Fast clear technique for display regions having subregions

摘要

A technique for performing clear operations in a region having a subregion. Responsive to a first clear command: perform an initialization in which stale information is eliminated from pixels outside the subregion. Responsive to subsequent clear commands: update a current clear count for the region; and write the updated current clear count into clear count values associated with pixels outside the subregion. Prior to creating the subregion, a conventional fast clear technique may be employed in the region. After creating the subregion and during its life, the inventive technique may be employed. After the subregion is discontinued, the conventional technique may once again be employed. The inventive technique may be employed optionally depending on the percentage of the region's area occupied by the subregion.