Add class CroppedBitmap

samples/ControlCatalog/Pages/ImagePage.xaml

@@ -7,7 +7,7 @@
       <TextBlock Classes="h2">Displays an image</TextBlock>
     </StackPanel>
 
-    <Grid ColumnDefinitions="*,*" RowDefinitions="Auto,*" Margin="64">
+    <Grid ColumnDefinitions="*,*,*" RowDefinitions="Auto,*" Margin="64">
       
       <DockPanel Grid.Column="0" Grid.Row="1" Margin="16">
         <TextBlock DockPanel.Dock="Top" Classes="h3" Margin="0 8">Bitmap</TextBlock>
@@ -22,6 +22,19 @@
       </DockPanel>
 
       <DockPanel Grid.Column="1" Grid.Row="1" Margin="16">
+        <TextBlock DockPanel.Dock="Top" Classes="h3" Margin="0 8">Crop</TextBlock>
+        <ComboBox Name="bitmapCrop" DockPanel.Dock="Top" SelectedIndex="0" SelectionChanged="BitmapCropChanged">
+          <ComboBoxItem>None</ComboBoxItem>
+          <ComboBoxItem>Center</ComboBoxItem>
+          <ComboBoxItem>TopLeft</ComboBoxItem>
+          <ComboBoxItem>TopRight</ComboBoxItem>
+          <ComboBoxItem>BottomLeft</ComboBoxItem>
+          <ComboBoxItem>BottomRight</ComboBoxItem>
+        </ComboBox>
+        <Image Name="croppedImage"/>
+      </DockPanel>
+
+      <DockPanel Grid.Column="2" Grid.Row="1" Margin="16">
         <TextBlock DockPanel.Dock="Top" Classes="h3" Margin="0 8">Drawing</TextBlock>
         <ComboBox Name="drawingStretch" DockPanel.Dock="Top" SelectedIndex="2" SelectionChanged="DrawingStretchChanged">
           <ComboBoxItem>None</ComboBoxItem>

samples/ControlCatalog/Pages/ImagePage.xaml.cs

@@ -1,6 +1,10 @@
+using System;
+using Avalonia;
 using Avalonia.Controls;
 using Avalonia.Markup.Xaml;
 using Avalonia.Media;
+using Avalonia.Media.Imaging;
+using Avalonia.Platform;
 
 namespace ControlCatalog.Pages
 {
@@ -8,12 +12,17 @@ namespace ControlCatalog.Pages
     {
         private readonly Image _bitmapImage;
         private readonly Image _drawingImage;
+        private readonly Image _croppedImage;
+        private readonly IBitmap _croppedBitmapSource;
 
         public ImagePage()
         {
             InitializeComponent();
             _bitmapImage = this.FindControl<Image>("bitmapImage");
             _drawingImage = this.FindControl<Image>("drawingImage");
+            _croppedImage = this.FindControl<Image>("croppedImage");
+            _croppedBitmapSource = LoadBitmap("avares://ControlCatalog/Assets/delicate-arch-896885_640.jpg");
+            _croppedImage.Source = new CroppedBitmap(_croppedBitmapSource, default);
         }
 
         private void InitializeComponent()
@@ -38,5 +47,37 @@ namespace ControlCatalog.Pages
                 _drawingImage.Stretch = (Stretch)comboxBox.SelectedIndex;
             }
         }
+
+        public void BitmapCropChanged(object sender, SelectionChangedEventArgs e)
+        {
+            if (_croppedImage != null)
+            {
+                var comboxBox = (ComboBox)sender;
+                _croppedImage.Source =  new CroppedBitmap( _croppedBitmapSource,  GetCropRect(comboxBox.SelectedIndex));
+            }
+        }
+
+        private PixelRect GetCropRect(int index)
+        {
+            var bitmapWidth = _croppedBitmapSource.PixelSize.Width;
+            var bitmapHeight = _croppedBitmapSource.PixelSize.Height;
+            var cropSize = new PixelSize(bitmapWidth / 2, bitmapHeight / 2);
+            return index switch
+            {
+                1 => new PixelRect(new PixelPoint((bitmapWidth - cropSize.Width) / 2, (bitmapHeight - cropSize.Width) / 2), cropSize),
+                2 => new PixelRect(new PixelPoint(0, 0), cropSize),
+                3 => new PixelRect(new PixelPoint(bitmapWidth - cropSize.Width, 0), cropSize),
+                4 => new PixelRect(new PixelPoint(0, bitmapHeight - cropSize.Height), cropSize),
+                5 => new PixelRect(new PixelPoint(bitmapWidth - cropSize.Width, bitmapHeight - cropSize.Height), cropSize),
+                _ => PixelRect.Empty
+            };
+            
+        }
+
+        private IBitmap LoadBitmap(string uri)
+        {
+            var assets = AvaloniaLocator.Current.GetService<IAssetLoader>();
+            return new Bitmap(assets.Open(new Uri(uri)));
+        }
     }
 }

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

@@ -0,0 +1,47 @@
+using System;
+using System.Collections.Generic;
+using System.Text;
+using Avalonia.Visuals.Media.Imaging;
+
+namespace Avalonia.Media.Imaging
+{
+    public class CroppedBitmap : IImage, IDisposable
+    {
+        public CroppedBitmap()
+        {
+            Source = null;
+            SourceRect = default;
+        }
+        public CroppedBitmap(IBitmap source, PixelRect sourceRect)
+        {
+            Source = source;
+            SourceRect = sourceRect;
+        }
+        public virtual void Dispose()
+        {
+            Source?.Dispose();
+        }
+
+        public Size Size {
+            get
+            {
+                if (Source == null)
+                    return Size.Empty;
+                if (SourceRect.IsEmpty)
+                    return Source.Size;
+                return SourceRect.Size.ToSizeWithDpi(Source.Dpi);
+            }
+        }
+
+        public void Draw(DrawingContext context, Rect sourceRect, Rect destRect, BitmapInterpolationMode bitmapInterpolationMode)
+        {
+            if (Source == null)
+                return;
+            var topLeft = SourceRect.TopLeft.ToPointWithDpi(Source.Dpi);
+            Source.Draw(context, sourceRect.Translate(new Vector(topLeft.X, topLeft.Y)), destRect, bitmapInterpolationMode);           
+        }
+
+        public IBitmap Source { get; }
+        public PixelRect SourceRect { get; }
+    }
+}