WPF: Zoom and Scroll to selection (sample) - wpf

Question

Is there anyone who experienced with the scrollviewer component in WPF? I have a basic selection zoom, and the problem is that it does not scroll to the right place.
Output, trying to zoom the flower:
Actually, the RectangleZoom (see bellow) method scales the picture, but it does not focus it on the specified rectangle, but always in the same position... I believe there is a way to scroll to that position, but till now, any success....
Here is my code:
XAML:
<Window x:Class="WpfApplication3.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="MainWindow" Height="350" Width="525">
<ScrollViewer x:Name="scrollViewer"
HorizontalScrollBarVisibility="Auto">
<Canvas Height="200" Name="mainCanvas" Width="400"
MouseLeftButtonDown="mainCanvas_MouseLeftButtonDown"
MouseLeftButtonUp="mainCanvas_MouseLeftButtonUp"
MouseMove="mainCanvas_MouseMove">
<Canvas.Background>
<ImageBrush ImageSource="/WpfApplication3;component/Images/natural-doodle.jpg"/>
</Canvas.Background>
<Canvas.LayoutTransform>
<TransformGroup>
<ScaleTransform x:Name="scaleTransform"/>
</TransformGroup>
</Canvas.LayoutTransform>
</Canvas>
</ScrollViewer>
</Window>
Code behind:
public partial class MainWindow : Window
{
private Point startPoint;
private Point endPoint;
private Shape rubberBand;
public MainWindow()
{
InitializeComponent();
}
private void mainCanvas_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
{
if (!mainCanvas.IsMouseCaptured)
{
startPoint = e.GetPosition(mainCanvas);
Mouse.Capture(mainCanvas);
}
}
private void mainCanvas_MouseLeftButtonUp(object sender, MouseButtonEventArgs e)
{
if (mainCanvas.IsMouseCaptured)
{
if (rubberBand != null)
{
this.RectangleZoom(
Canvas.GetLeft(rubberBand),
Canvas.GetTop(rubberBand),
rubberBand.Width,
rubberBand.Height);
mainCanvas.Children.Remove(rubberBand);
rubberBand = null;
mainCanvas.ReleaseMouseCapture();
}
}
}
private void mainCanvas_MouseMove(object sender, MouseEventArgs e)
{
if (mainCanvas.IsMouseCaptured)
{
endPoint = e.GetPosition(mainCanvas);
if (rubberBand == null)
{
rubberBand = new Rectangle();
rubberBand.Stroke = Brushes.Red;
rubberBand.StrokeDashArray = new DoubleCollection(new double[] { 4, 2 });
mainCanvas.Children.Add(rubberBand);
}
rubberBand.Width = Math.Abs(startPoint.X - endPoint.X);
rubberBand.Height = Math.Abs(startPoint.Y - endPoint.Y);
double left = Math.Min(startPoint.X, endPoint.X);
double top = Math.Min(startPoint.Y, endPoint.Y);
Canvas.SetLeft(rubberBand, left);
Canvas.SetTop(rubberBand, top);
}
}
private void RectangleZoom(double x, double y, double width, double height)
{
double rWidth = scrollViewer.ViewportWidth / width;
double rHeight = scrollViewer.ViewportHeight / height;
double rZoom = 1.0;
if (rWidth < rHeight)
rZoom = rWidth;
else
rZoom = rHeight;
scaleTransform.ScaleX = rZoom;
scaleTransform.ScaleY = rZoom;
}
}

Answer 1

You got it all but three lines:
Add these to the bottom of your RetangleZoom method:
Point newXY = scaleTransform.Transform(new Point(x, y));
scrollViewer.ScrollToHorizontalOffset(newXY.X);
scrollViewer.ScrollToVerticalOffset(newXY.Y);