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Re: address@hidden: mouse-drag.el and automatic-hscrolling interact poor

From: John Heidemann
Subject: Re: address@hidden: mouse-drag.el and automatic-hscrolling interact poorly]
Date: Tue, 05 Nov 2002 12:46:42 -0800

On Fri, 11 Oct 2002 00:42:14 EDT, Richard Stallman wrote: 
>Could you please take a look at this problem?

I looked at this bug and was able to reproduce it.  Unfortunately, the
fix suggested by Mr. Du Bois didn't work for me.  (I've attached the
patch below if you want to try it.)  It's the obvious (and sensible)
fix from a mouse-drag point of view---turn off automatic-hscrolling

A guess at the problem is that automatic-hscrolling includes some kind
of hook that runs after mouse-drag-safe-scroll does its work.

Can you forward this bug to the people who re-wrote
automatic-hscrolling?  I can't find the implementation of
automatic-hscroll (it seems to be in C since it doesn't show up by
grepping the lisp).

   -John Heidemann

This change below does NOT fix the problem, but is included for reference.
--- mouse-drag.el-      2002-11-05 12:14:57.000000000 -0800
+++ mouse-drag.el       2002-11-05 12:28:39.000000000 -0800
@@ -108,7 +108,11 @@
 (defun mouse-drag-safe-scroll (row-delta &optional col-delta)
   "Scroll down ROW-DELTA lines and right COL-DELTA, ignoring buffer edge 
 Keep the cursor on the screen as needed."
-  (let ((scroll-preserve-screen-position nil))
+  (let ((old-scroll-preserve-screen-position scroll-preserve-screen-position)
+       (old-automatic-hscrolling automatic-hscrolling))
+    ;; save user settings that interfer with mouse-drag
+    (setq scroll-preserve-screen-position nil
+         automatic-hscrolling nil)
     (if (and row-delta
             (/= 0 row-delta))
        (condition-case nil ;; catch and ignore movement errors
@@ -128,7 +132,10 @@
           ((< (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))))))))
+           (move-to-column (+ (window-width) (window-hscroll) -3))))))
+    ;; put things back for the user
+    (setq scroll-preserve-screen-position old-scroll-preserve-screen-position
+         automatic-hscrolling old-automatic-hscrolling)))
 (defun mouse-drag-repeatedly-safe-scroll (row-delta &optional col-delta)
   "Scroll ROW-DELTA rows and COL-DELTA cols until an event happens."

>------- Start of forwarded message -------
>Envelope-to: address@hidden
>Delivery-date: Wed, 09 Oct 2002 19:55:27 -0400
>From: Paul Du Bois <address@hidden>
>To: address@hidden
>Subject: mouse-drag.el and automatic-hscrolling interact poorly
>X-OriginalArrivalTime: 09 Oct 2002 23:57:04.0956 (UTC) 
>Sender: address@hidden
>Date: 9 Oct 2002 16:57:04 -0700
>This bug report will be sent to the Free Software Foundation,
>not to your local site managers!
>Please write in English, because the Emacs maintainers do not have
>translators to read other languages for them.
>Your bug report will be posted to the address@hidden mailing list,
>and to the gnu.emacs.bug news group.
>In GNU Emacs 21.2.1 (i386-msvc-nt5.1.2600)
> of 2002-03-19 on buffy
>configured using `configure --with-msvc (12.00)'
>Important settings:
>  value of $LC_ALL: nil
>  value of $LC_COLLATE: nil
>  value of $LC_CTYPE: nil
>  value of $LC_MESSAGES: nil
>  value of $LC_MONETARY: nil
>  value of $LC_NUMERIC: nil
>  value of $LC_TIME: nil
>  value of $LANG: ENU
>  locale-coding-system: iso-latin-1
>  default-enable-multibyte-characters: nil
>Please describe exactly what actions triggered the bug
>and the precise symptoms of the bug:
>;; eg
>(require 'mouse-drag)
>(define-key global-map [M-down-mouse-1] 'mouse-drag-drag)
>(setq automatic-hscrolling t)
>;; switch to an interesting buffer
>(setq truncate-lines t)
>;; 1. put point in the middle of a line
>;; 2. do a leftward M-drag
>;; 3. Notice that as the cursor approaches the left edge of the
>;; screen, the hscroll resets to 0
>A quick fix is to modify the (let (...) ) in mouse-drag-safe-scroll to
>temporarily unset automatic-hscrolling.  I don't know whether that's a real
>fix or just a workaround -- I don't understand this comment in scroll-right:
>   If `automatic-hscrolling' is non-nil, the argument ARG modifies
>   a lower bound for automatic scrolling, i.e. automatic scrolling
>   will not scroll a window to a column less than the value returned
>   by this function.
>Bug-gnu-emacs mailing list
>------- End of forwarded message -------

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