Michael Ekstrand <michael@elehack.net> writes:
> I'd find it quite helpful in reviewing my agenda if there was an option
> to skip displaying grid lines which happen in the middle of timed
> appointments.  Right now, I see the following:
>
> Saturday   18 October 2008
>                8:00...... ----------------
>               10:00...... ----------------
>               12:00...... ----------------
>               14:00...... ----------------
>               16:00...... ----------------
>   Church:     17:30-19:00 Saturday service
>               18:00...... ----------------
>   master:     19:00...... People over for supper
>               20:00...... ----------------
>
> If it could optionally and intelligently drop the 18:00 grid line
> because there is a previous timed appointment overlapping it, the
> resulting display would show me more clearly that I don't have time
> between it and the next event.

After doing some poking around in the org-mode sources, I found out that
the particular behavior described above isn't overly difficult to
implement; in fact, half the work is already done (at least in the
org-mode in Emacs CVS).  The first element of the `org-agenda-time-grid'
variable (the time grid options) supports an undocumented option
`remove-match' which causes `org-agenda-add-time-grid-maybe' to remove
grid lines which exactly correspond to the start time of an event.  It
is rather trivial to extend this logic to also remove grid lines
occluded by the duration of an event.

I have implemented this as a defadvice for
`org-agenda-add-time-grid-maybe' (I like to implement my org-mode logic
changes as defadvice so that they work on top of pristine org-mode and I
don't have to keep patches in sync or installed).  Code follows, if
anyone wants to throw it in their .emacs:

(defadvice org-agenda-add-time-grid-maybe (around mde-org-agenda-grid-tweakify
                                                  (list ndays todayp))
  (if (member 'remove-match (car org-agenda-time-grid))
      (flet ((extract-window
              (line)
              (let ((start (get-text-property 1 'time-of-day line))
                    (dur (get-text-property 1 'duration line)))
                (cond
                 ((and start dur) (cons start dur))
                 (start start)
                 (t nil)))))
        (let* ((windows (delq nil (mapcar 'extract-window list)))
               (org-agenda-time-grid
                (list (car org-agenda-time-grid)
                      (cadr org-agenda-time-grid)
                      (remove-if
                       (lambda (time)
                         (find-if (lambda (w)
                                    (if (numberp w)
                                        (equal w time)
                                      (and (>= time (car w))
                                           (< time (+ (car w) (cdr w))))))
                                  windows))
                       (caddr org-agenda-time-grid)))))
          ad-do-it))
    ad-do-it))
(ad-activate 'org-agenda-add-time-grid-maybe)

- Michael

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