Simple change to emulate the V2 resize behaviour - if either width or height is zero, then the image is scaled keeping its aspect ratio.

Former-commit-id: 624a5693a4bbc9181a113f64e126e70233cacdd9
Former-commit-id: 9741756887b97eb777904afb0782a1a0d481f7c1
Former-commit-id: 43d8122ac4ed7e214f704812f5614b701ed4a81b

src/ImageProcessor/Samplers/ImageSampleExtensions.cs

@@ -66,6 +66,7 @@ namespace ImageProcessor.Samplers
         /// <param name="width">The target image width.</param>
         /// <param name="height">The target image height.</param>
         /// <returns>The <see cref="Image"/></returns>
+        /// <remarks>Passing zero for one of height or width will automatically preserve the aspect ratio of the original image</remarks>
         public static Image Resize(this Image source, int width, int height)
         {
             return Resize(source, width, height, new RobidouxResampler());
@@ -79,6 +80,7 @@ namespace ImageProcessor.Samplers
         /// <param name="height">The target image height.</param>
         /// <param name="sampler">The <see cref="IResampler"/> to perform the resampling.</param>
         /// <returns>The <see cref="Image"/></returns>
+        /// <remarks>Passing zero for one of height or width will automatically preserve the aspect ratio of the original image</remarks>
         public static Image Resize(this Image source, int width, int height, IResampler sampler)
         {
             return Resize(source, width, height, sampler, source.Bounds);
@@ -96,8 +98,18 @@ namespace ImageProcessor.Samplers
         /// The <see cref="Rectangle"/> structure that specifies the portion of the image object to draw.
         /// </param>
         /// <returns>The <see cref="Image"/></returns>
+        /// <remarks>Passing zero for one of height or width will automatically preserve the aspect ratio of the original image</remarks>
         public static Image Resize(this Image source, int width, int height, IResampler sampler, Rectangle sourceRectangle)
         {
+            if (width == 0 && height > 0)
+            {
+                width = source.Width * height / source.Height;
+            }
+            if (height == 0 && width > 0)
+            {
+                height = source.Height * width / source.Width;
+            }
+
             return source.Process(width, height, sourceRectangle, new Rectangle(0, 0, width, height), new Resampler(sampler));
         }
 

tests/ImageProcessor.Tests/Processors/Samplers/SamplerTests.cs

@@ -65,6 +65,62 @@
             }
         }
 
+        [Fact]
+        public void ImageShouldResizeWidthAndKeepAspect()
+        {
+            if (!Directory.Exists("TestOutput/Resize"))
+            {
+                Directory.CreateDirectory("TestOutput/Resize");
+            }
+
+            var name = "FixedWidth";
+
+            foreach (string file in Files)
+            {
+                using (FileStream stream = File.OpenRead(file))
+                {
+                    Stopwatch watch = Stopwatch.StartNew();
+                    Image image = new Image(stream);
+                    string filename = Path.GetFileNameWithoutExtension(file) + "-" + name + Path.GetExtension(file);
+                    using (FileStream output = File.OpenWrite($"TestOutput/Resize/{filename}"))
+                    {
+                        image.Resize(image.Width / 3, 0, new TriangleResampler())
+                             .Save(output);
+                    }
+
+                    Trace.WriteLine($"{name}: {watch.ElapsedMilliseconds}ms");
+                }
+            }
+        }
+
+        [Fact]
+        public void ImageShouldResizeHeightAndKeepAspect()
+        {
+            if (!Directory.Exists("TestOutput/Resize"))
+            {
+                Directory.CreateDirectory("TestOutput/Resize");
+            }
+
+            var name = "FixedHeight";
+
+            foreach (string file in Files)
+            {
+                using (FileStream stream = File.OpenRead(file))
+                {
+                    Stopwatch watch = Stopwatch.StartNew();
+                    Image image = new Image(stream);
+                    string filename = Path.GetFileNameWithoutExtension(file) + "-" + name + Path.GetExtension(file);
+                    using (FileStream output = File.OpenWrite($"TestOutput/Resize/{filename}"))
+                    {
+                        image.Resize(0, image.Height / 3, new TriangleResampler())
+                             .Save(output);
+                    }
+
+                    Trace.WriteLine($"{name}: {watch.ElapsedMilliseconds}ms");
+                }
+            }
+        }
+
         [Theory]
         [MemberData("RotateFlips")]
         public void ImageShouldRotateFlip(RotateType rotateType, FlipType flipType)