Use space :align-to instead of manual computations

[DivineDominion]

Fixes #29

---

Looking at marginalia.el issues, code, and the README I found out about alignment propertization, and that fixes the problem of chopped-off characters for me:

(defun mode-line-render (left right)
  "Function to render the modeline LEFT to RIGHT."
  (concat left
          (propertize " "
                      'display `(space :align-to (- right ,(length right))))
          right))

You can also easily add a middle column later if you want:

(defun mode-line-render (left center right)
  "Function to render the modeline LEFT, CENTER, and RIGHT."
  (concat left
          (propertize " "
                      'display `(space :align-to (- center ,(length center))))
          center
          (propertize " "
                      'display `(space :align-to (- right ,(length right))))
          right))

With the space alignment stuff here, this even works on a per-pixel offset basis -- I can freely resize the window and the line and column indicators stick to the window edges.

Compare with

(setq frame-resize-pixelwise t)

... and you'll see that the current approach moves in units of 1 character, while this PR will move per pixel.

[DivineDominion]

Relevant docs: https://www.gnu.org/software/emacs/manual/html_node/elisp/Display-Property.html https://www.gnu.org/software/emacs/manual/html_node/elisp/Specified-Space.html

[rougier]

I remember having tried that but I got problem with the face using for alignment. For example, if you want to have a continuous underline, it was not working.

[DivineDominion]

@rougier Do you remember the particular setup? When I save my replacement for mode-line-render in elegant.el and launch emacs -q -l sanity.el -l elegance.el Splash.org & it looks fine.

[rougier]

Thanks. I need I'll merge. In the meantime, I'll try to adapt your code to nano-modeline