如何检测两个线段相交的位置？

P = (x1, y1)
Q = (x2, y2)
R = (x3, y3)
S = (x4, y4)

P = (x1, y1)
Q = (x2, y2)
R = (x3, y3)
S = (x4, y4)

// 计算交点
x = ((x1*y2 - y1*x2)*(x3 - x4) - (x1 - x2)*(x3*y4 - y3*x4)) / ((x1 - x2)*(y3 - y4) - (y1 - y2)*(x3 - x4))
y = ((x1*y2 - y1*x2)*(y3 - y4) - (y1 - y2)*(x3*y4 - y3*x4)) / ((x1 - x2)*(y3 - y4) - (y1 - y2)*(x3 - x4))

t1 = ((x - x1) * (x2 - x1) + (y - y1) * (y2 - y1)) / ((x2 - x1)^2 + (y2 - y1)^2)
t2 = ((x - x3) * (x4 - x3) + (y - y3) * (y4 - y3)) / ((x4 - x3)^2 + (y4 - y3)^2)

if (t1 >= 0 && t1 <= 1 && t2 >= 0 && t2 <= 1) {
    // 两条线段相交
} else {
    // 两条线段不相交
}