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Figure 1: Ambient occlusion without any shading. (left) 67 MPixels/s with our horizon-based algorithm. (right) 15 MPixels/s with ray marching and 4 rays per direction. Images rendered with N d = 8 and N s = 8 on GeForce 8800 GTX Ultra.

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Figure 1: Example effects using the k-buffer for multi-fragment processing. The Lucy model (28,055,742 triangles) is rendered with transparency on the left and with translucency on the right. These effects captured 8 fragments per pixel in a single geometry pass and were rendered with a current hardware implementation that avoids read-modify-write hazards. With our proposed extension to hardware, these hazards can be automatically avoided and performance improved. AbstractMany interactive rendering algorithms require operations on multiple fragments (i.e., ray intersections) at the same pixel location; however, current Graphics Processing Units (GPUs) capture only a single fragment per pixel. Example effects include transparency, translucency, constructive solid geometry, depth-of-field, direct volume rendering, and isosurface visualization. With current GPUs, programmers implement these effects using multiple passes over the scene geometry, often substantially limiting performance. This paper introduces a generalization of the Z-buffer, called the k-buffer, that makes it possible to efficiently implement such algorithms with only a single geometry pass, yet requires only a small, fixed amount of additional memory. The k-buffer uses framebuffer memory as a read-modify-write (RMW) pool of k entries whose use is programmatically defined by a small k-buffer program. We present two proposals for adding k-buffer support to future GPUs and demonstrate numerous multiple-fragment, single-pass graphics algorithms running on both a software-simulated k-buffer and a k-buffer implemented with current GPUs. The goal of this work is to demonstrate the large number of graphics algorithms that the k-buffer enables and that the efficiency is superior to current multipass approaches.

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