source: OGRE/trunk/ogrenew/OgreMain/src/OgreMath.cpp @ 692

/*
-----------------------------------------------------------------------------
This source file is part of OGRE
    (Object-oriented Graphics Rendering Engine)
For the latest info, see http://www.ogre3d.org/

Copyright (c) 2000-2005 The OGRE Team
Also see acknowledgements in Readme.html

This program is free software; you can redistribute it and/or modify it under
the terms of the GNU Lesser General Public License as published by the Free Software
Foundation; either version 2 of the License, or (at your option) any later
version.

This program 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 Lesser General Public License for more details.

You should have received a copy of the GNU Lesser General Public License along with
this program; if not, write to the Free Software Foundation, Inc., 59 Temple
Place - Suite 330, Boston, MA 02111-1307, USA, or go to
http://www.gnu.org/copyleft/lesser.txt.
-----------------------------------------------------------------------------
*/
#include "OgreStableHeaders.h"

#include "OgreMath.h"
#include "asm_math.h"
#include "OgreVector2.h"
#include "OgreVector3.h"
#include "OgreVector4.h"
#include "OgreRay.h"
#include "OgreSphere.h"
#include "OgreAxisAlignedBox.h"
#include "OgrePlane.h"


namespace Ogre
{

    const Real Math::POS_INFINITY = std::numeric_limits<Real>::infinity();
    const Real Math::NEG_INFINITY = -std::numeric_limits<Real>::infinity();
    const Real Math::PI = Real( 4.0 * atan( 1.0 ) );
    const Real Math::TWO_PI = Real( 2.0 * PI );
    const Real Math::HALF_PI = Real( 0.5 * PI );
        const Real Math::fDeg2Rad = PI / Real(180.0);
        const Real Math::fRad2Deg = Real(180.0) / PI;

    int Math::mTrigTableSize;
   Math::AngleUnit Math::msAngleUnit;

    Real  Math::mTrigTableFactor;
    Real *Math::mSinTable = NULL;
    Real *Math::mTanTable = NULL;

    //-----------------------------------------------------------------------
    Math::Math( unsigned int trigTableSize )
    {
        msAngleUnit = AU_DEGREE;

        mTrigTableSize = trigTableSize;
        mTrigTableFactor = mTrigTableSize / Math::TWO_PI;

        mSinTable = new Real[mTrigTableSize];
        mTanTable = new Real[mTrigTableSize];

        buildTrigTables();
    }

    //-----------------------------------------------------------------------
    Math::~Math()
    {
        delete [] mSinTable;
        delete [] mTanTable;
    }

    //-----------------------------------------------------------------------
    void Math::buildTrigTables(void)
    {
        // Build trig lookup tables
        // Could get away with building only PI sized Sin table but simpler this 
        // way. Who cares, it'll ony use an extra 8k of memory anyway and I like 
        // simplicity.
        Real angle;
        for (int i = 0; i < mTrigTableSize; ++i)
        {
            angle = Math::TWO_PI * i / mTrigTableSize;
            mSinTable[i] = sin(angle);
            mTanTable[i] = tan(angle);
        }
    }
        //-----------------------------------------------------------------------       
        Real Math::SinTable (Real fValue)
    {
        // Convert range to index values, wrap if required
        int idx;
        if (fValue >= 0)
        {
            idx = int(fValue * mTrigTableFactor) % mTrigTableSize;
        }
        else
        {
            idx = mTrigTableSize - (int(-fValue * mTrigTableFactor) % mTrigTableSize) - 1;
        }

        return mSinTable[idx];
    }
        //-----------------------------------------------------------------------
        Real Math::TanTable (Real fValue)
    {
        // Convert range to index values, wrap if required
                int idx = int(fValue *= mTrigTableFactor) % mTrigTableSize;
                return mTanTable[idx];
    }
    //-----------------------------------------------------------------------
    int Math::ISign (int iValue)
    {
        return ( iValue > 0 ? +1 : ( iValue < 0 ? -1 : 0 ) );
    }
    //-----------------------------------------------------------------------
    Radian Math::ACos (Real fValue)
    {
        if ( -1.0 < fValue )
        {
            if ( fValue < 1.0 )
                return Radian(acos(fValue));
            else
                return Radian(0.0);
        }
        else
        {
            return Radian(PI);
        }
    }
    //-----------------------------------------------------------------------
    Radian Math::ASin (Real fValue)
    {
        if ( -1.0 < fValue )
        {
            if ( fValue < 1.0 )
                return Radian(asin(fValue));
            else
                return Radian(HALF_PI);
        }
        else
        {
            return Radian(-HALF_PI);
        }
    }
    //-----------------------------------------------------------------------
    Real Math::Sign (Real fValue)
    {
        if ( fValue > 0.0 )
            return 1.0;

        if ( fValue < 0.0 )
            return -1.0;

        return 0.0;
    }
        //-----------------------------------------------------------------------
        Real Math::InvSqrt(Real fValue)
        {
                return Real(asm_rsq(fValue));
        }
    //-----------------------------------------------------------------------
    Real Math::UnitRandom ()
    {
        return asm_rand() / asm_rand_max();
    }
    
    //-----------------------------------------------------------------------
    Real Math::RangeRandom (Real fLow, Real fHigh)
    {
        return (fHigh-fLow)*UnitRandom() + fLow;
    }

    //-----------------------------------------------------------------------
    Real Math::SymmetricRandom ()
    {
                return 2.0f * UnitRandom() - 1.0f;
    }

   //-----------------------------------------------------------------------
    void Math::setAngleUnit(Math::AngleUnit unit)
   {
       msAngleUnit = unit;
   }
   //-----------------------------------------------------------------------
   Math::AngleUnit Math::getAngleUnit(void)
   {
       return msAngleUnit;
   }
    //-----------------------------------------------------------------------
    Real Math::AngleUnitsToRadians(Real angleunits)
    {
       if (msAngleUnit == AU_DEGREE)
           return angleunits * fDeg2Rad;
       else
           return angleunits;
    }

    //-----------------------------------------------------------------------
    Real Math::RadiansToAngleUnits(Real radians)
    {
       if (msAngleUnit == AU_DEGREE)
           return radians * fRad2Deg;
       else
           return radians;
    }

    //-----------------------------------------------------------------------
    Real Math::AngleUnitsToDegrees(Real angleunits)
    {
       if (msAngleUnit == AU_RADIAN)
           return angleunits * fRad2Deg;
       else
           return angleunits;
    }

    //-----------------------------------------------------------------------
    Real Math::DegreesToAngleUnits(Real degrees)
    {
       if (msAngleUnit == AU_RADIAN)
           return degrees * fDeg2Rad;
       else
           return degrees;
    }

    //-----------------------------------------------------------------------
        bool Math::pointInTri2D(const Vector2& p, const Vector2& a, 
                const Vector2& b, const Vector2& c)
    {
                // Winding must be consistent from all edges for point to be inside
                Vector2 v1, v2;
                Real dot[3];
                bool zeroDot[3];

                v1 = b - a;
                v2 = p - a;

                // Note we don't care about normalisation here since sign is all we need
                // It means we don't have to worry about magnitude of cross products either
                dot[0] = v1.crossProduct(v2);
                zeroDot[0] = Math::RealEqual(dot[0], 0.0f, 1e-3);


                v1 = c - b;
                v2 = p - b;

                dot[1] = v1.crossProduct(v2);
                zeroDot[1] = Math::RealEqual(dot[1], 0.0f, 1e-3);

                // Compare signs (ignore colinear / coincident points)
                if(!zeroDot[0] && !zeroDot[1] 
                && Math::Sign(dot[0]) != Math::Sign(dot[1]))
                {
                        return false;
                }

                v1 = a - c;
                v2 = p - c;

                dot[2] = v1.crossProduct(v2);
                zeroDot[2] = Math::RealEqual(dot[2], 0.0f, 1e-3);
                // Compare signs (ignore colinear / coincident points)
                if((!zeroDot[0] && !zeroDot[2] 
                        && Math::Sign(dot[0]) != Math::Sign(dot[2])) ||
                        (!zeroDot[1] && !zeroDot[2] 
                        && Math::Sign(dot[1]) != Math::Sign(dot[2])))
                {
                        return false;
                }


                return true;
    }
        //-----------------------------------------------------------------------
        bool Math::pointInTri3D(const Vector3& p, const Vector3& a, 
                const Vector3& b, const Vector3& c, const Vector3& normal)
        {
        // Winding must be consistent from all edges for point to be inside
                Vector3 v1, v2;
                Real dot[3];
                bool zeroDot[3];

        v1 = b - a;
        v2 = p - a;

                // Note we don't care about normalisation here since sign is all we need
                // It means we don't have to worry about magnitude of cross products either
        dot[0] = v1.crossProduct(v2).dotProduct(normal);
                zeroDot[0] = Math::RealEqual(dot[0], 0.0f, 1e-3);


        v1 = c - b;
        v2 = p - b;

                dot[1] = v1.crossProduct(v2).dotProduct(normal);
                zeroDot[1] = Math::RealEqual(dot[1], 0.0f, 1e-3);

                // Compare signs (ignore colinear / coincident points)
                if(!zeroDot[0] && !zeroDot[1] 
                        && Math::Sign(dot[0]) != Math::Sign(dot[1]))
                {
            return false;
                }

        v1 = a - c;
        v2 = p - c;

                dot[2] = v1.crossProduct(v2).dotProduct(normal);
                zeroDot[2] = Math::RealEqual(dot[2], 0.0f, 1e-3);
                // Compare signs (ignore colinear / coincident points)
                if((!zeroDot[0] && !zeroDot[2] 
                        && Math::Sign(dot[0]) != Math::Sign(dot[2])) ||
                        (!zeroDot[1] && !zeroDot[2] 
                        && Math::Sign(dot[1]) != Math::Sign(dot[2])))
                {
                        return false;
                }


        return true;
        }
    //-----------------------------------------------------------------------
    bool Math::RealEqual( Real a, Real b, Real tolerance )
    {
        if (fabs(b-a) <= tolerance)
            return true;
        else
            return false;
    }

    //-----------------------------------------------------------------------
    std::pair<bool, Real> Math::intersects(const Ray& ray, const Plane& plane)
    {

        Real denom = plane.normal.dotProduct(ray.getDirection());
        if (Math::Abs(denom) < std::numeric_limits<Real>::epsilon())
        {
            // Parallel
            return std::pair<bool, Real>(false, 0);
        }
        else
        {
            Real nom = plane.normal.dotProduct(ray.getOrigin()) + plane.d;
            Real t = -(nom/denom);
            return std::pair<bool, Real>(t >= 0, t);
        }
        
    }
    //-----------------------------------------------------------------------
    std::pair<bool, Real> Math::intersects(const Ray& ray, 
        const std::vector<Plane>& planes, bool normalIsOutside)
    {
        std::vector<Plane>::const_iterator planeit, planeitend;
        planeitend = planes.end();
        bool allInside = true;
        std::pair<bool, Real> ret;
        ret.first = false;
        ret.second = 0.0f;

        // derive side
        // NB we don't pass directly since that would require Plane::Side in 
        // interface, which results in recursive includes since Math is so fundamental
        Plane::Side outside = normalIsOutside ? Plane::POSITIVE_SIDE : Plane::NEGATIVE_SIDE;

        for (planeit = planes.begin(); planeit != planeitend; ++planeit)
        {
            const Plane& plane = *planeit;
            // is origin outside?
            if (plane.getSide(ray.getOrigin()) == outside)
            {
                allInside = false;
                // Test single plane
                std::pair<bool, Real> planeRes = 
                    ray.intersects(plane);
                if (planeRes.first)
                {
                    // Ok, we intersected
                    ret.first = true;
                    // Use the most distant result since convex volume
                    ret.second = std::max(ret.second, planeRes.second);
                }
            }
        }

        if (allInside)
        {
            // Intersecting at 0 distance since inside the volume!
            ret.first = true;
            ret.second = 0.0f;
        }

        return ret;
    }
    //-----------------------------------------------------------------------
    std::pair<bool, Real> Math::intersects(const Ray& ray, 
        const std::list<Plane>& planes, bool normalIsOutside)
    {
        std::list<Plane>::const_iterator planeit, planeitend;
        planeitend = planes.end();
        bool allInside = true;
        std::pair<bool, Real> ret;
        ret.first = false;
        ret.second = 0.0f;

        // derive side
        // NB we don't pass directly since that would require Plane::Side in 
        // interface, which results in recursive includes since Math is so fundamental
        Plane::Side outside = normalIsOutside ? Plane::POSITIVE_SIDE : Plane::NEGATIVE_SIDE;

        for (planeit = planes.begin(); planeit != planeitend; ++planeit)
        {
            const Plane& plane = *planeit;
            // is origin outside?
            if (plane.getSide(ray.getOrigin()) == outside)
            {
                allInside = false;
                // Test single plane
                std::pair<bool, Real> planeRes = 
                    ray.intersects(plane);
                if (planeRes.first)
                {
                    // Ok, we intersected
                    ret.first = true;
                    // Use the most distant result since convex volume
                    ret.second = std::max(ret.second, planeRes.second);
                }
            }
        }

        if (allInside)
        {
            // Intersecting at 0 distance since inside the volume!
            ret.first = true;
            ret.second = 0.0f;
        }

        return ret;
    }
    //-----------------------------------------------------------------------
    std::pair<bool, Real> Math::intersects(const Ray& ray, const Sphere& sphere, 
        bool discardInside)
    {
        const Vector3& raydir = ray.getDirection();
        // Adjust ray origin relative to sphere center
        const Vector3& rayorig = ray.getOrigin() - sphere.getCenter();
        Real radius = sphere.getRadius();

        // Check origin inside first
        if (rayorig.squaredLength() <= radius*radius && discardInside)
        {
            return std::pair<bool, Real>(true, 0);
        }

        // Mmm, quadratics
        // Build coeffs which can be used with std quadratic solver
        // ie t = (-b +/- sqrt(b*b + 4ac)) / 2a
        Real a = raydir.dotProduct(raydir);
        Real b = 2 * rayorig.dotProduct(raydir);
        Real c = rayorig.dotProduct(rayorig) - radius*radius;

        // Calc determinant
        Real d = (b*b) - (4 * a * c);
        if (d < 0)
        {
            // No intersection
            return std::pair<bool, Real>(false, 0);
        }
        else
        {
            // BTW, if d=0 there is one intersection, if d > 0 there are 2
            // But we only want the closest one, so that's ok, just use the 
            // '-' version of the solver
            Real t = ( -b - Math::Sqrt(d) ) / (2 * a);
            if (t < 0)
                t = ( -b + Math::Sqrt(d) ) / (2 * a);
            return std::pair<bool, Real>(true, t);
        }


    }
    //-----------------------------------------------------------------------
    std::pair<bool, Real> Math::intersects(const Ray& ray, const AxisAlignedBox& box)
    {
        if (box.isNull()) return std::pair<bool, Real>(false, 0);

        Real lowt = 0.0f;
        Real t;
        bool hit = false;
        Vector3 hitpoint;
        const Vector3& min = box.getMinimum();
        const Vector3& max = box.getMaximum();
        const Vector3& rayorig = ray.getOrigin();
        const Vector3& raydir = ray.getDirection();

        // Check origin inside first
        if ( rayorig > min && rayorig < max )
        {
            return std::pair<bool, Real>(true, 0);
        }

        // Check each face in turn, only check closest 3
        // Min x
        if (rayorig.x < min.x && raydir.x > 0)
        {
            t = (min.x - rayorig.x) / raydir.x;
            if (t > 0)
            {
                // Substitute t back into ray and check bounds and dist
                hitpoint = rayorig + raydir * t;
                if (hitpoint.y >= min.y && hitpoint.y <= max.y &&
                    hitpoint.z >= min.z && hitpoint.z <= max.z &&
                    (!hit || t < lowt))
                {
                    hit = true;
                    lowt = t;
                }
            }
        }
        // Max x
        if (rayorig.x > max.x && raydir.x < 0)
        {
            t = (max.x - rayorig.x) / raydir.x;
            if (t > 0)
            {
                // Substitute t back into ray and check bounds and dist
                hitpoint = rayorig + raydir * t;
                if (hitpoint.y >= min.y && hitpoint.y <= max.y &&
                    hitpoint.z >= min.z && hitpoint.z <= max.z &&
                    (!hit || t < lowt))
                {
                    hit = true;
                    lowt = t;
                }
            }
        }
        // Min y
        if (rayorig.y < min.y && raydir.y > 0)
        {
            t = (min.y - rayorig.y) / raydir.y;
            if (t > 0)
            {
                // Substitute t back into ray and check bounds and dist
                hitpoint = rayorig + raydir * t;
                if (hitpoint.x >= min.x && hitpoint.x <= max.x &&
                    hitpoint.z >= min.z && hitpoint.z <= max.z &&
                    (!hit || t < lowt))
                {
                    hit = true;
                    lowt = t;
                }
            }
        }
        // Max y
        if (rayorig.y > max.y && raydir.y < 0)
        {
            t = (max.y - rayorig.y) / raydir.y;
            if (t > 0)
            {
                // Substitute t back into ray and check bounds and dist
                hitpoint = rayorig + raydir * t;
                if (hitpoint.x >= min.x && hitpoint.x <= max.x &&
                    hitpoint.z >= min.z && hitpoint.z <= max.z &&
                    (!hit || t < lowt))
                {
                    hit = true;
                    lowt = t;
                }
            }
        }
        // Min z
        if (rayorig.z < min.z && raydir.z > 0)
        {
            t = (min.z - rayorig.z) / raydir.z;
            if (t > 0)
            {
                // Substitute t back into ray and check bounds and dist
                hitpoint = rayorig + raydir * t;
                if (hitpoint.x >= min.x && hitpoint.x <= max.x &&
                    hitpoint.y >= min.y && hitpoint.y <= max.y &&
                    (!hit || t < lowt))
                {
                    hit = true;
                    lowt = t;
                }
            }
        }
        // Max z
        if (rayorig.z > max.z && raydir.z < 0)
        {
            t = (max.z - rayorig.z) / raydir.z;
            if (t > 0)
            {
                // Substitute t back into ray and check bounds and dist
                hitpoint = rayorig + raydir * t;
                if (hitpoint.x >= min.x && hitpoint.x <= max.x &&
                    hitpoint.y >= min.y && hitpoint.y <= max.y &&
                    (!hit || t < lowt))
                {
                    hit = true;
                    lowt = t;
                }
            }
        }

        return std::pair<bool, Real>(hit, lowt);

    }
    //-----------------------------------------------------------------------
    bool Math::intersects(const Ray& ray, const AxisAlignedBox& box,
        Real* d1, Real* d2)
    {
        if (box.isNull())
            return false;

        const Vector3& min = box.getMinimum();
        const Vector3& max = box.getMaximum();
        const Vector3& rayorig = ray.getOrigin();
        const Vector3& raydir = ray.getDirection();

        Vector3 absDir;
        absDir[0] = Math::Abs(raydir[0]);
        absDir[1] = Math::Abs(raydir[1]);
        absDir[2] = Math::Abs(raydir[2]);

        // Sort the axis, ensure check minimise floating error axis first
        int imax = 0, imid = 1, imin = 2;
        if (absDir[0] < absDir[2])
        {
            imax = 2;
            imin = 0;
        }
        if (absDir[1] < absDir[imin])
        {
            imid = imin;
            imin = 1;
        }
        else if (absDir[1] > absDir[imax])
        {
            imid = imax;
            imax = 1;
        }

        Real start = 0, end = Math::POS_INFINITY;

#define _CALC_AXIS(i)                                       \
    do {                                                    \
        Real denom = 1 / raydir[i];                         \
        Real newstart = (min[i] - rayorig[i]) * denom;      \
        Real newend = (max[i] - rayorig[i]) * denom;        \
        if (newstart > newend) std::swap(newstart, newend); \
        if (newstart > end || newend < start) return false; \
        if (newstart > start) start = newstart;             \
        if (newend < end) end = newend;                     \
    } while(0)

        // Check each axis in turn

        _CALC_AXIS(imax);

        if (absDir[imid] < std::numeric_limits<Real>::epsilon())
        {
            // Parallel with middle and minimise axis, check bounds only
            if (rayorig[imid] < min[imid] || rayorig[imid] > max[imid] ||
                rayorig[imin] < min[imin] || rayorig[imin] > max[imin])
                return false;
        }
        else
        {
            _CALC_AXIS(imid);

            if (absDir[imin] < std::numeric_limits<Real>::epsilon())
            {
                // Parallel with minimise axis, check bounds only
                if (rayorig[imin] < min[imin] || rayorig[imin] > max[imin])
                    return false;
            }
            else
            {
                _CALC_AXIS(imin);
            }
        }
#undef _CALC_AXIS

        if (d1) *d1 = start;
        if (d2) *d2 = end;

        return true;
    }
    //-----------------------------------------------------------------------
    std::pair<bool, Real> Math::intersects(const Ray& ray, const Vector3& a,
        const Vector3& b, const Vector3& c, const Vector3& normal,
        bool positiveSide, bool negativeSide)
    {
        //
        // Calculate intersection with plane.
        //
        Real t;
        {
            Real denom = normal.dotProduct(ray.getDirection());

            // Check intersect side
            if (denom > + std::numeric_limits<Real>::epsilon())
            {
                if (!negativeSide)
                    return std::pair<bool, Real>(false, 0);
            }
            else if (denom < - std::numeric_limits<Real>::epsilon())
            {
                if (!positiveSide)
                    return std::pair<bool, Real>(false, 0);
            }
            else
            {
                // Parallel or triangle area is close to zero when
                // the plane normal not normalised.
                return std::pair<bool, Real>(false, 0);
            }

            t = normal.dotProduct(a - ray.getOrigin()) / denom;

            if (t < 0)
            {
                // Intersection is behind origin
                return std::pair<bool, Real>(false, 0);
            }
        }

        //
        // Calculate the largest area projection plane in X, Y or Z.
        //
        size_t i0, i1;
        {
            Real n0 = Math::Abs(normal[0]);
            Real n1 = Math::Abs(normal[1]);
            Real n2 = Math::Abs(normal[2]);

            i0 = 1; i1 = 2;
            if (n1 > n2)
            {
                if (n1 > n0) i0 = 0;
            }
            else
            {
                if (n2 > n0) i1 = 0;
            }
        }

        //
        // Check the intersection point is inside the triangle.
        //
        {
            Real u1 = b[i0] - a[i0];
            Real v1 = b[i1] - a[i1];
            Real u2 = c[i0] - a[i0];
            Real v2 = c[i1] - a[i1];
            Real u0 = t * ray.getDirection()[i0] + ray.getOrigin()[i0] - a[i0];
            Real v0 = t * ray.getDirection()[i1] + ray.getOrigin()[i1] - a[i1];

            Real alpha = u0 * v2 - u2 * v0;
            Real beta  = u1 * v0 - u0 * v1;
            Real area  = u1 * v2 - u2 * v1;

            // epsilon to avoid float precision error
            const Real EPSILON = 1e-3f;

            Real tolerance = - EPSILON * area;

            if (area > 0)
            {
                if (alpha < tolerance || beta < tolerance || alpha+beta > area-tolerance)
                    return std::pair<bool, Real>(false, 0);
            }
            else
            {
                if (alpha > tolerance || beta > tolerance || alpha+beta < area-tolerance)
                    return std::pair<bool, Real>(false, 0);
            }
        }

        return std::pair<bool, Real>(true, t);
    }
    //-----------------------------------------------------------------------
    std::pair<bool, Real> Math::intersects(const Ray& ray, const Vector3& a,
        const Vector3& b, const Vector3& c,
        bool positiveSide, bool negativeSide)
    {
        Vector3 normal = calculateBasicFaceNormalWithoutNormalize(a, b, c);
        return intersects(ray, a, b, c, normal, positiveSide, negativeSide);
    }
    //-----------------------------------------------------------------------
    bool Math::intersects(const Sphere& sphere, const AxisAlignedBox& box)
    {
        if (box.isNull()) return false;

        // Use splitting planes
        const Vector3& center = sphere.getCenter();
        Real radius = sphere.getRadius();
        const Vector3& min = box.getMinimum();
        const Vector3& max = box.getMaximum();

        // just test facing planes, early fail if sphere is totally outside
        if (center.x < min.x && 
            min.x - center.x > radius)
        {
            return false;
        }
        if (center.x > max.x && 
            center.x  - max.x > radius)
        {
            return false;
        }

        if (center.y < min.y && 
            min.y - center.y > radius)
        {
            return false;
        }
        if (center.y > max.y && 
            center.y  - max.y > radius)
        {
            return false;
        }

        if (center.z < min.z && 
            min.z - center.z > radius)
        {
            return false;
        }
        if (center.z > max.z && 
            center.z  - max.z > radius)
        {
            return false;
        }

        // Must intersect
        return true;

    }
    //-----------------------------------------------------------------------
    bool Math::intersects(const Plane& plane, const AxisAlignedBox& box)
    {
        if (box.isNull()) return false;

        // Get corners of the box
        const Vector3* pCorners = box.getAllCorners();


        // Test which side of the plane the corners are
        // Intersection occurs when at least one corner is on the 
        // opposite side to another
        Plane::Side lastSide = plane.getSide(pCorners[0]);
        for (int corner = 1; corner < 8; ++corner)
        {
            if (plane.getSide(pCorners[corner]) != lastSide)
            {
                return true;
            }
        }

        return false;
    }
    //-----------------------------------------------------------------------
    bool Math::intersects(const Sphere& sphere, const Plane& plane)
    {
        return (
            Math::Abs(plane.normal.dotProduct(sphere.getCenter()))
            <= sphere.getRadius() );
    }
    //-----------------------------------------------------------------------
    Vector3 Math::calculateTangentSpaceVector(
        const Vector3& position1, const Vector3& position2, const Vector3& position3,
        Real u1, Real v1, Real u2, Real v2, Real u3, Real v3)
    {
            //side0 is the vector along one side of the triangle of vertices passed in, 
            //and side1 is the vector along another side. Taking the cross product of these returns the normal.
            Vector3 side0 = position1 - position2;
            Vector3 side1 = position3 - position1;
            //Calculate face normal
            Vector3 normal = side1.crossProduct(side0);
            normal.normalise();
            //Now we use a formula to calculate the tangent. 
            Real deltaV0 = v1 - v2;
            Real deltaV1 = v3 - v1;
            Vector3 tangent = deltaV1 * side0 - deltaV0 * side1;
            tangent.normalise();
            //Calculate binormal
            Real deltaU0 = u1 - u2;
            Real deltaU1 = u3 - u1;
            Vector3 binormal = deltaU1 * side0 - deltaU0 * side1;
            binormal.normalise();
            //Now, we take the cross product of the tangents to get a vector which 
            //should point in the same direction as our normal calculated above. 
            //If it points in the opposite direction (the dot product between the normals is less than zero), 
            //then we need to reverse the s and t tangents. 
            //This is because the triangle has been mirrored when going from tangent space to object space.
            //reverse tangents if necessary
            Vector3 tangentCross = tangent.crossProduct(binormal);
            if (tangentCross.dotProduct(normal) < 0.0f)
            {
                    tangent = -tangent;
                    binormal = -binormal;
            }

        return tangent;

    }
    //-----------------------------------------------------------------------
    Matrix4 Math::buildReflectionMatrix(const Plane& p)
    {
        return Matrix4(
            -2 * p.normal.x * p.normal.x + 1,   -2 * p.normal.x * p.normal.y,       -2 * p.normal.x * p.normal.z,       -2 * p.normal.x * p.d, 
            -2 * p.normal.y * p.normal.x,       -2 * p.normal.y * p.normal.y + 1,   -2 * p.normal.y * p.normal.z,       -2 * p.normal.y * p.d, 
            -2 * p.normal.z * p.normal.x,       -2 * p.normal.z * p.normal.y,       -2 * p.normal.z * p.normal.z + 1,   -2 * p.normal.z * p.d, 
            0,                                  0,                                  0,                                  1);
    }
    //-----------------------------------------------------------------------
    Vector4 Math::calculateFaceNormal(const Vector3& v1, const Vector3& v2, const Vector3& v3)
    {
        Vector3 normal = calculateBasicFaceNormal(v1, v2, v3);
        // Now set up the w (distance of tri from origin
        return Vector4(normal.x, normal.y, normal.z, -(normal.dotProduct(v1)));
    }
    //-----------------------------------------------------------------------
    Vector3 Math::calculateBasicFaceNormal(const Vector3& v1, const Vector3& v2, const Vector3& v3)
    {
        Vector3 normal = (v2 - v1).crossProduct(v3 - v1);
        normal.normalise();
        return normal;
    }
    //-----------------------------------------------------------------------
    Vector4 Math::calculateFaceNormalWithoutNormalize(const Vector3& v1, const Vector3& v2, const Vector3& v3)
    {
        Vector3 normal = calculateBasicFaceNormalWithoutNormalize(v1, v2, v3);
        // Now set up the w (distance of tri from origin)
        return Vector4(normal.x, normal.y, normal.z, -(normal.dotProduct(v1)));
    }
    //-----------------------------------------------------------------------
    Vector3 Math::calculateBasicFaceNormalWithoutNormalize(const Vector3& v1, const Vector3& v2, const Vector3& v3)
    {
        Vector3 normal = (v2 - v1).crossProduct(v3 - v1);
        return normal;
    }
}