From ec50f7ab4f96315fc3850187362c2a08798ae601 Mon Sep 17 00:00:00 2001
From: James Jackson-South <james_south@hotmail.com>
Date: Fri, 29 Jul 2016 16:50:37 +1000
Subject: [PATCH] Alpha

Former-commit-id: a4b0ac45cb416e863496495ff9ac3d71585a46e6
Former-commit-id: ea2e5a6d2315d14f6ed566ff6c91b73c83b1feb5
Former-commit-id: 8a3cf0d04075c5da03b5d1ab747013d1efdd6491
---
 src/ImageProcessorCore/Filters/Alpha.cs       | 60 +++++++++++++++
 .../Filters/Processors/AlphaProcessor.cs      | 75 +++++++++++++++++++
 .../Filters/Processors/BrightnessProcessor.cs |  2 +-
 .../Processors/Filters/AlphaTest.cs           | 47 ++++++++++++
 4 files changed, 183 insertions(+), 1 deletion(-)
 create mode 100644 src/ImageProcessorCore/Filters/Alpha.cs
 create mode 100644 src/ImageProcessorCore/Filters/Processors/AlphaProcessor.cs
 create mode 100644 tests/ImageProcessorCore.Tests/Processors/Filters/AlphaTest.cs

diff --git a/src/ImageProcessorCore/Filters/Alpha.cs b/src/ImageProcessorCore/Filters/Alpha.cs
new file mode 100644
index 000000000..545639afa
--- /dev/null
+++ b/src/ImageProcessorCore/Filters/Alpha.cs
@@ -0,0 +1,60 @@
+// <copyright file="Alpha.cs" company="James Jackson-South">
+// Copyright (c) James Jackson-South and contributors.
+// Licensed under the Apache License, Version 2.0.
+// </copyright>
+
+namespace ImageProcessorCore
+{
+    using Processors;
+
+    /// <summary>
+    /// Extension methods for the <see cref="Image"/> type.
+    /// </summary>
+    public static partial class ImageExtensions
+    {
+        /// <summary>
+        /// Alters the alpha component of the image.
+        /// </summary>
+        /// <typeparam name="T">The pixel format.</typeparam>
+        /// <typeparam name="TP">The packed format. <example>long, float.</example></typeparam>
+        /// <param name="source">The image this method extends.</param>
+        /// <param name="percent">The new opacity of the image. Must be between 0 and 100.</param>
+        /// <param name="progressHandler">A delegate which is called as progress is made processing the image.</param>
+        /// <returns>The <see cref="Image{T,TP}"/>.</returns>
+        public static Image<T, TP> Alpha<T, TP>(this Image<T, TP> source, int percent, ProgressEventHandler progressHandler = null)
+            where T : IPackedVector<TP>
+            where TP : struct
+        {
+            return Alpha(source, percent, source.Bounds, progressHandler);
+        }
+
+        /// <summary>
+        /// Alters the alpha component of the image.
+        /// </summary>
+        /// <typeparam name="T">The pixel format.</typeparam>
+        /// <typeparam name="TP">The packed format. <example>long, float.</example></typeparam>
+        /// <param name="source">The image this method extends.</param>
+        /// <param name="percent">The new opacity of the image. Must be between 0 and 100.</param>
+        /// <param name="rectangle">
+        /// The <see cref="Rectangle"/> structure that specifies the portion of the image object to alter.
+        /// </param>
+        /// <param name="progressHandler">A delegate which is called as progress is made processing the image.</param>
+        /// <returns>The <see cref="Image"/>.</returns>
+        public static Image<T, TP> Alpha<T, TP>(this Image<T, TP> source, int percent, Rectangle rectangle, ProgressEventHandler progressHandler = null)
+            where T : IPackedVector<TP>
+            where TP : struct
+        {
+            AlphaProcessor<T, TP> processor = new AlphaProcessor<T, TP>(percent);
+            processor.OnProgress += progressHandler;
+
+            try
+            {
+                return source.Process(rectangle, processor);
+            }
+            finally
+            {
+                processor.OnProgress -= progressHandler;
+            }
+        }
+    }
+}
diff --git a/src/ImageProcessorCore/Filters/Processors/AlphaProcessor.cs b/src/ImageProcessorCore/Filters/Processors/AlphaProcessor.cs
new file mode 100644
index 000000000..b4595ac4b
--- /dev/null
+++ b/src/ImageProcessorCore/Filters/Processors/AlphaProcessor.cs
@@ -0,0 +1,75 @@
+// <copyright file="AlphaProcessor.cs" company="James Jackson-South">
+// Copyright (c) James Jackson-South and contributors.
+// Licensed under the Apache License, Version 2.0.
+// </copyright>
+
+namespace ImageProcessorCore.Processors
+{
+    using System.Numerics;
+    using System.Threading.Tasks;
+
+    /// <summary>
+    /// An <see cref="IImageProcessor"/> to change the Alpha of an <see cref="Image{T,TP}"/>.
+    /// </summary>
+    /// <typeparam name="T">The pixel format.</typeparam>
+    /// <typeparam name="TP">The packed format. <example>long, float.</example></typeparam>
+    public class AlphaProcessor<T, TP> : ImageProcessor<T, TP>
+        where T : IPackedVector<TP>
+        where TP : struct
+    {
+        /// <summary>
+        /// Initializes a new instance of the <see cref="AlphaProcessor"/> class.
+        /// </summary>
+        /// <param name="percent">The percentage to adjust the opacity of the image. Must be between 0 and 100.</param>
+        /// <exception cref="ArgumentException">
+        /// <paramref name="percent"/> is less than 0 or is greater than 100.
+        /// </exception>
+        public AlphaProcessor(int percent)
+        {
+            Guard.MustBeBetweenOrEqualTo(percent, 0, 100, nameof(percent));
+            this.Value = percent;
+        }
+
+        /// <summary>
+        /// Gets the alpha value.
+        /// </summary>
+        public int Value { get; }
+
+        /// <inheritdoc/>
+        protected override void Apply(ImageBase<T, TP> target, ImageBase<T, TP> source, Rectangle targetRectangle, Rectangle sourceRectangle, int startY, int endY)
+        {
+            float alpha = this.Value / 100f;
+            int sourceY = sourceRectangle.Y;
+            int sourceBottom = sourceRectangle.Bottom;
+            int startX = sourceRectangle.X;
+            int endX = sourceRectangle.Right;
+            Vector4 alphaVector = new Vector4(1, 1, 1, alpha);
+
+            using (IPixelAccessor<T, TP> sourcePixels = source.Lock())
+            using (IPixelAccessor<T, TP> targetPixels = target.Lock())
+            {
+                Parallel.For(
+                    startY,
+                    endY,
+                    y =>
+                        {
+                            if (y >= sourceY && y < sourceBottom)
+                            {
+                                for (int x = startX; x < endX; x++)
+                                {
+                                    Vector4 color = sourcePixels[x, y].ToVector4();
+                                    color *= alphaVector;
+
+                                    T packed = default(T);
+                                    packed.PackVector(color);
+                                    targetPixels[x, y] = packed;
+                                }
+
+                                this.OnRowProcessed();
+                            }
+                        });
+
+            }
+        }
+    }
+}
diff --git a/src/ImageProcessorCore/Filters/Processors/BrightnessProcessor.cs b/src/ImageProcessorCore/Filters/Processors/BrightnessProcessor.cs
index 3b3be22a5..f9197d143 100644
--- a/src/ImageProcessorCore/Filters/Processors/BrightnessProcessor.cs
+++ b/src/ImageProcessorCore/Filters/Processors/BrightnessProcessor.cs
@@ -9,7 +9,7 @@ namespace ImageProcessorCore.Processors
     using System.Threading.Tasks;
 
     /// <summary>
-    /// An <see cref="IImageProcessor"/> to change the brightness of an <see cref="Image"/>.
+    /// An <see cref="IImageProcessor"/> to change the brightness of an <see cref="Image{T,TP}"/>.
     /// </summary>
     /// <typeparam name="T">The pixel format.</typeparam>
     /// <typeparam name="TP">The packed format. <example>long, float.</example></typeparam>
diff --git a/tests/ImageProcessorCore.Tests/Processors/Filters/AlphaTest.cs b/tests/ImageProcessorCore.Tests/Processors/Filters/AlphaTest.cs
new file mode 100644
index 000000000..6176cbb71
--- /dev/null
+++ b/tests/ImageProcessorCore.Tests/Processors/Filters/AlphaTest.cs
@@ -0,0 +1,47 @@
+// <copyright file="AlphaTest.cs" company="James Jackson-South">
+// Copyright (c) James Jackson-South and contributors.
+// Licensed under the Apache License, Version 2.0.
+// </copyright>
+
+namespace ImageProcessorCore.Tests
+{
+    using System.IO;
+
+    using Xunit;
+
+    public class AlphaTest : FileTestBase
+    {
+        public static readonly TheoryData<int> AlphaValues
+        = new TheoryData<int>
+        {
+            20 ,
+            80 ,
+        };
+
+        [Theory]
+        [MemberData("AlphaValues")]
+        public void ImageShouldApplyAlphaFilter(int value)
+        {
+            const string path = "TestOutput/Alpha";
+            if (!Directory.Exists(path))
+            {
+                Directory.CreateDirectory(path);
+            }
+
+            foreach (string file in Files)
+            {
+                using (FileStream stream = File.OpenRead(file))
+                {
+                    string filename = Path.GetFileNameWithoutExtension(file) + "-" + value + Path.GetExtension(file);
+
+                    Image image = new Image(stream);
+                    using (FileStream output = File.OpenWrite($"{path}/{filename}"))
+                    {
+                        image.Alpha(value)
+                             .Save(output);
+                    }
+                }
+            }
+        }
+    }
+}
\ No newline at end of file