Add fade border filter

FilterLib.Tests/FilterTests/BorderTests.cs

@@ -14,5 +14,14 @@ public void TestJitterBorder()
             Assert.IsTrue(Common.CheckFilter("_input.bmp", "JitterBorder_20_Red_0.bmp",
                 new JitterBorderFilter(Size.Absolute(20), new RGB(255, 0, 0), 0), 1));
         }
+
+        [Test]
+        public void TestFadeBorder()
+        {
+            Assert.IsTrue(Common.CheckFilter("_input.bmp", "_input.bmp",
+                new FadeBorderFilter(Size.Absolute(0), new RGB(0, 0, 0)), 1));
+            Assert.IsTrue(Common.CheckFilter("_input.bmp", "FadeBorder_20_Red.bmp",
+                new FadeBorderFilter(Size.Absolute(20), new RGB(255, 0, 0)), 1));
+        }
     }
 }

FilterLib.Tests/ReflectiveApiTests/ApiTests.cs

@@ -7,7 +7,7 @@ public class ApiTests
     {
         [Test]
         public void TestListFilters() =>
-            Assert.AreEqual(55, ReflectiveApi.GetFilterTypes().ToArray().Length);
+            Assert.AreEqual(56, ReflectiveApi.GetFilterTypes().ToArray().Length);
 
         [Test]
         public void TestListBlends() =>

FilterLib.Tests/ReflectiveApiTests/BorderTests.cs

@@ -20,5 +20,16 @@ public void TestJitterBorder()
             Assert.AreEqual(new RGB(255, 0, 0), ff.Color);
             Assert.AreEqual(15, ff.Seed);
         }
+        [Test]
+        public void TestFadeBorder()
+        {
+            IFilter f = ReflectiveApi.ConstructFilterByName("FadeBorder");
+            Assert.IsInstanceOf<FadeBorderFilter>(f);
+            ReflectiveApi.SetFilterPropertyByName(f, "Width", "8px");
+            ReflectiveApi.SetFilterPropertyByName(f, "Color", "(255, 0, 0)");
+            FadeBorderFilter ff = f as FadeBorderFilter;
+            Assert.AreEqual(8, ff.Width.ToAbsolute(0));
+            Assert.AreEqual(new RGB(255, 0, 0), ff.Color);
+        }
     }
 }

FilterLib/Filters/Border/FadeBorderFilter.cs

@@ -0,0 +1,68 @@
+using FilterLib.Reporting;
+using FilterLib.Util;
+using System;
+using System.Drawing;
+
+namespace FilterLib.Filters.Border
+{
+    /// <summary>
+    /// Fade border filter.
+    /// </summary>
+    [Filter]
+    public sealed class FadeBorderFilter : FilterInPlaceBase
+    {
+        /// <summary>
+        /// Border width.
+        /// </summary>
+        [FilterParam]
+        public Util.Size Width { get; set; }
+
+        /// <summary>
+        /// Border color.
+        /// </summary>
+        [FilterParam]
+        public RGB Color { get; set; }
+
+        /// <summary>
+        /// Constructor.
+        /// </summary>
+        public FadeBorderFilter() : this(Util.Size.Absolute(0), new RGB(0, 0, 0)) { }
+
+        /// <summary>
+        /// Constructor.
+        /// </summary>
+        /// <param name="width">Border width</param>
+        /// <param name="color">Border color</param>
+        public FadeBorderFilter(Util.Size width, RGB color)
+        {
+            this.Width = width;
+            this.Color = color;
+        }
+
+        /// <summary>
+        /// Apply filter by modifying the original image.
+        /// </summary>
+        /// <param name="image">Input image</param>
+        /// <param name="reporter">Reporter (optional)</param>
+        public override void ApplyInPlace(Bitmap image, IReporter reporter = null)
+        {
+            reporter?.Start();
+            int w = image.Width, h = image.Height;
+            int borderWidth = Width.ToAbsolute(Math.Max(w, h));
+            using (Graphics gfx = Graphics.FromImage(image))
+            {
+                // Draw rectangles with decreasing alpha value
+                for (int k = 0; k < borderWidth; ++k)
+                {
+                    using Pen pen = new Pen(System.Drawing.Color.FromArgb((int)(255 - k / (float)(borderWidth - 1) * 255), Color.R, Color.G, Color.B));
+                    gfx.DrawLine(pen, 0, k, w, k);
+                    gfx.DrawLine(pen, k, 0, k, h);
+                    gfx.DrawLine(pen, 0, h - 1 - k, w, h - 1 - k);
+                    gfx.DrawLine(pen, w - 1 - k, 0, w - 1 - k, h);
+                    reporter?.Report(k, 0, borderWidth - 1);
+                }
+            }
+            reporter?.Done();
+        }
+    }
+}