Fast Clear Technique for Raster Displays
Original Publication Date: 1983-Aug-01
Included in the Prior Art Database: 2005-Feb-07
This article describes a technique for improving the performance of the clear bit plane function on a block-structured raster display system. Clearing the bit planes of a raster display involves setting every bit to zero. This may be a bit at a time, a word at a time or a block at a time, depending on the system. In the latter case a block typically consists of 16 x 16 bits. However, even with block updates, the clear function occupies a significant time. This may be reduced by maintaining a map having a single bit position for each bit plane block, the bit being set when at least one 'ON' pel is written into the corresponding block. Thus, the clear function can inspect the map and need only clear those blocks which contain 'ON' pels.