[1] The A-buffer method is a descendant of the well known Z-buffer, which provides good quality results in moderate time.
In 3-D image synthesis system, the balance between the quality and the cost of computation has always been needed.
A-buffer helps in using visibility techniques and supports all conceivable geometric modeling primitives: polygons, patches, quadrics, fractals, and so forth.
When all polygons intersecting a pixel have been processed, the area-weighted average of the colors of the pixel's visible surfaces is obtained by selecting fragments in depth-sorted order and using their bit masks to clip those of farther fragments.
Thus, the algorithm must make assumptions about the sub-pixel geometry in cases in which fragment bit masks overlap in z.