FSAA
Quality and Performance
ATI
uses the same method of FSAA that 3DFX did. A hardware accumulation buffer is
used to combine successive frames together and producing a sharper image.
Both 2 sample and 4 sample FSAA capabilities to the Radeon family with the 4.13.7041
driver release. To get an idea of the image improvements FSAA offers, these screenshots
are from the Q3DM1 Arena Gate map.
FSAA
OFF
2X
FSAA
Click on the
images for the high quality version.
At
the top we see a portion of a screenshot from Quake 3 running with FSAA disabled.
The Jagged edges are quite noticeable, and certainly detract from the overall
quality. On the bottom is the same frame but with 2 sample FSAA enabled. The difference
is immediately apparent, FSAA produces a much nicer looking image. For those wondering
about 4X FSAA, the largest improvement in image quality is from 0-2X, the noticeable
improvements from 2-4X are marginal. The cost for FSAA is performance, 2 sample
FSAA requires the video card to render twice the number of frames per second to
obtain an equivalent frame rate.
The
one problem we ran into was using 4 sample FSAA at resolutions above 800x600.
After enabling 4X in the drivers and rebooting, both OpenGL and Direct X applications
displayed no video. Switching back to 2X FSAA or 800x600 fixed the problems, yet
another bug in the drivers.
On the
performance side of things, we see the enormous frame rate hit when using
FSAA, well over 60% at the higher resolutions. The performance drop is nearly
linear using both 2X and 4X, 800x600 being about the highest resolution
playable. The large drops in performance would seem to indicate that the
memory is the bottleneck rather than the core. Radeon users have reported
modest gains in FSAA performance when overclocking so that may be an option
for purely performance oriented users.
Overclocking
