ATI CrossFire Technology White Paper

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esolution. This method has two main disadvantages. First, it requires rendering many more pixels than normal, which can have a drastic impact on performance. Second, it results in an ordered grid sample pattern, which does a poor job of anti-aliasing some types of jagged edges (specifically those that are nearly vertical or nearly horizontal, which tend to result in the most noticeable problems). Super AA overcomes both of these problems. It takes advantage of the second GPU to render the additional pixels required for each frame, so there is little or no performance impact. Also, it can make use of a more effective sample pattern (known as a rotated grid) that does a better job of anti-aliasing near-horizontal and near-vertical edges, resulting in better overall image quality. Two of the new Super AA modes use a combination of MSAA and SSAA to achieve the ultimate in image quality. They work by not only using different sample multi-sample locations on each GPU, but by also offsetting the pixel centers slightly as well. In effect, each GPU renders the image from a different viewpoint, about half a pixel width apart. The new 10x and 14x Super AA modes operate in this way, combining 2x SSAA with 4x and 6x MSAA respectively. 6x 6x AA AA 14x 14x SuperAA SuperAA Comparison of SmoothVision HD 6x Anti-Aliasing (left) and new 14x Super AA mode (right). Note how the branches and leaves look smoother and less pixelated in the image on the right. Images taken from Half-Life 2 by Valve Software. - 11 -
Anti-Aliasing Sample Patterns An added benefit of these modes is that they work together with SmoothVision HD Anisotropic Filtering (AF). This is a high quality filtering technique designed to produce sharper, clearer textures by blending multiple texture samples (2, 4, 8, or 16) for each pixel. Since Super AA can render each pixel from two slightly different viewpoints and combine them, the texture samples from each viewpoint get combined as well. This means the number of texture samples per pixel is effectively doubled, so up to 32x Anisotropic Filtering can be supported. The new Super AA modes can be enabled by users through the <strong>ATI</strong> Catalyst Control Center interface. New SmoothVision HD Anti-Aliasing Slider in Catalyst Control Center - 12 -
Page 1 and 2: ATI CrossFire Technology White Pap
Page 3 and 4: Background The world around us poss
Page 5 and 6: CrossFire - How it Works CrossFire
Page 7 and 8: Alternate Frame Rendering (AFR) Mod
Page 9 and 10: Scissor Mode In this mode, each fra
Page 11: Super AA Mode 6x AA 12x SuperAA Com

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