OpenGL glTranslate and glRotate

Question

I need a function that applies a translation like glTranslate() to a point. Does someone know of a function like glTranslate() and glRotate() to modify and retrieve a matrix to multiply?

Answer 1

There are thousands of free matrix classes out there. Have a hunt round google and then you can set up a translation and rotation without using the gl* functions at all ...

edit: If you really just want to create the matrix without using a more than handy matrix class then you can define glRotatef( angle, x, y, z ) as follows:

const float cosA = cosf( angle );
const float sinA = sinf( angle );
float m[16] = { cosA + ((x * x) * (1 - cosA)), ((x * y) * (1 - cosA)) - (z * sinA), ((x * z) * (1 - cosA)) + (y * sinA), 0.0f,
                ((y * x) * (1 - cosA)) + (z * sinA), cosA + ((y * y) * (1 - cosA)), ((y * z) * (1 - cosA)) - (x * sinA), 0.0f,
                ((z * x) * (1 - cosA)) - (y * sinA), ((z * y) * (1 - cosA)) + (x * sinA), cosA + ((z * z) * (1 - cosA)), 0.0f,
                0.0f, 0.0f, 0.0f, 1.0f
               };

As taken from wikipedia.

A translation matrix is really easy to create: glTranslatef( x, y, z) is define as follows:

float m[16] = { 1.0f, 0.0f, 0.0f, 0.0f,
                0.0f, 1.0f, 0.0f, 0.0f,
                0.0f, 0.0f, 1.0f, 0.0f,
                   x,    y,    z, 1.0f
               };

You can look up matrix multiplication and matrix-vector multiplication pretty easily.

To make your life simple, though, you could just download a matrix class which does all this for you ...

Answer 2

Here you can find general info about transformations using the matrices.

Here you can find examples and complete functions that does matrix multiplications (either scaling, rotating or whatever). It is written in objective C, but it shouldn't be to hard to rewrite it in c++..