When rendering an image plane with the global Variable N I have found out while using the following applied to 3 spheres and a gird

Clay
Basic Surface
Plastic
Gingham

Only the Gingham will render out the correct result for N. If this is a global variable surely it should not matter what material is applied. If this is not the case what do I need to add to the shaders that are not rendering N correctly

Strange problem, this. It seems to be a bug in Mantra. If you make your spheres anything other than NURBS, it seems to render you'd expect (Primitive or Polygon spheres).

I will log the bug

Rob

We had this problem in 8.2 couple of weeks ago with PRman. Unfortunately I don't have the test case with me but it was exactly as Jason found, everything apart from NURBS was outputting the normal properly (and we tried all sorts of tricks to make it work).

As I recall, it is working correctly but the normals are very “short” meaning you need to normalize them to see them properly. In Mplay try the Adapt button, or use a shader where you've output normalized normals (i.e. put a Normalize VOP between the input N and the output N)

Cheers,

Peter B

I think I've come across this before too, it always confused be that a default nurbs surface with no normals on it didn't calculate them as normalised, you have to do it yourself. Which is good practice I suppose…