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    NVIDIA GeForce 6800 Ultra (Reference)

Product :

GeForce 6800 Ultra

Manufacturer :

NVIDIA

Reviewed by :

Wayne Brooker

Price :

N/A

Date :

May 27th, 2004.

 

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Introduction:::...

I want to tell you a story about a kind and gentle giant known as NVIDIA. For years, the giant NVIDIA ruled the land and was loved by the village folk who relied on his power and his strength to work the fields and build new homes so that they could all live long and prosperous lives.

All was well until one day, there came a new giant. This new giant wasn't as strong as NVIDIA but what he couldn't do with muscle he did with intellect. He couldn't pull the plough himself so he built machinery that not only ploughed as fast, it also ploughed straighter, neater furrows. Nor could the new giant build the houses as fast because he couldn't carry the stone the way NVIDIA always had, so he developed new. lighter materials that made the houses warmer and stronger, and best of all they looked better too!

NVIDIA felt humiliated and spent the next few months explaining to the villagers how crooked furrows were actually better for them than straight ones, and that these new fandangled building materials would never catch on. The villagers were torn in two. They really appreciated all that NVIDIA had done for them in the past but times had changed. The new giant in town was making NVIDIA's work look shoddy, and they suddenly began to realise that not only were the furrows crooked, they also weren't deep enough. NVIDIA had been slacking off when nobody was looking!!

NVIDIA's protests went on, but the villagers grew weary of NVIDIA's constant noise and banished him to the haunted woods with a warning that he must mend his ways if he ever wanted to be welcomed in those parts again.

Well, he's back in town, and he claims to be leaner, smarter, faster and as honest as the day is long. Has the mighty NVIDIA righted his wrongs or are we hearing the desperate pleas of a lonely giant? Hopefully we'll soon know.

 

The Technology:::...

Alas we weren't amongst the elite who received the first rash of sample cards so there's not much point going in to the technology with too much detail, which I'm sure will please some of you. Instead we'll just touch on what we feel are the technologies that matter along with a simple look at how they work or what they do.

 

CineFX 3.0 Features

Displacement Mapping:::...

I'm sure by now you've all heard of bump mapping. Bump Mapping uses shading techniques to make flat surface textures look like they have a a 3d surface when in fact they don't. Using bump mapping, you can make the individual stones in a flat, stone wall texture cast shadows as if they were actually raised.

This is okay in most situations but when lighting in a scene is particularly complex, or when seeing a surface in profile gives away its butt-smooth surface and spoils the illusion, then something more is needed. That something more is Displacement Mapping.

Displacement mapping takes a simple, profile map of an object then physically changes the geometry so it matches the shape. In other words, instead of the Dinosaur head below having "virtual" wrinkles that don't properly interact with a scene's lighting and don't actually exist geometrically, displacement mapping creates real wrinkles out of the mesh of polygons that go to make up the head. This results in more realistic surfaces that can be viewed accurately from any angle and in any lighting.

Vertex Shader 3.0:::...

Vertex Shader 3.0 adds infinite length vertex programs where the operating system and API allows. Dynamic flow control can intelligently allow routing of data within the rendering pipeline so removing many of the previously imposed limitations.

Displacement Mapping is available to the 6800 as a direct result of its shader functionality.

Vertex Frequency Stream Divider:::...

Say what! Well, in layman's terms this lets programmers introduce fixed, preset differences into batch animations. This is almost like dialing in a controlled error or a variable, so if you were animating a battalion of troops for example each could be made to look slightly different by altering anything from height, uniform colour or even the way they move, the speed they walk at or even how high they swing their arms when they walk.

Multiple Render Targets:::...

Also known as deferred shading. There's no easy way to explain this, but I'll try. For complex shading techniques, such as per-pixel lighting techniques, it's often necessary to send the geometry through the rendering pipeline more than once before the final pixel colour is calculated. When the scene being rendered is already complex, this expensive multipass technique is often ruled out as it would simply take too long to perform.

Deferred shading extracts all the shading data required for the final scene and saves them to multiple attribute buffers. The data from these buffers is then unpacked and applied to the scene geometry after it has been calculated so saving the need to resubmit it.

In short then, deferring the shading/lighting calculations allows you to apply complex lighting and shading techniques while performing a single pass for normal vertex processing. This allows intricate effect to be applied to even polygon-heavy scenes.

So What?:::...

Shader Model 3.0 is not supported by ATi at the moment, and how much this matters depends on who you talk to. To say it's a gimmick would be harsh, but it is a gimmick at the moment until we see it used to its potential, by which time ATi may very well have hardware that can handle it.

32 bit precision throughout the entire pipeline open up a world of possibilities, but they're possibilities that won't be used unless there's enough power to make them workable. This time, I think that part of the equation may finally be fulfilled, at least partly.

 

Pixel Effect Features

Rotated Grid Antialiasing:::...

If you look at the diagram below, the example on the left shows the traditional subpixel sampling arrangement of a two by two grid essentially only samples two horizontal and two vertical values. By rotating the grid slightly as in the example on the right, that can be increased to cover four horizontal and four vertical values which should mean more accurate subpixel colour sampling at the edge of polygons in particular.

HPDR:::...

If you're a photography buff you'll probably understand this feature easier if I explain that it's just like increasing the latitude of your film. For the rest of us, it allows a scene to have a greater range of brightnesses without having to sacrifice details in either the shadows or the highlights.

The scene on the left is rendered without HPDR and has a dynamic range of about 100:1 while the scene on the right which is rendered using HDPR and is closer to 9000:1. Personally I think NVIDIA have chosen a really bad example of this technology with these pictures as I happen to prefer the image rendered without HPDR, but there are certainly situations where the ability to effectively lower contrast would be critical.

 

UltraShadow II :::...

In all the accusations of cheating it always struck me as odd that nobody every considered UltraShadow to be a cheat too. UltraShadow allows programmers to specify the zone within which shadow calculations are performed. In the example below, any shadows that fall in front of the near boundry (zmin) or behind the far boundry (zmax) are basically ignored. While this is a great technology in the right hands I can imagine all kinds of scenarios where it could be wrongly used to increase performance but with some fairly weird results.

 

 

The buzzword here is "Superscalar". The term Superscalar refers to the ability to execute more than one operation per clock cycle, and the addition of a second shader unit, the GeForce 6 is capable of up to four instructions and eight operations per pixel, compared to just two instructions and four operations in traditional architectures.

 

There's lots more we could talk about like the 222million transistors, the dedicated on-chip video acceleration, the dual 400MHz RAMDACs and the floating point frame buffer blending but if these are things you're interested in you've no doubt already read about them. Let's round

 

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