WPFExtensions ZoomControl - Pinch zoom is jumping

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);
                }
            }

        }

    }