;;; lazy-shot.el --- Lazy font locking for XEmacs

;; Copyright (C) 1997 Jan Vroonhof

;; Author: Jan Vroonhof <vroonhof@math.ethz.ch>
;; Keywords: languages, faces

;; This file is part of XEmacs

;; XEmacs 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.

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

;;; Synched up with:  Not synched.

;;; Commentary:

;; This versions has basic demand lock functionality. Somebody please
;; sync further with lazy-lock v2 from FSF, customize etc.
;;
;;
;; Idea for the stealth lock function:
;;
;;
;; On an Idle itimer
;;    Loop over all buffers with lazy-lock set
;;       mapcar-extent in the region  (point) point-max for
;;                      one-shot-function property
;;         If not found do the same for [point-min,point]
;;         font-lock the found region and delete the extent

;;; Code:

(require 'font-lock)

(defvar lazy-shot-mode nil)


(defvar lazy-shot-step-size (* 1 124)) ;; Please test diffent sizes

;;;###autoload
(defun lazy-shot-mode (&optional arg)
  "Toggle Lazy Lock mode.
With arg, turn Lazy Lock mode on if and only if arg is positive."
  (interactive "P")
  (set (make-local-variable 'lazy-shot-mode)
       (and (if arg (> (prefix-numeric-value arg) 0) (not lazy-shot-mode))))
  (cond ((and lazy-shot-mode (not font-lock-mode))
	 ;; Turned on `lazy-shot-mode' rather than `font-lock-mode'.
	 (let ((font-lock-support-mode 'lazy-shot-mode))
	   (font-lock-mode t)))
	(lazy-shot-mode
	 ;; Turn ourselves on.
	 (lazy-shot-install))
	(t
	 ;; Turn ourselves off.
	 (lazy-shot-unstall))))

;;;###autoload
(defun turn-on-lazy-shot ()
  "Unconditionally turn on Lazy Lock mode."
  (lazy-shot-mode t))


(defun lazy-shot-shot-function (extent)
   "Lazy lock the extent when it has become visisble"
   (let ((start (extent-start-position extent))
         (end   (extent-end-position extent))
	 (buffer (extent-buffer extent)))
     (delete-extent extent)
     (save-excursion 
       ;; This magic should really go into font-lock-fonity-region
       (goto-char start)
       (unless (bolp)
	 (beginning-of-line)
	 (setq start (point)))
       (goto-char end)
       (unless (bolp)
	 (forward-line)
	 (setq end (point)))
       (message "Lazy-shot fontifying from %s to %s in %s" start end buffer)
       (save-match-data
	   (font-lock-fontify-region start end)))))

(defun lazy-shot-install-extent (spos epos &optional buffer)
  "Make an extent that will lazy-shot if it is displayed"
     (let ((extent (make-extent spos epos buffer)))
       (when extent
         (set-extent-one-shot-function extent
                       'lazy-shot-shot-function))
       extent))

(defun lazy-shot-install-extents (fontifying)
  ;;
  ;; Add hook if lazy-shot.el is deferring or is fontifying on scrolling.
     (when fontifying
     (let ((start  (point-min)))
      (while (< start (point-max))
         (lazy-shot-install-extent start
           (min (point-max) (+ start lazy-shot-step-size)))
         (setq start (+ start lazy-shot-step-size))))))

(defun lazy-shot-install ()
  (make-local-variable 'font-lock-fontified)
  (setq font-lock-fontified t)
  (lazy-shot-install-extents font-lock-fontified))

(defun lazy-shot-unstall ()
  ;;
  ;; Remove the extents.
  (map-extents 
     (lambda (e arg) (delete-extent e) nil) 
     nil nil nil nil nil 'one-shot-function 'lazy-shot-shot-function)
  ;;
  ;; Remove the fontification hooks.
  (remove-hook 'after-change-functions 'lazy-shot-defer-after-change t)
  ;;
  ;; If Font Lock mode is still enabled, reinstall its hook.
  (when font-lock-mode
    (add-hook 'after-change-functions 'font-lock-after-change-function nil t)))


(provide 'lazy-shot)

;;; lazy-shot.el ends here