It can then be used for destination alpha blending. I will not go any further, just knowing it exists is more than enough. You'll never use it. The bad news it, that we can only use one of these buffers at the same time. This means, that if you use the z-buffer, you can't use alpha buffering.
Most people use the w-buffer.
We've learned that we can't just pass depth to the card, we have to pass a linear version. You can download some demos here. Design and graphics by Molasses . Inc. Other product names are trademarks of the respective holders.