virtual shadow cube map with fbo


I’m trying to figure out how to do virtual shadow cube map for omni directional lights. I know it is used in the mad mod mike demo from nvidia and that it was adapted from “Efficient Omnidirectional Shadow Maps” by Gary King & William Newhall in ShaderX3. Basically, you use one 2d texture containing the 6 faces of the shadow cube map, and you use a real cube map low resolution as look up table for texture coords.
(Some clue on a previous thread:;f=3;t=012238 )
For simple shadow mapping (spot & directional lights), I use FBO extension, but for virtual cube map, i need to render the light view only as a sub-part of the texture bound to the fbo, is it possible?
If not, do you think it would be an interesting feature to add to FBO?
Does anyone know if they use fbo or pbuffer for the nvidia mad mod mike demo?

Thanks in advance.

Well, i’ve just found a simple solution, just need to play with the viewport params when rendering in the fbo. :smiley: