A graphics subsystem in which a very fast clear operation is performed without the need to address each pixel, and without using memories which include a hardware fast-clear capability. This is implemented by using a reference frame counter: the window is divided up into n regions, where n is the...http://www.google.fr/patents/US5805868?utm_source=gb-gplus-shareBrevet US5805868 - Graphics subsystem with fast clear capability
