Emacs Line Height

Question

I am trying to set the line height of text in an Emacs buffer so there is space above and below the letters. From the documentation, I infer that the line-height text property may help me to accomplish this.

There is also a line-spacing variable which I can set like (setq-default line-spacing 0.25). This kind of works, except it does not produce space before text, only after it. I don’t like the way this looks when using modes like show-paren-mode, since it “dips” down:

Undesired current behavior (“hanging”)

Undesired current behavior

Desired behavior mockup (vertically-centered)

Desired behavior

I'd like to vertically-center the text.

I have discovered that I can temporarily get the effect I want with the following code:

(add-text-properties (point-min) (point-max)
                     '(line-spacing 0.25 line-height 1.25))

However, in some modes the properties go away in regions where I start typing. How do I make that top and bottom spacing the default? (Hooks won't work.)

I'm having difficulty reproducing the tall blue background bars with (setq-default line-spacing 0.25) and (show-paren-mode 1). Can you please clarify a bit what you mean by (setq-default line-spacing 0.25) . . . does not produce space before text, only after it. — lawlist
It is a bit hard to see at 0.25. In the above screenshot I used 1.0. emacs -q and M-: (show-paren-mode 1) and M-: (setq-default line-spacing 1.0) should produce the tall bars. — Jackson
In the documentation it says "First Emacs uses height as a height spec to control extra space above the line", however as you can see in the above screenshot, extra space is only added after the words. I want to get this "extra space above the line" that the documentation alludes to, such that the blue bar above would extend upwards half as many extra pixels it currently extends downwards, such that the text is vertically-centered within the blue bar. — Jackson

tam5 tam5 · Accepted Answer · 2018-07-06T03:24:10

Update

TLDR: I've succumbed to the fact that you can't really reliably achieve this natively with Emacs. You need to patch the font itself to include extra spacing. So, I created this script to take care of that.

Old/Incomplete Answer

TLDR: Add this somewhere in init file:

;; Set the padding between lines
(defvar line-padding 3)
(defun add-line-padding ()
  "Add extra padding between lines"

  ; remove padding overlays if they already exist
  (let ((overlays (overlays-at (point-min))))
    (while overlays
      (let ((overlay (car overlays)))
        (if (overlay-get overlay 'is-padding-overlay)
            (delete-overlay overlay)))
      (setq overlays (cdr overlays))))

  ; add a new padding overlay
  (let ((padding-overlay (make-overlay (point-min) (point-max))))
    (overlay-put padding-overlay 'is-padding-overlay t)
    (overlay-put padding-overlay 'line-spacing (* .1 line-padding))
    (overlay-put padding-overlay 'line-height (+ 1 (* .1 line-padding))))
  (setq mark-active nil))


(add-hook 'buffer-list-update-hook 'add-line-padding)

Increase or decrease the line-padding value to your liking.

This answer pretty much just summarizes the information in the above question, answer, and comments, so I suggest reading those first.

I use an overlay instead of text properties because it behaves more nicely when adding new text to the buffer (especially via copy/paste).

The buffer-list-update-hook is used as a means of identifying when a new buffer has been created and thus would need to have the overlay applied.

For performance reasons, to not continuously add overlays, the existing padding overlay is deleted if it aleady existed.