Heh, thanks for the help, but I've already got it worked out. All the gory details
Here if you're interested. Thanks for the help, though. I was really feeling lost there.
The long and the short of it is that different cards seem to require different format descriptions. ATI cards, for example, seem to assume that you always want an alpha buffer, whereas Nvidia cards require you to explicitly state that you want one. I ended up figuring this out when my program worked on my work computer, but not my home.
A few other notes: I am using depth testing for early z-out and correct depth sorting, but I'm controlling the states very carefully. My current order of operations:
Enable Depth Testing/Writing, Disable Blending
-Initial depth/ambient pass.
Disable Depth Writing
-For each light:
Disable Depth Testing/Color writing.
-Clear the Alpha buffer
-Render the lighting information to the alpha buffer
Enable Depth Testing
-Render Shadow Hulls
Enable Blending/Color Writing, Disable Alpha Writing
-Render All Geometry visible from this light.
Render the rest of the scene normally.
A few warnings I'd like to put out to people wanting to use this method. It's a great effect, but the fillrate requirements are HUGE. You're pretty much writing to each pixle on the screen an absolute mimimum of once per-light just for the alpha clearing pass plus once more for the ambient pass. On average you'll proably be redrawing the entire screen maybe 7-8 times for 3-4 visible lights.
Also, the soft shadowing portion of the code is anything but trivial. I'll post my actual code for it once I've completed it (getting close!) but it requires a lot of careful state-setting that's not covered in the article.
Not trying to discourge anyone here, because I love the effect itself, just a few things to be aware of!
// The user formerly known as Tojiro67445, formerly known as Toji [smile]