Silverlight panning capture

Question

I have a Canvas inside a ScrollViewer. I want the user to be able to grab the canvas and move it, with the thumb on the scroll bar refresh. My initial implementation calculates the offset at each mouse move and updates the scroll bars:

 // Calculate the new drag distance
 Point newOffsetPos = e.GetPosition(MapCanvas);
 System.Diagnostics.Debug.WriteLine("   newOffsetPos : " + newOffsetPos.X + " " + newOffsetPos.Y);

 double deltaX = newOffsetPos.X - _offsetPosition.X ;
 double deltaY = newOffsetPos.Y - _offsetPosition.Y ;

 System.Diagnostics.Debug.WriteLine("   delta X / Y : " + deltaX + " " + deltaY);
 System.Diagnostics.Debug.WriteLine("   sv offsets X / Y : " + _scrollViewer.HorizontalOffset + " " + _scrollViewer.VerticalOffset);

 _scrollViewer.ScrollToHorizontalOffset(_scrollViewer.HorizontalOffset - deltaX);
 _scrollViewer.ScrollToVerticalOffset(_scrollViewer.VerticalOffset - deltaY);

 _offsetPosition = newOffsetPos;

While this works, it is not very smooth.
Is there a better way to do this? If Transforms are used, will scrollbars automatically update when moving the canvas?
Thanks for any advice ...

Answer 1

. Silverlight.

- , , . , , . Repro: -

Silverlight . MainPage.Xaml : -

<UserControl x:Class="SilverlightApplication1.MainPage"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
    <Grid x:Name="LayoutRoot" Background="White">
        <ScrollViewer x:Name="Scroller" HorizontalScrollBarVisibility="Auto">
            <Image x:Name="Map" Source="test.jpg" Width="1600" Height="1200" />
        </ScrollViewer>
    </Grid>
</UserControl>

MainPage.xaml.cs: -

    public MainPage()
    {
        InitializeComponent();
        Map.MouseLeftButtonDown += new MouseButtonEventHandler(Map_MouseLeftButtonDown);
    }

    void Map_MouseLeftButtonDown(object sender, MouseButtonEventArgs e)
    {
        Point mapOrigin = new Point(Scroller.HorizontalOffset, Scroller.VerticalOffset);
        Point mouseOrigin = e.GetPosition(Application.Current.RootVisual);

        MouseEventHandler moveHandler = null;
        MouseButtonEventHandler upHandler = null;

        moveHandler = (s, args) =>
        {
            Point mouseNew = args.GetPosition(Application.Current.RootVisual);
            Scroller.ScrollToHorizontalOffset(mapOrigin.X - (mouseNew.X - mouseOrigin.X));
            Scroller.ScrollToVerticalOffset(mapOrigin.Y - (mouseNew.Y - mouseOrigin.Y));
        };


        upHandler = (s, args) =>
        {
            Scroller.MouseMove -= moveHandler;
            Scroller.MouseLeftButtonUp -= upHandler;
        };

        Scroller.MouseMove += moveHandler;
        Scroller.MouseLeftButtonUp += upHandler;
    }
}

test.jpg( 1600x1200 Image ).

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Answer 2

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