Точка "пробивает" линии прямоугольника и не отталкивается

CLS
SCREEN 9
LINE (100, 180)-(300, 180)
LINE (100, 230)-(300, 230)
LINE (100, 180)-(100, 230)
LINE (300, 180)-(300, 230)
x = 200: y = 200: dx = 0.00001: dy = 0.00001
1 PSET (x, y), 15
PSET (x, y), 0
IF y <= 181 OR y >= 229 THEN dy = -dy
IF x <= 101 OR x >= 299 THEN dx = -dx
x = x + dx: y = y + dy: GOTO 1

CLS: SCREEN 9: DIM x#, y#, dx#, dy#
LINE (100, 180)-(300, 180): LINE (100, 230)-(300, 230): LINE (100, 180)-(100, 230): LINE (300, 180)-(300, 230)
x = 400: y = 250: dx = 1 / 1024: dy = 1 / 1024
1 PSET (x, y), 15
PSET (x, y), 0
IF y = 180 AND 100 <= x AND x <= 300 THEN dy = -dy
IF x = 100 AND 180 <= y AND y <= 230 THEN dx = -dx
IF y = 230 AND 100 <= x AND x <= 300 THEN dy = -dy
IF x = 300 AND 180 <= y AND y <= 230 THEN dx = -dx
IF x <= 0 OR x >= 640 THEN dx = -dx
IF y <= 0 OR y >= 350 THEN dy = -dy
x = x + dx: y = y + dy: GOTO 1

CLS: SCREEN 9: DIM x&, y&, dx&, dy&
LINE (100, 180)-(300, 180): LINE (100, 230)-(300, 230): LINE (100, 180)-(100, 230): LINE (300, 180)-(300, 230)
x = 400: y = 250: dx = 1 / 1024 / 16: dy = 1 / 1024 / 16
1 PSET (x, y), 15
'PSET (x, y), 0
IF y = 180 AND 100 <= x AND x <= 300 THEN dy = -dy
IF x = 100 AND 180 <= y AND y <= 230 THEN dx = -dx
IF y = 230 AND 100 <= x AND x <= 300 THEN dy = -dy
IF x = 300 AND 180 <= y AND y <= 230 THEN dx = -dx
IF x <= 0 OR x >= 640 THEN dx = -dx
IF y <= 0 OR y >= 350 THEN dy = -dy
x = x + dx: y = y + dy: GOTO 1

SCREEN 9
CLS
x = 10: y = 50
x_run = 1: y_run = 1
 
PSET (x, y), 15
LINE (0, 0)-(419, 330), 15, B
 
LINE (50, 40)-(200, 120), 15, B
LINE (230, 240)-(200, 120), 15, B
LINE (320, 300)-(370, 320), 15, B
 
COLOR 3: LOCATE 25, 1: PRINT "Esc - EXIT";
 
DO
    PSET (x, y), 0
    IF POINT(x + x_run, y) = 15 THEN x_run = x_run * -1
    IF POINT(x, y + y_run) = 15 THEN y_run = y_run * -1
 
    x = x + x_run: y = y + y_run
    PSET (x, y), 15
 
    FOR zz = 0 TO 1300000: NEXT zz
LOOP UNTIL INKEY$ = CHR$(27)