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README.md

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+# fringe-current-line
+
+Show current line on the fringe.
+
+## Description
+
+fringe-current-line is a package to indicate current line on the fringe.
+You can use by the following steps.
+
+1. Place this file on your load-path.
+
+2. Add the following code into your init file:
+
+```lisp
+  (require 'fringe-current-line)
+```
+
+3. Activate the mode.
+
+* To enable it only in certain buffer, run `M-x fringe-current-line-mode`.
+  Run again and you can disable it.
+
+* To enable it globally, add the following into your init file:
+
+```lisp
+    (global-fringe-current-line-mode 1)
+```
+
+  You can toggle it by running `M-x global-fringe-current-line-mode`.
+
+
+## Limitation
+
+The indicator is not shown if the cursor is at the end of the buffer and the last line is empty.
+
+
+## License
+
+Copyright (C) 2014 Kouhei Yanagita
+
+This program is free software; you can redistribute it and/or modify
+it under the terms of the MIT License.

fringe-current-line.el

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+;;; fringe-current-line.el --- show current line on the fringe.
+;;
+;; Copyright: (C) 2014 Kouhei Yanagita
+;;
+;; Author: Kouhei Yanagita <yanagi@shakenbu.org>
+;; Github: http://github.com/kyanagi/fringe-current-line
+;; URL: http://github.com/kyanagi/fringe-current-line/raw/master/fringe-current-line.el
+;;
+;; This program is free software; you can redistribute it and/or modify
+;; it under the terms of the MIT License.
+;;
+;; Permission is hereby granted, free of charge, to any person obtaining
+;; a copy of this software and associated documentation files (the
+;; "Software"), to deal in the Software without restriction, including
+;; without limitation the rights to use, copy, modify, merge, publish,
+;; distribute, sublicense, and/or sell copies of the Software, and to
+;; permit persons to whom the Software is furnished to do so, subject to
+;; the following conditions:
+;;
+;; The above copyright notice and this permission notice shall be
+;; included in all copies or substantial portions of the Software.
+;;
+;; THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
+;; EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+;; MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
+;; NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
+;; LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+;; OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
+;; WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+;;
+;;; Commentary:
+;;
+;; fringe-current-line is a package to indicate current line on the fringe.
+;; You can use by the following steps.
+;;
+;; 1. Place this file on your load-path.
+;;
+;; 2. Add the following code into your init file:
+;;
+;;   (require 'fringe-current-line)
+;;
+;; 3. Activate the mode.
+;;
+;; * To enable it only in certain buffer, run `M-x fringe-current-line-mode'.
+;;   Run again and you can disable it.
+;;
+;; * To enable it globally, add the following into your init file:
+;;
+;;     (global-fringe-current-line-mode 1)
+;;
+;;   You can toggle it by running `M-x global-fringe-current-line-mode'.
+;;
+;;
+;; ## Limitation
+;;
+;; The indicator is not shown if the cursor is at the end of the buffer and the last line is empty.
+;;
+;;; Code:
+
+(defvar fcl-fringe-bitmap 'vertical-bar
+  "Bitmap to indicate current line.")
+
+;;; internal variable
+(defvar fcl-fringe-overlay nil
+  "Hold an overlay for the fringe bitmap.")
+(make-variable-buffer-local 'fcl-fringe-overlay)
+
+(defun fcl-display-fringe-bitmap-at-current-line ()
+  (let ((s "x")
+        (point (point)))
+    (fcl-clear-fringe-bitmap)
+    ;; Somehow the cursor disappears at the end of the buffer if the last line is empty.
+    ;; So don't display the bitmap on the fringe in that case.
+    (unless (and (eobp) (bolp))
+      (setq fcl-fringe-overlay (make-overlay point (1+ point)))
+      (put-text-property 0 1 'display (list 'left-fringe fcl-fringe-bitmap) s)
+      (overlay-put fcl-fringe-overlay 'before-string s))))
+
+(defun fcl-clear-fringe-bitmap ()
+  (when fcl-fringe-overlay
+    (delete-overlay fcl-fringe-overlay)
+    (setq fcl-fringe-overlay nil)))
+
+(defun fringe-current-line-mode-on ()
+  (add-hook 'post-command-hook 'fcl-display-fringe-bitmap-at-current-line nil t)
+  )
+
+(defun fringe-current-line-mode-off ()
+  (fcl-clear-fringe-bitmap)
+  (remove-hook 'post-command-hook 'fcl-display-fringe-bitmap-at-current-line t)
+  )
+
+(define-minor-mode fringe-current-line-mode
+  "Indicate current line on the fringe."
+  :global nil
+  (if fringe-current-line-mode
+      (fringe-current-line-mode-on)
+    (fringe-current-line-mode-off)))
+
+(define-global-minor-mode global-fringe-current-line-mode
+  fringe-current-line-mode
+  (lambda ()
+    (unless (minibufferp)
+      (fringe-current-line-mode 1))))
+
+(provide 'fringe-current-line)
+
+;;; fringe-current-line.el ends here