NVIDIA's GeForce 8800 (G80): GPUs Re-architected for DirectX 10
by Anand Lal Shimpi & Derek Wilson on November 8, 2006 6:01 PM EST- Posted in
- GPUs
Shader Model 4.0 Enhancements
Aside from defining the capabilities and instructions that the different shaders must support, Microsoft also specifies attributes like precision, number of instructions that can make up a shader program, and the number of registers available to the programmer. Here's a table comparing DX9 and DX10 shader models.
Along with these changes, Microsoft has made some lower level adjustments. Until now, shaders have been exclusively floating point. This means that operations like memory addressing and array indexing (which use integer values) must be done carefully if interpolation is to be avoided. With DX10, integer and bitwise operations have been added to the mix. This means programmers can make use of traditional data structures and memory operations. Increasing the flexibility of the hardware and enabling programmers to employ methods commonly used on more general purpose hardware will certainly be helpful in creating a better platform for developers to create the effects they desire.
Floating point operations have also been enhanced, as Microsoft has placed tighter requirements on how to handle the numbers. IEEE 754 is a specification that defines all aspects of floating point interaction. Sticking to such a standard allows programmers to guarantee that operations will be consistent between different types of hardware. Because Microsoft hasn't been as strict in the past, we've seen some issues where ATI and NVIDIA don't provide the exact same result due to rounding and accuracy differences. This time around, DX10 has very nearly IEEE 754 requirements. There are certain aspects of IEEE 754 that are not desirable in graphics hardware. These aspects have to do with over and underflow and denorms. The special results that are usually returned in these cases under IEEE specifications aren't as useful as clamping the value of a calculation to either the smallest possible result or largest possible result. With DX10, we do see the addition of NaN and infinity as possible results, and along with a better specification of accuracy and precision, those interested in general purpose computing on graphics processors (GPGPU) should be very happy.
What are Geometry Shaders?
A whole new shader type has been added this time around as well: Geometry shaders. These shaders are similar to vertex shaders in that they operate on geometry before it has been projected on to screen space where pixel processing can take over. Rather than operating on single vertices, however, geometry shaders operate on larger blocks: meshes. These meshes (made up of vertices) can be manipulated in a myriad of ways. Working with an object containing vertices gives programmer the ability to manipulate those vertices in relation to each other more easily. Vertices can even be added or removed from a mesh. The ability to write out data from the geometry shaders (rather than simply sending it on for pixel processing) will also allow software to reprocess vertices that have been added or altered by the geometry shaders. As an extension to geometry instancing, we will have more flexibility in manipulating instanced geometry in order to avoid the cut and paste look. All of these new features mean we should see things like particle systems move completely off of the CPU and on to the GPU, and geometry may begin to play a larger role in graphics in the future.
In the beginning, increasing the number of triangles that could be rendered in a scene was a huge factor in performance. After a certain point, software, CPUs, buses, and overhead in general started to get in the way of how much difference adding more triangles made. Rather than having millions of really tiny triangles moving around, it became much faster to use textures to simulate geometry. Currently, per pixel lighting combined with uncompressed normal maps do a great job of simulating a whole lot of geometry at the expense of a lot of pixel power. With the new 8k*8k texture sizes and other DX10 enhancements, there is a lot of potential for using pixel processing to simulate geometry even better. But the combination of unified shaders and geometry shaders in new hardware should start to give developers a whole lot more flexibility in how they approach the problem of fine detail in geometry.
Facebook
Twitter
RSS
111 Comments
View All Comments
Sunrise089 - Thursday, November 9, 2006 - link
Then I suppose he's in the market to part with an ugly old high-end CRT. I'd love to buy it from him. Seriously.JarredWalton - Thursday, November 9, 2006 - link
You want an older 21" Cornerstone CRT? It's a beast, but you can have it for the cost of shipping (which unfortunately would probably be ~$50). I'd also sell my Samsung 997DF 19" CRT for about $50, and maybe an NEC FE991-SB for $50 (which unfortunately has a scratch from my daughter in the anti-glare coating). If anyone lives in the Olympia, WA area, you know how to contact me (I hope). I'd rather someone come by to pick up any of these CRTs rather than shipping, as I don't think I have the original boxes.DerekWilson - Thursday, November 9, 2006 - link
lol next thing you know links to ebay auctions are gonna start showing up in our articles :-)yyrkoon - Thursday, November 9, 2006 - link
lol, I've got a 21" techtronics I'll sell for $200 usd, plus shipping ;) Hasnt been used since I purchased my Viewsonic VA1912wb (well, been used very little ).imaheadcase - Wednesday, November 8, 2006 - link
can't stand AA benchmarks myself :)Question: Do you have any info on what kinda card nvidia releasing this feb? Is it something in between these 2 cards or something even lower?
Im looking for a $300ish g80! :D
flexy - Wednesday, November 8, 2006 - link
if ANYTHING counts then how those high-end cards perform WITH their various AA settings.... the power of those cards (and the money spent on :) RIGHT translated into ---> IMAGE QUALITY/PERFORMANCE.Please dont tell you you would get an G80 but do NOT care about AA, this does NOT make any sense...sorry...
I am especially impressed reading that transparency AA has such a LITTLE performance impact. What game engine did you test this on ?
On the older ATI cards (and am i right that T.A. is the same as "adaptive antialiasing" ? )...this feature (depending on game engine) is the FPS killer....eg. w/ games like oblivion (WHERE ARE THE GOTHIC 3 BENCHEIS BTW ? :)...much vegetation etc. game-engines.
Enable transparency AA and see all those trees, grass etc. without jaggies.
imaheadcase - Thursday, November 9, 2006 - link
Well lots of people don't are for AA. Even if i had this card I would not use it. I visually see NO difference with it on or off. Its personal test. I don't even see "jaggies" on my older 9700 PRO card.flexy - Thursday, November 9, 2006 - link
you sure are talking about ANTIALIASING ???What resoltions do you run ? Not that my CRT can even handle more than 1600x1200..but even w/ 1600 i get VERY prominent jaggies if i dont run AA.
I made it a habit to run at least 4xAA in ANY game, and some engines (hl2:source engine) etc. run extremely well with 4xAA, even 6xAA is very playable at elast with HL2.
The very recent games, namely NWN2 and G3 now dont support AA, playing at 1280x1024 and it looks utterly horrible ! If you say you dont see jags in say ANY resolution under 1600..very hard to believe
imaheadcase - Thursday, November 9, 2006 - link
Yes im talking about antialiasing. I normally play BF2 and oblivion at 1024x768 (9700 pro remember).Fact is most people won't see them unless someone points them out. The brain is still better at rendering stuff the way you want to see it vs hardware :)
flexy - Thursday, November 9, 2006 - link
ok..but then it's also a performance problem. If it doesn't bother you, well ok.I also have to settle w/ the fact that many RECENT games are even unable to do AA..however i wish they would.
But once i get a 8800 i will do &&&& to get the most out of IQ, AA, AF, transparency/texture AF, you name it. ALONE also for the reason that i would need a super-high end monitor first to even run resolutions like 2000xsomething...and as long as i have a lame 19" CRT and CANNOT even go over 1600 (99,99% of games even running everything on 1280x or 1360x) i will use all the power to get out best possible IQ in those low resolutions.
Also..looking at the benchmarks..its NOT that you lose any real time gaming-experiencee since THOSE monster cards are made for exactly this...eg. running oblivion with all those settings at MAX AND AA on and HDR...and you are still in VERY reasobale FPS ranges.