The Complete Computer

emacs-lisp source: 
(provide 'cce/display-test-functions)

Calculating the display density is a pain in the ass because it's easier to parse xrandr output than it is to integrate with libXrandr. I guess I could write an elisp wrapper for it, but I would rather not right now. open threads

emacs-lisp source: 
(defun cce/external-display-dpis ()
  "Returns a list of integers, the DPI of the connected external Display Port displays. assumes square pixels, sorry."
  (let (results (xrandr-buffer (get-buffer-create " *xrandr*")))
    (with-current-buffer xrandr-buffer
      (erase-buffer)
      (call-process-shell-command "xrandr" nil xrandr-buffer)
      (goto-char (point-min))
      (setq-local results nil)
      (while (re-search-forward "^\\([^e][a-zA-Z]+\\(-?[0-9]+\\)+\\)" nil t)
        (when-let* ((eol (save-excursion (end-of-line) (point)))
                    (display-name (match-string 1))
                    (is-connected (re-search-forward "connected \\(primary \\)?\\([0-9]+\\)x\\([0-9]+\\)" eol t))
                    (pixels (string-to-number (match-string 3)))
                    (has-physical (re-search-forward "\\([0-9]+\\)mm x \\([0-9]+\\)mm" eol))
                    (physical (string-to-number (match-string 2)))
                    (dpi (if (equal 0 physical)
                             140
                             (floor (* 25.4 (/ (float pixels) physical))))))
          (add-to-list 'results (cons display-name dpi))))
      results)))

(defun cce/external-display-connected ()
  "returns t if there are external displayport monitors connected." 
  (let ((dpis (cce/external-display-dpis)))
    (> (length dpis) 0)))

(defun cce/connected-displays ()
  "Returns a list of displays currently connceted"
  (append (list "eDP-1")
          (mapcar
           (lambda (cons)
             (car cons))
           (cce/external-display-dpis))))

(defun cce/exwm-connected-displays ()
  "Return a list of displays for [`exwm-randr-workspace-monitor-plist']"
  (apply #'append
         (seq-map-indexed (lambda (elt idx)
                            (list idx elt))
                          (cce/connected-displays))))