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January 30th, 2003 - Name: John Carmack
Email:
Description: Programmer
Project:
Last Updated: 01/29/2003 18:53:43 (Central Standard Time)
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Jan 29, 2003
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NV30 vs R300, current developments, etc
At the moment, the NV30 is slightly faster on most scenes in Doom than the
R300, but I can still find some scenes where the R300 pulls a little bit
ahead. The issue is complicated because of the different ways the cards can
choose to run the game.
The R300 can run Doom in three different modes: ARB (minimum extensions, no
specular highlights, no vertex programs), R200 (full featured, almost always
single pass interaction rendering), ARB2 (floating point fragment shaders,
minor quality improvements, always single pass).
The NV30 can run DOOM in five different modes: ARB, NV10 (full featured, five
rendering passes, no vertex programs), NV20 (full featured, two or three
rendering passes), NV30 ( full featured, single pass), and ARB2.
The R200 path has a slight speed advantage over the ARB2 path on the R300, but
only by a small margin, so it defaults to using the ARB2 path for the quality
improvements. The NV30 runs the ARB2 path MUCH slower than the NV30 path.
Half the speed at the moment. This is unfortunate, because when you do an
exact, apples-to-apples comparison using exactly the same API, the R300 looks
twice as fast, but when you use the vendor-specific paths, the NV30 wins.
The reason for this is that ATI does everything at high precision all the
time, while Nvidia internally supports three different precisions with
different performances. To make it even more complicated, the exact
precision that ATI uses is in between the floating point precisions offered by
Nvidia, so when Nvidia runs fragment programs, they are at a higher precision
than ATI''s, which is some justification for the slower speed. Nvidia assures
me that there is a lot of room for improving the fragment program performance
with improved driver compiler technology.
The current NV30 cards do have some other disadvantages: They take up two
slots, and when the cooling fan fires up they are VERY LOUD. I''m not usually
one to care about fan noise, but the NV30 does annoy me.
I am using an NV30 in my primary work system now, largely so I can test more
of the rendering paths on one system, and because I feel Nvidia still has
somewhat better driver quality (ATI continues to improve, though). For a
typical consumer, I don''t think the decision is at all clear cut at the
moment.
For developers doing forward looking work, there is a different tradeoff --
the NV30....
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