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Fix #8930: [Win32] Don't handle printable keys on keydown if an edit box is in focus. #8976

merged 1 commit into from Apr 9, 2021


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@michicc michicc commented Apr 8, 2021

Motivation / Problem

On Windows, printable input for text input is handled by WM_CHAR messages.
The WM_KEYDOWN handler tries to predict if a keydown will be followed by WM_CHAR message to do the right thing, but this prediction can fail if IMEs are in play. This can lead to duplicate text input.


If a key press is in fact printable text, it will result in a WM_CHAR (or a WM_IME_*) message. If no WM_CHAR follows, it is not printable text. As such, handle printable input only on the WM_CHAR message. Without an edit box, do the handling in keydown as usual to support hotkeys.


I only tested normal German/latin input and the japanese IME. Some other IMEs or strange keyboard layouts might behave differently.

Checklist for review

Some things are not automated, and forgotten often. This list is a reminder for the reviewers.

  • The bug fix is important enough to be backported? (label: 'backport requested')
  • This PR affects the save game format? (label 'savegame upgrade')
  • This PR affects the GS/AI API? (label 'needs review: Script API')
    • ai_changelog.hpp, gs_changelog.hpp need updating.
    • The compatibility wrappers (compat_*.nut) need updating.
  • This PR affects the NewGRF API? (label 'needs review: NewGRF')
…n edit box is in focus.

Handle printable input only when the matching WM_CHAR message is incoming.
Without an edit box, do the handling in keydown as usual to support hotkeys.
nielsmh approved these changes Apr 9, 2021
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@nielsmh nielsmh left a comment

Fixes the issue by my own testing. There's still some weird delays in input when using IME and typing too fast, but not a problem during regular use.

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@michicc michicc commented Apr 9, 2021

The delay might be because we don't wait on messages, so if the IME takes a bit to post the WM_CHAR message, we might take a trip through drawing first.

@michicc michicc merged commit 96d33ab into OpenTTD:master Apr 9, 2021
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@michicc michicc deleted the pr/fix_8930 branch Apr 9, 2021
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3 participants