BoundingSphere.h

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/* Copyright (C) 2014 Wildfire Games.
 * This file is part of 0 A.D.
 *
 * 0 A.D. is free software: you can redistribute it and/or modify
 * it under the terms of the GNU General Public License as published by
 * the Free Software Foundation, either version 2 of the License, or
 * (at your option) any later version.
 *
 * 0 A.D. is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 * GNU General Public License for more details.
 *
 * You should have received a copy of the GNU General Public License
 * along with 0 A.D.  If not, see <http://www.gnu.org/licenses/>.
 */

#ifndef INCLUDED_BOUNDINGSPHERE
#define INCLUDED_BOUNDINGSPHERE

#include "maths/BoundingBoxAligned.h"
#include "maths/Vector3D.h"

class CBoundingSphere
{
private:
    CVector3D m_Center;
    float m_Radius;

public:
    CBoundingSphere() : m_Radius(0) { }

    CBoundingSphere(const CVector3D& center, float radius) : m_Center(center), m_Radius(radius) { }

    /**
     * Construct a bounding sphere that encompasses a bounding box
     * swept through all possible rotations around the origin.
     */
    static CBoundingSphere FromSweptBox(const CBoundingBoxAligned& bbox)
    {
        float maxX = std::max(fabsf(bbox[0].X), fabsf(bbox[1].X));
        float maxY = std::max(fabsf(bbox[0].Y), fabsf(bbox[1].Y));
        float maxZ = std::max(fabsf(bbox[0].Z), fabsf(bbox[1].Z));
        float radius = sqrtf(maxX*maxX + maxY*maxY + maxZ*maxZ);

        return CBoundingSphere(CVector3D(0.f, 0.f, 0.f), radius);
    }

    const CVector3D& GetCenter()
    {
        return m_Center;
    }

    float GetRadius() const
    {
        return m_Radius;
    }

    /**
     * Check if the ray, defined by an origin point and a direction unit vector
     * interesects with the sphere
     */
    bool RayIntersect(const CVector3D& origin, const CVector3D& dir) const
    {
        CVector3D v = m_Center - origin; // Vector v from the origin of the ray to the center of the sphere
        float pcLen = dir.Dot(v); // Length of the projection of v onto the direction vector of the ray
        if(pcLen <= 0)
            return false; // Sphere behind the ray
        // Get the shortest distance from the center of the sphere to the ray
        v  = (dir * pcLen) - v;
        if (v.LengthSquared() > m_Radius * m_Radius)
            return false; // Distance to sphere center more than radius
        return true;
    }
};

#endif // INCLUDED_BOUNDINGSPHERE