]> code.delx.au - gnu-emacs/blob - lisp/auto-show.el
(ps-print-preprint): Special handling if
[gnu-emacs] / lisp / auto-show.el
1 ;;; auto-show.el --- perform automatic horizontal scrolling as point moves
2 ;;; This file is in the public domain.
3
4 ;;; Keywords: scroll display minor-mode
5 ;;; Author: Pete Ware <ware@cis.ohio-state.edu>
6 ;;; Maintainer: FSF
7
8 ;;; Commentary:
9
10 ;;; This file provides functions that
11 ;;; automatically scroll the window horizontally when the point moves
12 ;;; off the left or right side of the window.
13
14 ;;; Once this library is loaded, automatic horizontal scrolling
15 ;;; occurs whenever long lines are being truncated.
16 ;;; To request truncation of long lines, set the variable
17 ;;; Setting the variable `truncate-lines' to non-nil.
18 ;;; You can do this for all buffers as follows:
19 ;;;
20 ;;; (set-default 'truncate-lines t)
21
22 ;;; Here is how to do it for C mode only:
23 ;;;
24 ;;; (set-default 'truncate-lines nil) ; this is the original value
25 ;;; (defun my-c-mode-hook ()
26 ;;; "Run when C-mode starts up. Changes ..."
27 ;;; ... set various personal preferences ...
28 ;;; (setq truncate-lines t))
29 ;;; (add-hook 'c-mode-hook 'my-c-mode-hook)
30 ;;;
31 ;;;
32 ;;; As a finer level of control, you can still have truncated lines but
33 ;;; without the automatic horizontal scrolling by setting the buffer
34 ;;; local variable `auto-show-mode' to nil. The default value is t.
35 ;;; The command `auto-show-mode' toggles the value of the variable
36 ;;; `auto-show-mode'.
37
38 ;;; Code:
39
40 (defvar auto-show-mode t
41 "*Non-nil enables automatic horizontal scrolling, when lines are truncated.
42 The default value is t. To change the default, do this:
43 (set-default 'auto-show-mode nil)
44 See also command `auto-show-mode'.
45 This variable has no effect when lines are not being truncated.")
46
47 (make-variable-buffer-local 'auto-show-mode)
48
49 (defvar auto-show-shift-amount 8
50 "*Extra columns to scroll. for automatic horizontal scrolling.")
51
52 (defvar auto-show-show-left-margin-threshold 50
53 "*Threshold column for automatic horizontal scrolling to the right.
54 If point is before this column, we try to scroll to make the left margin
55 visible. Setting this to 0 disables this feature.")
56
57 (defun auto-show-truncationp ()
58 "True if line truncation is enabled for the selected window."
59 (or truncate-lines
60 (and truncate-partial-width-windows
61 (< (window-width) (frame-width)))))
62
63 ;;;###autoload
64 (defun auto-show-mode (arg)
65 "Turn automatic horizontal scroll mode on or off.
66 With arg, turn auto scrolling on if arg is positive, off otherwise."
67 (interactive "P")
68 (setq auto-show-mode
69 (if (null arg)
70 (not auto-show-mode)
71 (> (prefix-numeric-value arg) 0))))
72
73 (defun auto-show-make-point-visible (&optional ignore-arg)
74 "Scroll horizontally to make point visible, if that is enabled.
75 This function only does something if `auto-show-mode' is non-nil
76 and longlines are being truncated in the selected window.
77 See also the command `auto-show-toggle'."
78 (interactive)
79 (if (and auto-show-mode (auto-show-truncationp)
80 (equal (window-buffer) (current-buffer)))
81 (let* ((col (current-column)) ;column on line point is at
82 (scroll (window-hscroll)) ;how far window is scrolled
83 (w-width (- (window-width)
84 (if (> scroll 0)
85 2 1))) ;how wide window is on the screen
86 (right-col (+ scroll w-width)))
87 (if (and (< col auto-show-show-left-margin-threshold)
88 (< col (window-width))
89 (> scroll 0))
90 (scroll-right scroll)
91 (if (< col scroll) ;to the left of the screen
92 (scroll-right (+ (- scroll col) auto-show-shift-amount))
93 (if (or (> col right-col) ;to the right of the screen
94 (and (= col right-col)
95 (not (eolp))))
96 (scroll-left (+ auto-show-shift-amount
97 (- col (+ scroll w-width))))
98 )
99 )
100 )
101 )
102 )
103 )
104
105 ;; Do auto-scrolling after commands.
106 (add-hook 'post-command-hook 'auto-show-make-point-visible)
107
108 ;; Do auto-scrolling in comint buffers after process output also.
109 (add-hook 'comint-output-filter-functions 'auto-show-make-point-visible t)
110
111 (provide 'auto-show)
112
113 ;; auto-show.el ends here
114