Re-align text after a bigger symbol

Question

I'd like to customize a bit mu4e in order to display nice utf-8 chars (or still better, colored emojis).

However, the problem is that the utf8 chars does not have the good width (even in the mono font), and may be bigger or smaller. So all the text after that char is shifted by a fraction of the normal width, which breaks the alignment. So I'm looking for a way to control spacing after displaying a big/small utf-8 char or picture. For example can I say something like:

• "Display the utf-8 char ⚴ and leave space after until you arrive at the point that would be reached by replacing X by two characters with the default font width".
• Or even better, would it be possible to say "Put the chars '⚓⚴❮' into at most 5 "normal" chars, fill with blank if needed, and then continue to write text as usual.
• Or still better, "Put the chars '⚓⚴❮', fill with blank until you reach the next "block", and let me know how many spaces you used.

And if possible, I also want to do the same thing for images.

Thank you!

Answer 1

I found a solution that basically uses this question to get the width of one char (based on font-get-glyphs), and then I use default-font-width to get the width of a column, and then I add a space using the display text property (I don't know why but I needed to create a new temporary variable to make sure it's a buffer-local variable, if you have a better code let me know).

;; https://emacs.stackexchange.com/questions/5495/how-can-i-determine-the-width-of-characters-on-the-screen
(defun my-char-width (char_str) 
  "Return the width in pixels of a character in the current
window's default font.  More precisely, this returns the
width of the letter ‘m’.  If the font is mono-spaced, this
will also be the width of all other printable characters."
  (let ((window (selected-window))
        (remapping face-remapping-alist))
    (with-temp-buffer
      (make-local-variable 'face-remapping-alist)
      (setq face-remapping-alist remapping)
      (set-window-buffer window (current-buffer))
      (insert char_str)
      (aref (aref (font-get-glyphs (font-at 1) 1 2) 0) 4))))

(defun insert_in_n_columns (cols_nb str)
  "Insert as much element of list_char as possible, until it goes
 out of n cols. 'Begin' is useless for the user."
  (cl-labels ((aux (rem_px rem_l)
           (if (null rem_l) ;; Empty list, fill with big space
               (progn
             ;; Cannot use the local variable...
             ;; Better way than using a tmp variable?
             (insert
              (propertize " "
                      'display
                      `(space . (:width (,rem_px))))))
             (progn
               ;; Get first element, remaining part,
               ;; and with of first elt
               (let* ((c (car rem_l))
                  (r (cdr rem_l))
                  (w (my-char-width c)))
             ;; If there is enough space for the char, insert it
             (if (<= w rem_px)
                 (progn
                   (insert c)
                   (aux (- rem_px w) r))
               (progn
                 (if (not (eq rem_px 0))
                 ;; Else fill with the good space
                 (progn
                   (insert
                    (propertize " "
                        'display
                        `(space . (:width (,rem_px)))))
                   )))))))))
    (aux (* cols_nb (default-font-width)) (string-to-list str))))

;; Demo:
;; (insert_in_n_columns 4 "ab⏚")
;; (insert_in_n_columns 4 "ab⚴d")
;; (insert_in_n_columns 4 "abc⏚d")

Demo:

NB: the same idea can be used with images.