Fluent.ComboBox.SetDragHeight C# (CSharp) Method

        private void SetDragHeight(DragDeltaEventArgs e)
        {
            if (!canSizeY) return;
            if (double.IsNaN(scrollViewer.Height)) scrollViewer.Height = scrollViewer.ActualHeight;
            if (ShowPopupOnTop)
            {
                double monitorTop = RibbonControl.GetControlMonitor(this).Top;

                // Calc shadow height
                double delta = this.PointToScreen(new Point()).Y - dropDownBorder.ActualHeight - e.VerticalChange - monitorTop;
                if (delta > 0)
                {
                    scrollViewer.Height =
                        Math.Min(Math.Max(galleryPanel.GetItemSize().Height, scrollViewer.Height + e.VerticalChange),
                                 MaxDropDownHeight);
                }
                else
                {
                    delta = this.PointToScreen(new Point()).Y - dropDownBorder.ActualHeight - monitorTop;
                    scrollViewer.Height =
                        Math.Min(Math.Max(galleryPanel.GetItemSize().Height, scrollViewer.Height + delta),
                                 MaxDropDownHeight);
                }
            }
            else
            {
                double monitorBottom = RibbonControl.GetControlMonitor(this).Bottom;
                FrameworkElement popupChild = popup.Child as FrameworkElement;
                double delta = monitorBottom - this.PointToScreen(new Point()).Y - ActualHeight - popupChild.ActualHeight - e.VerticalChange;
                if (delta > 0)
                {
                    scrollViewer.Height =
                        Math.Min(Math.Max(galleryPanel.GetItemSize().Height, scrollViewer.Height + e.VerticalChange),
                                 MaxDropDownHeight);
                }
                else
                {
                    delta = monitorBottom - this.PointToScreen(new Point()).Y - ActualHeight - popupChild.ActualHeight;
                    scrollViewer.Height =
                        Math.Min(Math.Max(galleryPanel.GetItemSize().Height, scrollViewer.Height + delta),
                                 MaxDropDownHeight);
                }
            }
        }