Pixel Merge Unit

Abstract

Multi-sample anti-aliasing is a popular technique for reducing geometric aliasing (jagged edges) and is supported in all modern graphics processors. With multi-sampling anti-aliasing, visibility and depth are sampled more than once per pixel, while shading is done only once per pixel per primitive. Although this significantly reduces the appearance of jagged edges around object boundaries, the image quality improvement in non-silhouette regions is hardly noticeable. We propose a hardware unit, called the pixel merge unit, which is located just after the early depth test unit but before the pixel shader. Our unit attempts to reduce the shading rate to once per pixel per group of connected primitives covering a pixel using a novel merging strategy. We demonstrate up to 15% reduction in pixel shader executions. Given the simple implementation that we propose, this is a substantial reduction.