Fix incorrect ComboxPopup position when used ScaleTransform #2179 (#2180)

* Fix incorrect ComboxPopup position when used ScaleTranform #2179

* Update ScaleHelper.cs

Author: FooPenguin

MaterialDesignThemes.Wpf/ComboBoxPopup.cs

@@ -287,6 +287,9 @@ private PositioningData GetPositioningData(IEnumerable<DependencyObject?> visual
             var mainVisual = visualAncestry.OfType<Visual>().LastOrDefault();
             if (mainVisual is null) throw new ArgumentException($"{nameof(visualAncestry)} must contains unless one {nameof(Visual)} control inside.");
 
+            var controlVisual = visualAncestry.OfType<Visual>().FirstOrDefault();
+            if (controlVisual == null) throw new ArgumentException($"{nameof(visualAncestry)} must contains unless one {nameof(Visual)} control inside.");
+
             var screen = Screen.FromPoint(locationFromScreen);
             var screenWidth = (int)screen.Bounds.Width;
             var screenHeight = (int)screen.Bounds.Height;
@@ -295,10 +298,10 @@ private PositioningData GetPositioningData(IEnumerable<DependencyObject?> visual
             var locationX = (int)(locationFromScreen.X - screen.Bounds.X) % screenWidth;
             var locationY = (int)(locationFromScreen.Y - screen.Bounds.Y) % screenHeight;
 
-            var upVerticalOffsetIndependent = DpiHelper.TransformToDeviceY(mainVisual, UpVerticalOffset);
+            var upVerticalOffsetIndependent = DpiHelper.TransformToDeviceY(mainVisual, UpVerticalOffset) * ScaleHelper.GetTotalTransformScaleY(controlVisual);
             var newUpY = upVerticalOffsetIndependent - popupSize.Height + targetSize.Height;
-            var newDownY = DpiHelper.TransformToDeviceY(mainVisual, DownVerticalOffset);
-            var offsetX = DpiHelper.TransformToDeviceX(mainVisual, RelativeHorizontalOffset);
+            var newDownY = DpiHelper.TransformToDeviceY(mainVisual, DownVerticalOffset) * ScaleHelper.GetTotalTransformScaleY(controlVisual);
+            var offsetX = DpiHelper.TransformToDeviceX(mainVisual, RelativeHorizontalOffset) * ScaleHelper.GetTotalTransformScaleX(controlVisual);
             if (FlowDirection == FlowDirection.LeftToRight)
                 offsetX = Round(offsetX);
             else

MaterialDesignThemes.Wpf/ScaleHelper.cs

@@ -0,0 +1,61 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Text;
+using System.Threading.Tasks;
+using System.Windows;
+using System.Windows.Media;
+
+namespace MaterialDesignThemes.Wpf
+{
+    internal static class ScaleHelper
+    {
+        internal static double GetTotalTransformScaleX(Visual visual)
+        {
+            double totalTransform = 1.0d;
+            DependencyObject currentVisualTreeElement = visual;
+            do
+            {
+                if (currentVisualTreeElement is Visual)
+                {
+                    visual = (Visual)currentVisualTreeElement;
+                    Transform transform = VisualTreeHelper.GetTransform(visual);
+                    if ((transform != null) &&
+                        (transform.Value.M12 == 0) &&
+                        (transform.Value.OffsetX == 0))
+                    {
+                        totalTransform *= transform.Value.M11;
+                    }
+                }
+                currentVisualTreeElement = VisualTreeHelper.GetParent(currentVisualTreeElement);
+            }
+            while (currentVisualTreeElement != null);
+
+            return totalTransform;
+        }
+
+        internal static double GetTotalTransformScaleY(Visual visual)
+        {
+            double totalTransform = 1.0d;
+            DependencyObject currentVisualTreeElement = visual;
+            do
+            {
+                if (currentVisualTreeElement is Visual)
+                {
+                    visual = (Visual)currentVisualTreeElement;
+                    Transform transform = VisualTreeHelper.GetTransform(visual);
+                    if ((transform != null) &&
+                        (transform.Value.M21 == 0) &&
+                        (transform.Value.OffsetY == 0))
+                    {
+                        totalTransform *= transform.Value.M22;
+                    }
+                }
+                currentVisualTreeElement = VisualTreeHelper.GetParent(currentVisualTreeElement);
+            }
+            while (currentVisualTreeElement != null);
+
+            return totalTransform;
+        }
+    }
+}