fix a bug where the zoom level of HTML viewer is always 200%

QuickLook.Plugin/QuickLook.Plugin.HtmlViewer/DpiHelpers.cs

@@ -0,0 +1,63 @@
+// Copyright <20> 2017 Paddy Xu
+// 
+// This file is part of QuickLook program.
+// 
+// This program is free software: you can redistribute it and/or modify
+// it under the terms of the GNU General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+// 
+// This program is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+// GNU General Public License for more details.
+// 
+// You should have received a copy of the GNU General Public License
+// along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+using System;
+using System.Drawing;
+using System.Runtime.InteropServices;
+
+namespace QuickLook.Plugin.HtmlViewer
+{
+    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; }
+    }
+}