public virtual void ProcessMouseLeftButtonDown(MouseButtonEventArgs e)
{
if (e.Handled)
{
return;
}
#if DEBUG
this.CheckMouseEventArgs(e);
#endif
if (!this.DraggedElement.CaptureMouse())
{
Debug.Fail("The DragSourceManager was unable to capture the mouse on the dragged element.");
return;
}
//Get the current window (which can be a popup) on which the drag is happening
var parent = this.GetDraggedElementWindow();
this.InitialMousePositionToDragContainerAdorner = e.GetPosition(this.AdornerLayerInsideDragContainer);
this.InitialMousePositionToDraggedElement = e.GetPosition(this.DraggedElement);
this.MouseToScreenPositionFactor = DragSourceManager.CalculateMouseToScreenPositionFactor(parent);
this.ParentWindowIsPopup = (parent is Popup);
var draggedElementMousePosition = e.GetPosition(this.DraggedElement);
m_draggedElementMouseOffset = new Vector(draggedElementMousePosition.X, draggedElementMousePosition.Y);
}
private static Vector CalculateMouseToScreenPositionFactor(FrameworkElement element)
{
if (element == null)
{
return(new Vector(1d, 1d));
}
var source = PresentationSource.FromVisual(element);
if (source == null)
{
var parent = DragSourceManager.GetPopupParent(element);
while (parent != null)
{
source = PresentationSource.FromDependencyObject(parent);
if (source != null)
{
break;
}
parent = DragSourceManager.GetPopupParent(parent);
}
}
double x, y;
if (source != null)
{
var deviceUnits = source.CompositionTarget.TransformToDevice;
x = deviceUnits.M11;
y = deviceUnits.M22;
}
else
{
using (var hwnd = new HwndSource(new HwndSourceParameters()))
{
var deviceUnits = hwnd.CompositionTarget.TransformToDevice;
x = deviceUnits.M11;
y = deviceUnits.M22;
}
}
return(new Vector((x == 0d) ? 1d : 1d / x, (y == 0d) ? 1d : 1d / y));
}