add function codes

src/Shared/HandyControl_Shared/Tools/Helper/DpiHelper.cs

@@ -1,14 +1,54 @@
 using System;
 using System.Windows;
 using System.Windows.Media;
+using HandyControl.Tools.Interop;
 
 namespace HandyControl.Tools
 {
-    internal class DpiHelper
+    internal static class DpiHelper
     {
-        [ThreadStatic]
+        private const double LogicalDpi = 96.0;
+
+        [ThreadStatic] 
         private static Matrix _transformToDip;
 
+        static DpiHelper()
+        {
+            var dC = InteropMethods.GetDC(IntPtr.Zero);
+            if (dC != IntPtr.Zero)
+            {
+                DeviceDpiX = InteropMethods.GetDeviceCaps(dC, 88);
+                DeviceDpiY = InteropMethods.GetDeviceCaps(dC, 90);
+                InteropMethods.ReleaseDC(IntPtr.Zero, dC);
+            }
+            else
+            {
+                DeviceDpiX = LogicalDpi;
+                DeviceDpiY = LogicalDpi;
+            }
+
+            var identity = Matrix.Identity;
+            var identity2 = Matrix.Identity;
+            identity.Scale(DeviceDpiX / LogicalDpi, DeviceDpiY / LogicalDpi);
+            identity2.Scale(LogicalDpi / DeviceDpiX, LogicalDpi / DeviceDpiY);
+            TransformFromDevice = new MatrixTransform(identity2);
+            TransformFromDevice.Freeze();
+            TransformToDevice = new MatrixTransform(identity);
+            TransformToDevice.Freeze();
+        }
+
+        public static MatrixTransform TransformFromDevice { get; }
+
+        public static MatrixTransform TransformToDevice { get; }
+
+        public static double DeviceDpiX { get; }
+
+        public static double DeviceDpiY { get; }
+
+        public static double LogicalToDeviceUnitsScalingFactorX => TransformToDevice.Matrix.M11;
+
+        public static double LogicalToDeviceUnitsScalingFactorY => TransformToDevice.Matrix.M22;
+
         public static Point DevicePixelsToLogical(Point devicePoint, double dpiScaleX, double dpiScaleY)
         {
             _transformToDip = Matrix.Identity;
@@ -18,9 +58,22 @@ namespace HandyControl.Tools
 
         public static Size DeviceSizeToLogical(Size deviceSize, double dpiScaleX, double dpiScaleY)
         {
-            Point pt = DevicePixelsToLogical(new Point(deviceSize.Width, deviceSize.Height), dpiScaleX, dpiScaleY);
-
+            var pt = DevicePixelsToLogical(new Point(deviceSize.Width, deviceSize.Height), dpiScaleX, dpiScaleY);
             return new Size(pt.X, pt.Y);
         }
+
+        public static Rect LogicalToDeviceUnits(this Rect logicalRect)
+        {
+            var result = logicalRect;
+            result.Transform(TransformToDevice.Matrix);
+            return result;
+        }
+
+        public static Rect DeviceToLogicalUnits(this Rect deviceRect)
+        {
+            var result = deviceRect;
+            result.Transform(TransformFromDevice.Matrix);
+            return result;
+        }
     }
 }