ATI X1900 User Guide - Page 117

CrossFire™ Rendering Modes 109 The main limitation of this mode is that it cannot be used in applications where the appearance of the current frame is dependent upon data generated in previous frames, since AFR generates successive frames simultaneously on different GPUs. In these cases, the SuperTiling or Scissor Mode is used instead. Super Anti-aliasing Mode Anti-aliasing (AA) is a rendering technique designed to remove jagged edges, shimmering, and pixelation problems that are common in rendered 3D images. Rather than simply determining the color of each pixel on the screen by sampling a single location at the pixel's center, anti-aliasing works by sampling multiple locations within each pixel and blending the results together to determine the final color. The latest generation of ATI's Radeon® GPUs with SmoothVision™ HD technology uses a method known as Multi-sample Anti-aliasing (MSAA). This method takes samples from 2, 4, or 6 programmable locations within each pixel, and uses gamma correct sample blending for high-quality smoothing of polygon edges. The new CrossFire Super Anti-aliasing mode takes advantage of the programmable sample capability of SmoothVision™ HD to provide higher quality anti-aliasing on CrossFire™ systems. It works by having each GPU render the same frame with anti-aliasing enabled, but uses different sample locations for each. When both versions of the frame are completed, they are blended in the CrossFire Compositing engine. The resulting image has effectively twice the number of samples, so 4x and 6x Anti-aliasing becomes 8x and 12x Super Anti-aliasing, respectively.