template <class Real>

bool IntrLine2Box2<Real>::Clip (Real fDenom, Real fNumer, Real& rfT0,

    Real& rfT1)

{

    // Return value is 'true' if line segment intersects the current test

    // plane.  Otherwise 'false' is returned in which case the line segment

    // is entirely clipped.

    if (fDenom > (Real)0.0)

    {

        if (fNumer > fDenom*rfT1)

        {

            return false;

        }

        if (fNumer > fDenom*rfT0)

        {

            rfT0 = fNumer/fDenom;

        }

        return true;

    }

    else if (fDenom < (Real)0.0)

    {

        if (fNumer > fDenom*rfT0)

        {

            return false;

        }

        if (fNumer > fDenom*rfT1)

        {

            rfT1 = fNumer/fDenom;

        }

        return true;

    }

    else

    {

        return fNumer <= (Real)0.0;

    }

}

//////////////////////////////////////////////////////////////////

template <class Real>

bool IntrLine2Box2<Real>::DoClipping (Real fT0, Real fT1,

    const Vector2<Real>& rkOrigin, const Vector2<Real>& rkDirection,

    const Box2<Real>& rkBox, bool bSolid, int& riQuantity,

    Vector2<Real> akPoint[2], int& riIntrType)

{

    assert(fT0 < fT1);

    // convert linear component to box coordinates

    Vector2<Real> kDiff = rkOrigin - rkBox.Center;

    Vector2<Real> kBOrigin(

        kDiff.Dot(rkBox.Axis[0]),

        kDiff.Dot(rkBox.Axis[1])

    );

    Vector2<Real> kBDirection(

        rkDirection.Dot(rkBox.Axis[0]),

        rkDirection.Dot(rkBox.Axis[1])

    );

    Real fSaveT0 = fT0, fSaveT1 = fT1;

    bool bNotAllClipped =

        Clip(+kBDirection.X(),-kBOrigin.X()-rkBox.Extent[0],fT0,fT1) &&

        Clip(-kBDirection.X(),+kBOrigin.X()-rkBox.Extent[0],fT0,fT1) &&

        Clip(+kBDirection.Y(),-kBOrigin.Y()-rkBox.Extent[1],fT0,fT1) &&

        Clip(-kBDirection.Y(),+kBOrigin.Y()-rkBox.Extent[1],fT0,fT1);

    if (bNotAllClipped && (bSolid || fT0 != fSaveT0 || fT1 != fSaveT1))

    {

        if (fT1 > fT0)

        {

            riIntrType = IT_SEGMENT;

            riQuantity = 2;

            akPoint[0] = rkOrigin + fT0*rkDirection;

            akPoint[1] = rkOrigin + fT1*rkDirection;

        }

        else

        {

            riIntrType = IT_POINT;

            riQuantity = 1;

            akPoint[0] = rkOrigin + fT0*rkDirection;

        }

    }

    else

    {

        riIntrType = IT_EMPTY;

        riQuantity = 0;

    }

    return riIntrType != IT_EMPTY;

}

调用DoClipping()即可获得交点坐标

代码来自开源引擎WildMagic4p9\GeometricTools\WildMagic4\LibFoundation\Intersection\Wm4IntrLine2Box2.cpp