title: Finding normal OpenGL
body: <p>I would like to know if we can get the normal on the object surface from window coordinates. gluUnProject() function converts window coordinates to object coordinates in 3D space. Likewise, I would need a function which gives the normal of the surface where my mouse pointer lie. I would be more than happy if we have an opengl functio which can give this. I would not want to do this with intersection of the ray and the objects(surface triangles).</p>