;;; hl-line.el --- highlight the current line

;; Copyright (C) 1998, 2000, 2001, 2003 Free Software Foundation, Inc.

;; Author:  Dave Love <fx@gnu.org>
;; Created: 1998-09-13
;; Keywords: faces, frames, emulation

;; This file is part of GNU Emacs.

;; GNU Emacs 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 2, or (at your option)
;; any later version.

;; GNU Emacs 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 GNU Emacs; see the file COPYING.  If not, write to the
;; Free Software Foundation, Inc., 59 Temple Place - Suite 330,
;; Boston, MA 02111-1307, USA.

;;; Commentary:

;; Provides a buffer-local minor mode (toggled by M-x hl-line-mode)
;; and a global minor mode (toggled by M-x global-hl-line-mode) to
;; highlight, on a suitable terminal, the line on which point is.  The
;; global mode highlights the current line in the selected window only
;; (except when the minibuffer window is selected).  This was
;; implemented to satisfy a request for a feature of Lesser Editors.
;; The local mode is sticky: it highlights the line about the buffer's
;; point even if the buffer's window is not selected.  Caveat: the
;; buffer's point might be different from the point of a non-selected
;; window.  Set the variable `hl-line-sticky-flag' to nil to make the
;; local mode behave like the global mode.

;; You probably don't really want to use the global mode; if the
;; cursor is difficult to spot, try changing its colour, relying on
;; `blink-cursor-mode' or both.  The hookery used might affect
;; response noticeably on a slow machine.  The local mode may be
;; useful in non-editing buffers such as Gnus or PCL-CVS though.

;; An overlay is used.  In the non-sticky cases, this overlay is
;; active only on the selected window.  A hook is added to
;; `post-command-hook' to activate the overlay and move it to the line
;; about point.  To get the non-sticky behavior, `hl-line-unhighlight'
;; is added to `pre-command-hook' as well.  This function deactivates
;; the overlay unconditionally in case the command changes the
;; selected window.  (It does so rather than keeping track of changes
;; in the selected window).

;; You could make variable `global-hl-line-mode' buffer-local and set
;; it to nil to avoid highlighting specific buffers, when the global
;; mode is used.

;;; Code:

(defgroup hl-line nil
  "Highlight the current line."
  :version "21.1"
  :group 'editing)

(defcustom hl-line-face 'highlight
  "Face with which to highlight the current line."
  :type 'face
  :group 'hl-line)

(defcustom hl-line-sticky-flag t
  "*Non-nil means highlight the current line in all windows.
Otherwise Hl-Line mode will highlight only in the selected
window.  Setting this variable takes effect the next time you use
the command `hl-line-mode' to turn Hl-Line mode on."
  :type 'boolean
  :version "21.4"
  :group 'hl-line)

(defvar hl-line-overlay nil
  "Overlay used by Hl-Line mode to highlight the current line.")
(make-variable-buffer-local 'hl-line-overlay)

(defvar global-hl-line-overlay nil
  "Overlay used by Global-Hl-Line mode to highlight the current line.")

;;;###autoload
(define-minor-mode hl-line-mode
  "Buffer-local minor mode to highlight the line about point.
With ARG, turn Hl-Line mode on if ARG is positive, off otherwise.

If `hl-line-sticky-flag' is non-nil, Hl-Line mode highlights the
line about the buffer's point in all windows.  Caveat: the
buffer's point might be different from the point of a
non-selected window.  Hl-Line mode uses the function
`hl-line-highlight' on `post-command-hook' in this case.

When `hl-line-sticky-flag' is nil, Hl-Line mode highlights the
line about point in the selected window only.  In this case, it
uses the function `hl-line-unhighlight' on `pre-command-hook' in
addition to `hl-line-highlight' on `post-command-hook'."
  nil nil nil
  (if hl-line-mode
      (progn
        ;; In case `kill-all-local-variables' is called.
        (add-hook 'change-major-mode-hook #'hl-line-unhighlight nil t)
        (if hl-line-sticky-flag
            (remove-hook 'pre-command-hook #'hl-line-unhighlight t)
          (add-hook 'pre-command-hook #'hl-line-unhighlight nil t))
        (hl-line-highlight)
	(add-hook 'post-command-hook #'hl-line-highlight nil t))
    (remove-hook 'post-command-hook #'hl-line-highlight t)
    (hl-line-unhighlight)
    (remove-hook 'change-major-mode-hook #'hl-line-unhighlight t)
    (remove-hook 'pre-command-hook #'hl-line-unhighlight t)))

(defun hl-line-highlight ()
  "Active the Hl-Line overlay on the current line."
  (if hl-line-mode	; Might be changed outside the mode function.
      (progn
        (unless hl-line-overlay
          (setq hl-line-overlay (make-overlay 1 1)) ; to be moved
          (overlay-put hl-line-overlay 'face hl-line-face))
        (overlay-put hl-line-overlay
                     'window (unless hl-line-sticky-flag (selected-window)))
        (move-overlay hl-line-overlay
                      (line-beginning-position) (line-beginning-position 2)))
    (hl-line-unhighlight)))

(defun hl-line-unhighlight ()
  "Deactivate the Hl-Line overlay on the current line."
  (if hl-line-overlay
      (delete-overlay hl-line-overlay)))

;;;###autoload
(define-minor-mode global-hl-line-mode
  "Global minor mode to highlight the line about point in the current window.
With ARG, turn Global-Hl-Line mode on if ARG is positive, off otherwise.

Global-Hl-Line mode uses the functions `global-hl-line-unhighlight' and
`global-hl-line-highlight' on `pre-command-hook' and `post-command-hook'."
  :global t
  :group 'hl-line
  (if global-hl-line-mode
      (progn
	(add-hook 'pre-command-hook #'global-hl-line-unhighlight)
	(add-hook 'post-command-hook #'global-hl-line-highlight))
    (global-hl-line-unhighlight)
    (remove-hook 'pre-command-hook #'global-hl-line-unhighlight)
    (remove-hook 'post-command-hook #'global-hl-line-highlight)))

(defun global-hl-line-highlight ()
  "Active the Global-Hl-Line overlay on the current line in the current window."
  (when global-hl-line-mode	; Might be changed outside the mode function.
    (unless (window-minibuffer-p (selected-window))
      (unless global-hl-line-overlay
        (setq global-hl-line-overlay (make-overlay 1 1)) ; to be moved
        (overlay-put global-hl-line-overlay 'face hl-line-face))
      (overlay-put global-hl-line-overlay 'window (selected-window))
      (move-overlay global-hl-line-overlay
                    (line-beginning-position) (line-beginning-position 2)))))

(defun global-hl-line-unhighlight ()
  "Deactivate the Global-Hl-Line overlay on the current line."
  (if global-hl-line-overlay
      (delete-overlay global-hl-line-overlay)))

(provide 'hl-line)

;;; hl-line.el ends here