Scan-Line Polygon Fill Algorithm

The Scan-Line Polygon Fill Algorithm is a computer graphics algorithm used to fill the interior of a polygon with a specified color. The algorithm works by dividing the polygon into a set of horizontal scan lines and determining which pixels on each line lie within the polygon. The pixels within the polygon are then colored with the specified fill color.

The steps of the Scan-Line Polygon Fill Algorithm can be summarized as follows:

1. Sort the vertices of the polygon in order of increasing y-coordinate.

2. For each scan line between the smallest and largest y-coordinate of the polygon:

   a. Determine the intersection points of the scan line with each edge of the polygon, and sort them in order of increasing x-coordinate.

   b. Fill in the pixels between each pair of adjacent intersection points on the scan line, using the specified fill color.

The intersection points of the scan line with each edge of the polygon can be determined using the following equation:

x = (y - y1) * (x2 - x1) / (y2 - y1) + x1

where (x1, y1) and (x2, y2) are the endpoints of the edge, and y is the y-coordinate of the current scan line.

The Scan-Line Polygon Fill Algorithm is efficient and produces accurate results, making it a popular choice for polygon filling in computer graphics. It can also be extended to handle polygons with holes and other complex shapes. However, it may be susceptible to issues such as edge cases and overlapping polygons, which can be addressed using various techniques such as edge flagging and depth buffering.