Z test and conditional merger of colliding pixels during batch building

摘要

Frame buffer memory bandwidth is conserved by performing a depth comparison between colliding pixels at batch building time. If the incoming pixel fails the depth comparison, then it may be "tossed" and excluded from any batches currently under construction. The batch building process may then continue without the need for a batch flush responsive to the occurrence of the pixel collision. If the incoming pixel passes the depth comparison, then it may yet be possible to avoid flushing: The current rendering mode of the pipeline is determined. If the current rendering mode does not require read-modify-write operations, then the incoming pixel may be merged with the buffered pixel with which it collides. Merger of the two pixels may be accomplished by overwriting the buffered RGBA pixel components with those of the incoming pixel, but only those components corresponding to asserted bits in the incoming pixel's BEN. The buffered BEN may be replaced with the logical OR of the stored BEN and the incoming pixel's BEN.