Re: Alternative to current-column that counts from visual line beginning

[Yuan Fu]

> On Dec 29, 2020, at 1:21 AM, Eli Zaretskii <eliz@gnu.org> wrote:
> 
> On December 29, 2020 7:01:16 AM GMT+02:00, Yuan Fu <casouri@gmail.com> wrote:
>> 
>> 
>>> On Dec 28, 2020, at 9:40 PM, Stefan Monnier
>> <monnier@iro.umontreal.ca> wrote:
>>> 
>>>> to get the column number counting from the visual line beginning.
>> Is
>>>> there a function that does what I want? If not, maybe we should add
>>>> one, or add an argument to current-column.
>>> 
>>> `posn-at-point`?
>>> 
>> 
>> That works, albeit a bit convoluted comparing to current-column and
>> only works when point is visible. Another less legit point is that
>> posn-at-point is a bit far-fetched semantically: for me it is more
>> about GUI pixel positions than text-based column and line positions.
>> All things considered, I still prefer a dedicated function or an
>> additional argument to current-column.
>> 
>> Yuan
> 
> The concept of "visual line" of some buffer position only makes sense in the 
> context of displaying the buffer in some window.  That's because window 
> dimensions and other window-specific aspects, such as faces and overlays, 
> have direct and prominent effect on how physical lines are divided into 
> visual lines.
> 
> Therefore, I don't think I understand how can a function exist that reports 
> the "visual column" of a buffer position without telling it the window in 
> which to display that buffer.  Could you perhaps outline the algorithm for 
> such a function?  Perhaps there is some misunderstanding.

I see your point. I use vertical-motion, which takes a window as argument (and 
defaults to the current window).

(save-excursion
   (let ((col (current-column)))
     ;; Go to visual line beginning.
     (vertical-motion 0)
     (- col (current-column))))


Yuan