ImageSharp/ImageSharp.Drawing/RoundedRectanglePolygon.cs

// Copyright (c) Six Labors.
// Licensed under the Six Labors Split License.

using System;
using System.Numerics;

namespace SixLabors.ImageSharp.Drawing {
  /// <summary>
  /// A closed rectangular path with rounded corners.
  /// </summary>
  public sealed class RoundedRectanglePolygon : Polygon
  {
      /// <summary>
      /// Initializes a new instance of the <see cref="RoundedRectanglePolygon"/> class.
      /// </summary>
      /// <param name="rectangle">The rectangle bounds.</param>
      /// <param name="radius">The x and y radius of each corner.</param>
      public RoundedRectanglePolygon(RectangleF rectangle, float radius)
          : this(rectangle, new SizeF(radius, radius))
      {
      }

      /// <summary>
      /// Initializes a new instance of the <see cref="RoundedRectanglePolygon"/> class.
      /// </summary>
      /// <param name="rectangle">The rectangle bounds.</param>
      /// <param name="radius">The x and y radii of each corner.</param>
      public RoundedRectanglePolygon(RectangleF rectangle, SizeF radius)
          : base(CreateSegments(rectangle, radius))
      {
      }

      /// <summary>
      /// Initializes a new instance of the <see cref="RoundedRectanglePolygon"/> class.
      /// </summary>
      /// <param name="x">The x-coordinate of the rectangle.</param>
      /// <param name="y">The y-coordinate of the rectangle.</param>
      /// <param name="width">The rectangle width.</param>
      /// <param name="height">The rectangle height.</param>
      /// <param name="radius">The x and y radius of each corner.</param>
      public RoundedRectanglePolygon(float x, float y, float width, float height, float radius)
          : this(new RectangleF(x, y, width, height), radius)
      {
      }

      /// <summary>
      /// Initializes a new instance of the <see cref="RoundedRectanglePolygon"/> class.
      /// </summary>
      /// <param name="x">The x-coordinate of the rectangle.</param>
      /// <param name="y">The y-coordinate of the rectangle.</param>
      /// <param name="width">The rectangle width.</param>
      /// <param name="height">The rectangle height.</param>
      /// <param name="radius">The x and y radii of each corner.</param>
      public RoundedRectanglePolygon(float x, float y, float width, float height, SizeF radius)
          : this(new RectangleF(x, y, width, height), radius)
      {
      }

      private RoundedRectanglePolygon(ILineSegment[] segments)
          : base(segments, true)
      {
      }

      /// <inheritdoc />
      public override IPath Transform(Matrix4x4 matrix)
      {
          if (matrix.IsIdentity)
          {
              return this;
          }

          ILineSegment[] segments = new ILineSegment[this.LineSegments.Count];

          for (int i = 0; i < segments.Length; i++)
          {
              segments[i] = this.LineSegments[i].Transform(matrix);
          }

          return new RoundedRectanglePolygon(segments);
      }

      private static ILineSegment[] CreateSegments(RectangleF rectangle, SizeF radius)
      {
          float left = MathF.Min(rectangle.Left, rectangle.Right);
          float top = MathF.Min(rectangle.Top, rectangle.Bottom);
          float right = MathF.Max(rectangle.Left, rectangle.Right);
          float bottom = MathF.Max(rectangle.Top, rectangle.Bottom);
          float width = right - left;
          float height = bottom - top;

          if (width <= 0 || height <= 0)
          {
              return [];
          }

          float radiusX = radius.Width;
          float radiusY = radius.Height;

          if (radiusX <= 0 || radiusY <= 0)
          {
              return
              [
                  new LinearLineSegment(
                      new PointF(left, top),
                      new PointF(right, top),
                      new PointF(right, bottom),
                      new PointF(left, bottom))
              ];
          }

          float radiusScale = MathF.Min(width / (radiusX + radiusX), height / (radiusY + radiusY));
          if (radiusScale < 1F)
          {
              // Preserve the supplied corner shape while shrinking it enough that opposing corners do not overlap.
              radiusX *= radiusScale;
              radiusY *= radiusScale;
          }

          SizeF cornerRadius = new(radiusX, radiusY);
          PointF topLeft = new(left + radiusX, top);
          PointF topRight = new(right - radiusX, top);
          PointF rightTop = new(right, top + radiusY);
          PointF rightBottom = new(right, bottom - radiusY);
          PointF bottomRight = new(right - radiusX, bottom);
          PointF bottomLeft = new(left + radiusX, bottom);
          PointF leftBottom = new(left, bottom - radiusY);
          PointF leftTop = new(left, top + radiusY);

          return
          [
              new LinearLineSegment(topLeft, topRight),
              new ArcLineSegment(new PointF(right - radiusX, top + radiusY), cornerRadius, 0F, -90F, 90F),
              new LinearLineSegment(rightTop, rightBottom),
              new ArcLineSegment(new PointF(right - radiusX, bottom - radiusY), cornerRadius, 0F, 0F, 90F),
              new LinearLineSegment(bottomRight, bottomLeft),
              new ArcLineSegment(new PointF(left + radiusX, bottom - radiusY), cornerRadius, 0F, 90F, 90F),
              new LinearLineSegment(leftBottom, leftTop),
              new ArcLineSegment(new PointF(left + radiusX, top + radiusY), cornerRadius, 0F, 180F, 90F)
          ];
      }
  }
}