8

Q: is there a way to set different scroll margins at the top and bottom of a window?

The variable scroll-margin (defined in the C source code) sets how many lines of text that Emacs displays, at a minimum, at the top and bottom of a window:

Number of lines of margin at the top and bottom of a window. Recenter the window whenever point gets within this many lines of the top or bottom of the window.

I'd like to use scroll-margin for the bottom of the window, but don't want it at the top (e.g., a positive value at the bottom, but 0 at the top). Is there a way to do so?

| improve this question | |
  • I don't know the answer, but in all likelihood scroll-margin is not the right tool for the job. You may need some function to put on post-command-hook to determine whether to scroll the window. – Harald Hanche-Olsen Jan 19 '15 at 15:29
  • To follow up on my previous comment, finding out how many lines are visible around point seems highly nontrivial, considering wrapped lines, hidden text and the like. I suspect the necessary information is easily available only inside the display code. You could try submitting a feature request to allow (for example) a cons (top . bottom) for scroll-margin. – Harald Hanche-Olsen Jan 19 '15 at 17:25
  • You might be interested in playing with the window-scroll-functions hook (which takes two arguments) and putting a recenter command into a function attached to that hook and then use a setting of (setq scroll-conservatively 101) -- in essence, you define when recentering occurs and turn off the built-in auto-scroll. Something like (when (and (>= (point) (window-end nil t)) (not (pos-visible-in-window-p (point) (get-buffer-window (current-buffer) (selected-frame))))) (recenter)) – lawlist Jan 19 '15 at 18:41
  • @lawlist: thanks for the suggestion, but the end of the docstring reads "Warning: Do not use this feature to alter the way the window is scrolled. It is not designed for that, and such use probably won't work." – Dan♦ Jan 19 '15 at 19:17
  • Interesting question, I am wondering why there is no comments/vote on the answer provided by PythonNut. – Name Jul 19 '15 at 7:36
1

The following works for me: 

(defun my-define-scroll-margins (&rest _args)
  (interactive)
  (with-demoted-errors
    (let ((computed-margin
            (if (> (cdr (nth 6 (posn-at-point)))
                  (/ (window-body-height) 2)) 5 0)))
      (setq
        scroll-margin computed-margin
        smooth-scroll-margin computed-margin))))

(add-hook 'post-command-hook #'my-define-scroll-margins)

Note that this is theoretically inefficient, but performance on my lame computer seems unaffected.

| improve this answer | |

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.