That's a long long time I didn't write shaders for mentalray, the answer is certainly obvious ...

I was wondering if I have somme access to data around the point being shaded in my surface shader.

I would like to plug a normal map in my shader, I will access to the texture point with current u,v coordinates corresponding to the point being shaded, but I need to access to neighbor texture points too !
I could get the texture point at (u +/- delta, v +/- delta) but I will certainly access to 2d points where texture is not defined (depending on how uvSet is defined ...) !

Is there a correct way to do that ?

Thanks for your help !