Álvaro Ramírez

10 January 2023 Emacs: org-present in style

I had been meaning to check out David Wilson's System Crafters post detailing his presentations style achieved with the help of org-present and his own customizations. If you're looking for ways to present from Emacs itself, David's post is well worth a look.

org-present's spartan but effective approach resonated with me. David's touches bring the wonderfully stylish icing to the cake. I personally liked his practice of collapsing slide subheadings by default. This lead me to think about slide navigation in general…

There were two things I wanted to achieve:

Easily jump between areas of interest. Subheadings, links, and code blocks would be a good start.
Collapse all but the current top-level heading within the slide, as navigation focus changes.

A quick search for existing functions led me to org-next-visible-heading, org-next-link, and org-next-block. While these make it easy to jump through jump between headings, links, org block on their own, I wanted to jump to whichever one of these is next (similar a web browser's tab behaviour). In a way, DWIM style.

I wrapped the existing functions to enable returning positions. This gave me ar/rg-next-visible-heading-pos, ar/rg-next-link-pos, and ar/rg-next-block-pos respectively. Now that I can find out the next location of either of these items, I can subsequently glue the navigation logic in a function like ar/org-present-next-item. To restore balance to the galaxy, I also added ar/org-present-previous-item.

(defun ar/org-present-next-item (&optional backward)
  "Present and reveal next item."
  (interactive "P")
  ;; Beginning of slide, go to previous slide.
  (if (and backward (eq (point) (point-min)))
      (org-present-prev)
    (let* ((heading-pos (ar/org-next-visible-heading-pos backward))
           (link-pos (ar/org-next-link-pos backward))
           (block-pos (ar/org-next-block-pos backward))
           (closest-pos (when (or heading-pos link-pos block-pos)
                          (apply (if backward #'max #'min)
                                 (seq-filter #'identity
                                             (list heading-pos
                                                   link-pos
                                                   block-pos))))))
      (if closest-pos
          (progn
            (cond ((eq heading-pos closest-pos)
                   (goto-char heading-pos))
                  ((eq link-pos closest-pos)
                   (goto-char link-pos))
                  ((eq block-pos closest-pos)
                   (goto-char block-pos)))
            ;; Reveal relevant content.
            (cond ((> (org-current-level) 1)
                   (ar/org-present-reveal-level2))
                  ((eq (org-current-level) 1)
                   ;; At level 1. Collapse children.
                   (org-overview)
                   (org-show-entry)
                   (org-show-children)
                   (run-hook-with-args 'org-cycle-hook 'children))))
        ;; End of slide, go to next slide.
        (org-present-next)))))

(defun ar/org-present-previous-item ()
  (interactive)
  (ar/org-present-next-item t))

(defun ar/org-next-visible-heading-pos (&optional backward)
  "Similar to `org-next-visible-heading' but for returning position.

Set BACKWARD to search backwards."
  (save-excursion
    (let ((pos-before (point))
          (pos-after (progn
                       (org-next-visible-heading (if backward -1 1))
                       (point))))
      (when (and pos-after (not (equal pos-before pos-after)))
        pos-after))))

(defun ar/org-next-link-pos (&optional backward)
  "Similar to `org-next-visible-heading' but for returning position.

Set BACKWARD to search backwards."
  (save-excursion
    (let* ((inhibit-message t)
           (pos-before (point))
           (pos-after (progn
                        (org-next-link backward)
                        (point))))
      (when (and pos-after (or (and backward (> pos-before pos-after))
                               (and (not backward) (> pos-after pos-before))))
        pos-after))))

(defun ar/org-next-block-pos (&optional backward)
  "Similar to `org-next-block' but for returning position.

Set BACKWARD to search backwards."
  (save-excursion
    (when (and backward (org-babel-where-is-src-block-head))
      (org-babel-goto-src-block-head))
    (let ((pos-before (point))
          (pos-after (ignore-errors
                       (org-next-block 1 backward)
                       (point))))
      (when (and pos-after (not (equal pos-before pos-after)))
        ;; Place point inside block body.
        (goto-char (line-beginning-position 2))
        (point)))))

(defun ar/org-present-reveal-level2 ()
  (interactive)
  (let ((loc (point))
        (level (org-current-level))
        (heading))
    (ignore-errors (org-back-to-heading t))
    (while (or (not level) (> level 2))
      (setq level (org-up-heading-safe)))
    (setq heading (point))
    (goto-char (point-min))
    (org-overview)
    (org-show-entry)
    (org-show-children)
    (run-hook-with-args 'org-cycle-hook 'children)
    (goto-char heading)
    (org-show-subtree)
    (goto-char loc)))

Beware, this was a minimal effort (with redundant code, duplication, etc) and should likely be considered a proof of concept of sorts, but the results look promising. You can see a demo in action.

org-navigate_x1.6.webp

While this was a fun exercise, I can't help but think there must be a cleaner way of doing it or there are existing packages that already do this for you. If you do know, I'd love to know.

Future versions of this code will likely be updated in my Emacs org config.

Update

Removed a bunch of duplication and now rely primarily on existing org-next-visible-heading, org-next-link, and org-next-block.

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