Hi!

Well, that´s exactly my question: How do you multiply a vector with a matrix. The result should be also a vector.

Maybe someone could post a little code please!

I was getting very confused writing it myself, because a tut on NeHe says that OpenGL handles marices ‘column-first’?!

My intention is to multiply a vector by the Modelview and ProjecionMatrix.

double v[4]; // the vector

double m[16]; // the matrix

double r[]={0, 0, 0, 0}; // result: matrix x vector

// define v and m here.

for (int i=0; i<=3; i++)

{

for (int j=0; j<=3; j++)

{

r[i] = r[i] + m[i+j*4] * v[j];

}

}

I never did that, but this should work. I remember that i read this column-first thing in the red book.Column-first means the matrix entries are stored in this order:

[ 0 4 8 12]

[ 1 5 9 13]

[ 2 6 10 14]

[ 3 7 11 15]

Am i right? Then the code above should work. Try it out.

[This message has been edited by plastichead (edited 01-16-2002).]