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WPF simple zoom and drag support in a ScrollViewer

, 6 Nov 2013
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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.

<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:

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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About the Author

Kevin Stumpf

Germany Germany
No Biography provided

Comments and Discussions

 
QuestionGreat work PinmemberGPans11-Oct-13 9:53 
GeneralMy vote of 5 PinmemberBijay Kant Salotry19-Sep-13 6:52 
GeneralMy vote of 5 PingroupJohn Bracey20-Jun-13 21:50 
NewsMy vote of 5 PinmemberShahin Khorshidnia11-Jun-13 21:19 
GeneralMy vote of 5 PinmemberAdolfoPerez6-Jun-13 4:27 
Questionrotation Pinmemberredjzuzzj4-Jun-13 15:22 
QuestionSplendid! PinmemberPorgram Lover24-Feb-13 11:34 
GeneralMy vote of 5 Pinmemberarturo134631-Oct-12 5:37 
GeneralMy vote of 5 PinmemberMember 406769614-Jun-12 23:21 
GeneralMy vote of 5 Pinmembernjdnjdnjdnjdnjd16-May-12 6:27 
GeneralMy vote of 5 PinmemberDezfoul18-Apr-12 19:29 
QuestionCreated some helper classes [modified] Pinmemberkgoulding18-Jan-12 10:03 
QuestionRe: Created some helper classes PinmemberMember 94426811-Jul-13 22:24 
GeneralMy vote of 5 PinmemberUbloobok22-Oct-11 21:46 
GeneralMy vote of 5 PinmemberKoss8712-Jun-11 14:22 
GeneralThanks for the Demo! Pinmember(noor)31-Mar-11 3:49 
GeneralSounds familiar... PinmemberAshley Davis30-Jul-10 3:03 
GeneralLike it, been there too, I did a Friction one too PinmvpSacha Barber29-Jul-10 23:11 
GeneralProblem to download Pinmembersinun29-Jul-10 11:46 
GeneralRe: Problem to download PinmemberD-Lay29-Jul-10 12:25 
GeneralFixed PinmemberKevin Stumpf29-Jul-10 14:32 

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