' A dot rebounding around the screen
' Press SPACE to redraw background

SCREEN 13
RANDOMIZE TIMER
CONST w = 320, h = 200

 ' Fill screen with random blocks of color
FOR d = 1 TO 200
  LINE (RND * w, RND * h)-(RND * w, RND * h), RND * 255, BF
NEXT d

' Fill middle area of screen with black color
FOR d = 1 TO 20
  x = INT(RND * (w - 80)) + 20
  y = INT(RND * (w - 80)) + 20
  LINE (x, y)-(x + 40, y + 40), 0, BF
NEXT d

' Draw a border around edge of screen
LINE (0, 0)-(w - 1, h - 1), 1, B

' Find an empty area
DO
  x = INT(RND * w): y = INT(RND * h)
LOOP UNTIL POINT(x, y) = 0

dx = 1.1: dy = 1.2

' Main loop to bounce dot around empty area
DO
  IF POINT(x + dx, y) <> 0 THEN dx = -dx: SOUND 450, .2
  IF POINT(x, y + dy) <> 0 THEN dy = -dy: SOUND 450, .2
  x = x + dx: y = y + dy
  PSET (x, y), 15
  WAIT &H3DA, 8
  PSET (x, y), 0
  k$ = INKEY$
  IF k$ = " " THEN RUN
LOOP UNTIL k$ = CHR$(27)