Add ComputeLength extension

Author: JimBobSquarePants

samples/DrawShapesWithImageSharp/Program.cs

@@ -77,7 +77,7 @@ private static void DrawText(string text, IPath path)
             var font = new Font(fam, 30);
             var style = new RendererOptions(font, 72)
             {
-                WrappingWidth = path.Bounds.Width,
+                WrappingWidth = path.ComputeLength(),
                 VerticalAlignment = VerticalAlignment.Top,
                 HorizontalAlignment = HorizontalAlignment.Center,
             };

src/ImageSharp.Drawing/Shapes/PathExtensions.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Six Labors.
 // Licensed under the Apache License, Version 2.0.
 
+using System;
 using System.Numerics;
 
 namespace SixLabors.ImageSharp.Drawing
@@ -121,5 +122,39 @@ public static IPath Scale(this IPath path, float scaleX, float scaleY)
         /// <returns>A <see cref="IPath"/> with a translate transform applied.</returns>
         public static IPath Scale(this IPath path, float scale)
             => path.Transform(Matrix3x2.CreateScale(scale, RectangleF.Center(path.Bounds)));
+
+        /// <summary>
+        /// Calculates the length of the path as though each segment were unrolled into a line.
+        /// </summary>
+        /// <param name="path">The path to compute the length for.</param>
+        /// <returns>
+        /// The <see cref="int"/> representing the unrolled length.
+        /// For closed paths, the length includes an implicit closing segment.
+        /// </returns>
+        public static float ComputeLength(this IPath path)
+        {
+            float dist = 0;
+            foreach (ISimplePath s in path.Flatten())
+            {
+                ReadOnlySpan<PointF> points = s.Points.Span;
+                if (points.Length < 2)
+                {
+                    // Only a single point
+                    continue;
+                }
+
+                for (int i = 1; i < points.Length; i++)
+                {
+                    dist += Vector2.Distance(points[i - 1], points[i]);
+                }
+
+                if (s.IsClosed)
+                {
+                    dist += Vector2.Distance(points[0], points[points.Length - 1]);
+                }
+            }
+
+            return dist;
+        }
     }
 }

tests/ImageSharp.Drawing.Tests/Drawing/Paths/ComputeLength.cs

@@ -0,0 +1,18 @@
+// Copyright (c) Six Labors.
+// Licensed under the Apache License, Version 2.0.
+
+using Xunit;
+
+namespace SixLabors.ImageSharp.Drawing.Tests.Drawing.Paths
+{
+    public class ComputeLength
+    {
+        [Fact]
+        public void CanComputeUnrolledLength()
+        {
+            var polygon = new RectangularPolygon(PointF.Empty, new PointF(100, 200));
+
+            Assert.Equal(600, polygon.ComputeLength());
+        }
+    }
+}