How to Pan and Zoom Images with Overlays in WPF using ViewBox, ImageBrush, and ScrollViewer?

Image pan and zoom in WPF

WPF provides an easy way to combine ViewBox, ImageBrush and ScrollViewer to create an image viewer that supports image pan, zoom and overlay functionality. Here’s how to do it:

1. Use ViewBox to pan and zoom:

ViewBox A container allows you to scale and position the child elements inside it. Place the image inside a ViewBox and you can easily pan and zoom the image by adjusting its Stretch and Offset properties.

2. Use ImageBrush to create overlays:

ImageBrush allows you to draw an image to a specified area. You can create an overlay by creating a ImageBrush and using it as a fill for a shape or control placed on top of the main image.

3. Use ScrollViewer to display the complete image:

If the image size exceeds the viewer size, you can use ScrollViewer as the parent of the main ViewBox. This allows you to scroll through the entire original image.

4. Pan and zoom implementation:

The following example demonstrates how to pan and zoom using ViewBox, ImageBrush, and ScrollViewer:

MainWindow.xaml:

<code class="language-xml"><Window ...>
    <ScrollViewer>
        <Viewbox x:Name="PannableViewBox">
            <Image Source="myImage.jpg"/>
            <ImageBrush Opacity="0.5" x:Name="OverlayImageBrush"/>
        </Viewbox>
    </ScrollViewer>
</Window></code>

MainWindow.xaml.cs:

<code class="language-csharp">public partial class MainWindow : Window
{
    private Point _start;
    private ScaleTransform _scaleTransform;
    private TranslateTransform _translateTransform;

    public MainWindow()
    {
        InitializeComponent();

        _scaleTransform = new ScaleTransform();
        _translateTransform = new TranslateTransform();

        PannableViewBox.RenderTransform = new TransformGroup()
        {
            Children = { _scaleTransform, _translateTransform }
        };
    }

    private void PannableViewBox_MouseWheel(object sender, MouseWheelEventArgs e)
    {
        if (Keyboard.IsKeyDown(Key.LeftCtrl))
        {
            _scaleTransform.ScaleX += e.Delta > 0 ? 0.1 : -0.1;
            _scaleTransform.ScaleY += e.Delta > 0 ? 0.1 : -0.1;
        }
    }

    private void PannableViewBox_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
    {
        _start = e.GetPosition(PannableViewBox);
        PannableViewBox.CaptureMouse();
    }

    private void PannableViewBox_MouseLeftButtonUp(object sender, MouseButtonEventArgs e)
    {
        PannableViewBox.ReleaseMouseCapture();
    }

    private void PannableViewBox_MouseMove(object sender, MouseEventArgs e)
    {
        if (PannableViewBox.IsMouseCaptured)
        {
            var point = e.GetPosition(PannableViewBox);
            _translateTransform.X -= point.X - _start.X;
            _translateTransform.Y -= point.Y - _start.Y;
            _start = point;
        }
    }
}</code>

This code demonstrates how to use ViewBox to create a pannable area, how to zoom in response to mouse wheel events, and how to handle mouse events for panning. You can further customize this solution to add overlays and other features.

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