Overlay graphics memory management method and apparatus

Abstract

The invention frees up memory to other uses by allocating memory to video graphics buffering only to the extent required. It also saves graphic processor bandwidth by processing, e.g. blending, only to the extent required. It does so by defining a regular grid of so-called tiles or cells in the overlay graphic data window, e.g orthogonally arrayed squares of 32-pixel sides, and allocating memory only to those requiring update, i.e. only those that are visible and subject to change between successive frames. Allocation is dynamic and requires little tagging overhead to keep track of the tiles in memory by location in the video graphic window. Processing is only of those tiles for which memory is allocated, since entirely transparent tiles within the window require no blending or processing whatsoever because they are invisible. In one implementation, only onscreen buffered graphics are tiled and the offscreen buffered graphics require full-sized memory allocation and in another offscreen buffered graphics are tiled also by clipping within variously sized buffers during successive passes through a drawing operation wherein the various sized buffers all are smaller than the entire window. New offscreen buffer-processed tiles may be swapped as they are processed for existing (visible) onscreen tiles directly, when there is less available memory, or new tiles may be processed and block-stored in memory until a wholesale swap can occur invisibly, when there is more memory available.