how can I fix incorrect character width?

Question

Emacs is telling me that a certain character only takes up 1 column, even though it clearly takes up two? Is there a way I can fix this?

The reason is that I'm doing some calculations in order to "right-align" part of my mode-line. I do this by getting the window-total-width and subtracting from it the (string-width left-part), then appropriately padding based on this. This works great until I show a multi-column character like this. I purposefully made my math involve the amount of columns the string takes, but as shown above, this shows up incorrectly.

Answer 1

syohex helped me out and pointed me to some code that adjusts the character widths of certain character codes. I adapted it to fit what I'm doing:

  (defun blaenk/set-char-widths (alist)
    (while (char-table-parent char-width-table)
      (setq char-width-table (char-table-parent char-width-table)))
    (dolist (pair alist)
      (let ((width (car pair))
            (chars (cdr pair))
            (table (make-char-table nil)))
        (dolist (char chars)
          (set-char-table-range table char width))
        (optimize-char-table table)
        (set-char-table-parent table char-width-table)
        (setq char-width-table table))))


  ;; argument is an alist of width and list of RANGEs,
  ;; which is the same as the RANGE that set-char-table-range accepts
  (blaenk/set-char-widths
   `((2 . (,(string-to-char (fontawesome "cloud"))))))