Logos (logos.el)
Simple focus mode for Emacs with page breaks or outlines
This manual, written by Protesilaos Stavrou, describes the customization
options for logos (or logos.el), and provides every other piece of
information pertinent to it.
The documentation furnished herein corresponds to stable version 1.2.0, released on 2024-09-03. Any reference to a newer feature which does not yet form part of the latest tagged commit, is explicitly marked as such.
Current development target is 1.3.0-dev.
- Package name (GNU ELPA):
logos - Official manual: https://protesilaos.com/emacs/logos
- Change log: https://protesilaos.com/emacs/logos-changelog
- Git repositories:
- Video demo: https://protesilaos.com/codelog/2022-03-11-emacs-logos-demo/
- Backronyms:
^LOnly Generates Ostensible Slides; Logos Optionally Goes through Outline Sections.
Table of Contents
- 1. COPYING
- 2. Overview
- 3. Installation
- 4. Sample configuration
- 5. Extra tweaks
- 6. Acknowledgements
- 7. GNU Free Documentation License
- 8. Indices
1. COPYING
Copyright (C) 2022-2023 Free Software Foundation, Inc.
Permission is granted to copy, distribute and/or modify this document under the terms of the GNU Free Documentation License, Version 1.3 or any later version published by the Free Software Foundation; with no Invariant Sections, with the Front-Cover Texts being “A GNU Manual,” and with the Back-Cover Texts as in (a) below. A copy of the license is included in the section entitled “GNU Free Documentation License.”
(a) The FSF’s Back-Cover Text is: “You have the freedom to copy and modify this GNU manual.”
2. Overview
This package provides a simple “focus mode” which can be applied to any
buffer for reading, writing, or even doing a presentation. The buffer
can be divided in pages using the page-delimiter, outline structure,
or any other pattern. Commands are provided to move between those
pages. These motions work even when narrowing is in effect (and they
preserve it). logos.el is designed to be simple by default and easy
to extend. This manual provides concrete examples to that end.
What constitutes a page delimiter is determined by the user options
logos-outlines-are-pages and logos-outline-regexp-alist. By
default, this only corresponds to the ^L character (which can be
inserted using the standard keys with C-q C-l).
Logos does not define any key bindings. Try something like this, if you want:
(let ((map global-map)) (define-key map [remap narrow-to-region] #'logos-narrow-dwim) (define-key map [remap forward-page] #'logos-forward-page-dwim) (define-key map [remap backward-page] #'logos-backward-page-dwim))
On standard Emacs, those key bindings are: C-x n n, C-x ], C-x [.
The logos-narrow-dwim is not necessary for users who already know how
to narrow effectively. Such users may still want to bind it to a key.
For users running Emacs version 28 or higher, Logos defines the
logos-repeat-map which is activated when repeat-mode is enabled.
This means that page motions, C-x ] and C-x [, can be repeated by
following them up with either ] or [. The repetition stops when
another command is invoked.
Logos provides some optional aesthetic tweaks which come into effect
when the buffer-local logos-focus-mode is enabled. These will hide
the cursor (logos-hide-cursor), hide the mode line
(logos-hide-mode-line), hide the header line
(logos-hide-header-line), disable the buffer boundary indicators
(indicate-buffer-boundaries), enable scroll-lock-mode
(logos-scroll-lock), use variable-pitch-mode in non-programming
buffers (logos-variable-pitch), make the buffer read-only
(logos-buffer-read-only), center the buffer in its window if the
olivetti package is installed (logos-olivetti), and hide the
fringe face (logos-hide-fringe). All these variables are
buffer-local.
Furthermore, the logos-focus-mode establishes a bespoke keymap, which
can be used to, for example, bind the arrow keys to page motions. The
keymap is logos-focus-mode-map and is empty by default (we do not
define any keys and trust the user to pick their own).
Logos is the familiar word derived from Greek (watch my presentation on philosophy about Cosmos, Logos, and the living universe: https://protesilaos.com/books/2022-02-05-cosmos-logos-living-universe/), though it also stands for these two perhaps equally insightful backronyms about the mechanics of this package:
^LOnly Generates Ostensible Slides- Logos Optionally Goes through Outline Sections
3. Installation
3.1. GNU ELPA package
The package is available as logos. Simply do:
M-x package-refresh-contents M-x package-install
And search for it.
GNU ELPA provides the latest stable release. Those who prefer to follow the development process in order to report bugs or suggest changes, can use the version of the package from the GNU-devel ELPA archive. Read: https://protesilaos.com/codelog/2022-05-13-emacs-elpa-devel/.
3.2. Manual installation
Assuming your Emacs files are found in ~/.emacs.d/, execute the
following commands in a shell prompt:
cd ~/.emacs.d # Create a directory for manually-installed packages mkdir manual-packages # Go to the new directory cd manual-packages # Clone this repo, naming it "logos" git clone https://github.com/protesilaos/logos logos
Finally, in your init.el (or equivalent) evaluate this:
;; Make Elisp files in that directory available to the user. (add-to-list 'load-path "~/.emacs.d/manual-packages/logos")
Everything is in place to set up the package.
4. Sample configuration
Logos does not bind its own keys and does not make any opinionated changes out-of-the-box (Extra tweaks):
- To get the do-what-I-mean page motions add your own key bindings. In
the example below, they take the stead of
forward-page(C-x ]) andbackward-page(C-x [). The commandlogos-narrow-dwimneed not be bound, especially if you are already familiar with the various narrowing commands (otherwise it maps toC-x n nin this example, assuming the default keys). - To have quick access to
logos-focus-mode, bind it to a key. This mode checks the variableslogos-hide-cursor,logos-hide-mode-line,logos-hide-header-line,logos-scroll-lock,logos-variable-pitch,logos-hide-buffer-boundaries,logos-buffer-read-only,logos-olivetti(requiresolivettipackage) and applies their effects if they are non-nil. Note that everything is buffer-local, so it is possible to use file variables as described in the Emacs manual.
(require 'logos)
;; If you want to use outlines instead of page breaks (the ^L):
(setq logos-outlines-are-pages t)
;; This is the default value for the outlines:
(setq logos-outline-regexp-alist
`((emacs-lisp-mode . "^;;;+ ")
(org-mode . "^\\*+ +")
(markdown-mode . "^\\#+ +")))
;; These apply when `logos-focus-mode' is enabled. Their value is
;; buffer-local.
(setq-default logos-hide-cursor nil
logos-hide-mode-line t
logos-hide-header-line t
logos-hide-buffer-boundaries t
logos-hide-fringe t
logos-variable-pitch nil
logos-buffer-read-only nil
logos-scroll-lock nil
logos-olivetti nil)
;; Also check this manual for `logos-focus-mode-hook'. It lets you
;; extend `logos-focus-mode'.
(let ((map global-map))
(define-key map [remap narrow-to-region] #'logos-narrow-dwim)
(define-key map [remap forward-page] #'logos-forward-page-dwim)
(define-key map [remap backward-page] #'logos-backward-page-dwim)
(define-key map (kbd "<f9>") #'logos-focus-mode))
;; Also consider adding keys to `logos-focus-mode-map'. They will take
;; effect when `logos-focus-mode' is enabled.
5. Extra tweaks
This section contains snippets of code that extend the functionality of
logos. These either apply to logos-focus-mode or enhance the page
motions through the logos-page-motion-hook.
5.1. Center the buffer in its window
Install the excellent olivetti package by Paul W. Rankin. Then set
logos-olivetti to non-nil.
The present author’s favourite settings given a fill-column of 72:
(setq olivetti-body-width 0.7
olivetti-minimum-body-width 80
olivetti-recall-visual-line-mode-entry-state t)
Though note that Olivetti works well even without a fill-column and
auto-fill-mode disabled.
5.2. Make EWW look like the rest of Emacs
By default, all M-x eww buffers use the shr-max-width which is set
to 120 characters. This is above the standard value of fill-column
and thus does not let text flow nicely while using olivetti package
(Center the buffer in its window).
For a general customization, the user can evaluate this:
(setq shr-max-width fill-column)
EWW buffers also default to variable-pitch typography by default (as
opposed to whatever the font family of the default face is). This too
can be made consistent with the rest of Emacs:
(setq shr-use-fonts nil)
[ For font-related customizations check the fontaine package on GNU
ELPA (by Protesilaos). ]
Note that all variables with the shr- prefix are about the built-in
Simple HTML Renderer, so they will affect any other package that relies
on them beside EWW (in principle, the aforementioned should not pose any
problem).
5.3. Automatically reveal Org or Outline subtree
The Logos page motions normally jump between positions. Though Org and
Outline require that Logos also reveals the headings’ contents. This is
necessary to avoid invisible motions inside a folded heading that
contains subheadings. The unfolding only applies to the current entry.
This is the relevant snippet from logos.el:
(defun logos-reveal-entry ()
"Reveal Org or Outline entry."
(cond
((and (eq major-mode 'org-mode)
(org-at-heading-p))
(org-show-entry))
((or (eq major-mode 'outline-mode)
(bound-and-true-p outline-minor-mode))
(outline-show-entry))))
(add-hook 'logos-page-motion-hook #'logos-reveal-entry)
Users may prefer to reveal the entire subtree instead of the current
entry: the heading at point and all of its subheadings. In this case,
one may override the definition of logos-reveal-entry:
;; glue code to expand an Org/Outline heading
(defun logos-reveal-entry ()
"Reveal Org or Outline entry."
(cond
((and (eq major-mode 'org-mode)
(org-at-heading-p))
(org-show-subtree))
((or (eq major-mode 'outline-mode)
(bound-and-true-p outline-minor-mode))
(outline-show-subtree))))
5.4. Recenter at the top upon page motion
Page motions normally reposition the point at the centre of the window
if necessary (this is standard Emacs behaviour). To always change the
placement invoke the recenter function with a numeric argument.
;; place point at the top when changing pages (defun my-logos-recenter-top () "Use `recenter' to reposition the view at the top." (recenter 0)) (add-hook 'logos-page-motion-hook #'my-logos-recenter-top)
The 0 argument refers to the topmost line. So 1 points to the line
below and so on.
If the recentering should not affect specific modes, tweak the function accordingly:
(defvar my-logos-no-recenter-top-modes
'(emacs-lisp-mode lisp-interaction-mode))
(defun my-logos-recenter-top ()
"Use `recenter' to reposition the view at the top."
(unless (memq major-mode my-logos-no-recenter-top-modes)
(recenter 0)))
Or simply exclude all programming modes:
(defun my-logos-recenter-top ()
"Use `recenter' to reposition the view at the top."
(unless (derived-mode-p 'prog-mode)
(recenter 0)))
5.5. Use outlines and page breaks
By default, the page motions only move between the ^L delimiters.
While the option logos-outlines-are-pages changes the behaviour to
move between outline headings instead. What constitutes an “outline
heading” is determined by the logos-outline-regexp-alist with an
automatic fallback to either outline-regexp or page-delimiter
(Logos handles this fallback condition internally).
Provided this:
(setq logos-outlines-are-pages t)
The default value of logos-outline-regexp-alist will affect
org-mode, emacs-lisp-mode, and any of their derivatives
(e.g. lisp-interaction-mode (the standard scratch buffer) is based on
emacs-lisp-mode). Its fallback value is whatever the major mode sets
as an outline, else the standard ^L.
(setq logos-outline-regexp-alist
`((emacs-lisp-mode . "^;;;+ ")
(org-mode . "^\\*+ +")))
It is possible to tweak those regular expressions to target both the outline and the page delimiters:
(setq logos-outline-regexp-alist
`((emacs-lisp-mode . ,(format "\\(^;;;+ \\|%s\\)" logos-page-delimiter))
(org-mode . ,(format "\\(^\\*+ +\\|%s\\)" logos-page-delimiter))))
The form ,(format "\\(^;;;+ \\|%s\\)" logos-page-delimiter)
expands to "\\(^;;;+ \\|^^L\\)" where ^L is the actual control character.
For Org it may be better to either not target the ^L or to also target
the horizontal rule (five hyphens on a line, else the ^-\\{5\\}$
pattern). Putting it all together:
(setq logos-outline-regexp-alist
`((emacs-lisp-mode . ,(format "\\(^;;;+ \\|%s\\)" logos-page-delimiter))
(org-mode . ,(format "\\(^\\*+ +\\|^-\\{5\\}$\\|%s\\)" logos-page-delimiter))))
Another Org-specific tweak is to use heading levels up to a specific
number. The idea would be that anything below that number is not
significant. For example, ^\\* + only applies to top-level headings,
while ^\\*\\{1,3\\} + covers heading levels 1 through 3. Accounting
for the aforementiond horizontal rule and generic page delimiter, the
end result can look like this:
(setq logos-outline-regexp-alist
`((emacs-lisp-mode . ,(format "\\(^;;;+ \\|%s\\)" logos-page-delimiter))
(org-mode . ,(format "\\(^\\*\\{1,3\\} +\\|^-\\{5\\}$\\|%s\\)" logos-page-delimiter))))
5.6. Leverage logos-focus-mode-hook
The logos-focus-mode-hook is a normal hook that runs when
logos-focus-mode is enabled. Each function is called without an
argument and looks like those in logos.el. An example that sets a
variable is logos--buffer-read-only; one that sets a mode is
logos--scroll-lock; another that sets the mode of an external
package is logos--olivetti; while logos--hide-fringe provides yet
another useful sample.
If a function cannot be like the aforementioned though still needs to
set its state both when logos-focus-mode is enabled and disabled, then
use the logos-focus-mode-hook instead.
5.6.1. Conditionally toggle org-indent-mode
Here is a snippet that relies on the logos-focus-mode-hook to extend
the functionality of logos-focus-mode (Leverage logos-focus-mode-hook).
It disables org-indent-mode when logos-focus-mode is enabled and
restores it when logos-focus-mode is disabled. The
logos-set-mode-arg function takes care of the technicalities.
(defun my-logos-org-indent ()
(when logos-focus-mode
(logos-set-mode-arg 'org-indent-mode -1)))
(add-hook 'logos-focus-mode-hook #'my-logos-org-indent)
5.6.2. Disable menu-bar, tool-bar, tab-bar, tab-line
Continuing with the examples in this section of the manual, the code
block below shows how to disable the menu-bar-mode, tool-bar-mode,
tab-bar-mode, and tab-line-mode when logos-focus-mode is
enabled. If the given mode is already disabled, the corresponding
function does nothing. Otherwise it toggles the mode off/on when
logos-focus-mode is enabled/disabled.
(defun my-logos-hide-menu-bar ()
(when logos-focus-mode
(logos-set-mode-arg 'menu-bar-mode -1)))
(add-hook 'logos-focus-mode-hook #'my-logos-hide-menu-bar)
;; Assuming the `tool-bar-mode' is enabled by default...
(defun my-logos-hide-tool-bar ()
(when logos-focus-mode
(logos-set-mode-arg 'tool-bar-mode -1)))
(add-hook 'logos-focus-mode-hook #'my-logos-hide-tool-bar)
;; Assuming the `tab-bar-mode' is enabled by default...
(defun my-logos-hide-tab-bar ()
(when logos-focus-mode
(logos-set-mode-arg 'tab-bar-mode -1)))
(add-hook 'logos-focus-mode-hook #'my-logos-hide-tab-bar)
;; Assuming the `tab-line-mode' is enabled by default...
(defun my-logos-hide-tab-line ()
(when logos-focus-mode
(logos-set-mode-arg 'tab-line-mode -1)))
(add-hook 'logos-focus-mode-hook #'my-logos-hide-tab-line)
5.7. Update fringe color on theme switch
The user option logos-hide-fringe does not actually remove the fringe,
as that would change the user’s preference for fringe-mode. Instead,
it remaps its background color to be the same as that of the default
face. For example, if the main background is white while the fringe is
gray, the fringe will become white as well.
The problem with this approach is that the color is not automatically
updated upon switching to a new theme, such as by toggling between one
with a light background to another with a dark one. The solution is to
assign the logos-update-fringe-in-buffers function to a hook that is
triggered by the theme-loading operation.
Some themes provide such a hook. For example, the modus-themes
package has the modus-themes-after-load-theme-hook (the themes
modus-operandi and modus-vivendi are built into Emacs version 28 or
higher).
(add-hook 'modus-themes-after-load-theme-hook #'logos-update-fringe-in-buffers)
Or use the special hook enable-theme-functions that is part of
Emacs 29.
(add-hook 'enable-theme-functions #'logos-update-fringe-in-buffers)
For older versions of Emacs before 29, a user-defined, theme-agnostic setup for such a hook can be configured thus:
(defvar after-enable-theme-hook nil "Normal hook run after enabling a theme.") (defun run-after-enable-theme-hook (&rest _args) "Run `after-enable-theme-hook'." (run-hooks 'after-enable-theme-hook)) (advice-add 'enable-theme :after #'run-after-enable-theme-hook)
Then use it like this:
(add-hook 'after-enable-theme-hook #'logos-update-fringe-in-buffers)
6. Acknowledgements
Logos is meant to be a collective effort. Every bit of help matters.
- Author/maintainer
- Protesilaos Stavrou.
- Contributions to code or the manual
- Daniel Mendler, Edgar Vincent, Lucy McPhail, Omar AntolĂn Camarena, Philip Kaludercic, Remco van ’t Veer, and user Ypot.
- Ideas and/or user feedback
- Daniel Mendler, Dave Abrahams, Lasse Lindner, Marcel Ventosa, Xiaoduan, Ypot.
7. GNU Free Documentation License
GNU Free Documentation License
Version 1.3, 3 November 2008
Copyright (C) 2000, 2001, 2002, 2007, 2008 Free Software Foundation, Inc.