What is the Z-Cache?

[ultrafly]

http://www.tomshardware.com/graphic/20030306/radeon9800pro-03.html

"The optimizations in HyperZ III+ mostly affect the improved Z-Cache, which is now more flexible and was optimized for stencil-buffer data. "

What is the Z-Cache?

Thanks.

 

[K.I.L.E.R]

Where z info is stored for fast fetching.

 

[ultrafly]

Where z info is stored for fast fetching.

How many bytes in the Z-Cache?

 

[Dave H]

Detailed info like cache sizes tends to be kept secret with GPUs. Stupid, IMO, but what can you do?

 

[ultrafly]

Detailed info like cache sizes tends to be kept secret with GPUs. Stupid, IMO, but what can you do?

The z-cache only store the z info.
The effect of the z-cache should be only in z-clear and z-test.
Why improved Z-Cache can optimize stencil-buffer operation?

 

[Dave Baumann]

They are talking about the Hierarcical-Z buffer, which is actully stored on chip.

 

[Dave H]

Z and stencil info are stored together: one 32 bit word has 24 bits devoted to z and 8 bits devoted to stencil.

But in any case, it appears that Tom got it wrong and that the z/stencil related improvement with 9800 is that it can enable all the z-optimizations (early z reject, hierarchical z) when doing depth-fail rendering (ala the stencil shadowing pass on Doom 3). So if that's the case it really has nothing to do with the cache anyways.

(edit: as Wavey points out, Hierarchical Z is a sort of cache. But the point is that the improvement is algorithmic in nature, so describing it as a cache improvement is a little odd.)

 

[ultrafly]

They are talking about the Hierarcical-Z buffer, which is actully stored on chip.

cache or mem?

 

[demalion]

The phrasing seems suitable to me, since both the data handling and the actual physical layout of data storage are represented in the hardware and can be called the "Z cache", or whatever term is most suitable. Since one or both has changed, it isn't (IMO) off-base like certain other comments that particular site might have made in the past and might continue to make.

I haven't read the article, however, so I don't know if there is something beyond that quote that might warrant correction.

 

[ultrafly]

that it can enable all the z-optimizations (early z reject, hierarchical z) when doing depth-fail rendering (ala the stencil shadowing pass on Doom 3)

Your means that the R9700 disable the z-optimizations (early z reject, hierarchical z) when doing depth-fail rendering?

 

[DeanoC]

that it can enable all the z-optimizations (early z reject, hierarchical z) when doing depth-fail rendering (ala the stencil shadowing pass on Doom 3)

Your means that the R9700 disable the z-optimizations (early z reject, hierarchical z) when doing depth-fail rendering?

IIRC so does GFFX, so far R9800 is the only one.