Specifications

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Chapter 15 Video Hardware
■ T-buffer. This technology eliminates aliasing (errors in onscreen images due to an undersampled
original) in computer graphics, such as the “jaggies” seen in onscreen diagonal lines; motion
stuttering; and inaccurate rendition of shadows, reflections, and object blur. The T-buffer
replaces the normal frame buffer with a buffer that accumulates multiple renderings before dis-
playing the image. Unlike some other 3D techniques, T-buffer technology doesn’t require
rewriting or optimization of 3D software to use this enhancement. The goal of T-buffer technol-
ogy is to provide a movie-like realism to 3D-rendered animations. The downside of enabling
antialiasing using a card with T-buffer support is that it can dramatically impact the perfor-
mance of an application. This technique originally was developed by now-defunct 3dfx.
However, this technology is incorporated into Microsoft DirectX 8.0 and above.
■ Integrated transform and lighting (T&L). The 3D display process includes transforming an object
from one frame to the next and handling the lighting changes that result from those transfor-
mations. T&L is a standard feature of DirectX starting with version 7. The NVIDIA GeForce 256
and original ATI RADEON were the first GPUs to integrate the T&L engines into the accelerator
chip, a now-standard feature.
■ Full-screen antialiasing. This technology reduces the jaggies visible at any resolution by adjusting
color boundaries to provide gradual, rather than abrupt, color changes. Whereas early 3D prod-
ucts used antialiasing for certain objects only, accelerators from NVIDIA (GeForce 4 Ti, GeForce
FX, and the 6800 series) and ATI (RADEON 9xxx and the X800 series) use various types of
highly optimized FSAA methods that allow high visual quality at high frame rates.
■ Ver tex skinning. Also referred to as vertex blending, this technique blends the connection
between two angles, such as the joints in an animated character’s arms or legs. NVIDIA’s
GeForce2, 3, and 4 series cards use a software technique to perform blending at two matrices,
whereas the ATI RADEON series chips use a more realistic hardware-based technique called
4-matrix skinning.
■ Keyframe interpolation. Also referred to as vertex morphing, this technique animates the transi-
tions between two facial expressions, allowing realistic expressions when skeletal animation
can’t be used or isn’t practical. See the ATI Web site for details.
■ Programmable vertex and pixel shading. Programmable vertex and pixel shading became a stan-
dard part of DirectX starting with version 8.0. However, NVIDIA introduced this technique with
the GeForce3’s nfiniteFX technology, enabling software developers to customize effects such as
vertex morphing and pixel shading (an enhanced form of bump mapping for irregular surfaces
that enables per-pixel lighting effects), rather than applying a narrow range of predefined
effects. The NVIDIA GeForce4 Ti’s nfiniteFXII pixel shader is DirectX 8 compatible and supports
up to four textures, whereas its dual vertex shaders provide high-speed rendering up to 50%
faster than the GeForce3. The ATI RADEON 8500 and 9000’s version, SmartShader, is supported
by DirectX 8.1. DirectX 8.1 supports more complex programs than nfiniteFX and provides com-
parable quality to nfiniteFXII. ATI 9700, 9800, and 9500 support DirectX 9’s floating-point pixel
shaders and more complex vertex shader. NVIDIA GeForce FX cards also support DirectX 9 pixel
and vertex shaders, but they add more features. NVIDIA’s 6800 series supports the new DirectX
9 Shader Model 3.0.
■ Floating-point calculations. Microsoft DirectX 9 supports floating-point data for more vivid and
accurate color and polygon rendition. ATI Radeon 9500, 9600, 9700, and 9800-series GPUs sup-
port standard DirectX 9 floating-point data, whereas the NVIDIA GeForce FX series supports
DirectX 9 and has additional precision. The NVIDIA 6800 series further increases precision
beyond the basic DirectX 9 requirements. The Matrox Parhelia supports this, but doesn’t sup-
port other DirectX 9 features.
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