How to fill outside of a polygon?

[talhazengin]

I could not do it.
Help me thanks.

[talhazengin]

I did this, but this methodology does not perform well. I need new ideas.

        for (int y = 0; y < image.Height; y++)
        {
            Span<Rgba32> pixelRowSpan = image.GetPixelRowSpan(y);
            
            for (int x = 0; x < image.Width; x++)
            {
                if (!polygon.Contains(new PointF(x, y)))
                {
                    pixelRowSpan[x] = myColorRgba;
                }
            }
        }

[tocsoft]

yeah don't do that, you can just clip the path out of a rectangle the size of your canvas... i've an example in my answer

[tocsoft]

The process would be to create a rectangle the size of your canvas, then clip from that rectangle the polygon you have this will give you a new polygon of the negative space, you then just fill it. this is an example extension method that can do it for you for simple colors.

public static class ImageExtensions
{
    public static IImageProcessingContext FillOuter(
        this IImageProcessingContext source,
        Color brush,
        IPath path)
    {
        var rectangle = new RectangularPolygon(PointF.Empty, source.GetCurrentSize());
        var clipped = rectangle.Clip(path);
        return source.Fill(brush, clipped);
    }
}

An example of use

Black circle on white background

var circle1 = new EllipsePolygon(new PointF(100, 100), 50);
var circle3 = new EllipsePolygon(new PointF(100, 100), 20);

var path2 = circle1.Clip(circle3);
using (var img = new Image<Rgba32>(300, 300, Color.White))
{
    img.Mutate(x => x.Fill(Color.Black, path2));
    img.Save("InnerFill2.png"); 
}

and the inverse fill

var circle1 = new EllipsePolygon(new PointF(100, 100), 50);
var circle3 = new EllipsePolygon(new PointF(100, 100), 20);

var path2 = circle1.Clip(circle3);
using (var img = new Image<Rgba32>(300, 300, Color.White))
{
    img.Mutate(x => x.FillOuter(Color.Black, path2));
    img.Save("InnerFillOuter2.png");
}

[talhazengin]

Thank you, good answer.