Very slow operations in a TextBox with large amount of characters

[luthfiampas]

Describe the bug
Operations in a TextBox control (such as selecting, typing, clicking) with 50000+ characters is very slow, and it uses 100% of CPU.

To Reproduce

1. Create TextBox control
2. Add 50000+ characters
3. Start selecting text either with mouse or keyboard, typing or change caret position

Expected behavior
Faster operations.

Screenshots

textbox.mp4

Desktop (please complete the following information):

• OS: Windows 10, Arch (KDE), Debian (dwm)
• Processor: i7-9700F @3.0GHz
• RAM: 16GB
• Version: 0.10.10

[Gillibald]

I don't see an issue here. TextBox isn't designed to deal with that scenario. I suggest using AvaloniaEdit.

[luthfiampas]

@Gillibald Looking at the WPF's TextBox or GTK's TextView, they can handle large text content very nicely. Seems that I pick the wrong label for this issue.

[Gillibald]

This is only slow because of selection highlighting. Each selection change causes a new text layout pass for the whole text. Nothing is cached or virtualized. WPF caches some portion of the text layout and isn't creating a new string each time the text is edited.