How to set margins of buffer when window changes?

How to set margins of buffer when window changes?

[edgar]

Hello dear Emacs users!

I am trying to have some buffers centre the text. I figured that I  
could do it with margins. I want this to adjust depending on the value  
of `fill-column' (could be any other variable) and the width of the  
window (if it is too small, don't centre). I have the code below, but  
I get the error: `Window ... too small for splitting' (replace `...'  
with the name of the buffer's window). I added a hook to the major  
mode list of hooks, but it could be something else.

The format is very similar to what they seek here:  
[https://stackoverflow.com/q/39083118]

How can I resize the window and adjust the margins depending on  
`fill-column'? Thanks.


     (with-eval-after-load 'python
      (defun centre-text-with-margins (&optional window width)
        "Moves the left and right margins to centre the contents of  
the current buffer in the current window"
        ;; https://stackoverflow.com/a/54098261
        ;; https://stackoverflow.com/q/39083118
         ;; (if (or (> left-margin-width 0) (> right-margin-width 0))
         ;;      (progn
               (setq left-margin-width 0)
               (setq right-margin-width 0)
               ;; (set-window-buffer nil (current-buffer))
               (set-window-margins window 0 0)
               ;; ))
           (let* ((txtwidth (cond (width) (fill-column)))
                  (space (max 0 (- (window-total-width) txtwidth)))
                  (leftside (floor (/ space 2)))
                  (rightside (- space leftside)))
             (setq left-margin-width leftside)
             (setq right-margin-width rightside)
             (set-window-buffer window (current-buffer))
             (format "lm:%s rm:%s sp:%s" left-margin-width  
right-margin-width space)))
      (defun py-margins-hook ()
        (add-hook 'window-state-change-hook #'centre-text-with-margins t t))
      (add-hook 'python-mode-hook 'py-margins-hook))


Emacs:
GNU Emacs 27.2 (build 1, x86_64-pc-linux-gnu, GTK+ Version 3.24.27,  
cairo version 1.17.4) of 2021-03-26


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Re: How to set margins of buffer when window changes?

[Joost Kremers]

On Wed, Sep 08 2021, edgar@openmail.cc wrote:
> I am trying to have some buffers centre the text. I figured that I could do it
> with margins. I want this to adjust depending on the value of `fill-column'
> (could be any other variable) and the width of the window (if it is too small,
> don't centre).

I've written a minor mode that does this:

https://github.com/joostkremers/visual-fill-column

To centre the text, set `visual-fill-column-center-text` to `t`.

Feel free to adapt the code to your needs or simply use it for inspiration. :-) 

-- 
Joost Kremers
Life has its moments

Re: How to set margins of buffer when window changes?

[Emanuel Berg via Users list for the GNU Emacs text editor]

edgar wrote:

> I have the code below, but I get the error: `Window ... too
> small for splitting' (replace `...'

But that code doesn't work (at all), for example what is
"window", "(width)", and "(fill-column)"?

Also please remove the commented-out lines ...

-- 
underground experts united
https://dataswamp.org/~incal

Re: How to set margins of buffer when window changes?

[Emanuel Berg via Users list for the GNU Emacs text editor]

>> I have the code below, but I get the error: `Window ... too
>> small for splitting' (replace `...'
>
> But that code doesn't work (at all), for example what is
> "window", "(width)", and "(fill-column)"?

OK, now I see, "window" is window! (I didn't see it because
I've never seen a `defun' inside a `with-eval-after-load'.)

(fill-column) is also correct because it isn't a function but
a `cond' clause ...

But (width) still doesn't work, it should look like
this, right?

  (cond (width (fill-column)))

If so, it is even better to use `when' here:

  (when width
    (fill-column) )

-- 
underground experts united
https://dataswamp.org/~incal

Re: How to set margins of buffer when window changes?

[Emanuel Berg via Users list for the GNU Emacs text editor]

>   (when width
>     (fill-column) )

Heh, I'm completely confused today, you will have to read what
I *think*, not what I type ... it should be `or'!

  (or width fill-column)

Anyway here is the complete, fixed function. I don't know if
the computation is correct (I didn't change that) but it is
a good starting point ...

Note that I renamed it!

(defun center-text-with-margins (&optional window width)
  (let ((win (or window (selected-window)))
        (wid (or width  fill-column) ))
    (let*((space (max 0 (- (window-total-width) wid)))
          (left  (floor (/ space 2)))
          (right (- space left)) )
      (set-window-margins win left right)
      (set-window-buffer win (current-buffer)) )))

-- 
underground experts united
https://dataswamp.org/~incal

Re: How to set margins of buffer when window changes?

[edgar]

On 2021-09-08 19:11, Joost Kremers wrote:
> 
> I've written a minor mode that does this:
> 
> https://github.com/joostkremers/visual-fill-column
> 
> To centre the text, set `visual-fill-column-center-text` to `t`.
> 
> Feel free to adapt the code to your needs or simply use it for 
> inspiration. :-)

This is all that I need. Thank you very much. I would recommend adding 
your answer here: https://stackoverflow.com/q/39083118 
https://stackoverflow.com/a/54098261 (I don't know how they make their 
money nor if you agree with that, but I've heard that people some times 
get royalties from websites :) ).

Thanks again!

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