WPF handle Pinch Zoom on Touchpad - wpf

Question

I have a WPF TextBlock. I am controlling the font size by using ManipulationDelta, to simulate zooming in/out. It's currently in a very crude way, but it works.
This works for a touchscreen, but I want the same behaviour to work on my laptop touchpad - i.e. two-finger pinch-zoom.
What's the event I need to hook into to make this work?
The touch code is as follows:
<TextBlock Name="txbl_displaySong" Foreground="White" FontFamily="Lucida Console"
FontSize="22" Text="{Binding Path=T.SelectedSong.TransposedChordsOverLyrics, Mode=OneWay, UpdateSourceTrigger=PropertyChanged}"
Padding="20" TextWrapping="Wrap" IsManipulationEnabled="True"
ManipulationDelta="txbl_displaySong_ManipulationDelta"
ManipulationCompleted="Txbl_displaySong_ManipulationCompleted"
TouchDown="Txbl_displaySong_TouchDown"
MouseDown="Txbl_displaySong_MouseDown"/>
Code Behind:
Dim isPinchIn As Boolean = False
Dim isPinchOut As Boolean = False
Dim prevScale As Double = 0
Private Sub Txbl_displaySong_ManipulationCompleted(sender As Object, e As ManipulationCompletedEventArgs)
prevScale = 0
isPinchIn = False
isPinchOut = False
End Sub
Private Sub txbl_displaySong_ManipulationDelta(sender As Object, e As ManipulationDeltaEventArgs)
Dim tScale As Double = e.CumulativeManipulation.Scale.Length
If (prevScale > 0) Then
isPinchIn = isPinchIn OrElse prevScale > tScale ' if same scale, assume no change
isPinchOut = isPinchOut OrElse prevScale < tScale ' if same scale, assume no change
End If
prevScale = tScale
Dim mCount As Integer = e.Manipulators.Count
...
If mCount = 2 Then
If isPinchIn Then
txbl_displaySong.FontSize = Math.Max(6.0, txbl_displaySong.FontSize - 0.2) ' limit to 6
ElseIf isPinchOut Then
txbl_displaySong.FontSize = Math.Min(40.0, txbl_displaySong.FontSize + 0.2) ' limit to 40
Else
End If
End If
End Sub
...

Answer 1

I have the same problem, and I figured out a workaround which half solves it:
Wire up some code to the MouseWheel event:
private void Canvas_MouseWheel(object sender, MouseWheelEventArgs e)
{
if (e.Delta > 0)
...
else if (e.Delta < 0)
...
}
With my touchpad, I get a Delta of either 120 or -120 depending on whether I'm pinching to zoom in or pinching to zoom out.