Description

How to get vertical line cross one point which out of line in line.

QPoint Line::VerticalPoint(QPoint pt)

{

    QPointF ptCross = pt;

    double dtY = static_cast<double>(y1() - y2());

    double dtX = static_cast<double>(x1() - x2());

    double k,b,m;

    /**  0 = kx +b -y;  对应垂线方程为 -x -ky + m = 0;(mm为系数) */

    if(abs(dtX - 0) < 1e-10){

        ptCross = QPointF(x1(),pt.y());

        goto _END;

    }

    if(abs(dtY - 0) < 1e-10){

        ptCross = QPointF(pt.x(),y1());

        goto _END;

    }

    k = dtY/dtX;

    b = (y1()-k*x1());

    m = pt.x() + k*pt.y();

    ptCross.setX((m-k*b)/(k*k + 1));

    ptCross.setY(k*ptCross.x()+b);

_END:

    return ptCross.toPoint();

}