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|Antialiasing through Multisampling
NVIDIA's GeForce3 graphics processing unit (GPU) introduces radical new technology designed to provide the industry's first solution for high-resolution antialiasing (HRAA). While other antialiasing solutions and their methods have been offered before, only GeForce3 can offer the unique combination of high resolutions and high frame rates in combination with high-quality antialiasing. By implementing hardware support for multisampling, as well as innovating new sampling technology, GeForce3 makes HRAA available for all real-time content.
Combatting the Aliasing Effect
One of the key image quality problems that has plagued PC users is aliasing, or the "jaggies". Aliasing is the stair-step effect on the edges of objects and can be extremely distracting for the PC user. The only way to combat aliasing is to create the effect of having more pixels on the screen. Historically, increasing the resolution was the best solution to this problem. The size of the "jaggy" or stair-step artifact is never larger than the size of the actual pixel. Hence, reducing the size of the pixel reduces the size of these artifacts. Changing the resolution is not always feasible, however. The user may already be using the maximum resolution
|supported by the monitor or the application itself may limit the resolution. Beyond these hard limits the only solution is to increase the effective resolution. The best way to do this is to use more sophisticated techniques for computing the color of each pixel of the display in a way that simulates having more pixels. These techniques are referred to as "antialiasing." |
"Supersampling" is an antialiasing technique that is simply a brute-force approach and is used in NVIDIA's GeForce2 GPUs and other modern graphics processors. A graphics processor that uses supersampling renders the screen image at a much higher resolution than the current display mode, and then scales and filters the image to the final resolution before it is sent to the display. A variety of methods exist for performing this operation, but each requires the graphics processor to render as many additional pixels as required by the supersampling method. Additionally, because the graphics processor is rendering more actual pixels than will be displayed, it must scale and filter those pixels down to the resolution for final display. This scaling and filtering can further reduce performance.
Multisampling: The Solution
The biggest problem with supersampling is performance. Users don't want to see their frame rate fall to one-half or one-fourth of what it should be. Multisampling is a more sophisticated technique than supersampling that involves higher quality output than standard rendering with much higher performance—a win/win scenario compared to either alternative. Multisampling requires a more sophisticated GPU, however, so only the newest GPUs available support this technique. The basic idea behind multisampling is to embed the intelligence behind antialiasing inside the core of the
GPU, in hardware. This makes the GPU more complex, but rewards the user with higher quality and higher performance. Multisampling works because the GPU itself is "aware" that multiple samples will be used to calculate the final pixel color."
You can think of these extra samples as extra "virtual pixels. The GeForce3 GPU has wider data paths internally so it can handle these extra virtual pixels without slowing down its standard rendering speed. In fact, the GeForce3 GPU can compute these "virtual pixels" or additional samples at full speed, with no reduction in engine performance whatsoever. These wider data paths enable GeForce3 to use the same texture data for all of the samples in the pixel and significantly reduce the memory bandwidth required to texture all of the AA samples.