Weiler-Atherton polygon clipping algorithm

The Weiler-Atherton polygon clipping algorithm is a method for clipping a polygon against another polygon. It works by finding the intersection points between the two polygons and using them to construct a new polygon that lies completely inside the clipping polygon.

The algorithm works as follows:

1. Identify all intersection points between the clip polygon and the subject polygon.

2. Divide the subject polygon into regions bounded by the intersection points.

3. For each region, determine whether it is inside or outside the clip polygon by testing whether a point known to be outside the clip polygon (such as a point at infinity) lies inside or outside the region.

4. Construct a new polygon by connecting the intersection points in the correct order.

5. Repeat steps 3 and 4 for each region to produce a set of clipped polygons.

The Weiler-Atherton algorithm is capable of handling concave polygons and multiple disjoint polygons, and it can be more efficient than the Sutherland-Hodgman algorithm for certain types of input. However, it can be more complex to implement and may require additional data structures to represent the polygons and their intersection points.