Pinch Zoom Images Associated in Listbox

Question

I am trying to implement scaling in my application. I found this article ( Fix Pinch-Zoom in Silverlight ) and it works fine for a single image. But the problem is that my images are in a list as shown below XAML:

<ListBox x:Name="lstImage" Margin="-20,-23,-12,32" Height="709" Width="480"> <ListBox.ItemTemplate> <DataTemplate> <Image Source="{Binding Path=ImageSource}" VerticalAlignment="Top" Margin="10,12,10,10" Width="640" Height="800"> </Image> </DataTemplate> </ListBox.ItemTemplate> </ListBox> 

I can’t figure out how to implement this solution. Thanks in advance.

Answer 1

Create a class called PinchZomBehavior.cs and add the following code.

  public class PinchZomBehavior : Behavior<Image> { private double _totalImageScale = 1d; private Point _imagePosition = new Point(0, 0); private const double MaxImageZoom = 5; private Point _oldFinger1; private Point _oldFinger2; private double _oldScaleFactor; private Image _imgZoom; protected override void OnAttached() { _imgZoom = AssociatedObject; _imgZoom.RenderTransform = new CompositeTransform { ScaleX = 1, ScaleY = 1, TranslateX = 0, TranslateY = 0 }; var listener = GestureService.GetGestureListener(AssociatedObject); listener.PinchStarted += OnPinchStarted; listener.PinchDelta += OnPinchDelta; listener.DragDelta += OnDragDelta; listener.DoubleTap += OnDoubleTap; base.OnAttached(); } #region Pinch and Zoom Logic #region Event handlers /// <summary> /// Initializes the zooming operation /// </summary> private void OnPinchStarted(object sender, PinchStartedGestureEventArgs e) { _oldFinger1 = e.GetPosition(_imgZoom, 0); _oldFinger2 = e.GetPosition(_imgZoom, 1); _oldScaleFactor = 1; } /// <summary> /// Computes the scaling and translation to correctly zoom around your fingers. /// </summary> private void OnPinchDelta(object sender, PinchGestureEventArgs e) { var scaleFactor = e.DistanceRatio / _oldScaleFactor; if (!IsScaleValid(scaleFactor)) return; var currentFinger1 = e.GetPosition(_imgZoom, 0); var currentFinger2 = e.GetPosition(_imgZoom, 1); var translationDelta = GetTranslationDelta( currentFinger1, currentFinger2, _oldFinger1, _oldFinger2, _imagePosition, scaleFactor); _oldFinger1 = currentFinger1; _oldFinger2 = currentFinger2; _oldScaleFactor = e.DistanceRatio; UpdateImageScale(scaleFactor); UpdateImagePosition(translationDelta); } /// <summary> /// Moves the image around following your finger. /// </summary> private void OnDragDelta(object sender, DragDeltaGestureEventArgs e) { var translationDelta = new Point(e.HorizontalChange, e.VerticalChange); if (IsDragValid(1, translationDelta)) UpdateImagePosition(translationDelta); } /// <summary> /// Resets the image scaling and position /// </summary> private void OnDoubleTap(object sender, GestureEventArgs e) { ResetImagePosition(); } #endregion #region Utils /// <summary> /// Computes the translation needed to keep the image centered between your fingers. /// </summary> private Point GetTranslationDelta( Point currentFinger1, Point currentFinger2, Point oldFinger1, Point oldFinger2, Point currentPosition, double scaleFactor) { var newPos1 = new Point( currentFinger1.X + (currentPosition.X - oldFinger1.X) * scaleFactor, currentFinger1.Y + (currentPosition.Y - oldFinger1.Y) * scaleFactor); var newPos2 = new Point( currentFinger2.X + (currentPosition.X - oldFinger2.X) * scaleFactor, currentFinger2.Y + (currentPosition.Y - oldFinger2.Y) * scaleFactor); var newPos = new Point( (newPos1.X + newPos2.X) / 2, (newPos1.Y + newPos2.Y) / 2); return new Point( newPos.X - currentPosition.X, newPos.Y - currentPosition.Y); } /// <summary> /// Updates the scaling factor by multiplying the delta. /// </summary> private void UpdateImageScale(double scaleFactor) { _totalImageScale *= scaleFactor; ApplyScale(); } /// <summary> /// Applies the computed scale to the image control. /// </summary> private void ApplyScale() { ((CompositeTransform)_imgZoom.RenderTransform).ScaleX = _totalImageScale; ((CompositeTransform)_imgZoom.RenderTransform).ScaleY = _totalImageScale; } /// <summary> /// Updates the image position by applying the delta. /// Checks that the image does not leave empty space around its edges. /// </summary> private void UpdateImagePosition(Point delta) { var newPosition = new Point(_imagePosition.X + delta.X, _imagePosition.Y + delta.Y); if (newPosition.X > 0) newPosition.X = 0; if (newPosition.Y > 0) newPosition.Y = 0; if ((_imgZoom.ActualWidth * _totalImageScale) + newPosition.X < _imgZoom.ActualWidth) newPosition.X = _imgZoom.ActualWidth - (_imgZoom.ActualWidth * _totalImageScale); if ((_imgZoom.ActualHeight * _totalImageScale) + newPosition.Y < _imgZoom.ActualHeight) newPosition.Y = _imgZoom.ActualHeight - (_imgZoom.ActualHeight * _totalImageScale); _imagePosition = newPosition; ApplyPosition(); } /// <summary> /// Applies the computed position to the image control. /// </summary> private void ApplyPosition() { ((CompositeTransform)_imgZoom.RenderTransform).TranslateX = _imagePosition.X; ((CompositeTransform)_imgZoom.RenderTransform).TranslateY = _imagePosition.Y; } /// <summary> /// Resets the zoom to its original scale and position /// </summary> private void ResetImagePosition() { _totalImageScale = 1; _imagePosition = new Point(0, 0); ApplyScale(); ApplyPosition(); } /// <summary> /// Checks that dragging by the given amount won't result in empty space around the image /// </summary> private bool IsDragValid(double scaleDelta, Point translateDelta) { if (_imagePosition.X + translateDelta.X > 0 || _imagePosition.Y + translateDelta.Y > 0) return false; if ((_imgZoom.ActualWidth * _totalImageScale * scaleDelta) + (_imagePosition.X + translateDelta.X) < _imgZoom.ActualWidth) return false; if ((_imgZoom.ActualHeight * _totalImageScale * scaleDelta) + (_imagePosition.Y + translateDelta.Y) < _imgZoom.ActualHeight) return false; return true; } /// <summary> /// Tells if the scaling is inside the desired range /// </summary> private bool IsScaleValid(double scaleDelta) { return (_totalImageScale * scaleDelta >= 1) && (_totalImageScale * scaleDelta <= MaxImageZoom); } #endregion #endregion } 

And attach behavior to image management like this

  xmlns:i="clr-namespace:System.Windows.Interactivity;assembly=System.Windows.Interactivity" <Image Stretch="Uniform" Source="{Binding Image}" CacheMode="BitmapCache"> <i:Interaction.Behaviors> <Behaviors:PinchZomBehavior/> </i:Interaction.Behaviors> </Image>