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Diffstat (limited to 'emacs.d')
| -rw-r--r-- | emacs.d/lisp/smooth-scrolling.el | 201 |
1 files changed, 201 insertions, 0 deletions
diff --git a/emacs.d/lisp/smooth-scrolling.el b/emacs.d/lisp/smooth-scrolling.el new file mode 100644 index 0000000..d3321ef --- /dev/null +++ b/emacs.d/lisp/smooth-scrolling.el @@ -0,0 +1,201 @@ +;; smooth-scrolling.el +;; $Id$ +;; Adam Spiers <emacs-ss@adamspiers.org> +;; +;; Make emacs scroll smoothly, keeping the point away from the top and +;; bottom of the current buffer's window in order to keep lines of +;; context around the point visible as much as possible, whilst +;; avoiding sudden scroll jumps which are visually confusing. +;; +;; This is a nice alternative to all the native scroll-* custom +;; variables, which unfortunately cannot provide this functionality +;; perfectly. `scroll-margin' comes closest, but has some bugs +;; (e.g. with handling of mouse clicks). See +;; +;; http://www.emacswiki.org/cgi-bin/wiki/SmoothScrolling +;; +;; for the gory details. +;; +;;;_* Installation +;; +;; Put somewhere on your `load-path' and include +;; +;; (require 'smooth-scrolling) +;; +;; in your .emacs initialization file. +;; +;;;_* Notes +;; +;; This only affects the behaviour of the `next-line' and +;; `previous-line' functions, usually bound to the cursor keys and +;; C-n/C-p, and repeated isearches (`isearch-repeat'). Other methods +;; of moving the point will behave as normal according to the standard +;; custom variables. +;; +;; Prefix arguments to `next-line' and `previous-line' are honoured. +;; The minimum number of lines are scrolled in order to keep the +;; point outside the margin. +;; +;; There is one case where moving the point in this fashion may cause +;; a jump: if the point is placed inside one of the margins by another +;; method (e.g. left mouse click, or M-x goto-line) and then moved in +;; the normal way, the advice code will scroll the minimum number of +;; lines in order to keep the point outside the margin. This jump may +;; cause some slight confusion at first, but hopefully it is justified +;; by the benefit of automatically ensuring `smooth-scroll-margin' +;; lines of context are visible around the point as often as possible. +;; +;;;_* TODO +;; +;; - Maybe add option to avoid scroll jumps when point is within +;; margin. +;; +;;;_* Acknowledgements +;; +;; Thanks to Mark Hulme-Jones and consolers on #emacs for helping +;; debug issues with line-wrapping. +;; +;;;_* License +;; +;; Released under the GNU General Public License v2 or later, with +;; all rights assigned to the Free Software Foundation. +;; + +;;;_* Code follows +;;;_ + disable `scroll-margin' +(setq scroll-margin 0) +;;;_ + defcustoms +(defcustom smooth-scroll-margin 10 + "Number of lines of visible margin at the top and bottom of a window. +If the point is within these margins, then scrolling will occur +smoothly for `previous-line' at the top of the window, and for +`next-line' at the bottom. + +This is very similar in its goal to `scroll-margin'. However, it +is implemented by activating `smooth-scroll-down' and +`smooth-scroll-up' advise via `defadvice' for `previous-line' and +`next-line' respectively. As a result it avoids problems +afflicting `scroll-margin', such as a sudden jump and unexpected +highlighting of a region when the mouse is clicked in the margin. + +Scrolling only occurs when the point is closer to the window +boundary it is heading for (top or bottom) than the middle of the +window. This is to intelligently handle the case where the +margins cover the whole buffer (e.g. `smooth-scroll-margin' set +to 5 and `window-height' returning 10 or less). + +See also `smooth-scroll-strict-margins'." + :type 'integer + :group 'windows) + +(defcustom smooth-scroll-strict-margins t + "If true, the advice code supporting `smooth-scroll-margin' +will use `count-screen-lines' to determine the number of +*visible* lines between the point and the window top/bottom, +rather than `count-lines' which obtains the number of actual +newlines. This is because there might be extra newlines hidden +by a mode such as folding-mode, outline-mode, org-mode etc., or +fewer due to very long lines being displayed wrapped when +`truncate-lines' is nil. + +However, using `count-screen-lines' can supposedly cause +performance issues in buffers with extremely long lines. Setting +`cache-long-line-scans' may be able to address this; +alternatively you can set this variable to nil so that the advice +code uses `count-lines', and put up with the fact that sometimes +the point will be allowed to stray into the margin." + :type 'boolean + :group 'windows) +;;;_ + helper functions +(defun smooth-scroll-lines-from-window-top () + "Work out, using the function indicated by +`smooth-scroll-strict-margins', what the current screen line is, +relative to the top of the window. Counting starts with 1 referring +to the top line in the window." + (interactive) + (cond ((= (window-start) (point)) + ;; In this case, count-screen-lines would return 0, so we override. + 1) + (smooth-scroll-strict-margins + (count-screen-lines (window-start) (point) 'count-final-newline)) + (t + (count-lines (window-start) (point))))) + +(defun smooth-scroll-lines-from-window-bottom () + "Work out, using the function indicated by +`smooth-scroll-strict-margins', how many screen lines there are +between the point and the bottom of the window. Counting starts +with 1 referring to the bottom line in the window." + (interactive) + (if smooth-scroll-strict-margins + (count-screen-lines (point) (window-end)) + (count-lines (point) (window-end)))) +;;;_ + after advice + +(defun smooth-scroll-down () + "Scroll down smoothly if cursor is within `smooth-scroll-margin' +lines of the top of the window." + (and + ;; Only scroll down if there is buffer above the start of the window. + (> (line-number-at-pos (window-start)) 1) + (let ((lines-from-window-top + (smooth-scroll-lines-from-window-top))) + (and + ;; Only scroll down if we're within the top margin + (<= lines-from-window-top smooth-scroll-margin) + ;; Only scroll down if we're in the top half of the window + (<= lines-from-window-top + ;; N.B. `window-height' includes modeline, so if it returned 21, + ;; that would mean exactly 10 lines in the top half and 10 in + ;; the bottom. 22 (or any even number) means there's one in the + ;; middle. In both cases the following expression will + ;; yield 10: + (/ (1- (window-height)) 2)) + (save-excursion + (scroll-down + (1+ (- smooth-scroll-margin lines-from-window-top)))))))) + +(defun smooth-scroll-up () + "Scroll up smoothly if cursor is within `smooth-scroll-margin' +lines of the bottom of the window." + (and + ;; Only scroll up if there is buffer below the end of the window. + (< (window-end) (buffer-end 1)) + (let ((lines-from-window-bottom + (smooth-scroll-lines-from-window-bottom))) + (and + ;; Only scroll up if we're within the bottom margin + (<= lines-from-window-bottom smooth-scroll-margin) + ;; Only scroll up if we're in the bottom half of the window. + (<= lines-from-window-bottom + ;; See above notes on `window-height'. + (/ (1- (window-height)) 2)) + (save-excursion + (scroll-up + (1+ (- smooth-scroll-margin lines-from-window-bottom)))))))) + +(defadvice previous-line (after smooth-scroll-down + (&optional arg try-vscroll) + activate) + (smooth-scroll-down)) +(defadvice next-line (after smooth-scroll-up + (&optional arg try-vscroll) + activate) + (smooth-scroll-up)) + +(defadvice isearch-repeat (after isearch-smooth-scroll + (direction) + activate) + (if (eq direction 'forward) + (smooth-scroll-up) + (smooth-scroll-down))) + +;;;_ + provide +(provide 'smooth-scrolling) + +;;;_* Local emacs variables + +;;Local variables: +;;allout-layout: (0 : -1 0) +;;mode: allout +;;End: |