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.

All GPUs are Created Equal: Say Goodbye to Cap Bits G80: A Mile High Overview
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  • DerekWilson - Thursday, November 09, 2006 - link

    i'm sure there was a lot burried in there ... sorry if it wasn't easy to find.

    8800 gtx and gtx are both no louder than 7900 gtx. 1950 xtx still takes the cake for loudest graphics card around by a long shot -- especially after it heats up in a game.
    Reply
  • crystal clear - Thursday, November 09, 2006 - link

    My comments in Daily Tech on this subject-

    More "G80" Derivatives in February R
    E: More info would be nice
    By crystal clear on 11/8/06, Rating: 2
    By crystal clear on 11/8/2006 8:03:43 AM , Rating: 2

    If you link VISTA -SANTA ROSA platform-Core2DUO(merom)CPU line up(T7300,7500,7700 models)then a matching Graphics card
    to complete the link.

    So a G80 for laptops/notebooks?

    The pairing of Intels Santa Rosa platform with Vista in the 2Q 07 is next big thing for the first tier notebook manufacturers & all they need is a matching G80 for this setup.

    Unquote-
    Nvidia currently caters to Desktop requirement/needs with the new G80 releases,wonder how the notebook/server versions will be-with Vista ofcourse.



    Reply
  • yyrkoon - Thursday, November 09, 2006 - link

    Vitual memory is probably a good thing for most cases, but in the graphics arena, this *could* potentially make for sloppy/ bad coding practises. Knowing a lot of game devers (some of which actually work for well known companies), I've heard them from time to time complain about maxing a 16x PCI-E pipe. What I'm trying to say here, is that while it would be a good thing for never having to run out of texture memory, but that system memory, and definately the swap disk can not hold a candle to the memory bandwidth that most Video cards are capable of. End result, is that you definately *will* get a performance hit. All this, and we already know the memory bandwidth capabilities of modern PCs, suffice it to say, the most we'll see from current systems is what ? 12-13K GB/s ? Even a 7800GS can do roughly 35 GB/s on card. A 7600GT ? 22GB/s ?

    Still I think Directx10 is a very good thing, and as I didnt read the whole article, perhaps a missed a little ? Reason being, I've been reading about Directx10 since April, and a friend of mine was privy to some of this information after an interview with ATI.

    http://www.gamedev.net/reference/programming/featu...">http://www.gamedev.net/reference/programming/featu...
    Reply
  • saratoga - Thursday, November 09, 2006 - link

    I don't know how they threading really works, but its quite possible VM support is required in order to allow multiple threads to run without stepping all over each other,. Reply
  • saratoga - Thursday, November 09, 2006 - link

    Sorry, should read "I don't know how THEIR threading works" Reply
  • falc0ne - Thursday, November 09, 2006 - link

    I don't know what is the problem but I'm really unable to see the images within the latest articles from Anand...Can anyone give me a suggestion? What might be the cause of that?
    The thing is I'm really, really interested in these articles and I need to see those images. Thanks
    Reply
  • yyrkoon - Thursday, November 09, 2006 - link

    Oh, er, then in the options tab of Firefox, (tools->options->content) check the "load images" check box ;) Reply
  • falc0ne - Thursday, November 09, 2006 - link

    well...it would've been simple but I'm afraid is not that...It might be the addblock extension from firefox, other than that I have nooo ideeea...Well I will use the IE tab option instead and load the pages using IE 7. Thanks anyway:) Reply
  • yyrkoon - Thursday, November 09, 2006 - link

    Checked the exceptions list ? I know that firefox makes it really simple to block images from a site (to a point of being too easy). Reply
  • JarredWalton - Thursday, November 09, 2006 - link

    If you've got AdBlock on Firefox, press Ctrl+Shift+A and you can see what it's blocking. If it blocks the images.anandtech.com stuff, you can then see which RegEx isn't working right and edit that. Reply

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