Plane.cpp

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/* Copyright (C) 2009 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/>.
 */

/*
 * A Plane in R3 and several utility methods.
 */

// Note that the format used for the plane equation is
// Ax + By + Cz + D = 0, where <A,B,C> is the normal vector.

#include "precompiled.h"

#include "Plane.h"
#include "MathUtil.h"

CPlane::CPlane ()
{
    m_Dist = 0.0f;
}

//sets the plane equation from 3 points on that plane
void CPlane::Set (const CVector3D &p1, const CVector3D &p2, const CVector3D &p3)
{
    CVector3D D1, D2;
    CVector3D Norm;

    //calculate two vectors on the surface of the plane
    D1 = p2-p1;
    D2 = p3-p1;

    //cross multiply gives normal
    Norm = D2.Cross(D1);

    Set (Norm, p1);
}

//sets the plane equation from a normal and a point on 
//that plane
void CPlane::Set (const CVector3D &norm, const CVector3D &point)
{
    m_Norm = norm;

    m_Dist = - (norm.X * point.X +
                norm.Y * point.Y +
                norm.Z * point.Z);

//  Normalize ();
}

//normalizes the plane equation
void CPlane::Normalize ()
{
    float Scale;

    Scale = 1.0f/m_Norm.Length ();

    m_Norm.X *= Scale;
    m_Norm.Y *= Scale;
    m_Norm.Z *= Scale;
    m_Dist *= Scale;
}

//returns the side of the plane on which this point
//lies.
PLANESIDE CPlane::ClassifyPoint (const CVector3D &point) const
{
    float Dist;

    Dist = m_Norm.X * point.X +
           m_Norm.Y * point.Y +
           m_Norm.Z * point.Z +
           m_Dist;

    const float EPS = 0.001f;

    if (Dist > EPS)
        return PS_FRONT;
    else if (Dist < -EPS)
        return PS_BACK;

    return PS_ON;
}

//solves the plane equation for a particular point
float CPlane::DistanceToPlane (const CVector3D &point) const
{
    float Dist;

    Dist = m_Norm.X * point.X +
           m_Norm.Y * point.Y +
           m_Norm.Z * point.Z +
           m_Dist;

    return Dist;
}

//calculates the intersection point of a line with this
//plane. Returns false if there is no intersection
bool CPlane::FindLineSegIntersection (const CVector3D &start, const CVector3D &end, CVector3D *intsect)
{
    float dist1 = DistanceToPlane( start );
    float dist2 = DistanceToPlane( end );

    if( (dist1 < 0 && dist2 < 0) || (dist1 >= 0 && dist2 >= 0) )
        return false;

    float t = (-dist1) / (dist2-dist1);
    *intsect = Interpolate( start, end, t );

    return true;
}

bool CPlane::FindRayIntersection (const CVector3D &start, const CVector3D &direction, CVector3D *intsect)
{
    float dot = m_Norm.Dot (direction);
    if (dot == 0.0f)
        return false;

    *intsect = start - (direction * (DistanceToPlane (start)/dot));
    return true;
}