add direct2d implementation.

src/Avalonia.Headless/HeadlessPlatformRenderInterface.cs

@@ -70,6 +70,28 @@ namespace Avalonia.Headless
             return new HeadlessBitmapStub(new Size(1, 1), new Vector(96, 96));
         }
 
+        public IWriteableBitmapImpl LoadWriteableBitmapToWidth(Stream stream, int width,
+            BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
+        {
+            return new HeadlessBitmapStub(new Size(1, 1), new Vector(96, 96));
+        }
+
+        public IWriteableBitmapImpl LoadWriteableBitmapToHeight(Stream stream, int height,
+            BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
+        {
+            return new HeadlessBitmapStub(new Size(1, 1), new Vector(96, 96));
+        }
+
+        public IWriteableBitmapImpl LoadWriteableBitmap(string fileName)
+        {
+            return new HeadlessBitmapStub(new Size(1, 1), new Vector(96, 96));
+        }
+
+        public IWriteableBitmapImpl LoadWriteableBitmap(Stream stream)
+        {
+            return new HeadlessBitmapStub(new Size(1, 1), new Vector(96, 96));
+        }
+
         public IBitmapImpl LoadBitmap(PixelFormat format, AlphaFormat alphaFormat, IntPtr data, PixelSize size, Vector dpi, int stride)
         {
             return new HeadlessBitmapStub(new Size(1, 1), new Vector(96, 96));

src/Windows/Avalonia.Direct2D1/Direct2D1Platform.cs

@@ -188,6 +188,28 @@ namespace Avalonia.Direct2D1
             return new WicBitmapImpl(stream);
         }
 
+        public IWriteableBitmapImpl LoadWriteableBitmapToWidth(Stream stream, int width,
+            BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
+        {
+            return new WriteableWicBitmapImpl(stream, width, true, interpolationMode);
+        }
+
+        public IWriteableBitmapImpl LoadWriteableBitmapToHeight(Stream stream, int height,
+            BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
+        {
+            return new WriteableWicBitmapImpl(stream, height, false, interpolationMode);
+        }
+
+        public IWriteableBitmapImpl LoadWriteableBitmap(string fileName)
+        {
+            return new WriteableWicBitmapImpl(fileName);
+        }
+
+        public IWriteableBitmapImpl LoadWriteableBitmap(Stream stream)
+        {
+            return new WriteableWicBitmapImpl(stream);
+        }
+
         /// <inheritdoc />
         public IBitmapImpl LoadBitmapToWidth(Stream stream, int width, BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
         {

src/Windows/Avalonia.Direct2D1/Media/Imaging/WriteableWicBitmapImpl.cs

@@ -1,4 +1,5 @@
 using System;
+using System.IO;
 using Avalonia.Platform;
 using SharpDX.WIC;
 using PixelFormat = Avalonia.Platform.PixelFormat;
@@ -7,11 +8,27 @@ namespace Avalonia.Direct2D1.Media.Imaging
 {
     class WriteableWicBitmapImpl : WicBitmapImpl, IWriteableBitmapImpl
     {
+        public WriteableWicBitmapImpl(Stream stream, int decodeSize, bool horizontal,
+            Avalonia.Visuals.Media.Imaging.BitmapInterpolationMode interpolationMode)
+        : base(stream, decodeSize, horizontal, interpolationMode)
+        {
+        }
+        
         public WriteableWicBitmapImpl(PixelSize size, Vector dpi, PixelFormat? pixelFormat, AlphaFormat? alphaFormat) 
             : base(size, dpi, pixelFormat, alphaFormat)
         {
         }
 
+        public WriteableWicBitmapImpl(Stream stream)
+            : base(stream)
+        {
+        }
+
+        public WriteableWicBitmapImpl(string fileName)
+            : base(fileName)
+        {
+        }
+
         class LockedBitmap : ILockedFramebuffer
         {
             private readonly WriteableWicBitmapImpl _parent;

tests/Avalonia.UnitTests/MockPlatformRenderInterface.cs

@@ -66,6 +66,28 @@ namespace Avalonia.UnitTests
             return Mock.Of<IBitmapImpl>();
         }
 
+        public IWriteableBitmapImpl LoadWriteableBitmapToWidth(Stream stream, int width,
+            BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
+        {
+            throw new NotImplementedException();
+        }
+
+        public IWriteableBitmapImpl LoadWriteableBitmapToHeight(Stream stream, int height,
+            BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
+        {
+            throw new NotImplementedException();
+        }
+
+        public IWriteableBitmapImpl LoadWriteableBitmap(string fileName)
+        {
+            throw new NotImplementedException();
+        }
+
+        public IWriteableBitmapImpl LoadWriteableBitmap(Stream stream)
+        {
+            throw new NotImplementedException();
+        }
+
         public IBitmapImpl LoadBitmap(string fileName)
         {
             return Mock.Of<IBitmapImpl>();