Video Hardware - Upgrading and Repairing PCs - page 642

you don't need to spend a fortune to achieve a reasonable level of 3D graphics. Many cards in the
$50-$150 range use lower-performance variants of current high-end GPUs, or they might use the
previous year's leading GPU. These cards typically provide more-than-adequate performance for 2D
business applications. All current 3D accelerators also support dual-display and TV-out or HDTV
capabilities, enabling you to work and play at the same time.
However, keep in mind that the more you spend on a 3D accelerator card, the greater the onboard
memory and the faster the accelerator chip you can enjoy. If money is no object, you can buy a
graphics card featuring the currently fastest GPU for more than $500. Fortunately, there are plenty of
choices using either NVIDIA or AMD GPUs in the less than $500 price range that offer plenty of 3D
gaming performance, including support for dual-GPU operations (NVIDIA SLI or AMD CrossFireX),
which split rendering chores across the GPUs in both video cards for faster game display than with a
single card. GPUs that support DirectX 10/11 are the preferred choice for anyone who wants to play
current generation games.
Mid-range cards costing $100-$300 are often based on GPUs that use designs similar to the high-end
products but might have slower memory and core clock speeds or a smaller number of rendering
pipelines. These cards provide a good middle ground for users who play games fairly often but can't
cost-justify high-end cards. Cards under $100 are best used for low-cost replacements for chipset-
integrated video. These cards typically have performance that is no better than that available from
current CPU-integrated video.
The basic function of 3D software is to convert image abstractions into the fully realized images that
are then displayed on the monitor. The image abstractions typically consist of the following elements:
• Vertices —Locations of objects in three-dimensional space, described in terms of their x, y,
and z coordinates on three axes representing height, width, and depth.
• Primitives —The simple geometric objects the application uses to create more complex
constructions, described in terms of the relative locations of their vertices. This serves not only
to specify the location of the object in the 2D image, but also to provide perspective because
the three axes can define any location in three-dimensional space.
• Textures —Two-dimensional bitmap images or surfaces designed to be mapped onto
primitives. The software enhances the 3D effect by modifying the appearance of the textures,
depending on the location and attitude of the primitive. This process is called perspective
correction . Some applications use another process, called MIP mapping , that uses different
versions of the same texture containing varying amounts of detail, depending on how close the
object is to the viewer in the three-dimensional space. Another technique, called depth cueing ,
reduces the color and intensity of an object's fill as the object moves farther away from the
viewer.
Using these elements, the abstract image descriptions must then be rendered, meaning they are
converted to visible form. Rendering depends on two standardized functions that convert the
abstractions into the completed image that is displayed onscreen. The standard functions performed in
rendering are as follows:
• Geometry —The sizing, orienting, and moving of primitives in space and the calculation of the
effects produced by the virtual light sources that illuminate the image
• Rasterization —The converting of primitives into pixels on the video display by filling the
shapes with properly illuminated shading, textures, or a combination of the two