SquircleProcessor for ImageSharp

SquircleProcessor.cs

using System;
using System.Collections.Generic;
using SixLabors.ImageSharp;
using SixLabors.ImageSharp.PixelFormats;
using SixLabors.ImageSharp.Processing;
using SixLabors.Primitives;
using SixLabors.Shapes;

namespace EQL.ImageSharp
{
    public static class SquircleProcessor
    {
        // Example use 4 as factor for iOS 7 style
        public static IImageProcessingContext ApplySquircle(this IImageProcessingContext ctx, float factor)
        {
            Size size = ctx.GetCurrentSize();
            IPathCollection corners = BuildCorners(size.Width, size.Height, factor);
            var graphicOptions = new GraphicsOptions(true)
            {
                AlphaCompositionMode = PixelAlphaCompositionMode.DestOut
            };
            return ctx.Fill(graphicOptions, Rgba32.Black, corners);
        }

        private static PointF CalculateSquirclePoint(float degrees, float radius, SizeF size)
        {
            var theta = (float)(degrees * (Math.PI / 180));
            var x = MathF.Pow(MathF.Abs(MathF.Cos(theta)), 2 / radius) * 0.5f * MathF.Sign(MathF.Cos(theta)) + 0.5f;
            var y = MathF.Pow(MathF.Abs(MathF.Sin(theta)), 2 / radius) * 0.5f * MathF.Sign(MathF.Sin(theta)) + 0.5f;
            return new PointF(x * size.Width, y * size.Height);
        }

        private static IPathCollection BuildCorners(int imageWidth, int imageHeight, float factor)
        {
            factor = MathF.Max(MathF.Min(factor, 100), 0.00000000001f);

            var size = new SizeF(imageWidth, imageHeight);

            var points = new List<PointF>();
            var maxDimension = Math.Max(imageWidth, imageHeight);
            for (var i = 0; i < maxDimension; i++)
            {
                var degrees = (360.0f / maxDimension) * i;
                points.Add(CalculateSquirclePoint(degrees, factor, size));
            }

            var pathBuilder = new PathBuilder();
            pathBuilder.AddLines(points.ToArray());
            pathBuilder.CloseFigure();

            var rect = new RectangularPolygon(0, 0, imageWidth, imageHeight);
            return new PathCollection(rect.Clip(pathBuilder.Build()));
        }
    }
}