Subject: Re: bug#48148: 27.2; ox-ascii breaks TITLE line wrongly when 2 width char is used

From: Eli Zaretskii <[email-masked]>
Date: Sun, 02 May 2021 10:03:36 +0300

> Date: Sun, 02 May 2021 08:52:13 +0900
> From: Shingo Tanaka <[email-masked]>
> 
> For example, when the title is "ＡＢＣＤＥＦ" (each character has width of
> 2), expected title would be like:
> 
>                      ━━━━━━━━━━━━━━━
>                               ＡＢＣＤＥＦ
>                      ━━━━━━━━━━━━━━━
> 
> However, the reality is:
> 
>                      ━━━━━━━━━━━━━━━
>                                  ＡＢＣ
>                                  ＤＥＦ
>                      ━━━━━━━━━━━━━━━
>                      
> This is because it uses `length' to detects the width, which only returns the
> number of characters (6 in this case) but not the actual width displayed (12
> in this case), and it tries to fill the line with that half width.
> `string-width' should be used instead.
> 
> Here is a potential patch.
> 
> --- ox-ascii.el.org	2021-03-26 09:28:44.000000000 +0900
> +++ ox-ascii.el	2021-05-02 08:11:57.657347150 +0900
> @@ -1033,7 +1033,7 @@
>  	     ;; Format TITLE.  It may be filled if it is too wide,
>  	     ;; that is wider than the two thirds of the total width.
>  	     (title-len (min (apply #'max
> -				    (mapcar #'length
> +				    (mapcar #'string-width
>  					    (org-split-string
>  					     (concat title "\n" subtitle) "\n")))
>  			     (/ (* 2 text-width) 3)))

Thanks, but the change you propose will not work reliably on GUI
frames, because the actual width of double-width characters on display
is not necessarily twice the width of a "normal" character.
Especially if this is done in a non-CJK locale, where the default font
is likely to be different from the font used for double-width
characters.

The accurate method of lining up in these cases is to use
window-text-pixel-size instead.  That function will return the exact
width of a string as it will displayed, in pixels, because it uses the
same code as the display engine.