Re: address@hidden: mouse and horizontal scrolling with long lines]

[Chong Yidong]

> Scrolling with the mouse in a buffer with lines wider than the window
> (with truncate-lines enabled) is problematic.
>
> emacs -q --no-site-file
>
> Delete the newlines in the initial message in the scratch buffer (so
> as to get a single long line of text wider than the window).
>
> M-x toggle-truncate-lines
>
> Click with the mouse within 5 columns of the right margin, but do not
> release the mouse button.
>
> At this stage, the window scrolls to centre point horizontally.
> The mouse cursor remains where it was, close to the right margin.
> The buffer basically looks as one would want it to.

Does this patch give good results?

*** emacs/lisp/mouse.el.~1.307.~        2006-11-27 10:34:35.000000000 -0500
--- emacs/lisp/mouse.el 2006-12-01 13:47:12.000000000 -0500
***************
*** 925,931 ****
         (click-count (1- (event-click-count start-event)))
         (remap-double-click (and on-link
                                  (eq mouse-1-click-follows-link 'double)
!                                 (= click-count 1))))
      (setq mouse-selection-click-count click-count)
      ;; In case the down click is in the middle of some intangible text,
      ;; use the end of that text, and put it in START-POINT.
--- 925,933 ----
         (click-count (1- (event-click-count start-event)))
         (remap-double-click (and on-link
                                  (eq mouse-1-click-follows-link 'double)
!                                 (= click-count 1)))
!        (automatic-hscrolling-saved automatic-hscrolling)
!        (automatic-hscrolling nil))
      (setq mouse-selection-click-count click-count)
      ;; In case the down click is in the middle of some intangible text,
      ;; use the end of that text, and put it in START-POINT.
***************
*** 946,951 ****
--- 948,960 ----
                       (memq (car-safe event) '(switch-frame select-window))))
            (if (memq (car-safe event) '(switch-frame select-window))
              nil
+           ;; We suppress automatic hscrolling initially, which would
+           ;; otherwise it would occur during the `read-event' call;
+           ;; otherwise, it would interfere with the act of setting
+           ;; point in text near the right fringe.  However, if the
+           ;; mouse is dragged, we go ahead and perform the hscroll.
+           (let ((automatic-hscrolling automatic-hscrolling-saved))
+             (redisplay))
            (setq end (event-end event)
                  end-point (posn-point end))
            (if (numberp end-point)