Z3: an economical hardware technique for high-quality antialiasing and transparency

In this paper we present an algorithm for low-cost hardware antialiasing and transparency. This technique keeps a central Z value along with 8-bit floating-point Z gradients in the X and Y dimensions for each fragment within a pixel (hence the name Z 3). It uses a small fixed amount of storage per pixel. If there are more fragments generated for a pixel than the space available, it merges only as many fragments as necessary in order to fit in the available per-pixel memory. The merging occurs on those fragments having the closest Z values. This combines different fragments from the same surface, resulting in both storage and processing efficiency. When operating with opaque surfaces, Z 3 can provide superior image quality over sparse supersampling methods that use eight samples per pixel while using storage for only three fragments. Z 3 also makes the use of large numbers of samples (e.g., 16) feasible in inexpensive hardware, enabling higher quality images. It is simple to implement because it uses a small fixed number of fragments per pixel. Z can also provide order-independent transparency even if many transparent surfaces are present. Moreover, unlike the original A-buffer algorithm it correctly antialiases interpenetrating transparent surfaces because it has three-dimensional Z information within each pixel.