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+;;; mouse-drag.el
+;;; Copyright (C) 1996 Free Software Foundation, Inc.
+
+;;; Author: John Heidemann <johnh@ISI.EDU>
+;;; Keywords: mouse
+
+;; 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:
+
+;;; What is ``mouse-drag.el''?
+;;;
+;;; Doesn't that scroll bar seem far away when you want to scroll?
+;;; This module overloads mouse-2 to do ``throw'' scrolling.  You
+;;; click and drag.  The distance you move from your original click
+;;; turns into a scroll amount.  The scroll amount is scaled
+;;; exponentially to make both large moves and short adjustments easy.
+;;; What this boils down to is that you can easily scroll around the
+;;; buffer without much mouse movement.  Finally, clicks which aren't
+;;; drags are passed off to the old mouse-2 binding, so old mouse-2
+;;; operations (find-file in dired-mode, yanking in most other modes)
+;;; still work.
+;;;
+;;; There is an alternative way to scroll, ``drag'' scrolling.  You
+;;; can click on a character and then drag it around, scrolling the
+;;; buffer with you.  The character always stays under the mouse.
+;;; Compared to throw-scrolling, this approach provides direct
+;;; manipulation (nice) but requires more mouse movement
+;;; (unfortunate).  It is offered as an alternative for those who
+;;; prefer it.
+;;;
+;;; If you like mouse-drag, you should also check out mouse-copy
+;;; for ``one-click text copy and move''.
+;;;
+;;; To use mouse-drag, place the following in your .emacs file:
+;;;	(require 'mouse-drag)
+;;; -and either-
+;;;     (global-set-key [down-mouse-2] 'mouse-drag-throw)
+;;; -or-
+;;;     (global-set-key [down-mouse-2] 'mouse-drag-drag)
+;;;
+;;;
+;;;
+;;; Options:
+;;;
+;;; - reverse the throw-scroll direction with \\[mouse-throw-with-scroll-bar]
+;;; - work around a bug with \\[mouse-extras-work-around-drag-bug]
+;;;
+;;;
+;;; History and related work:
+;;;
+;;; One-click copying and moving was inspired by lemacs-19.8.
+;;; Throw-scrolling was inspired by MacPaint's ``hand'' and by Tk's
+;;; mouse-2 scrolling.  The package mouse-scroll.el by Tom Wurgler
+;;; <twurgler@goodyear.com> is similar to mouse-drag-throw, but
+;;; doesn't pass clicks through.
+;;;
+;;; These functions have been tested in emacs version 19.30,
+;;; and this package has run in the past on 19.25-19.29.
+;;;
+;;; Originally mouse-drag was part of a larger package.
+;;; As of 11 July 96 the scrolling functions were split out
+;;; in preparation for incorporation into (the future) emacs-19.32.
+;;;
+;;;
+;;; Thanks:
+;;;
+;;; Thanks to Kai Grossjohann
+;;; <grossjoh@dusty.informatik.uni-dortmund.de> for reporting bugs, to
+;;; Tom Wurgler <twurgler@goodyear.com> for reporting bugs and
+;;; suggesting fixes, and to Joel Graber <jgraber@ti.com> for
+;;; prompting me to do drag-scrolling and for an initial
+;;; implementation of horizontal drag-scrolling.
+;;;
+;;;    -johnh@isi.edu, 11-Jul-96
+;;;
+;;;
+;;; Old changes, for reference:
+;;;
+;;; What's new with mouse-extras 2.21?
+;;;
+;;; - support for emacs-19.{29,30}
+;;; - point now stays on the visible screen during horizontal scrolling
+;;;   (bug identified and fix suggested by Tom Wurgler <twurgler@goodyear.com>)
+;;; - better work-around for lost-mouse-events bug (supports double/triple
+;;;   clicks), see \\[mouse-extras-work-around-drag-bug] for details.
+;;; - work-around for lost-mouse-events bug now is OFF by default;
+;;;   enable it if you have problems
+;;;
+
+
+
+;;; Code:
+
+;;
+;; scrolling code
+;;
+
+(defun mouse-drag-safe-scroll (row-delta &optional col-delta)
+  "* Scroll down ROW-DELTA lines and right COL-DELTA, ignoring buffer edge errors.
+Keep the cursor on the screen as needed."
+  (if (and row-delta
+	   (/= 0 row-delta))
+      (condition-case nil   ;; catch and ignore movement errors
+	  (scroll-down row-delta)
+	(beginning-of-buffer (message "Beginning of buffer"))
+	(end-of-buffer (message "End of buffer"))))
+  (if (and col-delta
+	   (/= 0 col-delta))
+      (progn
+	(scroll-right col-delta)
+	;; Make sure that the point stays on the visible screen
+	;; (if truncation-lines in set).
+	;; This code mimics the behavior we automatically get 
+	;; when doing vertical scrolling.
+	;; Problem identified and a fix suggested by Tom Wurgler.
+	(cond
+	 ((< (current-column) (window-hscroll))
+	  (move-to-column (window-hscroll))) ; make on left column
+	 ((> (- (current-column) (window-hscroll) (window-width) -2) 0)
+	  (move-to-column (+ (window-width) (window-hscroll) -3)))))))
+
+(defun mouse-drag-repeatedly-safe-scroll (row-delta &optional col-delta)
+  "* Scroll ROW-DELTA rows and COL-DELTA cols until an event happens."
+  (while (sit-for mouse-scroll-delay)
+    (mouse-drag-safe-scroll row-delta col-delta)))
+
+(defun mouse-drag-events-are-point-events-p (start-posn end-posn)
+  "* Determine if START-POSN and END-POSN are \"close\"."
+  (let*
+      ((start-col-row (posn-col-row start-posn))
+       (end-col-row (posn-col-row end-posn)))
+    (and
+;; We no longer exclude things by time.
+;;     (< (- (posn-timestamp end-posn) (posn-timestamp start-posn))
+;;	(if (numberp double-click-time)
+;;	    (* 2 double-click-time)   ;; stretch it a little
+;;	  999999)) ;; non-numeric => check by position alone
+     (= (car start-col-row) (car end-col-row))
+     (= (cdr start-col-row) (cdr end-col-row)))))
+
+(defun mouse-drag-should-do-col-scrolling ()
+  "* Determine if it's wise to enable col-scrolling for the current window."
+  (or truncate-lines
+      (> (window-hscroll (selected-window)) 0)
+      (< (window-width) (screen-width))))
+
+(defvar mouse-throw-with-scroll-bar nil
+  "* Set direction of mouse-throwing.
+If nil, the text moves in the direction the mouse moves.
+If t, the scroll bar moves in the direction the mouse moves.")
+(defconst mouse-throw-magnifier-with-scroll-bar 
+      [-16 -8 -4 -2 -1 0 0 0  1  2  4  8  16])
+(defconst mouse-throw-magnifier-with-mouse-movement
+      [ 16  8  4  2  1 0 0 0 -1 -2 -4 -8 -16])
+(defconst mouse-throw-magnifier-min -6)
+(defconst mouse-throw-magnifier-max 6)
+
+(defun mouse-drag-throw (start-event)
+  "\"Throw\" the page according to a mouse drag.
+
+A \"throw\" is scrolling the page at a speed relative to the distance
+from the original mouse click to the current mouse location.  Try it;
+you'll like it.  It's easier to observe than to explain.
+
+If the mouse is clicked and released in the same place of time we
+assume that the user didn't want to scdebugroll but wanted to whatever
+mouse-2 used to do, so we pass it through.
+
+Throw scrolling was inspired (but is not identical to) the \"hand\"
+option in MacPaint, or the middle button in Tk text widgets.
+
+If `mouse-throw-with-scroll-bar' is non-nil, then this command scrolls
+in the opposite direction.  (Different people have different ideas
+about which direction is natural.  Perhaps it has to do with which
+hemisphere you're in.)
+
+To test this function, evaluate:
+    (global-set-key [down-mouse-2] 'mouse-drag-throw)"
+  (interactive "e")
+  ;; we want to do save-selected-window, but that requires 19.29
+  (let* ((start-posn (event-start start-event))
+	 (start-window (posn-window start-posn))
+	 (start-row (cdr (posn-col-row start-posn)))
+	 (start-col (car (posn-col-row start-posn)))
+	 (old-selected-window (selected-window))
+	 event end row mouse-delta scroll-delta
+	 have-scrolled point-event-p old-binding
+	 window-last-row
+	 col mouse-col-delta window-last-col
+	 (scroll-col-delta 0)
+	 adjusted-mouse-col-delta
+	 ;; be conservative about allowing horizontal scrolling
+	 (col-scrolling-p (mouse-drag-should-do-col-scrolling)))
+    (select-window start-window)
+    (track-mouse
+      (while (progn
+	       (setq event (read-event)
+		     end (event-end event)
+		     row (cdr (posn-col-row end))
+		     col (car (posn-col-row end)))
+	       (or (mouse-movement-p event)
+		   (eq (car-safe event) 'switch-frame)))
+	(if (eq start-window (posn-window end))
+	    (progn
+	      (setq mouse-delta (- start-row row)
+		    adjusted-mouse-delta
+		    (- (cond
+			((<= mouse-delta mouse-throw-magnifier-min)
+			 mouse-throw-magnifier-min)
+			((>= mouse-delta mouse-throw-magnifier-max)
+			 mouse-throw-magnifier-max)
+			(t mouse-delta))
+		       mouse-throw-magnifier-min)
+		    scroll-delta (aref (if mouse-throw-with-scroll-bar
+					   mouse-throw-magnifier-with-scroll-bar
+					 mouse-throw-magnifier-with-mouse-movement)
+				       adjusted-mouse-delta))
+	      (if col-scrolling-p
+		  (setq mouse-col-delta (- start-col col)
+			adjusted-mouse-col-delta
+			(- (cond
+			    ((<= mouse-col-delta mouse-throw-magnifier-min)
+			     mouse-throw-magnifier-min)
+			    ((>= mouse-col-delta mouse-throw-magnifier-max)
+			     mouse-throw-magnifier-max)
+			    (t mouse-col-delta))
+			   mouse-throw-magnifier-min)
+			scroll-col-delta (aref (if mouse-throw-with-scroll-bar
+						   mouse-throw-magnifier-with-scroll-bar
+						 mouse-throw-magnifier-with-mouse-movement)
+					       adjusted-mouse-col-delta)))))
+	(if (or (/= 0 scroll-delta)
+		(/= 0 scroll-col-delta))
+	    (progn
+	      (setq have-scrolled t)
+	      (mouse-drag-safe-scroll scroll-delta scroll-col-delta)
+	      (mouse-drag-repeatedly-safe-scroll scroll-delta scroll-col-delta))))) ;xxx
+    ;; If it was a click and not a drag, prepare to pass the event on.
+    ;; Note:  We must determine the pass-through event before restoring
+    ;; the window, but invoke it after.  Sigh.
+    (if (and (not have-scrolled)
+	     (mouse-drag-events-are-point-events-p start-posn end))
+	(setq point-event-p t
+	      old-binding (key-binding
+			   (vector (event-basic-type start-event)))))
+    ;; Now restore the old window.
+    (select-window old-selected-window)
+    ;; For clicks, call the old function.
+    (if point-event-p
+	(call-interactively old-binding))))
+
+(defun mouse-drag-drag (start-event)
+  "\"Drag\" the page according to a mouse drag.
+
+Drag scrolling moves the page according to the movement of the mouse.
+You \"grab\" the character under the mouse and move it around.
+
+If the mouse is clicked and released in the same place of time we
+assume that the user didn't want to scroll but wanted to whatever
+mouse-2 used to do, so we pass it through.
+
+Drag scrolling is identical to the \"hand\" option in MacPaint, or the
+middle button in Tk text widgets.
+
+To test this function, evaluate:
+    (global-set-key [down-mouse-2] 'mouse-drag-drag)"
+  (interactive "e")
+  ;; we want to do save-selected-window, but that requires 19.29
+  (let* ((start-posn (event-start start-event))
+	 (start-window (posn-window start-posn))
+	 (start-row (cdr (posn-col-row start-posn)))
+	 (start-col (car (posn-col-row start-posn)))
+	 (old-selected-window (selected-window))
+	 event end row mouse-delta scroll-delta
+	 have-scrolled point-event-p old-binding
+	 window-last-row
+	 col mouse-col-delta window-last-col
+	 (scroll-col-delta 0)
+	 ;; be conservative about allowing horizontal scrolling
+	 (col-scrolling-p (mouse-drag-should-do-col-scrolling)))
+    (select-window start-window)
+    (setq window-last-row (- (window-height) 2)
+	  window-last-col (- (window-width) 2))
+    (track-mouse
+      (while (progn
+	       (setq event (read-event)
+		     end (event-end event)
+		     row (cdr (posn-col-row end))
+		     col (car (posn-col-row end)))
+	       (or (mouse-movement-p event)
+		   (eq (car-safe event) 'switch-frame)))
+	;; Scroll if see if we're on the edge.
+	;; NEEDSWORK: should handle mouse-in-other window.
+	(cond
+	 ((not (eq start-window (posn-window end)))
+	  t) ; wait for return to original window
+	 ((<= row 0) (mouse-drag-repeatedly-safe-scroll -1 0))
+	 ((>= row window-last-row) (mouse-drag-repeatedly-safe-scroll 1 0))
+	 ((and col-scrolling-p (<= col 1)) (mouse-drag-repeatedly-safe-scroll 0 -1))
+	 ((and col-scrolling-p (>= col window-last-col)) (mouse-drag-repeatedly-safe-scroll 0 1))
+	 (t
+	  (setq scroll-delta (- row start-row)
+		start-row row)
+	  (if col-scrolling-p
+	      (setq scroll-col-delta (- col start-col)
+		    start-col col))
+	  (if (or (/= 0 scroll-delta)
+		  (/= 0 scroll-col-delta))
+	      (progn
+		(setq have-scrolled t)
+		(mouse-drag-safe-scroll scroll-delta scroll-col-delta)))))))
+    ;; If it was a click and not a drag, prepare to pass the event on.
+    ;; Note:  We must determine the pass-through event before restoring
+    ;; the window, but invoke it after.  Sigh.
+    (if (and (not have-scrolled)
+	     (mouse-drag-events-are-point-events-p start-posn end))
+	(setq point-event-p t
+	      old-binding (key-binding
+			   (vector (event-basic-type start-event)))))
+    ;; Now restore the old window.
+    (select-window old-selected-window)
+    ;; For clicks, call the old function.
+    (if point-event-p
+	(call-interactively old-binding))))
+
+(provide 'mouse-drag)
+
+;;; mouse-drag.el ends here