' Circles demo for PowerBASIC
' by Dave Navarro, Jr.

RANDOMIZE TIMER
DEFINT A-Z
SCREEN 12

z = 40
DIM x1(1:z), y1(1:z), r1(1:z)

x1 = (RND * 640) : x2 = (RND * 640)
y1 = (RND * 480) : y2 = (RND * 480)

c1  = 9 : c2  = 14 : bool = 0 : r = 20

xd1 = 9
yd1 = 6

DO

  ARRAY DELETE x1(1)
  ARRAY DELETE y1(1)
  ARRAY DELETE r1(1)

  CIRCLE (x1, y1), r, c1
  CIRCLE (x1(1), y1(1)), r1(1), 0

  x1(z) = x1
  y1(z) = y1
  r1(z) = r

  INCR x1, xd1
  INCR y1, yd1

  IF (x1 < 1) OR (x1 > 638) THEN
    xd1 = 0 - xd1
  END IF

  IF (y1 < 1) OR (y1 > 478) THEN
    yd1 = 0 - yd1
  END IF

  INCR x

  IF x = 200 THEN
    INCR c1
    DECR c2
    IF c1 = 16 THEN c1 =  9
    IF c2 =  8 THEN c2 = 15
    x = 0
  END IF

  IF Bool THEN
    INCR r, 2
    IF r > 80 THEN Bool = 0
  ELSE
    DECR r, 2
    IF r < 10 THEN BOOL = -1
  END IF

  DELAY .08

LOOP UNTIL LEN(INKEY$)

SCREEN 0