SystemParameters与DPI

对于固定大小宽高的wpf程序，
如果在低分屏上能够全屏显示，由于高分屏比低分屏大，那么在高分屏上只能占高分屏的一部分，无法沾满整个屏幕。
但是这对于程序来说体验就很差，
windows可以自动处理这个问题，有几个选项。

DPI Awareness Mode	Windows Version Introduced	Application's view of DPI	Behavior on DPI change
Unaware	N/A	All displays are 96 DPI	Bitmap-stretching (blurry)
System	Vista	All displays have the same DPI (the DPI of the primary display at the time the current user session was started)	Bitmap-stretching (blurry)
Per-Monitor	8.1	The DPI of the display that the application window is primarily located on	• Top-level HWND is notified of DPI change
			• No DPI scaling of any UI elements.
Per-Monitor V2	Windows 10 Creators Update (1703)	The DPI of the display that the application window is primarily located on	• Top-level and child HWNDs are notified of DPI change
			Automatic DPI scaling of:
			• Non-client area
			• Theme-drawn bitmaps in common controls (comctl32 V6)
			• Dialogs (CreateDialog)

首先：
Windows Presentation Foundation (WPF)应用程序自动感知 DPI，无需
选择加入。选择加入此设置的 Windows 窗体应用程序(目标设定为 .NET Framework 4.6 )还应
在其 app.config 中将 "EnableWindowsFormsHighDpiAutoResizing" 设置设置为 "true"。
因此WPF程序是不需要特意设置dpiAware就可以自动缩放。

所以如果我们在一个wpf程序中使用SystemParameters获取屏幕宽高的时候，实际的尺寸为真正的尺寸*缩放比率