Use current display scale in WPF ContextMenu

Question

My WPF application is Per-Monitor Aware and normally scales well. But when the app window is on a second monitor with scale=150% and I open a context menu it uses scale=100% from the main display making menu items quite small:

(Interestingly the submenu items use correct 150% scale)

I open the context menu setting IsOpen = true:

        private void Button_Click(object sender, RoutedEventArgs e)
        {
            ContextMenu menu = new ContextMenu();

            menu.Items.Add("item 1");
            menu.Items.Add("item 2");

            MenuItem submenu = new MenuItem();
            submenu.Header = "submenu";
            submenu.Items.Add("more 1");
            submenu.Items.Add("more 2");
            menu.Items.Add(submenu);

            menu.IsOpen = true;
        }

How to configure context menu to use display settings it is opened on, not from the default main display?

Which .NET version are you using? Starting from 4.6.2 per monitor DPI aware is enabled by default, check this [thread](https://stackoverflow.com/questions/35865238/my-wpf-app-is-per-monitor-dpi-aware-out-of-the-box-i-was-not-expecting-that) — Pavel Anikhouski, Jul 08 '19 at 14:06
@PavelAnikhouski My app is targeting .NET Framework 4.7.2 and I have .NET Framework 4.8 installed. — Sergey Vlasov, Jul 08 '19 at 16:25

score 0 · Accepted Answer · answered Jun 16 '20 at 14:58

You can RenderTransform to undo Scaling from PrimaryScreen and Scale to dpiScale from Visual:

var visual = e.Source as Visual;
if (visual != null)
{
     var dpiScale = VisualTreeHelper.GetDpi(visual);
     System.Windows.Forms.Screen.PrimaryScreen.
           GetDpi(DpiType.Effective, out uint dpiX, out uint dpiY);
     menu.RenderTransform = 
          new ScaleTransform(dpiScale.DpiScaleX / ((double)dpiX / 96), 
                            dpiScale.DpiScaleY / ((double)dpiY / 96));
     menu.IsOpen = true;
}

Use current display scale in WPF ContextMenu

1 Answers1