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Posted 29 Jul 2010

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WPF simple zoom and drag support in a ScrollViewer

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4.98/5 (60 votes)
6 Nov 2013CPOL
A sample describing a way to zoom with the mouse wheel or a slider and drag limited content which is hosted by a ScrollViewer.

WpfZoomAndDragPanel/Overview_Resized.png

Introduction

I've been looking for a while for Open Source solutions that show a simple way of zooming and dragging arbitrary content which is hosted and managed by a ScrollViewer.

As I did not find a free one, I decided to write my own one and share it with you. It supports zooming by a slider as well as by the mouse wheel.

Using the code

If you have any questions regarding the usage, please feel free to post and I'll try to get back to you ASAP. 

The main view is defined by the XAML below. The content that is to be zoomed and dragged is part of the "grid" control.

XML
<Window x:Class="ZoomExample.MainWindow"
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
        Title="MainWindow" Height="500" Width="500">
    <Window.Resources>
        <ResourceDictionary>
            <ResourceDictionary.MergedDictionaries>
                <ResourceDictionary Source="Resources.xaml"/>
            </ResourceDictionary.MergedDictionaries>
        </ResourceDictionary>
    </Window.Resources>
    <Grid>
        <Grid.ColumnDefinitions>
            <ColumnDefinition Width="Auto"/>
            <ColumnDefinition Width="*"/>
        </Grid.ColumnDefinitions>
        <Slider Grid.Column="0" Orientation="Vertical" 
           HorizontalAlignment="Left" Minimum="1" x:Name="slider"/>
        <ScrollViewer Name="scrollViewer" Grid.Column="1" 
              VerticalScrollBarVisibility="Visible" 
              HorizontalScrollBarVisibility="Visible">
            
            <Grid Name="grid" Width="400" 
              Height="400" RenderTransformOrigin="0.5,0.5">
                <Grid.LayoutTransform>
                    <TransformGroup>
                        <ScaleTransform x:Name="scaleTransform"/>
                    </TransformGroup>
                </Grid.LayoutTransform>
                <Viewbox Grid.Column="0" Grid.Row="0">
                    <ContentPresenter Content="{StaticResource Kompass}"/>
                </Viewbox>
            </Grid>
            
        </ScrollViewer>
    </Grid>
</Window>

Zooming and dragging is managed by the code-behind:

C#
public partial class MainWindow : Window
{
    Point? lastCenterPositionOnTarget;
    Point? lastMousePositionOnTarget;
    Point? lastDragPoint;

    public MainWindow()
    {
        InitializeComponent();

        scrollViewer.ScrollChanged += OnScrollViewerScrollChanged;
        scrollViewer.MouseLeftButtonUp += OnMouseLeftButtonUp;
        scrollViewer.PreviewMouseLeftButtonUp += OnMouseLeftButtonUp;
        scrollViewer.PreviewMouseWheel += OnPreviewMouseWheel;

        scrollViewer.PreviewMouseLeftButtonDown += OnMouseLeftButtonDown;
        scrollViewer.MouseMove += OnMouseMove;

        slider.ValueChanged += OnSliderValueChanged;
    }

    void OnMouseMove(object sender, MouseEventArgs e)
    {
        if (lastDragPoint.HasValue)
        {
            Point posNow = e.GetPosition(scrollViewer);

            double dX = posNow.X - lastDragPoint.Value.X;
            double dY = posNow.Y - lastDragPoint.Value.Y;

            lastDragPoint = posNow;

            scrollViewer.ScrollToHorizontalOffset(scrollViewer.HorizontalOffset - dX);
            scrollViewer.ScrollToVerticalOffset(scrollViewer.VerticalOffset - dY);
        }
    }

    void OnMouseLeftButtonDown(object sender, MouseButtonEventArgs e)
    {
        var mousePos = e.GetPosition(scrollViewer);
        if (mousePos.X <= scrollViewer.ViewportWidth && mousePos.Y < 
            scrollViewer.ViewportHeight) //make sure we still can use the scrollbars
        {
            scrollViewer.Cursor = Cursors.SizeAll;
            lastDragPoint = mousePos;
            Mouse.Capture(scrollViewer);
        }
    }

    void OnPreviewMouseWheel(object sender, MouseWheelEventArgs e)
    {
        lastMousePositionOnTarget = Mouse.GetPosition(grid);

        if (e.Delta > 0)
        {
            slider.Value += 1;
        }
        if (e.Delta < 0)
        {
            slider.Value -= 1;
        }

        e.Handled = true;
    }

    void OnMouseLeftButtonUp(object sender, MouseButtonEventArgs e)
    {
        scrollViewer.Cursor = Cursors.Arrow;
        scrollViewer.ReleaseMouseCapture();
        lastDragPoint = null;
    }

    void OnSliderValueChanged(object sender, 
         RoutedPropertyChangedEventArgs<double> e)
    {
        scaleTransform.ScaleX = e.NewValue;
        scaleTransform.ScaleY = e.NewValue;

        var centerOfViewport = new Point(scrollViewer.ViewportWidth/2, 
                                         scrollViewer.ViewportHeight/2);
        lastCenterPositionOnTarget = scrollViewer.TranslatePoint(centerOfViewport, grid);
    }

    void OnScrollViewerScrollChanged(object sender, ScrollChangedEventArgs e)
    {
        if (e.ExtentHeightChange != 0 || e.ExtentWidthChange != 0)
        {
            Point? targetBefore = null;
            Point? targetNow = null;

            if (!lastMousePositionOnTarget.HasValue)
            {
                if (lastCenterPositionOnTarget.HasValue)
                {
                    var centerOfViewport = new Point(scrollViewer.ViewportWidth/2, 
                                                     scrollViewer.ViewportHeight/2);
                    Point centerOfTargetNow = 
                          scrollViewer.TranslatePoint(centerOfViewport, grid);

                    targetBefore = lastCenterPositionOnTarget;
                    targetNow = centerOfTargetNow;
                }
            }
            else
            {
                targetBefore = lastMousePositionOnTarget;
                targetNow = Mouse.GetPosition(grid);

                lastMousePositionOnTarget = null;
            }

            if (targetBefore.HasValue)
            {
                double dXInTargetPixels = targetNow.Value.X - targetBefore.Value.X;
                double dYInTargetPixels = targetNow.Value.Y - targetBefore.Value.Y;

                double multiplicatorX = e.ExtentWidth/grid.Width;
                double multiplicatorY = e.ExtentHeight/grid.Height;

                double newOffsetX = scrollViewer.HorizontalOffset - 
                                    dXInTargetPixels*multiplicatorX;
                double newOffsetY = scrollViewer.VerticalOffset - 
                                    dYInTargetPixels*multiplicatorY;

                if (double.IsNaN(newOffsetX) || double.IsNaN(newOffsetY))
                {
                    return;
                }

                scrollViewer.ScrollToHorizontalOffset(newOffsetX);
                scrollViewer.ScrollToVerticalOffset(newOffsetY);
            }
        }
    }
}

License

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


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Comments and Discussions

 
Questionhow to use with image component? Pin
Wagner Elias 202131-Mar-22 20:45
Wagner Elias 202131-Mar-22 20:45 
QuestionExcelent Pin
ALEX06219-Jul-16 2:01
ALEX06219-Jul-16 2:01 
GeneralMy vote of 5 Pin
mkaze9-Aug-15 0:43
mkaze9-Aug-15 0:43 
Suggestionif consider ... Pin
Akcrios5-May-15 17:37
Akcrios5-May-15 17:37 
GeneralThank you very much for you article! Pin
Akcrios5-May-15 17:27
Akcrios5-May-15 17:27 
QuestionZoom on a click Pin
Shyamala_12316-Feb-15 19:52
Shyamala_12316-Feb-15 19:52 
GeneralMy vote of 5 Pin
amir_pro3-Feb-15 9:45
amir_pro3-Feb-15 9:45 
GeneralMy vote of 5 Pin
amir_pro3-Feb-15 9:43
amir_pro3-Feb-15 9:43 
QuestionGreat work Pin
GPans11-Oct-13 10:53
GPans11-Oct-13 10:53 
GeneralMy vote of 5 Pin
Bijay Kant Salotry19-Sep-13 7:52
Bijay Kant Salotry19-Sep-13 7:52 
GeneralMy vote of 5 Pin
John Bracey20-Jun-13 22:50
John Bracey20-Jun-13 22:50 
NewsMy vote of 5 Pin
Shahin Khorshidnia11-Jun-13 22:19
professionalShahin Khorshidnia11-Jun-13 22:19 
GeneralMy vote of 5 Pin
AdolfoPerez6-Jun-13 5:27
AdolfoPerez6-Jun-13 5:27 
Questionrotation Pin
redjzuzzj4-Jun-13 16:22
redjzuzzj4-Jun-13 16:22 
QuestionSplendid! Pin
Porgram Lover24-Feb-13 12:34
Porgram Lover24-Feb-13 12:34 
GeneralMy vote of 5 Pin
arturo134631-Oct-12 6:37
arturo134631-Oct-12 6:37 
GeneralMy vote of 5 Pin
Vivek Sharma 215-Jun-12 0:21
Vivek Sharma 215-Jun-12 0:21 
GeneralMy vote of 5 Pin
njdnjdnjdnjdnjd16-May-12 7:27
njdnjdnjdnjdnjd16-May-12 7:27 
GeneralMy vote of 5 Pin
Dezfoul18-Apr-12 20:29
Dezfoul18-Apr-12 20:29 
EXCELLENT
QuestionCreated some helper classes Pin
kgoulding18-Jan-12 11:03
kgoulding18-Jan-12 11:03 
QuestionRe: Created some helper classes Pin
Member 94426811-Jul-13 23:24
Member 94426811-Jul-13 23:24 
GeneralMy vote of 5 Pin
Ubloobok22-Oct-11 22:46
Ubloobok22-Oct-11 22:46 
GeneralMy vote of 5 Pin
Koss8712-Jun-11 15:22
Koss8712-Jun-11 15:22 
GeneralThanks for the Demo! Pin
(noor)31-Mar-11 4:49
(noor)31-Mar-11 4:49 
GeneralRe: Thanks for the Demo! Pin
Akcrios5-May-15 17:17
Akcrios5-May-15 17:17 

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