Scaling the non-client area (title bar, menu bar) for per-monitor high-DPI support

In any up-to-date Windows Insider builds (build >= 14342, SDK version# >= 14332) there is an EnableNonClientDpiScaling API (which takes an HWND as its argument) that will enable non-client DPI scaling for top-level HWNDs. This functionality requires that the top-level window be running in per-monitor DPI-awareness mode. This API should be called from the WM_NCCREATE handler for the window. When this API is called on a top-level window, its caption bar, top-level scrollbars, system menu and menubar will DPI scale when the application’s DPI changes (this can happen when the app is moved to a display with a different display scaling value or when the DPI changes for other reasons such as the user making a settings change or when an RDP connection changes the scale factor).

This API does not support scaling non-client area for child windows, such as scroll bars in a child window.

To my knowledge there is no way to have non-client area DPI scale automatically without this API.

Note that this API has not yet been finalized, and it may change prior to being released in the Windows 10 Anniversary update. Keep your eye on MSDN for official documentation when it becomes final.

With Per Monitor V2 DPI awareness in Windows 10 Creators Update (build 15063) you can resolve this easily without the EnableNonClientDpiScaling.

To enable Per Monitor V2 DPI awareness, while still supporting old Per Monitor DPI awareness on older Windows 10 builds and Windows 8.1 and DPI awareness on yet older versions of Windows, make your application manifest like this:

<assembly ...>
    <!-- ... --->
    <asmv3:application>
        <asmv3:windowsSettings xmlns="http://schemas.microsoft.com/SMI/2005/WindowsSettings">
            <dpiAware>True/PM</dpiAware>
            <dpiAwareness xmlns="http://schemas.microsoft.com/SMI/2016/WindowsSettings">PerMonitorV2,PerMonitor</dpiAwareness>
        </asmv3:windowsSettings>
    </asmv3:application>
</assembly>

References:

• High DPI Improvements for Desktop App Developers in the Windows 10 Creators Update – video
• Application Manifests – reference