Delay occurs while getting the size from the FormattedText

• .NET Core Version: .Net 6.0
• Windows version: Windows11- 22000.675
• Does the bug reproduce also in WPF for .NET Framework 4.8?: Yes
• Is this bug related specifically to tooling in Visual Studio -No

Problem description: Delay Occurs while getting the size from the Formatted Text.

Expected behavior: Delay should not be occured. Minimal repro: 1.Run the sample 2.Click the Initialize Formatted Text button.

Note : Delay occurs, button is in pressed state for a long time. Please refer the below code snippet and gif file.

private void Button_Click(object sender, RoutedEventArgs e)
{

    for (int i = 0; i <= 30000; i++)
    {
        FormattedText text = new FormattedText("Demo", System.Globalization.CultureInfo.CurrentCulture, FlowDirection.LeftToRight, new Typeface(FontFamily, new FontStyle(), FontWeights.Normal, FontStretch), 14, Brushes.Black);
        Size demo = new Size(text.Width, text.Height);
    }
    MessageBox.Show("Initialized");
}

[miloush]

@sethuramkumar I think this issue needs a bit more information. Is the performance affecting a scenario in your application? Why would 30000 iterations be too few or too many, how many iterations would be reasonable to take the time it is taking now?

[miloush]

How are you assessing the delay? If I press the button using spacebar, with mouse away from it, and use Normal, the button stays blue while processing. With Render (or lower), it gets gray and then starts processing. If you use mouse, the button is blue on hover, the processing starts and then if you move mouse away, that enqueues another render, which will not execute until your processing is done (regardless of its priority).

Either way, dispatcher can either be rendering or doing other things.

If you want to do stuff simultaneously, you will have to either need to be pre-emptive and make sure you give dispatcher chance to process other operations every now and then, or, you need a completely separate thread like @ygra suggested. Good news for you is that you don’t need a dispatcher for measuring FormattedText, so separate thread works fine. If it is just for a short task, you can use Task:

var typef = new Typeface(FontFamily, new FontStyle(), FontWeights.Normal, FontStretch);
Task.Run(() =>
{
    for (int i = 0; i <= 30000; i++)
    {
        FormattedText text = new FormattedText("Demo", System.Globalization.CultureInfo.CurrentCulture, FlowDirection.LeftToRight, typef, 14, Brushes.Black);
        Size demo = new Size(text.Width, text.Height);
    }
    MessageBox.Show("Initialized");
});

(Caveat is obviously you can’t touch any objects that require Dispatcher from the other thread.)