X-bit labs

NVIDIA GeForce3 Guide

Category: Video

by FastSite

[ 04/25/2001 | 12:00 AM ]

Our ultimate guide devoted to the newest graphics accelerator from NVIDIA covers all the aspects you could ever think of.In this article you will find not only the details on GeForce3 architecture and technologies, but also an indepth study ofhow all this stuff works as well as the whole bunch of benchmarks and screenshots.

Table of contents:

• NVIDIA GeForce3 Specs
  
• nFinite FX Technology, Pixel and Vertex Shaders
  
• Anti-Aliasing by Multisampling and Quincunx
  
• Anisotropic Filtering
  
• Bump Mapping: EMBM and DotProduct3
  
• RTPatches - Hardware Tessellation of Smooth Surfaces
  
• HSR, Z-Buffer Compression
  
• Lightspeed Memory Architecture
  
• Graphics Cards: Closer Look
  
• Testbed
  
• Testing Method
  
• Overclocking and Architecture Bottlenecks
  
• Test Results: Quake3 Arena
  
• Test Results: Unreal Tournament
  
• Test Results: 3DMark2001
  
• Game 1 - Car Chase
  
• Game 2 - Dragothic
  
• Game 3 - Lobby
  
• Game 4 - Nature
  
• Fillrate
  
• High Polygon Count
  
• Vertex Shaders
  
• Test Results: Aquanox
  
• Conclusion
  

During the last couple of years NVIDIA has turned into the world's leader in the consumer 3D graphics market. Their six-month cycle strategy, when we saw a new product developed and launched every half a year, always put their competitors in the catching-up position.

The graphics chips evolution was based on the increase in chip frequencies and in the amount of pipelines used. In other words, NVIDIA improved the performance of its solutions without introducing any new technologies. That is why by autumn 2000 the company finally understood that this would lead them to a dead end one day.

The best proof of this point is the successful defile of ATI RADEON. A chip with lower working frequencies and fewer pipelines, managed to catch up with the contemporary NVIDIA's solutions only due to the implementation of some tile architecture ideas.

And tile KYRO from PowerVR/STM, which couldn't boast high working frequencies as well appeared unexpectedly fast in games, even though it seemed a pretty weak solution, according to NVIDIA's standards.

Well, at last there appeared the so long-awaited GeForce3, NVIDIA was so proud of. When working on this solution, NVIDIA's engineers, besides some other innovations, finally made a small move towards tile architecture for only one single purpose: to get rid of the current architecture drawbacks.

NVIDIA GeForce3 Specs

• Manufacturing technology process: 0.15 micron;
• Number of transistors in the core: 57 million;
• Core frequency: 200MHz;
• Number of pixel pipelines: 4 with 2 texturing units each (8 texturing units altogether);
• Laying up to 4 textures over 1 pixel per pass (two clocks, 2 textures per clock);
• Graphics memory: 128MB 128bit DDR SDRAM;
• Lightspeed memory architecture, data caching;
• Hardware T&L with nFinite FX technology;
• Triangle tessellation based on spline building;
• Fully DirectX 8.0 compliant, including full support for Pixel Shaders and Vertex Shaders version 1.1;
• Full OpenGL 1.2 support;
• S3TC and DirectX DXT1-DXT5 texture compression support;
• Volumetric textures support;
• Cube environment mapping support;
• Bump mapping support, namely: DotProduct3 and Environment Mapped Bump Mapping (EMBM);
• Anisotropic filtering with 8, 16, 32 samples in DirectX and OpenGL;
• Full-Scene Anti-Aliasing with multisampling and Quincunx methods;
• Z-buffer compression, HSR (Hidden Surface Removal) based on early Z-test.

Judging by the specs of the new graphics chip we can see that GeForce3 has a number of improvements and innovations compared to the previous generation products: GeForce2, GeForce2 Pro and GeForce2 Ultra.

And now we would like to focus on the advantages the newcomer can boast.

nFinite FX Technology, Pixel and Vertex Shaders

The mere name of this technology speaks for itself: now the developers have inexhaustible opportunities for creation of various graphics effects and highly realistic scenes.

nFinite FX technology represents a combination of hardware features of the new GeForce3 core and some flexible means for GeForce3 geometry control, i.e. Pixel and Vertex Shaders.

Shaders are none other but some special programs, and if we try to describe them verbally, then the Pixel Shaders will be special programs for TMU control, which in particular deal with texturing and pixel color calculating, while Vertex Shaders will be special means for the developer to program T&L unit for geometric calculations and transformations.

Compared with the GeForce2, the new GeForce3 features a much more flexible core structure. For instance, Pixel Shaders by GeForce2 (NSR, NVIDIA Shading Rasterizer) isn't compliant with Microsoft DirectX 8:

As you can see from the chart above, GeForce2 allows combining only 2 textures to create a single pixel color. However, there was no loopback, so effects that needed combining more textures and required dependent texture reads, such as true, reflective bump mapping were simply not possible. In other words, the programmers were somewhat limited by NSR because of its architecture imperfection.

GeForce3 Pixel Shaders don't have the described drawback.

It means that its blending unit supports up to 8 texture-blend operations, and dependent texture reads. Besides, the pipelines are connected with each other and don't lack the "loopback" anymore. At the same time, Pixel Shader isn't interpreted by the GeForce3 core but is transferred into a set of parameters involved in different stages of texturing units rendering. The number of texturing stages determines the size of Pixel Shader program. GeForce3 features 8 texturing stages, i.e. it can perform up to 8 operations on textures and intermediate results to get the proper pixel color in the end. Unfortunately, there are no games yet, which could boast using Pixel Shaders mechanism to the full extent.

Pixel Shaders technology is very closely connected with Vertex Shaders. Each vertex is defined by a minimum of three coordinates: x, y, and z that describe its location. In most cases, a vertex may also include data for color, alpha-channel, texture, and lighting characteristics. In fact, Vertex Shaders allow flexible control over the T&L engine and represent special programs, which are interpreted by the GeForce3 geometric coprocessor. For instance, if you set the initial and the final data sets for a vertex with the help of Vertex Shaders, you will automatically get the lighting, transparency and transformation coordinates calculated for each intermediate point of the trajectory. Of course, this is not the only application for Vertex Shaders. For instance, they can help you to easily get volumetric fog or lighting, different object deformations, etc. The only thing that may be considered a limitation here is just the imagination of the developer and the maximum allowed size for the Vertex Shader program. GeForce3 is capable of interpreting Vertex Shaders with the maximum of 128 commands, which is more than enough for programming the most complex transformations. The results obtained here are later used as the initial data for Pixel Shaders when the end image is created. This way Pixel and Vertex Shaders are very closely connected with each other. It is worth mentioning that Vertex Shaders doesn't only help creating new effects and simplify the programming of the already existing effects, but also unloads the CPU quite considerably. For instance, GeForce3 can take upon itself some routine geometric transformations for a set of objects, which will be carried out by only one shader.

Now there are no games, which could boast using GeForce3's features in full, especially, Vertex and Pixel Shaders. That is why we have to offer you some screenshots from 3Dmark2001 and Aquanox (a recently announced game optimized for GeForce3 and using Pixel Shaders v.1.1 and Vertex Shaders v.1.0):

Here vertex Shaders are most likely to be used to get the effect of the brownish water layer just above the seabed, moving plankton, shadows. Together with the Pixel Shaders, Vertex Shaders also provide dancing light spots on all the objects of the scene, which are none other but the effect of the sunlight refraction on the water surface.

Pixel Shaders can't be emulated when the graphics card turns out incapable of supporting them, because ordinary graphics cards can produce only combinations of textures, so to speak. And Pixel Shaders imply the possibility of saving intermediate results and the "loopback" between the pipelines. Vertex Shaders, however, can be emulated due to the fact that some of the scene geometry can be calculated by the system CPU. Of course, this may lead to inevitable performance drop, which we will actually see later on in this review when we study the performance of GeForce3 and the previous generation graphics cards in Aquanox.

Anti-Aliasing by Multisampling and Quincunx

The common image we get in most 3D games without full-scene anti-aliasing is usually spoilt by the so-called stair-step effect at the triangle edges:

GeForce2 eliminated this drawback by means of supersampling technology. Here are the key ideas of this method:

• At first, the image is created in a separate buffer, and the buffer resolution is increased compared with the screen resolution. The increase is carried out as 2x1 or 2x, i.e. the scene is built in a buffer, which horizontal dimension is doubled.
• In case of 2x2 or 4x anti-aliasing, both dimensions of the buffer are twice as big as the required image size.
• Then the colors of two neighboring samples (in case of two-sample anti-aliasing) or of four neighboring samples (in case of four-sample anti-aliasing) are blended and the resulting color is assigned to a pixel in the frame buffer.

In GeForce3 NVIDIA decided not to resort to supersampling to eliminate this stair-step effect. The developers made up their mind not only to improve the anti-aliased image quality but also to reduce the performance drop in case of FSAA.

To cut the long story short, GeForce3 applies anti-aliasing only where necessary, i.e. to the edges of the triangles.

Like in case of GeForce2, the image is created in a larger buffer. And just like in the previous case the buffer is doubled along the horizontal axis for 2-sample anti-aliasing and along the horizontal and vertical axes - for four-sample anti-aliasing.

However, the difference lies with the way GeForce3 creates the image in this buffer.

Let's consider the four-sample anti-alising case.

By GeForce2 the four samples stored in the larger buffer should be blended to define the color of the pixel in the frame buffer.

And what about GeForce3? When the triangles are produced by the geometric engine, the rasterizing unit colors them. At the same time, it is constantly checked if the "2 samples x 2 samples" block fits into the boundaries of the triangle currently textured. If the block made of 2x2 samples fits into the triangle completely, then GeForce3 calculates only one color, interpolating the textures for the pixel in the middle of this block. Then it fills this block with a single color. And when not all the samples of a "2 samples x 2 samples" block fit into the triangle, i.e. when the block crosses the triangle edge, those samples, which belong to the triangle currently textured are drawn in a larger buffer in the common order. The remaining samples, which do not belong to this particular triangle, will be textured later, when other triangles are processed. As soon as the sample colors of 2x2 blocks in the larger buffer are blended and the scene is built, the frame buffer is created.

As a result of the larger buffer rasterization described above, the textures lying within the triangle boundaries do not get blurred, and the color of those pixels situated close to the triangle edges are obtained as a mixture of four sample colors from the larger buffer. In other words, this anti-aliasing method appeared very much like supersampling with that only difference that it is applied only to the triangle edges, which allows eliminating stair-steps without washing out the textures.

Besides, there are almost four times as few samples that should be processed, which reduces the number of operations needed to build a larger image. Definitely, it saves a lot of time and provides much better image quality due to no blurring and washing out within each triangle.

2x anti-aliasing acts the same way, but in this case GeForce3 uses 2x1 sample blocks made of 2 samples only.

Also GeForce3 allows doing scene anti-aliasing with the help of Quincunx technology.

According to NVIDIA, the patented Quincunx technology offers quality comparable to FSAA 4x, with performance similar to that FSAA 2x. To get the pixel color there are 5 samples used. Note that these samples are positioned in a specific manner, which is marked with red color on the picture below:

GeForce3 anti-aliasing can be controlled via driver properties:

Well, now let's take a look at the image quality provided by 2-sample and 4-sample anti-aliasing by GeForce2 and compare it with 2-sample, 4-sample and Quincunx anti-aliasing by GeForce3. To illustrate our study we selected Homeworld: Cataclysm:

No AntiAliasing		GeForce2 2x AntiAliasing		GeForce3 2x AntiAliasing
GeForce3 Quincunx AntiAliasing		GeForce2 4x AntiAliasing		GeForce3 4x AntiAliasing

Unfortunately, it was exactly in Homeworld: Cataclysm that we observed very unpleasant artifacts in the game menu, when we enabled any anti-aliasing modes for GeForce3:

We don't think it is a hardware problem of GeForce3. It looks more like some driver bug, because we didn't come across anything of the kind in Quake3 and Unreal Tournament: anti-aliasing worked perfectly well there.

In order to figure out how much of the performance of our GeForce3 we will sacrifice for the sake of FSAA, we took Quake3 Arena. For a better comparison we also tested ATI RADEON DDR, Creative 3D Blaster Annihilator 2 Ultra (NVIDIA GeForce2 Ultra) and ASUS V7700 64MB (NVIDIA GeForce2 Pro), having set its core to 200MHz and overclocked the memory up to 230MHz (460MHz DDR), which is the working frequencies of NVIDIA GeForce3:

Due to optimized multisampling methods, GeForce3 core requires much fewer samples for FSAA and hence it makes fewer calculations and needs less data from the memory. That is why only GeForce3 can provide acceptable gaming performance and beautiful image quality at 1024x768 and higher resolutions in case Full-Scene Anti-Aliasing is enabled. GeForce2 Pro and GeForce2 Ultra suffer memory bus bandwidth limitations in this case and hence cannot compete.

You may be surprised to see GeForce3 show such high results in 1600x1200x32 for 4x anti-aliasing. Well, this is no wonder: there was not enough graphics memory in this mode and 4x anti-aliasing in Quake3 simply got disabled :-)