Graphics accelerator area fill system

A graphics accelerator system which provides improved image rendering speed. One significant bottleneck in such systems is the step of filling in a defined area, i.e. identifying every pixel in the interior of a given polygonal shape. One commonly used operation of this type is a "fill area set" operation. In a first mode of operation, the disclosed system very rapidly calculates the interior of a complex bounding polygon, by performing sequential XOR operations on shapes which are complementary to the various boundary elements of the polygon. An important advantage of this is that such XOR operations can be highly parallel. If two bounding polygons in the fill area set intersect, this mode of operation will not correctly identify points which are interior to both bounding polygons. In some applications this is generally recognized as acceptable; but in other cases this is not acceptable. Conventionally, where overlapping polygons must be precisely handled by fill area set calculations, winding number calculations are used to distinguish between pixels which are not in the interior and pixels which are doubly in the interior. In a second mode of operation, the disclosed system performs rapid fill area set calculations, even if winding number calculations are necessary. This embodiment differs from the first embodiment in that binary arithmetic operations are used instead of XOR operations, but this embodiment too permits the use of a very high degree of parallelism. The boundary elements of the bounding polygon do not have to be strictly limited to line segments, but may include curves.