ImageSharp/samples/AvatarWithRoundedCorner/Program.cs

namespace AvatarWithRoundedCorner
{
    using System;
    using System.Numerics;
    using ImageSharp;
    using SixLabors.Primitives;
    using SixLabors.Shapes;

    static class Program
    {
        static void Main(string[] args)
        {
            System.IO.Directory.CreateDirectory("output");
            using (var img = Image.Load("fb.jpg"))
            {
                // as generate returns a new IImage make sure we dispose of it
                using (Image<Rgba32> destRound = img.Clone(x => x.ConvertToAvatar(new Size(200, 200), 20)))
                {
                    destRound.Save("output/fb.png");
                }

                using (Image<Rgba32> destRound = img.Clone(x => x.ConvertToAvatar(new Size(200, 200), 100)))
                {
                    destRound.Save("output/fb-round.png");
                }

                using (Image<Rgba32> destRound = img.Clone(x => x.ConvertToAvatar(new Size(200, 200), 150)))
                {
                    destRound.Save("output/fb-rounder.png");
                }

                using (Image<Rgba32> destRound = img.CloneAndConvertToAvatarWithoutApply(new Size(200, 200), 150))
                {
                    destRound.Save("output/fb-rounder-without-apply.png");
                }

                // the original `img` object has not been altered at all.
            }
        }

        // 1. The short way: 
        // Implements a full image mutating pipeline operating on IImageProcessingContext<Rgba32>
        // We need the dimensions of the resized image to deduce 'IPathCollection' needed to build the corners,
        // so we implement an "inline" image processor by utilizing 'ImageExtensions.Apply()'
        private static IImageProcessingContext<Rgba32> ConvertToAvatar(this IImageProcessingContext<Rgba32> processingContext, Size size, float cornerRadius)
        {
            return processingContext.Resize(new ImageSharp.Processing.ResizeOptions
            {
                Size = size,
                Mode = ImageSharp.Processing.ResizeMode.Crop
            }).Apply(i => ApplyRoundedCorners(i, cornerRadius));
        }

        // 2. A more verbose way, avoiding 'Apply()':
        // First we create a resized clone of the image, then we draw the corners on that that instance it with Mutate().
        private static Image<Rgba32> CloneAndConvertToAvatarWithoutApply(this Image<Rgba32> image, Size size, float cornerRadius)
        {
            Image<Rgba32> result = image.Clone(
                ctx => ctx.Resize(
                    new ImageSharp.Processing.ResizeOptions
                        {
                            Size = size,
                            Mode = ImageSharp.Processing.ResizeMode.Crop
                        }));

            ApplyRoundedCorners(result, cornerRadius);
            return result;
        }

        // This method can be seen as an inline implementation of an `IImageProcessor`:
        // (The combination of `IImageOperations.Apply()` + this could be replaced with an `IImageProcessor`)
        public static void ApplyRoundedCorners(Image<Rgba32> img, float cornerRadius)
        {
            IPathCollection corners = BuildCorners(img.Width, img.Height, cornerRadius);

            // mutating in here as we already have a cloned original
            img.Mutate(x => x.Fill(Rgba32.Transparent, corners, new GraphicsOptions(true)
            {
                BlenderMode = ImageSharp.PixelFormats.PixelBlenderMode.Src // enforces that any part of this shape that has color is punched out of the background
            }));
        }

        public static IPathCollection BuildCorners(int imageWidth, int imageHeight, float cornerRadius)
        {
            // first create a square
            var rect = new RectangularePolygon(-0.5f, -0.5f, cornerRadius, cornerRadius);

            // then cut out of the square a circle so we are left with a corner
            IPath cornerToptLeft = rect.Clip(new EllipsePolygon(cornerRadius - 0.5f, cornerRadius - 0.5f, cornerRadius));

            // corner is now a corner shape positions top left
            //lets make 3 more positioned correctly, we can do that by translating the orgional artound the center of the image
            var center = new Vector2(imageWidth / 2F, imageHeight / 2F);

            float rightPos = imageWidth - cornerToptLeft.Bounds.Width + 1;
            float bottomPos = imageHeight - cornerToptLeft.Bounds.Height + 1;

            // move it across the widthof the image - the width of the shape
            IPath cornerTopRight = cornerToptLeft.RotateDegree(90).Translate(rightPos, 0);
            IPath cornerBottomLeft = cornerToptLeft.RotateDegree(-90).Translate(0, bottomPos);
            IPath cornerBottomRight = cornerToptLeft.RotateDegree(180).Translate(rightPos, bottomPos);

            return new PathCollection(cornerToptLeft, cornerBottomLeft, cornerTopRight, cornerBottomRight);
        }
    }
}