Modern Opengl (4.x) unproject

Ok… so my old code used GLU unproject to transform mouse coords into world coords.

Now that i have converted to OpenGL 4.x i have run into an issue.

The param used to call unproject include the viewport matrix. I used to get this by asking opengl to return it to me.
Now it seems i will have to create the matrix my self before calling the function.

anyone ever found any documentation on how to convert your width / height into a view port matrix?

thanks
j.