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Matrix implementation: Searching for older post


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#1 cdoubleplusgood   Members   -  Reputation: 847

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Posted 23 July 2013 - 02:35 AM

Hi folks,

 

Some time ago, maybe last year, I read a post here at gamedev containing a very cool matrix implemenation in C++ (or a link to that implementation). The cool stuff was accessing both row and column vectors without changing the "simple" memory layout (e.g. a 4x4 matrix needed only 16 * sizeof(float)). IIRC it used function pointers or functors internally.

There was a lengthy discussion with some guys trying to be smarter... but their proposals required additional data members.

 

My problem: I can't find that post or thread anymore. If your memory or searching skills are better than mine... can you give me a hint?

 

Thanks,

 

cdoubleplusgood

 



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#2 RobTheBloke   Crossbones+   -  Reputation: 2341

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Posted 23 July 2013 - 07:53 AM

Something like this?

 

#include <iostream>

struct Vector4
{
    Vector4() {}
    Vector4(float a, float b, float c, float d) : x(a), y(b), z(c), w(d) {}
    float x;
    float y;
    float z;
    float w;
};


struct ConstVector4Column
{
    ConstVector4Column(const float* pp)
        : mp(pp) {}
    const float* mp;
    operator Vector4 () const
    {
        return Vector4( mp[0], mp[4], mp[8], mp[12] );
    }
};

struct Vector4Column : public ConstVector4Column
{
    Vector4Column(float* pp)
        : ConstVector4Column(pp) {}
    const Vector4& operator = (const Vector4& v)
    {
        float* p = const_cast<float*>(mp);
        p[0] = v.x;
        p[4] = v.y;
        p[8] = v.z;
        p[12] = v.w;
        return v;
    }
};

struct Matrix
{
    Vector4 x;
    Vector4 y;
    Vector4 z;
    Vector4 w;

    Vector4& operator[] (size_t i) { return (&x)[i]; }
    const Vector4& operator[] (size_t i) const { return (&x)[i]; }

    Vector4Column operator() (size_t i) { return Vector4Column( (&x.x) + i ); }
    ConstVector4Column operator() (size_t i) const { return ConstVector4Column( (&x.x) + i ); }
};

std::ostream& operator << (std::ostream& os, const Vector4& v)
{
    return os << v.x << " " << v.y << " " << v.z << " " << v.w << std::endl;
}

int main()
{
    Matrix m;
    m.x = Vector4(1.0f,2.0f,3.0f,4.0f);
    m.y = Vector4(5.0f,6.0f,7.0f,8.0f);
    m.z = Vector4(9.0f,10.0f,11.0f,12.0f);
    m.w = Vector4(13.0f,14.0f,15.0f,16.0f);
    
    std::cout << m[0] << std::endl;
    std::cout << m[1] << std::endl;
    std::cout << m[2] << std::endl;
    std::cout << m[3] << std::endl;
    
    std::cout << m(0) << std::endl;
    std::cout << m(1) << std::endl;
    std::cout << m(2) << std::endl;
    std::cout << m(3) << std::endl;
    
    return 1;
}



#3 cdoubleplusgood   Members   -  Reputation: 847

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Posted 23 July 2013 - 09:01 AM

Um, no, doesn't ring a bell.

But your code is an option. Thanks.






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