal in BASIC

fractal.bas

SCREEN 12
CLS

RANDOMIZE TIMER
maxx = 640
maxy = 480
x1% = INT(RND * maxx) + 1
y1% = INT(RND * maxy) + 1
TYPE VERTEX
   XC AS DOUBLE
   YC AS DOUBLE
END TYPE
DIM POINTS(3) AS VERTEX
POINTS(1).XC = 0
POINTS(1).YC = maxy
POINTS(2).XC = maxx / 2
POINTS(2).YC = 0
POINTS(3).XC = maxx
POINTS(3).YC = maxy

WHILE INKEY$ = ""
   P = INT(RND * 3) + 1
   x1 = x1 - ((x1 - POINTS(P).XC) / 2)
   y1 = (y1 - ((y1 - POINTS(P).YC) / 2))
   PSET (x1, y1), 11
WEND

DO: LOOP WHILE INKEY$ = ""

DO
   CLS

   POINTS(1).XC = INT(RND * maxx) + 1
   POINTS(1).YC = INT(RND * maxy) + 1
   POINTS(2).XC = INT(RND * maxx) + 1
   POINTS(2).YC = INT(RND * maxy) + 1
   POINTS(3).XC = INT(RND * maxx) + 1
   POINTS(3).YC = INT(RND * maxy) + 1
WHILE INKEY$ <> CHR$(27)
   P = INT(RND * 3) + 1
   x1 = x1 - ((x1 - POINTS(P).XC) / 2)
   y1 = (y1 - ((y1 - POINTS(P).YC) / 2))
   PSET (x1, y1), 10
WEND
LOOP

DO: LOOP WHILE INKEY$ = ""