imathboxalgo.h

对gif

    min2new = max2new = M[3][2];
    a = M[0][2] * min0;
    b = M[0][2] * max0;
    if (a < b) {
        min2new += a;
        max2new += b;
    } else {
        min2new += b;
        max2new += a;
    }
    a = M[1][2] * min1;
    b = M[1][2] * max1;
    if (a < b) {
        min2new += a;
        max2new += b;
    } else {
        min2new += b;
        max2new += a;
    }
    a = M[2][2] * min2;
    b = M[2][2] * max2;
    if (a < b) {
        min2new += a;
        max2new += b;
    } else {
        min2new += b;
        max2new += a;
    }

    Box< Vec3<T> > xbbox;

    xbbox.min[0] = min0new;
    xbbox.max[0] = max0new;
    xbbox.min[1] = min1new;
    xbbox.max[1] = max1new;
    xbbox.min[2] = min2new;
    xbbox.max[2] = max2new;

    return xbbox;
}


template <class T>
bool findEntryAndExitPoints(const Line3<T>& line,
			    const Box<Vec3<T> >& box,
			    Vec3<T> &enterPoint,
			    Vec3<T> &exitPoint)
{
    if ( box.isEmpty() ) return false;
    if ( line.distanceTo(box.center()) > box.size().length()/2. ) return false;

    Vec3<T>	points[8], inter, bary;
    Plane3<T>	plane;
    int		i, v0, v1, v2;
    bool	front = false, valid, validIntersection = false;

    // set up the eight coords of the corners of the box
    for(i = 0; i < 8; i++) 
    {
	points[i].setValue( i & 01 ? box.min[0] : box.max[0],
			    i & 02 ? box.min[1] : box.max[1],
			    i & 04 ? box.min[2] : box.max[2]);
    }

    // intersect the 12 triangles.
    for(i = 0; i < 12; i++) 
    {
	switch(i) 
        {
	case  0: v0 = 2; v1 = 1; v2 = 0; break;		// +z
	case  1: v0 = 2; v1 = 3; v2 = 1; break;

	case  2: v0 = 4; v1 = 5; v2 = 6; break;		// -z
	case  3: v0 = 6; v1 = 5; v2 = 7; break;

	case  4: v0 = 0; v1 = 6; v2 = 2; break;		// -x
	case  5: v0 = 0; v1 = 4; v2 = 6; break;

	case  6: v0 = 1; v1 = 3; v2 = 7; break;		// +x
	case  7: v0 = 1; v1 = 7; v2 = 5; break;

	case  8: v0 = 1; v1 = 4; v2 = 0; break;		// -y
	case  9: v0 = 1; v1 = 5; v2 = 4; break;

	case 10: v0 = 2; v1 = 7; v2 = 3; break;		// +y
	case 11: v0 = 2; v1 = 6; v2 = 7; break;
	}
	if((valid=intersect (line, points[v0], points[v1], points[v2],
                             inter, bary, front)) == true) 
        {
	    if(front == true) 
            {
		enterPoint = inter;
		validIntersection = valid;
	    }
	    else 
            {
		exitPoint = inter;
		validIntersection = valid;
	    }
	}
    }
    return validIntersection;
}


template<class T>
bool
intersects (const Box< Vec3<T> > &b, const Line3<T> &r, Vec3<T> &ip)
{
    //
    // Intersect a ray, r, with a box, b, and compute the intersection
    // point, ip:
    //
    // intersect() returns
    //
    //     - true if the ray starts inside the box or if the
    //       ray starts outside and intersects the box
    //
    //     - false if the ray starts outside the box and intersects it,
    //       but the intersection is behind the ray's origin.
    //
    //     - false if the ray starts outside and does not intersect it
    //
    // The intersection point is
    //
    //     - the ray's origin if the ray starts inside the box
    //
    //     - a point on one of the faces of the box if the ray
    //       starts outside the box
    //
    //     - undefined when intersect() returns false
    //

    if (b.isEmpty())
    {
	//
	// No ray intersects an empty box
	//

	return false;
    }

    if (b.intersects (r.pos))
    {
	//
	// The ray starts inside the box
	//

	ip = r.pos;
	return true;
    }

    //
    // The ray starts outside the box.  Between one and three "frontfacing"
    // sides of the box are oriented towards the ray, and between one and
    // three "backfacing" sides are oriented away from the ray.
    // We intersect the ray with the planes that contain the sides of the
    // box, and compare the distances between the ray-plane intersections.
    // The ray intersects the box if the most distant frontfacing intersection
    // is nearer than the nearest backfacing intersection.  If the ray does
    // intersect the box, then the most distant frontfacing ray-plane
    // intersection is the ray-box intersection.
    //

    const T TMAX = limits<T>::max();

    T tFrontMax = -1;
    T tBackMin = TMAX;

    //
    // Minimum and maximum X sides.
    //

    if (r.dir.x > 0)
    {
	if (r.pos.x > b.max.x)
	    return false;

	T d = b.max.x - r.pos.x;

	if (r.dir.x > 1 || d < TMAX * r.dir.x)
	{
	    T t = d / r.dir.x;

	    if (tBackMin > t)
		tBackMin = t;
	}

	if (r.pos.x <= b.min.x)
	{
	    T d = b.min.x - r.pos.x;
	    T t = (r.dir.x > 1 || d < TMAX * r.dir.x)? d / r.dir.x: TMAX;

	    if (tFrontMax < t)
	    {
		tFrontMax = t;

		ip.x = b.min.x; 
		ip.y = clamp (r.pos.y + t * r.dir.y, b.min.y, b.max.y);
		ip.z = clamp (r.pos.z + t * r.dir.z, b.min.z, b.max.z);
	    }
	}
    }
    else if (r.dir.x < 0)
    {
	if (r.pos.x < b.min.x)
	    return false;

	T d = b.min.x - r.pos.x;

	if (r.dir.x < -1 || d > TMAX * r.dir.x)
	{
	    T t = d / r.dir.x;

	    if (tBackMin > t)
		tBackMin = t;
	}

	if (r.pos.x >= b.max.x)
	{
	    T d = b.max.x - r.pos.x;
	    T t = (r.dir.x < -1 || d > TMAX * r.dir.x)? d / r.dir.x: TMAX;

	    if (tFrontMax < t)
	    {
		tFrontMax = t;

		ip.x = b.max.x; 
		ip.y = clamp (r.pos.y + t * r.dir.y, b.min.y, b.max.y);
		ip.z = clamp (r.pos.z + t * r.dir.z, b.min.z, b.max.z);
	    }
	}
    }
    else // r.dir.x == 0
    {
	if (r.pos.x < b.min.x || r.pos.x > b.max.x)
	    return false;
    }

    //
    // Minimum and maximum Y sides.
    //

    if (r.dir.y > 0)
    {
	if (r.pos.y > b.max.y)
	    return false;

	T d = b.max.y - r.pos.y;

	if (r.dir.y > 1 || d < TMAX * r.dir.y)
	{
	    T t = d / r.dir.y;

	    if (tBackMin > t)
		tBackMin = t;
	}

	if (r.pos.y <= b.min.y)
	{
	    T d = b.min.y - r.pos.y;
	    T t = (r.dir.y > 1 || d < TMAX * r.dir.y)? d / r.dir.y: TMAX;

	    if (tFrontMax < t)
	    {
		tFrontMax = t;

		ip.x = clamp (r.pos.x + t * r.dir.x, b.min.x, b.max.x);
		ip.y = b.min.y; 
		ip.z = clamp (r.pos.z + t * r.dir.z, b.min.z, b.max.z);
	    }
	}
    }
    else if (r.dir.y < 0)
    {
	if (r.pos.y < b.min.y)
	    return false;

	T d = b.min.y - r.pos.y;

	if (r.dir.y < -1 || d > TMAX * r.dir.y)
	{
	    T t = d / r.dir.y;

	    if (tBackMin > t)
		tBackMin = t;
	}

	if (r.pos.y >= b.max.y)
	{
	    T d = b.max.y - r.pos.y;
	    T t = (r.dir.y < -1 || d > TMAX * r.dir.y)? d / r.dir.y: TMAX;
	    
	    if (tFrontMax < t)
	    {
		tFrontMax = t;

		ip.x = clamp (r.pos.x + t * r.dir.x, b.min.x, b.max.x);
		ip.y = b.max.y; 
		ip.z = clamp (r.pos.z + t * r.dir.z, b.min.z, b.max.z);
	    }
	}
    }
    else // r.dir.y == 0
    {
	if (r.pos.y < b.min.y || r.pos.y > b.max.y)
	    return false;
    }

    //
    // Minimum and maximum Z sides.
    //

    if (r.dir.z > 0)
    {
	if (r.pos.z > b.max.z)
	    return false;

	T d = b.max.z - r.pos.z;

	if (r.dir.z > 1 || d < TMAX * r.dir.z)
	{
	    T t = d / r.dir.z;

	    if (tBackMin > t)
		tBackMin = t;
	}

	if (r.pos.z <= b.min.z)
	{
	    T d = b.min.z - r.pos.z;
	    T t = (r.dir.z > 1 || d < TMAX * r.dir.z)? d / r.dir.z: TMAX;
	    
	    if (tFrontMax < t)
	    {
		tFrontMax = t;

		ip.x = clamp (r.pos.x + t * r.dir.x, b.min.x, b.max.x);
		ip.y = clamp (r.pos.y + t * r.dir.y, b.min.y, b.max.y);
		ip.z = b.min.z; 
	    }
	}
    }
    else if (r.dir.z < 0)
    {
	if (r.pos.z < b.min.z)
	    return false;

	T d = b.min.z - r.pos.z;

	if (r.dir.z < -1 || d > TMAX * r.dir.z)
	{
	    T t = d / r.dir.z;

	    if (tBackMin > t)
		tBackMin = t;
	}

	if (r.pos.z >= b.max.z)
	{
	    T d = b.max.z - r.pos.z;
	    T t = (r.dir.z < -1 || d > TMAX * r.dir.z)? d / r.dir.z: TMAX;
	    
	    if (tFrontMax < t)
	    {
		tFrontMax = t;

		ip.x = clamp (r.pos.x + t * r.dir.x, b.min.x, b.max.x);
		ip.y = clamp (r.pos.y + t * r.dir.y, b.min.y, b.max.y);
		ip.z = b.max.z; 
	    }
	}
    }
    else // r.dir.z == 0
    {
	if (r.pos.z < b.min.z || r.pos.z > b.max.z)
	    return false;
    }

    return tFrontMax <= tBackMin;
}


template<class T>
bool
intersects (const Box< Vec3<T> > &box, const Line3<T> &ray)
{
    Vec3<T> ignored;
    return intersects (box, ray, ignored);
}


} // namespace Imath

#endif