Patent ID: 7408549

Claim:
A graphics system comprising: a frame buffer configured to store an array of data structures corresponding to an array of pixels, wherein each data structure, corresponds to a single pixel, and includes N slots and a tag, wherein N is an integer greater than or equal to two, wherein each of the N slots is configured to store a color value and z value for a corresponding fragment, wherein the tag indicates, for each of the N slots, whether the slot is empty, wherein the tag also indicates an ordering according to z value for the slots that are non-empty; a processing unit configured to: (a) generate a new fragment corresponding to a first pixel, wherein the new fragment specifies a color value and z value, (b) read the tag from the data structure corresponding to the first pixel, (c) examine the tag to determine if there is at least one empty slot among the N slots of the data structure; (d) compare the z value of the new fragment to the two largest z values among the z values in the N slots of the data structure if said examination of the tag determines that there are no empty slots in the data structure; and (e) if said comparison determines that the z value of the new fragment is smaller than the two largest z values: blend color values of the two slots corresponding to the two largest z values as indicated by the tag to obtain a resultant color, compose a resultant fragment from the resultant color and the smaller of the two largest z values, and write the resultant fragment to one of the two slots and write the new fragment to the other of the two slots.