The Graphics Card - Features: AGP Modes, Dual Display, Anti-Aliasing, Filtering and Programmable Shading
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Features When you encounter a graphics card, be it on the web or in a store, you’re faced with a barrage of 3-D terminology and glossy marketing monikers describing the card’s features. Unfortunately, few definitions are given, so to many confused gamers it comes off as a lot of mystical mumbo jumbo.
AGP Modes Speedy AGP is important. It allows for a direct pipeline between the graphics card and the computer’s main memory. AGP lets video data that won’t fit into a graphics card’s local memory be stored into the aperture space in the system’s own bank of memory.
ATI’s Radeon 9700 and 9500 series, Nvidia’s NV18-based GeForce4 MX440, its NV28-based GeForce4 Ti 4200, and its GeForce FX series all support AGP 8X. AGP 8X, also known as AGP 3.0, is the fastest current AGP speed available. For it to function, both a compliant graphics card and motherboard are required.
Other graphics equipment, such as ATI Radeon 9000 chipsets and those based on the Nvidia GeForce4 Ti 4600, are AGP 4X compliant. That does not mean they’re half as fast overall as their AGP 8X counterparts; it means that video data has half the bus bandwidth to swap data from system memory.
Dual-Display Support Both ATI and Nvidia cards offer support for a pair of displays. Nvidia calls its dual-display support Nview, while ATI refers to the same concept as HydraVision. Dual displays allow you, for example, to display one application on one monitor and the other on a second display, to watch a DVD on a TV while crunching a spreadsheet on a monitor, or to stretch the Windows desktop across two displays.
Anti-Aliasing Anti-aliasing, also called full-scene anti-aliasing (FSAA), is a method of blending the colors at the edges of textures or polygons to eliminate jagged diagonal lines and artifacts that they cause, like shimmering distance textures. Early forms of anti-aliasing carried a high performance overhead, greatly reducing games’ frame rates. They also notoriously blurred the edges of textures and polygons, reducing the sharpness of the game scene.
Current cards have the muscle to allow gamers to turn on anti-aliasing while keeping the frame rates playable. They also provide sharper, more accurate scenes than early anti-aliasing techniques could provide. Nvidia calls its latest anti-aliasing technology Intellisample Technology. ATI calls its current anti-aliasing technique SmoothVision 2.0.
Filtering Similar to anti-aliasing, filtering is used to blend textures to reduce blockiness and pixilation and to smooth transitions between textures as they move nearer to, or farther from, the point of view (MIP mapping).
Three types of filtering can be used: bilinear, trilinear, and anisotropic. Bilinear filtering blends flat textures from a two-dimensional point of view. Trilinear filtering adds a z value, which helps smooth the transition between MIP maps. MIP mapping involves using less-detailed textures as an object gets farther from the viewpoint, similar to what the human eye does when viewing distances. Anisotropic filtering can be used with bilinear or trilinear filtering, and it increases the filtering precision by using a wider range of texels (textured pixels).
Both ATI and Nvidia allow you to force anisotropic filtering through their driver interfaces. ATI’s driver interface allows you to set the level of anisotropic filtering from 2X to 16X, while Nvidia’s GeForce 4 and earlier chipset’s drivers allow you to force anisotropic filtering only from 2X to 8X. We have yet to see the GeForce FX or its driver interface.
Programmable Shaders A relatively recent feature in 3-D graphics chipsets, programmable pixel and vertex shaders allow programmers to create blazingly realistic lighting effects of their own design. Programmers are no longer limited to the lighting effects included with Direct3D, as they can create their own routines in assembly language to achieve any effect they desire. ATI calls its programmable shaders SmartShaders, and they’re currently in their second incarnation (SmartShader 2.0). Nvidia calls its shaders the infinite FX II Engine for its GeForce4 Ti parts, and CineFX for the GeForce FX.
 This chapter is from Build Your Own High Performance Gamers' Mod PC, by Chen and Durham (McGraw-Hill/Osborne, 2004, ISBN: 0072229012). Check it out at your favorite bookstore today. Buy this book now. |
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