Re: Add a function that returns pixel distance between points?

[Eli Zaretskii <eliz@gnu.org>]

> From: Yuan Fu <casouri@gmail.com>
> Date: Mon, 1 Feb 2021 09:16:52 -0500
> Cc: "emacs-devel\\@gnu.org" <emacs-devel@gnu.org>
> 
> > IOW, can you show a test case where using window-text-pixel-size
> > returns incorrect results for :align-to due to line-prefix?
> 
> Here is an example:
> 
> (let ((width))
>   (insert "woome")
>   (setq width (car (window-text-pixel-size
>                     nil (line-beginning-position) (point))))
>   (put-text-property (line-beginning-position) (point)
>                      'line-prefix "   ")
>   (message "true width: %d returned width: %d"
>            width (car (window-text-pixel-size
>                        nil (line-beginning-position) (point)))))
> 
> Run it in an empty buffer and it will print the expected width and returned width. In the snippet I’m trying to measure the width of the text.

This says:

  true width: 40 returned width: 64

However, if I use :align-to with the value of 64 pixels, the stretch
of whitespace ends where I'd expect it to end: aligned to right after
"woome".

So I still don't understand the problem you are facing.  Which is why
I asked for an example code which uses :align-to in a way similar to
what you intend to do in your table rendering code, because I wanted
to see a situation where :align-to produces incorrect results when
using the return value of window-text-pixel-size in the presence of
line-prefix.  But the example you show doesn't use :align-to.