Character Overlap during Korean IME Composition

[KennethanCeyer]

Environment

Windows version

Microsoft Windows [Version 10.0.18362.720]

Terminal version

Version: 0.10.761.0

Steps to reproduce

1. Open "Terminal" app
2. Type "테스트" (It means test in Korean)
3. You can probably see the letters overlapping

Expected behavior

Rather than a long explanation, I'd rather attach the behavior of another operating system terminal.

In the case of MacOS, the cursor is positioned under the letter being combined during the Korean language composition process, and there is no collision of letters.

In the Ubuntu 18.04 X Window system environment, if the same operation is performed in the terminal, You can expect that Hangul characters are under the composition process in a cursor shape. And the Hangul characters do not overlap.

Actual behavior

In Version: 0.10.761.0, there is a problem that the Korean characters are overlapped as shown in the picture above.

If this problem is expected to be relatively minor by the core development team, please give a hint to the source code that is expected to be a problem so that I can give you a PR.

[jdebp]

A data point: pasting in the same character sequence from the clipboard did not cause such an effect when I tried it, out of curiosity. I didn't try a Hangeul input method, though.

[KennethanCeyer]

@jdebp Thanks for the additional comments! This problem is reproduced in the process of combining IME Hangul characters, so it is difficult to reproduce it by copying the clipboard.

[KennethanCeyer]

If you test by typing the letters ㅌ, ㅔ, ㅅ, ㅡ, ㅌ, ㅡ in order, you can check the problem.

[leonMSFT]

So at first glance, it seems like the TSFInputControl is getting its set of LayoutRequested events before the Terminal manages to update its cursor, leading to the TextBlock staying in the same place when it should have moved over to where the cursor currently is. If you then type one extra character after the first overlapping keypress, the LayoutRequested will fire again, and will update the TextBlock to the correct position of the cursor.

What's funny is that while debugging this by building it in Visual Studio and running it with the debugger, my breakpoints slow the events down enough that sometimes the Terminal updates its cursor before the LayoutRequested event is received, which makes the text not overlap.

@KennethanCeyer I think the fix might be simple, depending on how difficult it is to figure out when we should be re-drawing where the TextBlock should be, instead of relying on LayoutRequested to do it. If you're willing to take a stab at it, let me know and I can answer questions if you have any! 😄