xwt/Xwt.WPF/Xwt.WPFBackend/WpfDesktopBackend.cs

//
// WpfDesktopBackend.cs
//
// Author:
//       Lluis Sanchez <lluis@xamarin.com>
//
// Copyright (c) 2013 Xamarin Inc.
//
// Permission is hereby granted, free of charge, to any person obtaining a copy
// of this software and associated documentation files (the "Software"), to deal
// in the Software without restriction, including without limitation the rights
// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
// copies of the Software, and to permit persons to whom the Software is
// furnished to do so, subject to the following conditions:
//
// The above copyright notice and this permission notice shall be included in
// all copies or substantial portions of the Software.
//
// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
// THE SOFTWARE.
using System;
using System.Reflection;
using System.Runtime.InteropServices;
using Xwt.Backends;
using SWF = System.Windows.Forms;
using System.Collections.Generic;

namespace Xwt.WPFBackend
{
	public class WpfDesktopBackend: DesktopBackend
	{
		// http://msdn.microsoft.com/en-us/library/windows/desktop/dd464660(v=vs.85).aspx#determining_the_dpi_scale_factor
		const double BASELINE_DPI = 96d;

		public WpfDesktopBackend ()
		{
			Microsoft.Win32.SystemEvents.DisplaySettingsChanged += delegate
			{
				System.Windows.Application.Current.Dispatcher.BeginInvoke (new Action (OnScreensChanged));
			};
		}

		static bool cannotCallGetDpiForMonitor;
		public override double GetScaleFactor (object backend)
		{
			//FIXME: Is it possible for the Y dpi to differ from the X dpi,
			//  and if so, what should we do about it?
			int dpi = (int)BASELINE_DPI;

			// In Windows 8.1, there can be a different dpi per monitor
			if (!cannotCallGetDpiForMonitor) {
				// .. I wish there was a less hacky way of getting the HMONITOR from the SWF.Screen :/
				var hmonitorField = typeof (SWF.Screen).GetField ("hmonitor", BindingFlags.Instance | BindingFlags.NonPublic);
				if (hmonitorField == null) {
					cannotCallGetDpiForMonitor = true;
				} else {
					try {
						int dpiY;
						GetDpiForMonitor ((IntPtr)hmonitorField.GetValue (backend), MDT_Effective_DPI, out dpi, out dpiY);
					} catch {
						cannotCallGetDpiForMonitor = true;
					}
				}
			}
			if (cannotCallGetDpiForMonitor) {
				// Get system-wide dpi
				var hdc = GetDC (IntPtr.Zero);
				if (hdc != IntPtr.Zero) {
					try {
						dpi = GetDeviceCaps (hdc, LOGPIXELSX);
					} finally {
						ReleaseDC (IntPtr.Zero, hdc);
					}
				}
			}
			return dpi / BASELINE_DPI;
		}

		#region implemented abstract members of DesktopBackend

		public override Point GetMouseLocation()
		{
			var loc = SWF.Cursor.Position;
			var screen = SWF.Screen.FromPoint (loc);
			var scale = GetScaleFactor (screen);

			// We need to convert the device pixels into WPF's device-independent pixels..
			return new Point (loc.X / scale, loc.Y / scale);
		}

		public override IEnumerable<object> GetScreens ()
		{
			return SWF.Screen.AllScreens;
		}

		public override bool IsPrimaryScreen (object backend)
		{
			return ((SWF.Screen)backend) == SWF.Screen.PrimaryScreen;
		}

		public override Rectangle GetScreenBounds (object backend)
		{
			var r = ((SWF.Screen)backend).Bounds;
			return new Rectangle (r.X, r.Y, r.Width, r.Height);
		}

		public override Rectangle GetScreenVisibleBounds (object backend)
		{
			var r = ((SWF.Screen)backend).WorkingArea;
			return new Rectangle (r.X, r.Y, r.Width, r.Height);
		}

		public override string GetScreenDeviceName (object backend)
		{
			return ((SWF.Screen)backend).DeviceName;
		}

		#endregion

		#region P/Invoke

		const int LOGPIXELSX = 88;
		const int LOGPIXELSY = 90;
		const int MDT_Effective_DPI = 0;

		[DllImport ("user32")] static extern IntPtr GetDC (IntPtr hWnd);
		[DllImport ("user32")] static extern int ReleaseDC (IntPtr hWnd, IntPtr hdc);
		[DllImport ("gdi32")]  static extern int GetDeviceCaps (IntPtr hdc, int nIndex);
		[DllImport ("Shcore")] static extern int GetDpiForMonitor (IntPtr hmonitor, int dpiType, out int dpiX, out int dpiY);
		#endregion
	}
}