QtWindingFill

QtWindingFill is a mode used in Qt's graphics subsystem for determining how to fill complex shapes, particularly those with self-intersections or holes. It is one of two available fill rules, the other being Qt.OddEvenFill. The winding fill rule calculates the fill region by considering the direction in which the path segments are drawn.

When a point is evaluated, Qt traces a ray from that point infinitely in one direction. It then counts how many times the path segments cross this ray. For winding fill, the count is incremented for segments crossing the ray in one direction (e.g., counter-clockwise) and decremented for segments crossing in the opposite direction (e.g., clockwise). If the final count is non-zero, the point is considered inside the shape and is filled. A zero count indicates the point is outside.

This method effectively distinguishes between the "inside" and "outside" of a shape, even if the shape is intricate. It is particularly useful for creating effects like holes within shapes or for drawing paths that cross over themselves. The winding fill rule is a standard algorithm in computer graphics for handling complex polygon filling.