Cases for Subdivisions of Polygon
No additional subdivisions of a particular area are desired, if one of the subsequent conditions is true as:
Case 1: All the polygons are disjoint from the region. In this condition, the background color can be displayed in the region.
Case 2: Accurately one polygon faces, after projection, comprised or intersecting in the square region. In this condition the area is first filled along with the background color, and after that the part of the polygon comprised in the region is scan converted.
Case 3: There is a particular surrounding polygon, although no intersecting or comprised polygons. In this condition the region is filled along with the color of the surrounding polygon.
Case 4: More than one polygon is contained in surrounding the area, although one is a surrounding polygon which is in front of all another polygon. Finding whether a surrounding polygon is in front is done through computing the z coordinates of the planes of all surrounding, contained and intersecting polygons at the four corners of the area; if there is a surrounding polygon that four corner z coordinates are larger than one that of any other polygons so the entire region can be filled along with the color of this surrounding polygon.