Decomposition of arbitrary polygons into trapezoids

Abstract

A technique for decomposing any simple or complex arbitrary polygon into a trapezoid having at least one edge parallel to the scan direction for more efficient scan conversion by rasterization circuitry. An input polygon is split into 'slabs', which are adjacent regions bounded by lines parallel to the scan direction. Initially the polygon is split at the y coordinate of every vertex to define the slabs. Then, for each slab, it is determined which edges are present in the slab and whether there are any unacceptable edge intersections. If an unacceptable edge intersection is found in a slab, that slab is broken into two or more slabs at the y coordinates of the intersection points of the edges. Each of the slabs is then processed independently. Once no unacceptable intersections are found in any slab, trapezoids are rendered from adjacent pairs of edges and sent to the rasterization circuitry. Since edge intersections may be accounted for in accordance with the invention, any input polygon, no matter how complex, may be correctly rendered in an efficient manner.