Cg and OpenTK Matrix4

The 'out' keyword tells that your parameter is written to by the function (which is probably not what SetMatrixParameter is supposed to do), use 'ref' instead. Imho the Cg binding is incorrect there, if Cg.cgSetMAtrixParameterfr(proj, out projectionMatrix.Row0.X); compiles.

To obtain a pointer to the first element of the Matrix4 struct, use MyMatrix.Row0.X, not MyMatrix.Row0

I don't know anything about Tao.Cg - that's why you got no answer for your other Cg related problem - but you should be warned that passing pointers to Tao bindings often requires you to pin the associated array manually.

If you need to learn a little about pointers and unsafe code in C#, then take a look at this page to see how pointers work: http://www.softsteel.co.uk/tutorials/cSharp/lesson5.html

I'm not too hot at this myself either, but if you specify a block of code as unsafe, you can fix ("pin") fields in memory, so that they won't get moved around by the garbage collector, something like this:

        public static unsafe void setTheta1Degrees(ref Vector2 vector, float angleInDegrees)
        {
            while(angleInDegrees > 360)
                angleInDegrees -= 360;
 
            fixed (Vector2* V2 = &vector)
            {
                float l = (*V2).Length;
                (*V2).X = l * (float)Math.Cos((double)Functions.DegreesToRadians(angleInDegrees));
                (*V2).Y = l * (float)Math.Sin((double)Functions.DegreesToRadians(angleInDegrees));
            }
        }

This was something I wrote ages ago when I'd just started learning C#, before I realised that passing structs using the "ref" keyword lets you change the original object (rather than just copying the data, which is how they are usually passed). It's a pretty redundant (or even highly inefficient) way of using pointers in C#, but I wrote it after reading the page I've posted above, and it serves as a decent example of unsafe code and fixed objects.

Hope that helps, and I'm sorry if it's much more info than you needed! :-)

Thanks for the info so far. I actually did not know I could use pointers like I do in C++ in C#.

Even though I have now tried working with pointers, I still does not work. I figure that it is more of a Tao.Cg or Cg problem than OpenTK. What I have done now is:

//  First: I do not fix, since the projectionMatrix.Row0.X is "already a fixed expression". I have also tried to declare this within the unsafe block.
unsafe
{    
    CgGl.cgGLSetMAtrixParameterArrayfr(proj, 0,1, &projectionMatrix.Row0.X); // assuming there's a float* overload
 
} 
 
// second using the normal float[] array as showed earlier
unsafe
{ 
    fixed (float* MyPtr = &array)
    {  
        CgGl.cgGLSetMAtrixParameterArrayfr(proj, 0,1, MyPtr); // assuming there's a float* overload
    }   
}
 
// Third the same deal with Cg.cgSetMatrixParameterfr(proj, out *MyPtr)

Any ideas?

I have tried that with no luck either. :\

The CgGl.cgGLSetMatrixParameterArrayfr function means that it uses rows - hence the r appended. It has a CgGl.cgGLSetMatrixParameterArrayfc equivalent as well. So this should not be a problem :\

Thanks so far.