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ToolTech
09-03-2002, 10:52 AM
I heard that there is an extension making stencil work in one pass. SO i can use it to do both front z fail and back face z fail etc. in one pass.

Will this extension be available for multiple HWs ?

mcraighead
09-03-2002, 12:00 PM
I can't speak for other vendors, but you can find the extension here:
http://oss.sgi.com/projects/ogl-sample/registry/EXT/stencil_two_side.txt

You can guess what hardware might support this by playing with the emulation registry keys in our latest drivers.

- Matt

ToolTech
09-03-2002, 12:13 PM
If i feel that the app is fill rate limited by shadow volumes. Will i benefit from the two side version then by 100 % faster ?

PH
09-03-2002, 12:38 PM
No. From the spec,



In a fill-rate limited situation, rendering front-facing primitives, then back-facing primitives in two passes will generate the same number of rasterized fragments as rendering front- and back-facing primitives in a single pass.

cass
09-03-2002, 10:22 PM
To elaborate on this point, if the two-pass approach is *always* fill bound, then two-sided stencil won't help.

Often, though, in the two-pass approach there are large sequences of triangles that will all be culled. This can leave you transform or geometry transfer bound for significant portions of the shadow volume rendering (depending on internal fifo sizes and such).

If fill is ever *not* the bottleneck in the two-pass approach, you can expect some improvement with two-sided stencil.

Thanks -
Cass