Well at the minimum you'll need to sample every texture in the material, the lightmap, every relevant shadow map, and some kind of envmap or environment probe... then you can start considering the cost of more advanced effects
But TBH I'm using forward on that project because I'm not casting shadows or at least very few and they have to be done with some hacks or shadow volumes. I'm doing a side-scroller game so typical shadow maps don't work that well.
I can't really have every torch and other light sources render their own cube shadow map. Even removing the back and front face that would kill performance on so many GPUs that would otherwise be fine :P
I'll probably use the 2D vector collision map to software-calculate cast light as polygons and render that into a 2D light map and fake the hell out of it :)
I am building 3d graphic engine while destroying performances. ATM I render the scene multiple times over and over just to make sure things are being drawn correctly.
also I render shadow map for each light, destroying the performances.
I wana go home but bus comes at 10... ;_; 4 more hours
