TYPE linetype
x1 AS SINGLE
x2 AS SINGLE
y1 AS SINGLE
y2 AS SINGLE
END TYPE

DECLARE FUNCTION intersect (line1 AS linetype, line2 AS linetype)
SCREEN 13

DIM lines(0 TO 4) AS linetype

lines(0).x1 = 0
lines(0).y1 = 50
lines(0).x2 = 20
lines(0).y2 = 70

lines(1).x1 = 20
lines(1).y1 = 70
lines(1).x2 = 50
lines(1).y2 = 150

lines(2).x1 = 50
lines(2).y1 = 150
lines(2).x2 = 120
lines(2).y2 = 120

lines(3).x1 = 120
lines(3).y1 = 120
lines(3).x2 = 280
lines(3).y2 = 80

lines(4).x1 = 280
lines(4).y1 = 80
lines(4).x2 = 320
lines(4).y2 = 110


x = 6
y = 2
xold = 0
yold = 0
xdelta = 12
ydelta = 4
DIM l AS linetype
WHILE 1
FOR u = 0 TO 4
LINE (lines(u).x1, lines(u).y1)-(lines(u).x2, lines(u).y2), 1
NEXT
l.x1 = xold
l.y1 = yold
l.x2 = x
l.y2 = y
LINE (l.x1, l.y1)-(l.x2, l.y2), 1
FOR i = 0 TO 4
a = intersect(lines(i), l)
NEXT
IF INKEY$ <> "" THEN
DO WHILE INKEY$ = "": LOOP
END IF
LINE (l.x1, l.y1)-(l.x2, l.y2), 14
xold = x
yold = y
x = x + xdelta
ydelta = ydelta + .2
y = y + ydelta
FOR u = 0 TO 10000: NEXT
WEND

FUNCTION intersect (line1 AS linetype, line2 AS linetype)
CIRCLE (line1.x1, line1.y1), 2, 15
CIRCLE (line1.x2, line1.y2), 2, 15
CIRCLE (line2.x1, line2.y1), 2, 26
CIRCLE (line2.x2, line2.y2), 2, 26
IF line1.x1 > line1.x2 THEN SWAP line1.x1, line1.x2
IF line1.y1 > line1.y2 THEN SWAP line1.y1, line1.y2
IF line2.x1 > line2.x2 THEN SWAP line2.x1, line2.x2
IF line2.y1 > line2.y2 THEN SWAP line2.y1, line2.y2

m1 = (line1.y2 - line1.y1) / (line1.x2 - line1.x1)
m2 = (line2.y2 - line2.y1) / (line2.x2 - line2.x1)
IF m1 = m2 THEN intersect = 0: EXIT FUNCTION
b1 = line1.y1 - m1 * line1.x1
b2 = line2.y1 - m2 * line2.x1
x = -(b2 - b1) / (m2 - m1)
y = x * m1 + b1
IF (x < line1.x2 AND x > line1.x1) AND (x < line2.x2 AND x > line2.x1) THEN
IF (y < line1.y2 AND y > line1.y1) AND (y < line2.y2 AND y > line2.y1) THEN
CIRCLE (x, y), 2, 4
intersect = 1
'EXIT FUNCTION
END IF
'ELSE intersect = 0
END IF
END FUNCTION