Deep Zoom for WPF

using System;
using System.Windows;
using System.Windows.Media;
using System.Windows.Media.Animation;

namespace DeepZoom.Controls
{
    /// <summary>
    /// Simple FrameworkElement that draws and animates an image in the screen with the lowest possible overhead.
    /// </summary>
    public class TileHost : FrameworkElement
    {
        // Create a collection of child visual objects.
        private DrawingVisual _visual;
        private static readonly AnimationTimeline _opacityAnimation = 
            new DoubleAnimation(1, TimeSpan.FromMilliseconds(500)) { EasingFunction = new ExponentialEase() };

        public TileHost()
        {
            IsHitTestVisible = false;
        }

        public TileHost(ImageSource source, double scale)
            : this()
        {
            Source = source;
            Scale = scale;
        }

        #region Dependency Properties

        #region Source

        /// <summary>
        /// Source Dependency Property
        /// </summary>
        public static readonly DependencyProperty SourceProperty =
            DependencyProperty.Register("Source", typeof(ImageSource), typeof(TileHost),
                new FrameworkPropertyMetadata(null,
                    new PropertyChangedCallback(RefreshTile)));

        /// <summary>
        /// Gets or sets the Source property. This dependency property 
        /// indicates the source of the image to be displayed.
        /// </summary>
        public ImageSource Source
        {
            get { return (ImageSource)GetValue(SourceProperty); }
            set { SetValue(SourceProperty, value); }
        }

        #endregion

        #region Scale

        /// <summary>
        /// Scale Dependency Property
        /// </summary>
        public static readonly DependencyProperty ScaleProperty =
            DependencyProperty.Register("Scale", typeof(double), typeof(TileHost),
                new FrameworkPropertyMetadata(1.0,
                    new PropertyChangedCallback(RefreshTile)));

        /// <summary>
        /// Gets or sets the Scale property. This dependency property 
        /// indicates the scaling to be applied to this tile.
        /// </summary>
        public double Scale
        {
            get { return (double)GetValue(ScaleProperty); }
            set { SetValue(ScaleProperty, value); }
        }

        #endregion

        #endregion

        #region Private methods

        /// <summary>
        /// Called when the tile should be refreshed (Scale or Source changed)
        /// </summary>
        private static void RefreshTile(DependencyObject d, DependencyPropertyChangedEventArgs e)
        {
            var tileHost = d as TileHost;
            if (tileHost != null && tileHost.Source != null && tileHost.Scale > 0)
                tileHost.RenderTile();
        }

        private void RenderTile()
        {
            _visual = new DrawingVisual();
            Width = Source.Width * Scale;
            Height = Source.Height * Scale;
            var dc = _visual.RenderOpen();
            dc.DrawImage(Source, new Rect(0, 0, Width, Height));
            dc.Close();

            CacheMode = new BitmapCache(1 / Scale);

            // Animate opacity
            Opacity = 0;
            BeginAnimation(OpacityProperty, _opacityAnimation);
        }

        #endregion

        #region FrameworkElement overrides

        // Provide a required override for the VisualChildrenCount property.
        protected override int VisualChildrenCount
        {
            get { return _visual == null ? 0 : 1; }
        }

        // Provide a required override for the GetVisualChild method.
        protected override Visual GetVisualChild(int index)
        {
            return _visual;
        }

        #endregion
    }
}