Radeon 9700 doesn't support Shadow Buffer algorithm?

[embargiel]

According to Dani Lepage (3D programmer of SC), Radeon 9700 uses different shadow algorithm as those in GF3/4 Ti/ XBox. It uses the same algorithm as those in GF2/Radeon 7500/GF4MX. What's the big deal with that? Doesn't Radeon 9700 support Shadow Buffer? If so, then why they use th Shadow Projector Algorithm?

Take a glimpse into this link:
http://forums.ubi.com/messages/message_view.asp?name=pcdemo&id=zzmee

[Humus]

The 9700 most certainly supports shadow buffers. Afaict it's only that the app doesn't support it when running on a 9700 for whatever reason.

[DeanoC]

The 9700 'support' for shadow buffers is different from the nvidia's which means another code path, dev time (especially on ports) is far more of a resource than card capability. The key thing is that they talk about DX8.NV which implies using the nvidia extensions to Dx8, its no different from using an extensions under OpenGL. If a card doesn't support that extension you fall back to another stragety.

AFAIK the 9700 does not support shadow buffers in the same way the nVidia chips do, you cannot create a depth surface directly. Under Dx8 you would have to use a pixel shader to combine 2/3 8 bit channels to gain the native precision of the nVidia shadow buffers. This would also mean rewriting all pixel shaders (and upgrading them to PS1.4) changing alot of code etc.

Actually the 4 extra texture slots (required for bilnear PCF shadow maps) would have fit PS.1.4 quite nicely, so a PS.1.4 version could have been full featured but would have took alot of dev time (writing, testing and bug fixing).

Not every project can afford the dev time to do 7 different rendering paths(like Doom3 can). It can take alot of work to make an XBox project work on non-nvidia chips, so don't expect much 'upgrading' for better chips (high res and working on a variety of chips uses up most of the time budget, trust me :-) )