TileCanvas.cs

    public class TileCanvas : Canvas
    {
        public static readonly DependencyProperty ImageSourceProperty = DependencyProperty.Register(
            "ImageSource",
            typeof(ImageSource),
            typeof(TileCanvas),
            new PropertyMetadata(null, ImageSourceChanged));

        private Size _lastActualSize;

        public TileCanvas()
        {
            LayoutUpdated += OnLayoutUpdated;
        }

        public ImageSource ImageSource
        {
            get { return (ImageSource)GetValue(ImageSourceProperty); }
            set { SetValue(ImageSourceProperty, value); }
        }

        private void OnLayoutUpdated(object sender, object o)
        {
            var newSize = new Size(ActualWidth, ActualHeight);
            if (_lastActualSize == newSize)
                return;
            _lastActualSize = newSize;
            Rebuild();
        }

        private static void ImageSourceChanged(DependencyObject o, DependencyPropertyChangedEventArgs args)
        {
            var self = (TileCanvas)o;
            var src = self.ImageSource;
            if (src == null) return;
            var image = new Image { Source = src };
            image.ImageOpened += self.ImageOnImageOpened;
            image.ImageFailed += self.ImageOnImageFailed;

            //add it to the visual tree to kick off ImageOpened
            self.Children.Add(image);
        }

        private void ImageOnImageFailed(object sender, ExceptionRoutedEventArgs exceptionRoutedEventArgs)
        {
            ManageImageEvent((Image)sender);
            Children.Add(new TextBlock
            {
                Text = exceptionRoutedEventArgs.ErrorException.Message,
                Foreground = new SolidColorBrush(Colors.Red)
            });
        }

        private void ImageOnImageOpened(object sender, RoutedEventArgs routedEventArgs)
        {
            ManageImageEvent((Image)sender);
            Children.Clear();
            Rebuild();
        }

        private void ManageImageEvent(Image image)
        {
            image.ImageOpened -= ImageOnImageOpened;
            image.ImageFailed -= ImageOnImageFailed;
        }

        private void Rebuild()
        {
            var bmp = ImageSource as BitmapSource;
            if (bmp == null
                || bmp.PixelWidth == 0 || bmp.PixelHeight == 0
                || ActualWidth.Equals(0) || ActualHeight.Equals(0))
                return;

            double currentTiledWidth = -1;
            double currentTiledHeight = -1;
            foreach (var child in Children.Where(c => c is Image).Cast<Image>())
            {
                var childTop = GetTop(child);
                var childLeft = GetLeft(child);
                if (childLeft >= ActualWidth || childTop >= ActualHeight)
                    Children.Remove(child);
                else
                {
                    currentTiledWidth = Math.Max(childLeft, currentTiledWidth);
                    currentTiledHeight = Math.Max(childTop, currentTiledHeight);
                }
            }

            for (var x = 0; x < ActualWidth; x += bmp.PixelWidth)
                for (var y = 0; y < ActualHeight; y += bmp.PixelHeight)
                    if (x > currentTiledWidth || y > currentTiledHeight)
                    {
                        var image = new Image { Source = ImageSource };
                        SetLeft(image, x);
                        SetTop(image, y);
                        Children.Add(image);
                    }
            Clip = new RectangleGeometry { Rect = new Rect(0, 0, ActualWidth, ActualHeight) };
        }
    }