A Silverlight custom control for zooming and panning with a small window to see he image with thumb

• Download source code - 1.74 MB

Introduction

This article provides the ability to interactively view high resolution images. You can zoom in and zoom out images. This Silverlight custom control enables deep zooming using Storyboard animation and smooth panning by handling the MouseLeftButtonDown, MouseLeftButtonUp, and MouseMove events. The following features are included:

• Deep zooming
• Panning an image
• Small window with thumb to view the exact location of the zoomed image

Background

Deep zooming is a pretty straightforward functionality and is done with the ScaleTransform property. Panning is done by setting the offset X and Y of the content. Silverlight 3 has a MultiscaleImage control for zooming multi-resolution images. It has a Source property to set multiple images.

In this article, I have created a custom zoom control for zooming and panning single images with animation for smooth panning.

Using the Code

1. Creating a custom zoom and pan control using Silverlight 4 Class Library

First, create a class for zoom and pan which inherits from ContentControl and implements the IScrollInfo interface to move the thumb image within the area. This class contains Rectangle properties and animation methods for setting the content offset in X,Y coordinates with point zooming. It overrides the Size method to change the image size and scale of images. It has a Generic Style for setting the Template for the control with properties. This style is imported to the class.

2. Using the control in a Silverlight application
• Create a Silverlight application to use the zoom and pan custom Silverlight control.

In the Silverlight application, create an enum to handle the mouse modes.

MouseHandlingMode.cs

public enum MouseHandlingMode
{
    None,
    DraggingRectangles,
    Panning,
    Zooming,
    DragZooming,
}

Create a class having Dependency Properties for setting the scale, width, height, offset etc., and implement the InotifyPropertyChanged interface to change the property value.

• Declare all the Dependecy properties and the collection for the example.

public class DataModel : INotifyPropertyChanged
{
    private ObservableCollection<RectangleData> rectangles = 
            new ObservableCollection<RectangleData>();
    private double contentScale = 1;
 
    public static DataModel Instance
    {
        get{return instance; }
    }
    public ObservableCollection<RectangleData> Rectangles
    {
        get{return rectangles; }
    }
    public double ContentScale
    {
        get{return contentScale; }
        set
        {
            contentScale = value;
            OnPropertyChanged("ContentScale");
        }
    }

    . . . . .
}

Create a Converter class to convert the scale value to percent for the Slider control:

public class ScaleToPercentConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, 
                          CultureInfo culture)
    {   
        return (double)(int)((double)value * 100.0);
    }

    public object ConvertBack(object value, Type targetType, object parameter, 
                              CultureInfo culture)
    {
        return (double)value / 100.0;
    }
}

Create a class for drawing the rectangle.

• Now create the UserControl (HAEZoomingControl.xaml) to use the custom Silverlight control in the page.
• Add the custom ZoomingAndPanning control to the page.

<ZoomAndPan:ZoomAndPanControl Grid.Row="0"
    x:Name="zoomAndPanControl"
    ContentScale= "{Binding Source={StaticResource 
                 TypeProvider}, Path=Instance.ContentScale, Mode=TwoWay}"
    ContentOffsetX= "{Binding Source={StaticResource 
                 TypeProvider}, Path=Instance.ContentOffsetX, Mode=TwoWay}"
    ContentOffsetY= "{Binding Source={StaticResource TypeProvider}, 
                 Path=Instance.ContentOffsetY, Mode=TwoWay}"
    ContentViewportWidth="{Binding Source={StaticResource TypeProvider}, 
                 Path=Instance.ContentViewportWidth, Mode=TwoWay}"
    ContentViewportHeight= "{Binding Source={StaticResource TypeProvider}, 
                 Path=Instance.ContentViewportHeight, Mode=TwoWay}"
    Background="{StaticResource pageBackground}"
    MouseMove="zoomAndPanControl_MouseMove"
    MouseWheel="zoomAndPanControl_MouseWheel"
    MouseLeftButtonDown="zoomAndPanControl_MouseLeftButtonDown"
    MouseLeftButtonUp="zoomAndPanControl_MouseLeftButtonUp">
    .
    .
    .
</ZoomAndPan:ZoomAndPanControl>

• Add ZoomIn, ZoomOut buttons and a Silder:

<Button x:Name="btnZoomOut"
    Grid.Column="8" 
    Click="btnZoomOut_Click">-</Button>
       <Slider Grid.Column="10"
          x:Name="changeSlider"
          Minimum="{Binding MinPercentage}"
          Maximum="{Binding MaxPercentage}"
          Value= "{Binding ElementName=zoomAndPanControl, 
                  Path=ContentScale, Converter={StaticResource 
                  scaleToPercentConverter},Mode=TwoWay}" />
       <Button x:Name="btnZoomIn"
          Grid.Column="12"
          Click="btnZoomIn_Click">+</Button>

• Add a popup the contains a small image in a grid and a thumb (rectangle) to view the zooming image position.

<Popup x:Name="MyPOP"
        MouseLeftButtonDown="MyPOP_MouseLeftButtonDown"
        IsOpen="False">
    <StackPanel Width="200" Height="200">
    <ZoomAndPan:ZoomAndPanControl x:Name="overview"
        Width="200" Height="200"
        Background="{StaticResource popupBackground}"
        SizeChanged="overview_SizeChanged"
        Opacity="0.9">
    <Grid Width="{Binding Source={StaticResource TypeProvider}, 
                    Path=Instance.ContentWidth,Mode=TwoWay}"
       Height="{Binding Source={StaticResource TypeProvider}, 
               Path=Instance.ContentHeight,Mode=TwoWay}"
       SizeChanged="overview_SizeChanged">
    <Image x:Name="content2" Source="{Binding ImgSource}"
        VerticalAlignment="Center" HorizontalAlignment="Center"></Image>
    <Canvas>
      <Thumb x:Name="overviewZoomRectThumb"
        Canvas.Left="{Binding Source={StaticResource TypeProvider}, 
                     Path=Instance.ContentOffsetX, Mode=TwoWay}"
        Canvas.Top="{Binding Source={StaticResource TypeProvider}, 
                    Path=Instance.ContentOffsetY, Mode=TwoWay}"
        Width="{Binding Source={StaticResource TypeProvider}, 
               Path=Instance.ContentViewportWidth, Mode=TwoWay}"
        Height="{Binding Source={StaticResource TypeProvider}, 
                Path=Instance.ContentViewportHeight, Mode=TwoWay}"
        DragDelta="overviewZoomRectThumb_DragDelta"
        Opacity="0.5">
     <Thumb.Template>

<ControlTemplate TargetType="Thumb">
  <Border BorderBrush="Black"
      BorderThickness="3" Background="Yellow"
      CornerRadius="3" />
 </ControlTemplate>
</Thumb.Template>
</Thumb>
</Canvas>
</Grid>
</ZoomAndPan:ZoomAndPanControl>
</StackPanel>
</Popup>

• In the code-behind (HAEZoomingControl.xaml.cs), write events for MouseMove, LeftButtonDown, LeftButtonUp, and DoubleClcik. The MouseDoubleClick event is not available in Silverlight so you can use MouseLeftButtonDown instead to count clicks.

For example:

• Declare a timer variable to detect double click:

DispatcherTimer _timer;

• Declare an interval variable:

private static int INTERVAL = 200;

• In the default constructor, create an instance of the timer.

public HAEZoomingControl()
{
    InitializeComponent();
    _timer = new DispatcherTimer();
    zoomAndPanControl.ContentOffsetY = 200;
    _timer.Interval = new TimeSpan(0, 0, 0, 0, INTERVAL);
    _timer.Tick += new EventHandler(_timer_Tick);
}

• Add an event to stop the timer:

void _timer_Tick(object sender, EventArgs e)
{
    _timer.Stop();
}

• In the MouseLeftButtonDown event of the control use, times to check for double click.

private void zoomAndPanControl_MouseLeftButtonDown(
        object sender, MouseButtonEventArgs e)
{
    if (zoomAndPanControl.ContentScale <= (MaxPercentage / 100))
        btnZoomIn.IsEnabled = true;
    if (zoomAndPanControl.ContentScale >= (MinPercentage / 100))
        btnZoomOut.IsEnabled = true;
    if (_timer.IsEnabled)
    {
        if (zoomAndPanControl.ContentScale <= (MaxPercentage / 100))
        {
            _timer.Stop();
            sb = new Storyboard();
            DoubleAnimation db = new DoubleAnimation();
            sb.Children.Add(db);
            sb.Completed += new EventHandler(sb_Completed);
            db.To = zoomAndPanControl.ContentScale + 0.2;
            db.Duration = new Duration(TimeSpan.FromSeconds(0.3));
            Storyboard.SetTarget(db, zoomAndPanControl);
            Storyboard.SetTargetProperty(db, 
                       new PropertyPath("ContentScale"));
            sb.Begin();
        }
        else
        {
            btnZoomIn.IsEnabled = false;
        }
    }
    else
    {
        _timer.Start();
        if (zoomAndPanControl.ContentScale >= (MinPercentage / 100))
        {
            origZoomAndPanControlMouseDownPoint = 
                    e.GetPosition(zoomAndPanControl);
            origContentMouseDownPoint = e.GetPosition(content);
            mouseHandlingMode = MouseHandlingMode.Panning;
            if (mouseHandlingMode != MouseHandlingMode.None)
            {
                zoomAndPanControl.CaptureMouse();
                e.Handled = true;
            }
        }
    }
}

• Write code for the other events and run the application.

In the image below, you can see a zoomed image and a small image on the bottom-right side of the canvas to see the offset position of the zoomed image using the yellow thumb marker.

You can zoom the image using these controls in the bottom-right corner of the page: ZoomIn, ZoomOut buttons and the Slider control.

Points of Interest

Before creating this application in Silverlight, I referred to this article byf Ashley Davis: A WPF custom control for zooming and panning). His article was great for understanding how to create rectangles, use a Dependency Property, create a custom control with Themes using the DefaultStyleKey property, and scale images etc. Here is the link to the control:

• http://www.codeproject.com/KB/WPF/zoomandpancontrol.aspx

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)