Add options builder extension

src/ImageSharp/GraphicOptionsDefaultsExtensions.cs

@@ -11,6 +11,30 @@ namespace SixLabors.ImageSharp
     /// </summary>
     public static class GraphicOptionsDefaultsExtensions
     {
+        /// <summary>
+        /// Sets the default options against the image processing context.
+        /// </summary>
+        /// <param name="context">The image processing context to store default against.</param>
+        /// <param name="optionsBuilder">The action to update instance of the default options used.</param>
+        public static void SetDefaultOptions(this IImageProcessingContext context, Action<GraphicsOptions> optionsBuilder)
+        {
+            var cloned = context.GetDefaultGraphicsOptions().DeepClone();
+            optionsBuilder(cloned);
+            context.Properties[typeof(GraphicsOptions)] = cloned;
+        }
+
+        /// <summary>
+        /// Sets the default options against the configuration.
+        /// </summary>
+        /// <param name="context">The image processing context to store default against.</param>
+        /// <param name="optionsBuilder">The default options to use.</param>
+        public static void SetDefaultGraphicsOptions(this Configuration context, Action<GraphicsOptions> optionsBuilder)
+        {
+            var cloned = context.GetDefaultGraphicsOptions().DeepClone();
+            optionsBuilder(cloned);
+            context.Properties[typeof(GraphicsOptions)] = cloned;
+        }
+
         /// <summary>
         /// Sets the default options against the image processing context.
         /// </summary>
@@ -26,7 +50,7 @@ namespace SixLabors.ImageSharp
         /// </summary>
         /// <param name="context">The image processing context to store default against.</param>
         /// <param name="options">The default options to use.</param>
-        public static void SetDefaultOptions(this Configuration context, GraphicsOptions options)
+        public static void SetDefaultGraphicsOptions(this Configuration context, GraphicsOptions options)
         {
             context.Properties[typeof(GraphicsOptions)] = options;
         }

tests/ImageSharp.Tests/GraphicOptionsDefaultsExtensionsTests.cs

@@ -3,6 +3,7 @@
 
 using SixLabors.ImageSharp.PixelFormats;
 using SixLabors.ImageSharp.Tests.Processing;
+using SixLabors.ImageSharp.Tests.TestUtilities;
 using Xunit;
 
 namespace SixLabors.ImageSharp.Tests
@@ -23,17 +24,60 @@ namespace SixLabors.ImageSharp.Tests
             Assert.DoesNotContain(typeof(GraphicsOptions), config.Properties.Keys);
         }
 
+        [Fact]
+        public void UpdateDefaultOptionsOnProcessingContext_AlwaysNewInstance()
+        {
+            var option = new GraphicsOptions()
+            {
+                BlendPercentage = 0.9f
+            };
+            var config = new Configuration();
+            var context = new FakeImageOperationsProvider.FakeImageOperations<Rgba32>(config, null, true);
+            context.SetDefaultOptions(option);
+
+            context.SetDefaultOptions(o =>
+            {
+                Assert.Equal(0.9f, o.BlendPercentage); // has origional values
+                o.BlendPercentage = 0.4f;
+            });
+
+            var returnedOption = context.GetDefaultGraphicsOptions();
+            Assert.Equal(0.4f, returnedOption.BlendPercentage);
+            Assert.Equal(0.9f, option.BlendPercentage); // hasn't been mutated
+        }
+
         [Fact]
         public void SetDefaultOptionsOnConfiguration()
         {
             var option = new GraphicsOptions();
             var config = new Configuration();
 
-            config.SetDefaultOptions(option);
+            config.SetDefaultGraphicsOptions(option);
 
             Assert.Equal(option, config.Properties[typeof(GraphicsOptions)]);
         }
 
+        [Fact]
+        public void UpdateDefaultOptionsOnConfiguration_AlwaysNewInstance()
+        {
+            var option = new GraphicsOptions()
+            {
+                BlendPercentage = 0.9f
+            };
+            var config = new Configuration();
+            config.SetDefaultGraphicsOptions(option);
+
+            config.SetDefaultGraphicsOptions(o =>
+            {
+                Assert.Equal(0.9f, o.BlendPercentage); // has origional values
+                o.BlendPercentage = 0.4f;
+            });
+
+            var returnedOption = config.GetDefaultGraphicsOptions();
+            Assert.Equal(0.4f, returnedOption.BlendPercentage);
+            Assert.Equal(0.9f, option.BlendPercentage); // hasn't been mutated
+        }
+
         [Fact]
         public void GetDefaultOptionsFromConfiguration_SettingNullThenReturnsNewInstance()
         {
@@ -41,7 +85,7 @@ namespace SixLabors.ImageSharp.Tests
 
             var options = config.GetDefaultGraphicsOptions();
             Assert.NotNull(options);
-            config.SetDefaultOptions((GraphicsOptions)null);
+            config.SetDefaultGraphicsOptions((GraphicsOptions)null);
 
             var options2 = config.GetDefaultGraphicsOptions();
             Assert.NotNull(options2);
@@ -107,7 +151,7 @@ namespace SixLabors.ImageSharp.Tests
         {
             var option = new GraphicsOptions();
             var config = new Configuration();
-            config.SetDefaultOptions(option);
+            config.SetDefaultGraphicsOptions(option);
             var context = new FakeImageOperationsProvider.FakeImageOperations<Rgba32>(config, null, true);
 
             var ctxOptions = context.GetDefaultGraphicsOptions();