Show free blocks of time in org-mode's agenda

Question

I would like to make it easy to find where are the free blocks of time in my org-mode agenda.

For instance, if I have two appointments one 9:30am-10:30am and another 11:15am-12:30pm, I would like to see at a glance that the 10:30am-11:15am block is free.

In other words, I want to be able to distinguish free time as easily as it is done in a graphical agenda such as Google calendar.

Is there a way to make the empty blocks of time easy to see? Perhaps to colorize the empty blocks that are longer than a given number of minutes?

Answer 1

Because of this question of my own I looked at the function org-agenda-add-time-grid-maybe which creates the time grid. The code posted there (which is not written by me) does remove a grid line if the time is busy as requested in the OP's comment.

Like you, I wanted to create a visual block in some way. By mixing up the original code of org-agenda-add-time-grid-maybe and the defadvice by Michael Ekstrand posted in the other thread I came up with the following code for org-agenda-add-time-grid-maybe. It will output the grid lines in a different color (for the moment I use the face org-archived) and the times will be followed by a different string. Both can be changed to your liking.

(defun org-agenda-add-time-grid-maybe (list ndays todayp)
  "Add a time-grid for agenda items which need it.

LIST is the list of agenda items formatted by `org-agenda-list'.
NDAYS is the span of the current agenda view.
TODAYP is t when the current agenda view is on today."

  (catch 'exit
   (cond ((not org-agenda-use-time-grid) (throw 'exit list))
         ((and todayp (member 'today (car org-agenda-time-grid))))
         ((and (= ndays 1) (member 'daily (car org-agenda-time-grid))))
         ((member 'weekly (car org-agenda-time-grid)))
         (t (throw 'exit list)))
   (let* ((blocks (mapcar (lambda (x)
                            (let ((start (get-text-property 1 'time-of-day x))
                                  (dur (get-text-property 1 'duration x)))
                              (cond
                               ((and start dur) (cons start
                                                      (org-time-from-minutes
                                                       (truncate
                                                        (+ dur (org-time-to-minutes start))))))
                               (start start)
                               (t nil))))
                          list))
          (have (delq nil (mapcar
                           (lambda (x) (get-text-property 1 'time-of-day x))
                           list)))
          (string (nth 3 org-agenda-time-grid))
          (gridtimes (nth 1 org-agenda-time-grid))
          (req (car org-agenda-time-grid))
          (remove (member 'remove-match req))
          new time)
     (if (and (member 'require-timed req) (not have))
         ;; don't show empty grid
         (throw 'exit list))

     (while (setq time (pop gridtimes))
       (unless (and remove (member time have))
         (let* ((windows (delq nil blocks))
                (hit nil))
           (dolist (busy windows)
             (unless hit
               (when (and (>= time (car busy))
                          (< time (cdr busy)))
                 (setq hit t))))
           (setq time (replace-regexp-in-string " " "0" (format "%04s" time)))
           (if hit
               (progn
                 (push (org-agenda-format-item
                        (concat string " dito") string nil "" nil
                        (concat (substring time 0 -2) ":" (substring time -2)))
                       new)
                 (put-text-property 2 (length (car new)) 'face 'org-archived (car new)))
             (progn
               (push (org-agenda-format-item
                      nil string nil "" nil
                      (concat (substring time 0 -2) ":" (substring time -2)))
                     new)
               (put-text-property 2 (length (car new)) 'face 'org-time-grid (car new))))
           (setq hit nil))))

     (when (and todayp org-agenda-show-current-time-in-grid)
       (push (org-agenda-format-item
              nil org-agenda-current-time-string nil "" nil
              (format-time-string "%H:%M "))
             new)
       (put-text-property
        2 (length (car new)) 'face 'org-agenda-current-time (car new)))

     (if (member 'time-up org-agenda-sorting-strategy-selected)
         (append new list)
       (append list new)))))

(defun org-time-to-minutes (time)
  "Convert an HHMM TIME to minutes."
  (+ (* (/ time 100) 60) (% time 100)))

(defun org-time-from-minutes (minutes)
  "Convert a number of MINUTES to an HHMM time."
  (+ (* (/ minutes 60) 100) (% minutes 60)))

Obviously, it would be more elegant to use defadvice, but I could not figure out where exactly to intervene. The function itself goes through every grid time (set in org-agenda-time-grid) and creates a new list with the final grid including faces (new).