Custom resizing to mouse position different then cursor position - wpf

Question

I want to resize a custom window, so windowstyle=none.
For that I do not want to use some Open-Sourelib.
So I found this article via google.
After I changed the code a bit, since i want to use a button instead of a rectangle for resizing the code looks like this:
Private bottomResize As Boolean = False
Private initBtmY As Double
Private Sub BottomResizeRect_MouseEnter _
(ByVal sender As Object, ByVal e As _
System.Windows.Input.MouseEventArgs) _
Handles btResizeAndFold.MouseEnter
bottomResize = False
'Console.WriteLine("Mouse Enter called")
End Sub
Dim boing As Boolean = False
Private Sub BottomResizeRect_MouseLeftButtonDown _
(ByVal sender As Object, ByVal e As _
System.Windows.Input.MouseButtonEventArgs) _
Handles btResizeAndFold.PreviewMouseLeftButtonDown
bottomResize = True
boing = True
'Console.WriteLine("Mouse left down called")
'Get the initial Y coordinate
'cursor location on our window
initBtmY = e.GetPosition(Me).Y
End Sub
Private Sub BottomResizeRect_MouseLeftButtonUp _
(ByVal sender As Object,
ByVal e As System.Windows.Input.MouseButtonEventArgs) _
Handles btResizeAndFold.PreviewMouseLeftButtonUp
'Console.WriteLine("Mouse left up called")
bottomResize = False
btResizeAndFold.ReleaseMouseCapture()
End Sub
Private Sub BottomResizeRect_MouseMove _
(ByVal sender As Object, ByVal e As _
System.Windows.Input.MouseEventArgs) _
Handles btResizeAndFold.PreviewMouseMove
'Get the new Y coordinate cursor location
Dim newBtmY As Double = e.GetPosition(Me).Y
'Get the change between the initial and
'new cursor location
Dim diff As Double = initBtmY - newBtmY
'Minimum window height
Dim minHeight As Integer = 200
Dim differnceConstant = 5
If bottomResize = True And (diff > differnceConstant Or diff < (differnceConstant * -1)) Then
'Let our rectangle capture the mouse
btResizeAndFold.CaptureMouse()
Dim newHeight = e.GetPosition(Me).Y - diff
If newHeight > minHeight Then
Me.Height = newHeight
End If
End If
End Sub
The problem now is, that if i try to resize my window by pressing the left mouse button and then drag the mouse, the increase/decrease of the height of my window is not synchonosly to the movement of my mouse cursor, so the question is: how to make the movement of the mouse sychronos to growth of the window

Answer 1

Instead of Button you could use Thumb, which provide with DragDelta Event that suits your requirement:
https://wpf.2000things.com/2012/12/19/715-using-the-thumb-control-to-drag-objects-on-a-canvas/
That way you dont need to capture the mouse(you shouldnt've put the CaptureMouse in the PreivewMouseMove anyway, it will do that a lot).
And just set the height as the current height + the delta Y.