The technique described here is often referred to as the z-pass technique. It has one fatal flaw. If the camera is located within a shadow volume, this technique breaks down because the counts in the stencil buffer will be off by at least one. A common solution is to basically invert the problem and trace a ray from infinity toward the view point. This is called the z-fail technique or Carmack's reverse.
The fail and pass here refer to whether or not we are counting when the depth test passes or fails.
Care must be taken when using z-fail because it is important to draw the caps of the shadow volumes. However, the technique is very similar to z-pass. Instead of incrementing/decrementing when the depth test passes, we do so ...
