Nvidia's Last Chance Gas


Does anyone have any ideas on the techniques used for the softshadowing in the Last Chance Gas demo
There are some strange textures in the textures\softshadows subdirectory… horizon maps or something??


I’d bet it’s prebaked in those shots. Basically a light map.


I thought the demo did a time advance of day to night? Surely pre-baked shadows wouldn’t work for this.

Could be wrong tho. Best bet is to ask Simon Green.

Originally posted by Simon Green (on cgshaders.org):
I didn’t work on the Gas Station demo but I can describe the basics. The light maps were done in Softimage XSI using Mental Ray. We experimented with ambient occlusion and bent normals, but in the end
used GI/final gathering. The soft shadows were done using a hybrid technique that precomputes the times at which each point enters and leaves shadow as the sun (modelled as a linear light source) moves across the sky in a line. This information is stored in multiple textures, and a custom fragment program interpolates between these values to determine the amount of shadowing given the current time. I believe Joe Demers will be describing this in more detail in our upcoming “GPU Gems” book.

Now that’s what i call a Trick, with a big T.


This demo to me is just plain frickin cool. I was very impressed by it. When I watched the video of it I found it hard to keep my mouth closed. It may not be doing all of the fancy GI calcs and all that on the card in real-time (not possible yet) but it sure as heck looked like it.