bug#81487: problem rendering thai text from a utf8 input file

> From: Keith Hill <[email protected]>
> CC: "[email protected]" <[email protected]>
> Date: Mon, 27 Jul 2026 18:44:28 +0000
> 
> The same problem appears. 
> Invocation setup: prepend C:\msys64\mingw64\bin;C:\emacs\bin; to PATH
> Invocation shell: cmd.exe
> Invocation: emacs -Q -nw UTF-8-demo.txt
> Result: after hitting 5 PgDn keys to reach the bottom of the file, some Thai text now appears in the right side of
> the screen. With each PgUp key, this text appears at the same place in the screen, though it is not present in
> the input file. Attached file thai-render-artifact.png shows what I see at the first point an error could be
> detected, with artifact circled in red. FYI: The executable was built from source code on Jan-13-2026 using
> mingw-W64-mingw32-gcc toolchain, with the ./configure arguments shown in the original email.

Previously, you were talking about alignment of the second column.
Now you are talking only about artifacts.  Is alignment no longer the
problem?

I can indeed reproduce the artifacts in Emacs 30.2, but not in
the latest pretest of what will soon become Emacs 31.1 (where the way
we display on text-only frames was completely redesigned and
reimplemented).  So I think this problem is already solved in the
latest development code.  If you can try the latest pretest (binaries
are available from alpha.gnu.org) or build the emacs-31 branch of the
Emacs Git repository yourself, please try there and tell if you still
see the artifacts.