Texture On Demand

Darwyn Peachey

Abstract:

Texture On Demand (TOD) is a technique for organizing large amounts of stored texture data in disk files and accessing it efficiently. Simply reading entire texture images into memory is not a good solution for real memory systems or for virtual memory systems. Texture data should be read from disk files only on demand. In the TOD technique, each texture image is stored as a sequence of fixed-size rectangular regions called tiles, rather than in the conventional raster scanline order. Tiles are an appropriate unit of texture data to read into memory on demand. As fixed-size units with good locality of reference in a variety of rendering schemes, tiles can be cached in main memory using the paging algorithms common in virtual memory systems. Good results have been obtained using an LRU tile replacement algorithm to select a tile to be deleted when main memory space is required.

Prefiltered textures are an important means of limiting bandwidth. TOD uses a set of prefiltered texture images called an r-set, a generalization of the texture pyramid (mip map). Texture filtering methods are reconsidered in terms of their performance in the TOD environment. Efficient filtering methods using the r-set are described.

The paper describes various implementations of TOD, including a virtual memory implementation and a distributed implementation on a 16-processor multicomputer.

Available as Pixar Technical Memo #217