PointDiskNearest.h

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/*  Copyright (C) 2003-2021 Free Electron Organization
    Any use of this software requires a license.  If a valid license
    was not distributed with this file, visit freeelectron.org. */

/** @file */

#ifndef __geometry_PointDiskNearest_h__
#define __geometry_PointDiskNearest_h__

namespace fe
{
namespace ext
{

/**************************************************************************//**
    @brief Find point nearest to a circular solid

    @ingroup geometry
*//***************************************************************************/
template <typename T>
class PointDiskNearest
{
    public:
static  T   solve(const Vector<3,T>& center,const Vector<3,T>& facing,
                    const T radius,const Vector<3,T>& origin,
                    Vector<3,T>& direction,Vector<3,T>& intersection);
};

template <typename T>
inline T PointDiskNearest<T>::solve(const Vector<3,T>& center,
        const Vector<3,T>& facing,T radius,
        const Vector<3,T>& origin,Vector<3,T>& direction,
        Vector<3,T>& intersection)
{
//  feLog("center %s facing %s radius %.6G\n",
//          c_print(center),c_print(facing),radius);
//  feLog("origin: %s\n",c_print(origin));
//  feLog("direction: %s\n",c_print(direction));

    const Vector<3,T> to_origin=origin-center;
    const T displacement=dot(facing,to_origin);
    intersection=origin-displacement*facing;
    const Vector<3,T> radial=intersection-center;
    const T outward2=magnitudeSquared(radial);
//  feLog("displacement %.6G radial %s\n",displacement,c_print(radial));
//  feLog("intersection: %s sq %.6G vs %.6G\n",c_print(intersection),
//          outward2,radius*radius);

    if(outward2<=radius*radius)
    {
        direction= -facing;
        return displacement;
    }

    intersection=center+radius/sqrt(outward2)*radial;
    direction=intersection-origin;
    T mag=magnitude(direction);
    direction*=T(1)/mag;
    return mag;
}

} /* namespace ext */
} /* namespace fe */

#endif /* __geometry_PointDiskNearest_h__ */