Implement ability to decode a bitmap at a specified width or height.

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

@@ -11,6 +11,18 @@ namespace Avalonia.Media.Imaging
     /// </summary>
     public class Bitmap : IBitmap
     {
+        public static Bitmap DecodeToWidth(Stream stream, int width, BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
+        {
+            IPlatformRenderInterface factory = AvaloniaLocator.Current.GetService<IPlatformRenderInterface>();
+            return new Bitmap(factory.LoadBitmapToWidth(stream, width, interpolationMode));
+        }
+
+        public static Bitmap DecodeToHeight(Stream stream, int height, BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
+        {
+            IPlatformRenderInterface factory = AvaloniaLocator.Current.GetService<IPlatformRenderInterface>();
+            return new Bitmap(factory.LoadBitmapToHeight(stream, height, interpolationMode));
+        }
+
         /// <summary>
         /// Initializes a new instance of the <see cref="Bitmap"/> class.
         /// </summary>
@@ -31,18 +43,6 @@ 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

@@ -1,11 +0,0 @@
-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

@@ -3,6 +3,7 @@ using System.Collections.Generic;
 using System.IO;
 using Avalonia.Media;
 using Avalonia.Media.Imaging;
+using Avalonia.Visuals.Media.Imaging;
 
 namespace Avalonia.Platform
 {
@@ -88,18 +89,30 @@ namespace Avalonia.Platform
         /// <summary>
         /// Loads a bitmap implementation from a file..
         /// </summary>
-        /// <param name="fileName">The filename of the bitmap.</param>
+        /// <param name="fileName">The filename of the bitmap.</param>        
-        /// <param name="decodeOptions">Decode options that specify the size of the decoded bitmap.</param>
         /// <returns>An <see cref="IBitmapImpl"/>.</returns>
-        IBitmapImpl LoadBitmap(string fileName, BitmapDecodeOptions? decodeOptions = null);
+        IBitmapImpl LoadBitmap(string fileName);        
 
         /// <summary>
         /// Loads a bitmap implementation from a file..
         /// </summary>
-        /// <param name="stream">The stream to read the bitmap from.</param>
+        /// <param name="stream">The stream to read the bitmap from.</param>        
-        /// <param name="decodeOptions">Decode options that specify the size of the decoded bitmap.</param>
         /// <returns>An <see cref="IBitmapImpl"/>.</returns>
-        IBitmapImpl LoadBitmap(Stream stream, BitmapDecodeOptions? decodeOptions = null);
+        IBitmapImpl LoadBitmap(Stream stream);
+
+        /// <summary>
+        /// Loads a bitmap implementation from a file..
+        /// </summary>
+        /// <param name="stream">The stream to read the bitmap from.</param>        
+        /// <returns>An <see cref="IBitmapImpl"/>.</returns>
+        IBitmapImpl LoadBitmapToWidth(Stream stream, int width, BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality);
+
+        /// <summary>
+        /// Loads a bitmap implementation from a file..
+        /// </summary>
+        /// <param name="stream">The stream to read the bitmap from.</param>        
+        /// <returns>An <see cref="IBitmapImpl"/>.</returns>
+        IBitmapImpl LoadBitmapToHeight(Stream stream, int height, BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality);
 
         /// <summary>
         /// Loads a bitmap implementation from a pixels in memory.

src/Skia/Avalonia.Skia/ImmutableBitmap.cs

@@ -1,7 +1,11 @@
 using System;
 using System.IO;
+using System.Runtime.CompilerServices;
+using System.Security.Cryptography;
+using Avalonia.Media.Imaging;
 using Avalonia.Platform;
 using Avalonia.Skia.Helpers;
+using Avalonia.Visuals.Media.Imaging;
 using SkiaSharp;
 
 namespace Avalonia.Skia
@@ -36,6 +40,63 @@ namespace Avalonia.Skia
             }
         }
 
+        // NOTE, putting the stream before options in the parameters, causes an exception
+        // inside SKCodec.Create with optimized code. Probably a bug in .net compiler.
+        // Other option is to have the argument order as desired and use PreserveSig options.
+        [MethodImpl(MethodImplOptions.PreserveSig)]
+        public ImmutableBitmap(Stream stream, int decodeSize, bool horizontal, BitmapInterpolationMode interpolationMode)
+        {
+            // create the codec
+            var codec = SKCodec.Create(stream);
+            var info = codec.Info;
+
+            // get the scale that is nearest to what we want (eg: jpg returned 512)
+            var supportedScale = codec.GetScaledDimensions(horizontal ? ((float)decodeSize / info.Width) : ((float)decodeSize / info.Height));
+
+            // decode the bitmap at the nearest size
+            var nearest = new SKImageInfo(supportedScale.Width, supportedScale.Height);
+            var bmp = SKBitmap.Decode(codec, nearest);
+
+            // now scale that to the size that we want
+            var realScale = horizontal ? ((double)info.Height / info.Width) : ((double)info.Width / info.Height);
+
+            SKImageInfo desired;
+
+
+            if (horizontal)
+            {
+                desired = new SKImageInfo(decodeSize, (int)(realScale * decodeSize));
+            }
+            else
+            {
+                desired = new SKImageInfo((int)(realScale * decodeSize), decodeSize);
+            }
+
+            if (bmp.Width != desired.Width || bmp.Height != desired.Height)
+            {
+                if (bmp.Height != bmp.Width)
+                {
+
+                }
+                var scaledBmp = bmp.Resize(desired, interpolationMode.ToSKFilterQuality());
+                bmp.Dispose();
+                bmp = scaledBmp;
+            }
+
+            _image = SKImage.FromBitmap(bmp);
+            bmp.Dispose();
+
+            if (_image == null)
+            {
+                throw new ArgumentException("Unable to load bitmap from provided data");
+            }
+
+            PixelSize = new PixelSize(_image.Width, _image.Height);
+
+            // TODO: Skia doesn't have an API for DPI.
+            Dpi = new Vector(96, 96);
+        }
+
         /// <summary>
         /// Create immutable bitmap from given pixel data copy.
         /// </summary>

src/Skia/Avalonia.Skia/PlatformRenderInterface.cs

@@ -1,11 +1,13 @@
 using System;
 using System.Collections.Generic;
 using System.IO;
+using System.Security.Cryptography;
 using Avalonia.Controls.Platform.Surfaces;
 using Avalonia.Media;
 using Avalonia.Media.Imaging;
 using Avalonia.OpenGL;
 using Avalonia.Platform;
+using Avalonia.Visuals.Media.Imaging;
 using SkiaSharp;
 
 namespace Avalonia.Skia
@@ -78,37 +80,27 @@ namespace Avalonia.Skia
             return new StreamGeometryImpl();
         }
 
-        /// <inheritdoc />
+        public IBitmapImpl LoadBitmap(string fileName)
-        public unsafe IBitmapImpl LoadBitmap(Stream stream, BitmapDecodeOptions? decodeOptions = null)
+        {
-        {            
+            using (var stream = File.OpenRead(fileName))
-            if (decodeOptions is null)
             {
-                return new ImmutableBitmap(stream);
+                return LoadBitmap(stream);
             }
-            else
+        }
-            {
-                var options = decodeOptions.Value;
-
-                var skBitmap = SKBitmap.Decode(stream);
-
-                skBitmap = skBitmap.Resize(new SKImageInfo(options.DecodePixelSize.Width, options.DecodePixelSize.Height), options.InterpolationMode.ToSKFilterQuality());
 
-                fixed (byte* p = skBitmap.Bytes)
+        public IBitmapImpl LoadBitmap(Stream stream)
-                {
+        {
-                    IntPtr ptr = (IntPtr)p;
+            return new ImmutableBitmap(stream);
+        }
 
-                    return LoadBitmap(PixelFormat.Bgra8888, ptr, new PixelSize(skBitmap.Width, skBitmap.Height), new Vector(96, 96), skBitmap.RowBytes);
+        public IBitmapImpl LoadBitmapToWidth(Stream stream, int width, BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
-                }
+        {
-            }
+            return new ImmutableBitmap(stream, width, true, interpolationMode);
         }
 
-        /// <inheritdoc />
+        public IBitmapImpl LoadBitmapToHeight(Stream stream, int height, BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
-        public IBitmapImpl LoadBitmap(string fileName, BitmapDecodeOptions? decodeOptions = null)
         {
-            using (var stream = File.OpenRead(fileName))
+            return new ImmutableBitmap(stream, height, false, interpolationMode);
-            {
-                return LoadBitmap(stream, decodeOptions);
-            }
         }
 
         /// <inheritdoc />

src/Windows/Avalonia.Direct2D1/Direct2D1Platform.cs

@@ -9,6 +9,7 @@ using Avalonia.Direct2D1.Media.Imaging;
 using Avalonia.Media;
 using Avalonia.Media.Imaging;
 using Avalonia.Platform;
+using Avalonia.Visuals.Media.Imaging;
 using SharpDX.DirectWrite;
 using GlyphRun = Avalonia.Media.GlyphRun;
 using TextAlignment = Avalonia.Media.TextAlignment;
@@ -180,16 +181,26 @@ namespace Avalonia.Direct2D1
         public IGeometryImpl CreateRectangleGeometry(Rect rect) => new RectangleGeometryImpl(rect);
         public IStreamGeometryImpl CreateStreamGeometry() => new StreamGeometryImpl();
 
-        public IBitmapImpl LoadBitmap(string fileName, BitmapDecodeOptions? options = null)
+        public IBitmapImpl LoadBitmap(string fileName)
         {
             return new WicBitmapImpl(fileName);
         }
 
-        public IBitmapImpl LoadBitmap(Stream stream, BitmapDecodeOptions? options = null)
+        public IBitmapImpl LoadBitmap(Stream stream)
         {
             return new WicBitmapImpl(stream);
         }
 
+        public IBitmapImpl LoadBitmapToWidth(Stream stream, int width, BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
+        {
+            throw new NotImplementedException();
+        }
+
+        public IBitmapImpl LoadBitmapToHeight(Stream stream, int height, BitmapInterpolationMode interpolationMode = BitmapInterpolationMode.HighQuality)
+        {
+            throw new NotImplementedException();
+        }
+
         public IBitmapImpl LoadBitmap(PixelFormat format, IntPtr data, PixelSize size, Vector dpi, int stride)
         {
             return new WicBitmapImpl(format, data, size, dpi, stride);