I just wanted to post some information on 2D graphic rendering on billboards. I was having trouble because my graphics were too large and expanded way over the billboard. I solved it by moving back the camera. I am pretty sure that this might not be the best solution, but if this can help someone hey
Peace.
NB If I locate the proper way..I'll update the post if it does not have to be resurrected from to long back
well obviously your billboard was just too big to fit in the cameras view with respect to the billboard's and camera's initial positions, so moving the camera back meant you got to see more of the billboard