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View Full Version : Rendering the depth buffer to a texture + FSAA == slow?



Ostsol
01-26-2003, 04:32 PM
I modified the "Render to a Texture" tutorial at GameTutorials.com to render the depth buffer to the texture instead of the colour buffer. For good measure, I decided to incorporate the ARB_depth_texture extension. Normally the thing ran at more than 700 fps, but after my modfications I got 8 fps. After a bunch of fooling around I found that turning off FSAA resulted in the correct framerate of >700 fps again. Does anyone know why this occurs?

I'm using a Radeon 9700 Pro with the Catalyst 3.0a drivers, BTW. . .

Humus
01-26-2003, 10:41 PM
Sounds like a driver bug. I don't get that behaviour though, I see only a small performance decrease by enabling FSAA, like 156fps -> 142fps.

Ostsol
01-27-2003, 03:37 AM
Which drivers are you using?

Humus
01-27-2003, 09:52 AM
6275

dorbie
01-27-2003, 03:15 PM
It could be the framebuffer format vs the texture format used. If they are incompatible there might be some expensive swizzle going on, perhaps even in software back on the CPU.

Ostsol
01-27-2003, 04:51 PM
Where'd you find that driver, Humus? I'm using 6255, which is the latest version on ATI's site. . .

Humus
01-28-2003, 01:36 AM
Well, it's up on the developer site, but has been leaked for almost as long as it's been up there, a quick google search on "ati 6275" gave me several links.

Ostsol
01-28-2003, 11:24 AM
Ah. . . those. . . Thanks!