BoundingBoxOriented.h

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/* Copyright (C) 2011 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_BOX
#define INCLUDED_BOX

#include "maths/Vector3D.h"

class CBoundingBoxAligned;

/*
 * Generic oriented box. Originally intended to be used an Oriented Bounding Box (OBB), 
 * as opposed to CBoundingBoxAligned which is always aligned to the world-space axes (AABB).
 * However, it could also be used to represent more generic shapes, such as parallelepipeds.
 */
class CBoundingBoxOriented 
{
public:
    
    /// Empty constructor; creates an empty box
    CBoundingBoxOriented() { SetEmpty(); }

    /**
     * Constructs a new oriented box centered at @p center and with normalized side vectors @p u,
     * @p v and @p w. These vectors should be mutually orthonormal for a proper rectangular box.
     * The half-widths of the box in each dimension are given by the corresponding components of
     * @p halfSizes.
     */
    CBoundingBoxOriented(const CVector3D& center, const CVector3D& u, const CVector3D& v, const CVector3D& w, const CVector3D& halfSizes)
        : m_Center(center), m_HalfSizes(halfSizes)
    {
        m_Basis[0] = u;
        m_Basis[1] = v;
        m_Basis[2] = w;
    }

    /// Constructs a new box from an axis-aligned bounding box (AABB).
    explicit CBoundingBoxOriented(const CBoundingBoxAligned& bound);

    /**
     * Check if a given ray intersects this box. Must not be used if IsEmpty() is true.
     * See Real-Time Rendering, Third Edition by T. Akenine-Möller, p. 741--744.
     *
     * @param[in] origin Origin of the ray.
     * @param[in] dir Direction vector of the ray, defining the positive direction of the ray.
     *            Must be of unit length.
     * @param[out] tMin,tMax Distance in the positive direction from the origin of the ray to the
     *             entry and exit points in the box, provided that the ray intersects the box. if
     *             the ray does not intersect the box, no values are written to these variables.
     *             If the origin is inside the box, then this is counted as an intersection and one
     *             of @p tMin and @p tMax may be negative.
     *
     * @return true If the ray originating in @p origin and with unit direction vector @p dir intersects
     *         this box, false otherwise.
     */
    bool RayIntersect(const CVector3D& origin, const CVector3D& dir, float& tMin, float& tMax) const;

    /**
     * Returns the corner at coordinate (@p u, @p v, @p w). Each of @p u, @p v and @p w must be exactly 1 or -1.
     * Must not be used if IsEmpty() is true.
     */
    void GetCorner(int u, int v, int w, CVector3D& out) const
    {
        out = m_Center + m_Basis[0]*(u*m_HalfSizes[0]) + m_Basis[1]*(v*m_HalfSizes[1]) + m_Basis[2]*(w*m_HalfSizes[2]);
    }

    void SetEmpty()
    {
        // everything is zero
        m_Center = CVector3D();
        m_Basis[0] = CVector3D();
        m_Basis[1] = CVector3D();
        m_Basis[2] = CVector3D();
        m_HalfSizes = CVector3D();
    }

    bool IsEmpty() const
    {
        CVector3D empty;
        return (m_Center == empty && 
                m_Basis[0] == empty && 
                m_Basis[1] == empty && 
                m_Basis[2] == empty && 
                m_HalfSizes == empty);
    }

public:
    CVector3D m_Center; ///< Centroid location of the box
    CVector3D m_HalfSizes; ///< Half the sizes of the box in each dimension (u,v,w). Positive values are expected.
    /// Basis vectors (u,v,w) of the sides. Must always be normalized, and should be 
    /// orthogonal for a proper rectangular cuboid.
    CVector3D m_Basis[3];

    static const CBoundingBoxOriented EMPTY;
};

#endif // INCLUDED_BOX