How is a Filled Polygon Different From an Unfilled One?

When an unfilled polygon is rendered, only the points on the perimeter of the polygon are drawn. Examples of unfilled polygons are shown in the polygon type demos on the previous page.

However, when a polygon is filled, the interior of the polygon must be considered. All of the pixels within the boundaries of the polygon must be set to the specified color or pattern. Here, we deal only with solid colors. The following application demonstrates the difference between filled and unfilled polygons.

In order to determine which pixels are inside the polygon, the odd-parity rule is used within the scan-line polygon fill algorithm. This is discussed next.

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