I haven't read either of the source codes, but is it similar to
lisp/cedet/pulse.el?


--
Kaushal Modi

On Thu, Oct 15, 2015 at 1:02 PM, Artur Malabarba <bruce.connor.am@gmail.com>
wrote:

> Whenever the window scrolls or the buffer changes a light will shine on
> top of your cursor so you know where it is.
>
> That’s it. See this gif for example:
> https://github.com/Malabarba/beacon/raw/master/example-beacon.gif
>
>
> ----------
>
>
> ;;; beacon.el --- Highlight the cursor when the window scrolls  -*-
> lexical-binding: t; -*-
>
> ;; Copyright (C) 2015 Free Software Foundation, Inc.
>
> ;; Author: Artur Malabarba <emacs@endlessparentheses.com>
> ;; URL: https://github.com/Malabarba/beacon
> ;; Keywords: convenience
> ;; Version: 0.1
> ;; Package-Requires: ((seq "1.9"))
>
> ;; This program is free software; you can redistribute it and/or modify
> ;; it under the terms of the GNU General Public License as published by
> ;; the Free Software Foundation, either version 3 of the License, or
> ;; (at your option) any later version.
>
> ;; This program is distributed in the hope that it will be useful,
> ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
> ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
> ;; GNU General Public License for more details.
>
> ;; You should have received a copy of the GNU General Public License
> ;; along with this program.  If not, see <http://www.gnu.org/licenses/>.
>
> ;;; Commentary:
>
> ;; This is a global minor-mode. Turn it on everywhere with:
> ;; ┌────
> ;; │ (beacon-mode 1)
> ;; └────
> ;;
> ;; Whenever the window scrolls or the buffer changes a light will shine on
> ;; top of your cursor so you know where it is.
> ;;
> ;; That’s it.
> ;;
> ;;
> ;; 1 Customizations
> ;; ════════════════
> ;;
> ;;   • To customize the appearance of the beacon, configure `beacon-size'
> ;;     and `beacon-color'.
> ;;
> ;;   • To customize how long it lasts, configure `beacon-blink-duration'
> ;;       and `beacon-blink-delay'.
> ;;
> ;;   • To customize /when/ it is used at all, configure
> ;;     `beacon-blink-when-window-scrolls',
> ;;     `beacon-blink-when-buffer-changes', and
> ;;     `beacon-blink-when-point-moves'.
>
> ;;; Code:
>
> (require 'seq)
>
> (defgroup beacon nil
>   "Customization group for beacon."
>   :group 'emacs
>   :prefix "beacon-")
>
> (defvar beacon--timer nil)
>
> (defcustom beacon-push-mark nil
>   "Should the mark be pushed before long movements?
> If nil, `beacon' will not push the mark.
> Otherwise this should be a number, and `beacon' will push the
> mark whenever point moves more than that many lines."
>   :type '(choice integer (const nil)))
>
> (defcustom beacon-blink-when-point-moves nil
>   "Should the beacon blink when moving a long distance?
> If nil, don't blink due to plain movement.
> If non-nil, this should be an integer, which is the minimum
> movement distance (in lines) that triggers a beacon blink."
>   :type '(choice integer (const nil)))
>
> (defcustom beacon-blink-when-buffer-changes t
>   "Should the beacon blink when changing buffer?"
>   :type 'boolean)
>
> (defcustom beacon-blink-when-window-scrolls t
>   "Should the beacon blink when the window scrolls?"
>   :type 'boolean)
>
> (defcustom beacon-blink-duration 0.3
>   "Time, in seconds, that the blink should last."
>   :type 'number)
>
> (defcustom beacon-blink-delay 0.3
>   "Time, in seconds, before starting to fade the beacon."
>   :type 'number)
>
> (defcustom beacon-size 40
>   "Size of the beacon in characters."
>   :type 'number)
>
> (defcustom beacon-color 0.5
>   "Color of the beacon.
> This can be a string or a number.
>
> If it is a number, the color is taken to be white or
> black (depending on the current theme's background) and this
> number is a float between 0 and 1 specifing the brightness.
>
> If it is a string, it is a color name or specification,
> e.g. \"#666600\"."
>   :type '(choice number color))
>
>
> ;;; Overlays
> (defvar beacon--ovs nil)
>
> (defun beacon--colored-overlay (color)
>   "Put an overlay at point with background COLOR."
>   (let ((ov (make-overlay (point) (1+ (point)))))
>     (overlay-put ov 'face (list :background color))
>     (overlay-put ov 'beacon t)
>     (push ov beacon--ovs)))
>
> (defun beacon--ov-put-after-string (overlay colors)
>   "Add an after-string property to OVERLAY.
> The property's value is a string of spaces with background
> COLORS applied to each one."
>   (if (not colors)
>       (delete-overlay overlay)
>     (overlay-put overlay 'beacon-colors colors)
>     (overlay-put overlay 'after-string
>                  (propertize
>                   (mapconcat (lambda (c) (propertize " " 'face (list
> :background c)))
>                              colors
>                              "")
>                   'cursor 1000))))
>
> (defun beacon--after-string-overlay (colors)
>   "Put an overlay at point with an after-string property.
> The property's value is a string of spaces with background
> COLORS applied to each one."
>   (let ((ov (make-overlay (point) (point)))
>         ;; The after-string must not be longer than the remaining columns
> from
>         ;; point to right window-end else it will be wrapped around
> (assuming
>         ;; truncate-lines is nil) introducing an ugly wrap-around for a
>         ;; fraction of a second.
>         (colors (seq-take colors (- (window-width) (current-column)))))
>     (beacon--ov-put-after-string ov colors)
>     (overlay-put ov 'beacon t)
>     (push ov beacon--ovs)))
>
> (defun beacon--ov-at-point ()
>   (car (or (seq-filter (lambda (o) (overlay-get o 'beacon))
>                      (overlays-in (point) (point)))
>            (seq-filter (lambda (o) (overlay-get o 'beacon))
>                      (overlays-at (point))))))
>
> (defun beacon--vanish ()
>   "Turn off the beacon."
>   (when (timerp beacon--timer)
>     (cancel-timer beacon--timer))
>   (mapc #'delete-overlay beacon--ovs)
>   (setq beacon--ovs nil))
>
>
> ;;; Colors
> (defun beacon--int-range (a b)
>   "Return a list of integers between A inclusive and B exclusive.
> Only returns `beacon-size' elements."
>   (let ((d (/ (- b a) beacon-size))
>         (out (list a)))
>     (dotimes (_ (1- beacon-size))
>       (push (+ (car out) d) out))
>     (nreverse out)))
>
> (defun beacon--color-range ()
>   "Return a list of background colors for the beacon."
>   (let* ((bg (color-values (face-attribute 'default :background)))
>          (fg (cond
>               ((stringp beacon-color) (color-values beacon-color))
>               ((< (color-distance "black" bg)
>                   (color-distance "white" bg))
>                (make-list 3 (* beacon-color 65535)))
>               (t (make-list 3 (* (- 1 beacon-color) 65535))))))
>     (apply #'cl-mapcar (lambda (r g b) (format "#%04x%04x%04x" r g b))
>            (mapcar (lambda (n) (butlast (beacon--int-range (elt fg n)
> (elt bg n))))
>                    [0 1 2]))))
>
>
> ;;; Blinking
> (defun beacon--shine ()
>   "Shine a beacon at point."
>   (let ((colors (beacon--color-range)))
>     (save-excursion
>       (while colors
>         (if (looking-at "$")
>             (progn
>               (beacon--after-string-overlay colors)
>               (setq colors nil))
>           (beacon--colored-overlay (pop colors))
>           (forward-char 1))))))
>
> (defun beacon--dec ()
>   "Decrease the beacon brightness by one."
>   (pcase (beacon--ov-at-point)
>     (`nil (beacon--vanish))
>     ((and o (let c (overlay-get o 'beacon-colors)) (guard c))
>      (beacon--ov-put-after-string o (cdr c)))
>     (o
>      (delete-overlay o)
>      (save-excursion
>        (while (progn (forward-char 1)
>                      (setq o (beacon--ov-at-point)))
>          (let ((colors (overlay-get o 'beacon-colors)))
>            (if (not colors)
>                (move-overlay o (1- (point)) (point))
>              (forward-char -1)
>              (beacon--colored-overlay (pop colors))
>              (beacon--ov-put-after-string o colors)
>              (forward-char 1))))))))
>
> (defun beacon-blink ()
>   "Blink the beacon at the position of the cursor."
>   (interactive)
>   (beacon--vanish)
>   (beacon--shine)
>   (setq beacon--timer
>         (run-at-time beacon-blink-delay
>                      (/ beacon-blink-duration 1.0 beacon-size)
>                      #'beacon--dec)))
>
>
> ;;; Movement detection
> (defvar beacon--window-scrolled nil)
> (defvar beacon--previous-place nil)
> (defvar beacon--previous-mark-head nil)
>
> (defun beacon--movement-> (delta)
>   "Return non-nil if latest point movement is > DELTA.
> If DELTA is nil, return nil."
>   (and delta
>        (markerp beacon--previous-place)
>        (equal (marker-buffer beacon--previous-place)
>               (current-buffer))
>        (> (abs (- (point) beacon--previous-place))
>           delta)
>        (> (count-screen-lines (min (point) beacon--previous-place)
>                               (max (point) beacon--previous-place))
>           delta)))
>
> (defun beacon--maybe-push-mark ()
>   "Push mark if it seems to be safe."
>   (when (and (not mark-active)
>              (beacon--movement-> beacon-push-mark))
>     (let ((head (car mark-ring)))
>       (when (and (eq beacon--previous-mark-head head)
>                  (not (equal head beacon--previous-place)))
>         (push-mark beacon--previous-place)))))
>
> (defun beacon--post-command ()
>   "Blink if point moved very far."
>   (cond
>    ((not (markerp beacon--previous-place))
>     (beacon--vanish))
>    ;; Blink because we changed buffer.
>    ((not (equal (marker-buffer beacon--previous-place)
>                 (current-buffer)))
>     (when beacon-blink-when-buffer-changes
>       (unless (window-minibuffer-p)
>         (beacon-blink))))
>    ;; Blink for scrolling.
>    ((and beacon-blink-when-window-scrolls
>          beacon--window-scrolled
>          (equal beacon--window-scrolled (selected-window)))
>     (beacon-blink)
>     (setq beacon--window-scrolled nil))
>    ;; Blink for movement
>    ((beacon--movement-> beacon-blink-when-point-moves)
>     (beacon-blink))
>    ;; Even if we don't blink, vanish any previous beacon.
>    (t (beacon--vanish)))
>   (beacon--maybe-push-mark)
>   (unless (window-minibuffer-p)
>     (setq beacon--previous-mark-head (car mark-ring))
>     (setq beacon--previous-place (point-marker))))
>
> (defun beacon--window-scroll-function (win _start-pos)
>   "Blink the beacon or record that window has been scrolled.
> If invoked during the command loop, record the current window so
> that it may be blinked on post-command.  This is because the
> scrolled window might not be active, but we only know that at
> `post-command-hook'.
>
> If invoked outside the command loop, `post-command-hook' would be
> unreliable, so just blink immediately."
>   (if this-command
>       (setq beacon--window-scrolled win)
>     (beacon-blink)))
>
>
> ;;; Minor-mode
> (defcustom beacon-lighter
>   (cond
>    ((char-displayable-p ?💡) " 💡")
>    ((char-displayable-p ?Λ) " Λ")
>    (t " *"))
>   "Lighter string used on the mode-line."
>   :type 'string)
>
> ;;;###autoload
> (define-minor-mode beacon-mode
>   nil nil beacon-lighter nil
>   :global t
>   (if beacon-mode
>       (progn
>         (add-hook 'window-scroll-functions
> #'beacon--window-scroll-function)
>         (add-hook 'post-command-hook #'beacon--post-command))
>     (remove-hook 'window-scroll-functions #'beacon--window-scroll-function)
>     (remove-hook 'post-command-hook #'beacon--post-command)))
>
> (provide 'beacon)
> ;;; beacon.el ends here
>
>