lisp/auto-show.el

   1 ;;; This file is in the public domain.
   2
   3 ;;; Keywords: scroll display minor-mode
   4 ;;; Author: Pete Ware <ware@cis.ohio-state.edu>
   5 ;;; Maintainer: FSF
   6
   7 ;;; Commentary:
   8
   9 ;;; This file provides functions that
  10 ;;; automatically scroll the window horizontally when the point moves
  11 ;;; off the left or right side of the window.
  12
  13 ;;; Once this library is loaded, automatic horizontal scrolling
  14 ;;; occurs whenever long lines are being truncated.
  15 ;;; To request truncation of long lines, set the variable
  16 ;;; Setting the variable `truncate-lines' to non-nil.
  17 ;;; You can do this for all buffers as follows:
  18 ;;;
  19 ;;; (set-default 'truncate-lines t)
  20
  21 ;;; Here is how to do it for C mode only:
  22 ;;;
  23 ;;; (set-default 'truncate-lines nil)   ; this is the original value
  24 ;;; (defun my-c-mode-hook ()
  25 ;;;   "Run when C-mode starts up.  Changes ..."
  26 ;;;   ... set various personal preferences ...
  27 ;;;   (setq truncate-lines t))
  28 ;;; (add-hook 'c-mode-hook 'my-c-mode-hook)
  29 ;;;
  30 ;;;
  31 ;;; As a finer level of control, you can still have truncated lines but
  32 ;;; without the automatic horizontal scrolling by setting the buffer
  33 ;;; local variable `auto-show-mode' to nil.  The default value is t.
  34 ;;; The command `auto-show-mode' toggles the value of the variable
  35 ;;; `auto-show-mode'.
  36
  37 ;;; Code:
  38
  39 (defvar auto-show-mode t
  40   "*Non-nil enables automatic horizontal scrolling, when lines are truncated.
  41 The default value is t.  To change the default, do this:
  42         (set-default 'auto-show-mode nil)
  43 See also command `auto-show-mode'.
  44 This variable has no effect when lines are not being truncated.")
  45
  46 (make-variable-buffer-local 'auto-show-mode)
  47
  48 (defvar auto-show-shift-amount 8
  49   "*Extra columns to scroll. for automatic horizontal scrolling.")
  50
  51 (defvar auto-show-show-left-margin-threshold 50
  52   "*Threshold column for automatic horizontal scrolling to the right.
  53 If point is before this column, we try to scroll to make the left margin
  54 visible.  Setting this to 0 disables this feature.")
  55
  56 (defun auto-show-truncationp ()
  57   "True if line truncation is enabled for the selected window."
  58   (or truncate-lines
  59       (and truncate-partial-width-windows
  60            (< (window-width) (frame-width)))))
  61
  62 ;;;###autoload
  63 (defun auto-show-mode (arg)
  64   "Turn automatic horizontal scroll mode on or off.
  65 With arg, turn auto scrolling on if arg is positive, off otherwise."
  66   (interactive "P")
  67   (setq auto-show-mode
  68         (if (null arg)
  69             (not auto-show-mode)
  70           (> (prefix-numeric-value arg) 0))))
  71
  72 (defun auto-show-make-point-visible (&optional ignore-arg)
  73   "Scroll horizontally to make point visible, if that is enabled.
  74 This function only does something if `auto-show-mode' is non-nil
  75 and longlines are being truncated in the selected window.
  76 See also the command `auto-show-toggle'."
  77   (interactive)
  78   (if (and auto-show-mode (auto-show-truncationp)
  79            (equal (window-buffer) (current-buffer)))
  80       (let* ((col (current-column))     ;column on line point is at
  81              (scroll (window-hscroll))  ;how far window is scrolled
  82              (w-width (- (window-width)
  83                          (if (> scroll 0)
  84                              2 1)))     ;how wide window is on the screen
  85              (right-col (+ scroll w-width)))
  86         (if (and (< col auto-show-show-left-margin-threshold)
  87                  (< col (window-width))
  88                  (> scroll 0))
  89             (scroll-right scroll)
  90           (if (< col scroll)            ;to the left of the screen
  91               (scroll-right (+ (- scroll col) auto-show-shift-amount))
  92             (if (or (> col right-col)   ;to the right of the screen
  93                     (and (= col right-col)
  94                          (not (eolp))))
  95                 (scroll-left (+ auto-show-shift-amount
  96                                 (- col (+ scroll w-width))))
  97               )
  98             )
  99           )
 100         )
 101     )
 102   )
 103
 104 ;; Do auto-scrolling after commands.
 105 (add-hook 'post-command-hook 'auto-show-make-point-visible)
 106
 107 ;; Do auto-scrolling in comint buffers after process output also.
 108 (add-hook 'comint-output-filter-functions 'auto-show-make-point-visible t)
 109
 110 (provide 'auto-show)
 111
 112 ;; auto-show.el ends here
 113