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Winding modes

  • Artikkeli

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.NET Multi-platform App UI (.NET MAUI) graphics provides a WindingMode enumeration that enables you to specify the fill algorithm to be used by the FillPath method. Contours in a path can overlap, and any enclosed area can potentially be filled, but you might not want to fill all the enclosed areas. For more information about paths, see Draw a path.

The WindingMode enumeration defines NonZero and EvenOdd members. Each member represents a different algorithm for determining whether a point is in the fill region of an enclosed area.

Note

The ClipPath method has an overload that enables a WindingMode argument to be specified. By default, this argument is set to WindingMode.NonZero.

NonZero

The NonZero winding mode draws a hypothetical ray from the point to infinity in any direction and then examines the places where a path contour crosses the ray. The count starts at zero and is incremented each time a contour crosses the ray from left to right and decremented each time a contour crosses the ray from right to left. If the count of crossings is zero, the area isn't filled. Otherwise, the area is filled.

The following example fills a five-pointed star using the NonZero winding mode:

float radius = 0.45f * Math.Min(dirtyRect.Width, dirtyRect.Height);

PathF path = new PathF();
path.MoveTo(dirtyRect.Center.X, dirtyRect.Center.Y - radius);

for (int i = 1; i < 5; i++)
{
    double angle = i * 4 * Math.PI / 5;
    path.LineTo(new PointF(radius * (float)Math.Sin(angle) + dirtyRect.Center.X, -radius * (float)Math.Cos(angle) + dirtyRect.Center.Y));
}
path.Close();

canvas.StrokeSize = 15;
canvas.StrokeLineJoin = LineJoin.Round;
canvas.StrokeColor = Colors.Red;
canvas.FillColor = Colors.Blue;
canvas.FillPath(path); // Overload automatically uses a NonZero winding mode
canvas.DrawPath(path);

In this example, the path is drawn twice. The FillPath method is used to fill the path with blue, while the DrawPath method outlines the path with a red stroke. The FillPath overload used omits the WindingMode argument, and instead automatically uses the NonZero winding mode. This results in all the enclosed areas of the path being filled:

Screenshot of a five-pointed star, using the non-zero winding mode.

Note

For many paths, the NonZero winding mode often fills all the enclosed areas of a path.

EvenOdd

The EvenOdd winding mode draws a hypothetical ray from the point to infinity in any direction and counts the number of path contours that the ray crosses. If this number is odd, then the area is filled. Otherwise, the area isn't filled.

The following example fills a five-pointed star using the EvenOdd winding mode:

float radius = 0.45f * Math.Min(dirtyRect.Width, dirtyRect.Height);

PathF path = new PathF();
path.MoveTo(dirtyRect.Center.X, dirtyRect.Center.Y - radius);

for (int i = 1; i < 5; i++)
{
    double angle = i * 4 * Math.PI / 5;
    path.LineTo(new PointF(radius * (float)Math.Sin(angle) + dirtyRect.Center.X, -radius * (float)Math.Cos(angle) + dirtyRect.Center.Y));
}
path.Close();

canvas.StrokeSize = 15;
canvas.StrokeLineJoin = LineJoin.Round;
canvas.StrokeColor = Colors.Red;
canvas.FillColor = Colors.Blue;
canvas.FillPath(path, WindingMode.EvenOdd);
canvas.DrawPath(path);

In this example, the path is drawn twice. The FillPath method is used to fill the path with blue, while the DrawPath method outlines the path with a red stroke. The FillPath overload used specifies that the EvenOdd winding mode is used. This mode results in the central area of the star not being filled:

Screenshot of a five-pointed star, using the even-odd winding mode.