decode bitmaps at a specified size.

src/Avalonia.Visuals/Media/Imaging/Bitmap.cs

@@ -31,6 +31,18 @@ namespace Avalonia.Media.Imaging
             PlatformImpl = RefCountable.Create(factory.LoadBitmap(stream));
         }
 
+        public Bitmap(Stream stream, BitmapDecodeOptions decodeOptions)
+        {
+            IPlatformRenderInterface factory = AvaloniaLocator.Current.GetService<IPlatformRenderInterface>();
+            PlatformImpl = RefCountable.Create(factory.LoadBitmap(stream, decodeOptions));
+        }
+
+        public Bitmap(string file, BitmapDecodeOptions decodeOptions)
+        {
+            IPlatformRenderInterface factory = AvaloniaLocator.Current.GetService<IPlatformRenderInterface>();
+            PlatformImpl = RefCountable.Create(factory.LoadBitmap(file, decodeOptions));
+        }
+
         /// <summary>
         /// Initializes a new instance of the <see cref="Bitmap"/> class.
         /// </summary>

src/Avalonia.Visuals/Media/Imaging/BitmapDecodeOptions.cs

@@ -0,0 +1,11 @@
+using Avalonia.Visuals.Media.Imaging;
+
+namespace Avalonia.Media.Imaging
+{
+    public struct BitmapDecodeOptions
+    {
+        public PixelSize DecodePixelSize { get; set; }
+
+        public BitmapInterpolationMode InterpolationMode { get; set; }
+    }
+}

src/Avalonia.Visuals/Platform/IPlatformRenderInterface.cs

@@ -2,6 +2,7 @@ using System;
 using System.Collections.Generic;
 using System.IO;
 using Avalonia.Media;
+using Avalonia.Media.Imaging;
 
 namespace Avalonia.Platform
 {
@@ -84,6 +85,10 @@ namespace Avalonia.Platform
         /// <returns>An <see cref="IWriteableBitmapImpl"/>.</returns>
         IWriteableBitmapImpl CreateWriteableBitmap(PixelSize size, Vector dpi, PixelFormat? format = null);
 
+        IBitmapImpl LoadBitmap(string fileName, BitmapDecodeOptions decodeOptions);
+
+        IBitmapImpl LoadBitmap(Stream stream, BitmapDecodeOptions decodeOptions);
+
         /// <summary>
         /// Loads a bitmap implementation from a file..
         /// </summary>

src/Skia/Avalonia.Skia/DrawingContextImpl.cs

@@ -123,29 +123,12 @@ namespace Avalonia.Skia
                     Color = new SKColor(255, 255, 255, (byte)(255 * opacity * _currentOpacity))
                 })
             {
-                paint.FilterQuality = GetInterpolationMode(bitmapInterpolationMode);
+                paint.FilterQuality = bitmapInterpolationMode.ToSKFilterQuality();
 
                 drawableImage.Draw(this, s, d, paint);
             }
         }
 
-        private static SKFilterQuality GetInterpolationMode(BitmapInterpolationMode interpolationMode)
-        {
-            switch (interpolationMode)
-            {
-                case BitmapInterpolationMode.LowQuality:
-                    return SKFilterQuality.Low;
-                case BitmapInterpolationMode.MediumQuality:
-                    return SKFilterQuality.Medium;
-                case BitmapInterpolationMode.HighQuality:
-                    return SKFilterQuality.High;
-                case BitmapInterpolationMode.Default:
-                    return SKFilterQuality.None;
-                default:
-                    throw new ArgumentOutOfRangeException(nameof(interpolationMode), interpolationMode, null);
-            }
-        }
-
         /// <inheritdoc />
         public void DrawBitmap(IRef<IBitmapImpl> source, IBrush opacityMask, Rect opacityMaskRect, Rect destRect)
         {

src/Skia/Avalonia.Skia/PlatformRenderInterface.cs

@@ -3,6 +3,7 @@ using System.Collections.Generic;
 using System.IO;
 using Avalonia.Controls.Platform.Surfaces;
 using Avalonia.Media;
+using Avalonia.Media.Imaging;
 using Avalonia.OpenGL;
 using Avalonia.Platform;
 using SkiaSharp;
@@ -77,6 +78,28 @@ namespace Avalonia.Skia
             return new StreamGeometryImpl();
         }
 
+        public IBitmapImpl LoadBitmap(string fileName, BitmapDecodeOptions decodeOptions)
+        {
+            using (var stream = File.OpenRead(fileName))
+            {
+                return LoadBitmap(stream, decodeOptions);
+            }
+        }
+
+        public unsafe IBitmapImpl LoadBitmap(Stream stream, BitmapDecodeOptions decodeOptions)
+        {
+            var skBitmap = SKBitmap.Decode(stream);
+
+            skBitmap = skBitmap.Resize(new SKImageInfo(decodeOptions.DecodePixelSize.Width, decodeOptions.DecodePixelSize.Height), decodeOptions.InterpolationMode.ToSKFilterQuality());
+
+            fixed (byte* p = skBitmap.Bytes)
+            {
+                IntPtr ptr = (IntPtr)p;
+
+                return LoadBitmap(PixelFormat.Bgra8888, ptr, new PixelSize(skBitmap.Width, skBitmap.Height), new Vector(96, 96), skBitmap.RowBytes);                
+            }
+        }
+
         /// <inheritdoc />
         public IBitmapImpl LoadBitmap(Stream stream)
         {

src/Skia/Avalonia.Skia/SkiaSharpExtensions.cs

@@ -1,12 +1,30 @@
 using System;
 using Avalonia.Media;
 using Avalonia.Platform;
+using Avalonia.Visuals.Media.Imaging;
 using SkiaSharp;
 
 namespace Avalonia.Skia
 {
     public static class SkiaSharpExtensions
     {
+        public static SKFilterQuality ToSKFilterQuality(this BitmapInterpolationMode interpolationMode)
+        {
+            switch (interpolationMode)
+            {
+                case BitmapInterpolationMode.LowQuality:
+                    return SKFilterQuality.Low;
+                case BitmapInterpolationMode.MediumQuality:
+                    return SKFilterQuality.Medium;
+                case BitmapInterpolationMode.HighQuality:
+                    return SKFilterQuality.High;
+                case BitmapInterpolationMode.Default:
+                    return SKFilterQuality.None;
+                default:
+                    throw new ArgumentOutOfRangeException(nameof(interpolationMode), interpolationMode, null);
+            }
+        }
+
         public static SKPoint ToSKPoint(this Point p)
         {
             return new SKPoint((float)p.X, (float)p.Y);

src/Windows/Avalonia.Direct2D1/Direct2D1Platform.cs

@@ -7,6 +7,7 @@ using Avalonia.Controls.Platform.Surfaces;
 using Avalonia.Direct2D1.Media;
 using Avalonia.Direct2D1.Media.Imaging;
 using Avalonia.Media;
+using Avalonia.Media.Imaging;
 using Avalonia.Platform;
 using SharpDX.DirectWrite;
 using GlyphRun = Avalonia.Media.GlyphRun;
@@ -194,6 +195,16 @@ namespace Avalonia.Direct2D1
             return new WicBitmapImpl(format, data, size, dpi, stride);
         }
 
+        public IBitmapImpl LoadBitmap(string fileName, BitmapDecodeOptions decodeOptions)
+        {
+            throw new NotImplementedException();
+        }
+
+        public IBitmapImpl LoadBitmap(Stream stream, BitmapDecodeOptions decodeOptions)
+        {
+            throw new NotImplementedException();
+        }
+
         public IGlyphRunImpl CreateGlyphRun(GlyphRun glyphRun, out double width)
         {
             var glyphTypeface = (GlyphTypefaceImpl)glyphRun.GlyphTypeface.PlatformImpl;