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QuickLook.Plugin/QuickLook.Plugin.PDFViewer/DpiHelpers.cs

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+using System;
+using System.Drawing;
+using System.Runtime.InteropServices;
+
+namespace QuickLook.Plugin.PDFViewer
+{
+    internal static class DpiHelper
+    {
+        public enum DeviceCap
+        {
+            /// <summary>
+            ///     Logical pixels inch in X
+            /// </summary>
+            LOGPIXELSX = 88,
+            /// <summary>
+            ///     Logical pixels inch in Y
+            /// </summary>
+            LOGPIXELSY = 90
+        }
+
+        public const float DEFAULT_DPI = 96;
+
+        public static Dpi GetCurrentDpi()
+        {
+            var g = Graphics.FromHwnd(IntPtr.Zero);
+            var desktop = g.GetHdc();
+
+            var dpi = new Dpi
+            {
+                HorizontalDpi = GetDeviceCaps(desktop, (int) DeviceCap.LOGPIXELSX),
+                VerticalDpi = GetDeviceCaps(desktop, (int) DeviceCap.LOGPIXELSY)
+            };
+
+            return dpi;
+        }
+
+        [DllImport("gdi32.dll", CharSet = CharSet.Auto, SetLastError = true, ExactSpelling = true)]
+        public static extern int GetDeviceCaps(IntPtr hDC, int nIndex);
+    }
+
+    internal class Dpi
+    {
+        public float HorizontalDpi { get; set; }
+        public float VerticalDpi { get; set; }
+    }
+}