An application fills the interior of a path using one of two fill modes: alternate or winding. The mode determines how to fill and clip the interior of a closed figure.
The default mode is xtd::drawing::drawin2d::fill_mode::alternate. To determine the interiors of closed figures in the alternate mode, draw a line from any arbitrary start point in the path to some point obviously outside the path. If the line crosses an odd number of path segments, the starting point is inside the closed region and is therefore part of the fill or clipping area. An even number of crossings means that the point is not in an area to be filled or clipped. An open figure is filled or clipped by using a line to connect the last point to the first point of the figure.
The xtd::drawing::drawin2d::fill_mode::winding mode considers the direction of the path segments at each intersection. It adds one for every clockwise intersection, and subtracts one for every counterclockwise intersection. If the result is nonzero, the point is considered inside the fill or clip area. A zero count means that the point lies outside the fill or clip area.
A figure is considered clockwise or counterclockwise based on the order in which the segments of the figure are drawn.