Sprite engine

Abstract

A sprite engine or compositor that is well-adapted to a variety ofadaptable to a host platforms and that minimizes the amount of drawing that occurs on a refresh of a framebuffer display area. The invention exploits the host platform's abilities to perform both back-to-front and front-to-back drawing algorithms, where the choice of algorithm used depends upon whether a sprite is opaque or transparent. Each sprite registers itself with a sprite engine, identifying whether or not the sprite is wholly opaque or notis transparent, the bounding area of the sprite, and the function that the sprite uses to draw. The function can be the drawing routine that is available from the host platform or operating system. The sprite engine keeps track of the Z position of each sprite and examines each sprite to determine if the sprite overlaps a particular region that needs to be refreshed. Sprites that are rectangular and opaque are considered special cases that can be easily drawn using athe host platform's front-to-back drawing algorithm. In a top-down manner, by Z position, all sprites that are opaque are allowed to draw. All other kinds of sprites are drawn in a back-to-front manner. When a transparent sprite is found, the sprite engine searches the remaining sprites in a bottom-up manner and draws the sprites with a Z position below the transparent sprite, finishing with the transparent sprite, using a back-to-front algorithm in the remaining region.