One of our Winform applications uses a WPF user control, which is hosted in a System.Windows.Forms.Integration.ElementHost control. It worked fine until recently we tried to run it on a new 10-inch tablet which has Windows 8.1 as the OS. The font of the app became very tiny on the screen and almost unreadable. The resolution of the tablet was 1920 * 1200 and the DPI was set to 'Large', which was 144(150%), which was the default Windows 8.1 setting on this tablet. Our other Winform applications which did not using WPF control were scaled automatically to the normal, human-readable size. Only this one with WPF control had the problem.
I searched on Google about ElementHost scale problem something like that and found that some people using ElementHost or WPF control in Winform application encountered similar problem, but no one provided a valid solution.
Solution
After a couple of hours research, I finally found a very simple solution -- adding <dpiAware> to the application manifest. Here is an example from Microsoft's website.
<assembly xmlns="urn:schemas-microsoft-com:asm.v1" manifestVersion="1.0" xmlns:asmv3="urn:schemas-microsoft-com:asm.v3" >
<asmv3:application>
<asmv3:windowsSettings xmlns="http://schemas.microsoft.com/SMI/2005/WindowsSettings">
<dpiAware>True</dpiAware>
</asmv3:windowsSettings>
</asmv3:application>
</assembly>
For my case, I need to set the <dpiAware> to Per-monitor to make it work normally. That is, change the line in the middle to <dpiAware>Per-monitor</dpiAware>. The differences between each value are listed below(These are from MSDN, for more detail information, please see the reference links below).
| DPI awareness manifest value | Description |
|---|---|
| False | Sets the application to not DPI-aware. |
| True | Sets the application to system DPI–aware. |
| Per-monitor | On Windows 8.1, sets the application to per monitor-DPI aware. On Windows Vista through Windows 8, sets the application to not DPI–aware. |
| True/PM | On Windows 8.1, sets the application to per monitor-DPI aware. On Windows Vista through Windows 8, sets the application to system-DPI aware. |
So that is something about DPI-Aware application. For those who is interested in how to write a DPI-Aware application, there are some very detailed contents on Microsoft's website:
Tutorial: Writing High-DPI Win32 Applications
Writing DPI-Aware Desktop and Win32 Applications
Developing a Per-Monitor DPI-Aware WPF Application
