'===========================================================================
' Subject: BALL PATTERN USING XOR            Date: Unknown Date (00:00:00)
' Author:  Scott Bailey                      Code: QB, QBasic             
' Keys:    BALL,PATTERN,XOR                Packet: EGAVGA.ABC
'===========================================================================
'BALLPTRN.BAS by Scott Bailey
'public domain
'draws patterns by XORing the ball bouncing off the walls
'hitting the spacebar starts a different pattern

DEFINT A-Z
RANDOMIZE TIMER
SCREEN 12
CLS
CIRCLE (10, 10), 2, 3
CIRCLE (10, 10), 1, 9
DIM fly(0 TO 19)
GET (7, 7)-(12, 12), fly

restart:
    CLS
    FOR h = 0 TO 639 STEP 10
        LINE (0, h)-(639, h), 4
        LINE (h, 0)-(h, 479), 4
    NEXT
   
    LINE (0, 0)-(639, 479), 4, B
   
    direction = INT(RND * 4) + 1
    x = RND * 300 + 10
    y = RND * 460 + 10

DO
    a$ = INKEY$
    IF a$ = CHR$(27) THEN END
    IF a$ = " " THEN GOTO restart
   
    SELECT CASE direction
        CASE 1
            x = x + 4
            y = y - 4
        CASE 2
            y = y + 4
            x = x + 4
        CASE 3
            x = x - 4
            y = y + 4
        CASE 4
            x = x - 4
            y = y - 4
    END SELECT

    IF x > 620 OR x < 20 OR y > 460 OR y < 20 THEN
        SELECT CASE direction
            CASE 1
                direction = 2
            CASE 2
                direction = 3
            CASE 3
                direction = 4
            CASE 4
                direction = 1
        END SELECT
    END IF
    PUT (x, y), fly
LOOP