WPFExtensions ZoomControl - Pinch zoom is jumping - wpf

Question

I want to use the pinch gesture too zoom with the WPFExtensions.Controls.ZoomControl.
Based on this answer - i know how to detect the pinch gesture. I use it as member _detector. I use ZoomControl.ManipulationDelta to do the zoom.
So I thought i just take ManipulationDelta and Zoom like this:
private void AssociatedObject_ManipulationDelta(object sender, System.Windows.Input.ManipulationDeltaEventArgs e)
{
if (_detector.IsScalingAllowed) // this just tells me if it is a pinch gesture or not
{
if ((e.DeltaManipulation.Scale.X < 1)
|| (e.DeltaManipulation.Scale.X > 1))
{
//AssociatedObject is ZoomControl
AssociatedObject.Zoom = Math.Max(e.DeltaManipulation.Scale.X, e.DeltaManipulation.Scale.Y);
}
}
}
But this will just make my ZoomControl zoom pretty poor with for and back jumps.
My complete code looks like this:
public class ZoomBoxBehaviour : Behavior<ZoomControl>
{
private GestureDetector _detector;
protected override void OnAttached()
{
base.OnAttached();
if (AssociatedObject != null)
{
_detector = new GestureDetector(AssociatedObject);
if (!AssociatedObject.IsManipulationEnabled) AssociatedObject.IsManipulationEnabled = true;
AssociatedObject.ManipulationDelta += AssociatedObject_ManipulationDelta;
}
}
protected override void OnDetaching()
{
if (AssociatedObject != null)
{
AssociatedObject.ManipulationDelta -= AssociatedObject_ManipulationDelta;
}
base.OnDetaching();
}
private void AssociatedObject_ManipulationDelta(object sender, System.Windows.Input.ManipulationDeltaEventArgs e)
{
if (_detector.IsScalingAllowed) // this just tells me if it is a pinch gesture or not
{
if ((e.DeltaManipulation.Scale.X < 1)
|| (e.DeltaManipulation.Scale.X > 1))
{
AssociatedObject.Zoom = Math.Max(e.DeltaManipulation.Scale.X, e.DeltaManipulation.Scale.Y);
}
}
}
}
You can get the GestureDetector here from the first answer.
UPDATE
I made it to zoom properly to the center
private void AssociatedObject_ManipulationDelta(object sender, System.Windows.Input.ManipulationDeltaEventArgs e)
{
if (_detector.IsScalingAllowed) // this just tells me if it is a pinch gesture or not
{
if ((e.DeltaManipulation.Scale.X < 1)
|| (e.DeltaManipulation.Scale.X > 1))
{
AssociatedObject.Zoom = Math.Max(e.CumulativeManipulation.Scale.X, e.CumulativeManipulation.Scale.Y);
//Size newSize = new Size(AssociatedObject.ZoomBox.Size.Width * e.CumulativeManipulation.Scale.X,
// AssociatedObject.ZoomBox.Size.Height * e.CumulativeManipulation.Scale.Y);
//AssociatedObject.ZoomTo(new Rect(new Point(0,0), newSize));
}
}
}
But now i want to Zoom to the Center of my gesture, but this commented code will just zoom in to max .... Why?

Answer 1

I solved it
public class ZoomBoxBehaviour : Behavior<ZoomControl>
{
private GestureDetector _detector;
protected override void OnAttached()
{
base.OnAttached();
if (AssociatedObject != null)
{
_detector = new GestureDetector(AssociatedObject);
if (!AssociatedObject.IsManipulationEnabled) AssociatedObject.IsManipulationEnabled = true;
AssociatedObject.ManipulationDelta += AssociatedObject_ManipulationDelta;
}
}
protected override void OnDetaching()
{
if (AssociatedObject != null)
{
AssociatedObject.ManipulationDelta -= AssociatedObject_ManipulationDelta;
}
base.OnDetaching();
}
private void AssociatedObject_ManipulationStarting(object sender, ManipulationStartingEventArgs e)
{
e.ManipulationContainer = ((FrameworkElement)e.Source).Parent as FrameworkElement;
}
private void AssociatedObject_ManipulationDelta(object sender, System.Windows.Input.ManipulationDeltaEventArgs e)
{
if (_detector.IsPanningAllowed)
{
// Limit the X/Y translation extent to prevent the element from 'jumping' when using slow touchscreens, or many touch points.
const double translationThreshold = 100.0;
//Perform a translation(pan) tranformation
if ((e.DeltaManipulation.Translation.X < translationThreshold &&
e.DeltaManipulation.Translation.X > -translationThreshold)
)
{
AssociatedObject.TranslateX += e.DeltaManipulation.Translation.X;
}
if ((e.DeltaManipulation.Translation.Y < translationThreshold &&
e.DeltaManipulation.Translation.Y > -translationThreshold))
{
AssociatedObject.TranslateY += e.DeltaManipulation.Translation.Y;
}
}
if (_detector.IsScalingAllowed) // this just tells me if it is a pinch gesture or not
{
if ((e.CumulativeManipulation.Scale.X < 1)
|| (e.CumulativeManipulation.Scale.X > 1))
{
AssociatedObject.Zoom = Math.Max(e.CumulativeManipulation.Scale.X, e.CumulativeManipulation.Scale.Y);
}
}
}
}