Lights can be conservatively bounded within a depth range. When image
pixels are outside of a light's depth range, an associated volume
fragment does not have to be rendered. Depth bounds registers can be used
to store minimum and maximum depth values for a light. As graphics
hardware processes volume fragments overlapping the image, the image's
depth values are compared with the values in the depth bounds register.
If the image's depth is outside of the depth range for the light, stencil
buffer and illumination operations for this volume fragment are bypassed.
This optimization can be performed on a per-pixel basis, or
simultaneously on a group of adjacent pixels. The depth bounds are
calculated from the light, or from the intersection of the volume with
one or more other features. A rendering application uses API functions to
set the depth bounds for each light and to activate depth bounds
checking.
