On 5/29/2025 9:39 PM, Eli Zaretskii wrote:
> If the string's text is already in a buffer, we have
> buffer-text-pixel-size and window-text-pixel-size for that purpose.
> If the text is not in any buffer, then string-pixel-width should do
> the job, and do it well.  In particular, it strives to turn on/off all
> the features that affect display as they are in the original buffer
> (which can be passed to it as an optional argument), and applies all
> the buffer-local settings that could matter.  This includes face
> remapping (which is how text-scaling is implemented).
>
> So I still don't understand the nature of the problem.

The problem was simply that the original script to reproduce the issue
didn't pass the optional buffer argument to 'string-pixel-width', so the
relevant buffer-local settings (face remapping) weren't used. Instead,
the original script tried to approximate the remapping using its own
calculations which weren't quite the same as the display engine.