Fix a bug in the state cache mechanism. Refactor this a bit.
[emacs.git] / lisp / reposition.el
blob0bd276540654578e803f565ad5755446cdfbc35d
1 ;;; reposition.el --- center a Lisp function or comment on the screen
3 ;; Copyright (C) 1991, 1994, 2001-2013 Free Software Foundation, Inc.
5 ;; Author: Michael D. Ernst <mernst@theory.lcs.mit.edu>
6 ;; Created: Jan 1991
7 ;; Maintainer: FSF
9 ;; This file is part of GNU Emacs.
11 ;; GNU Emacs is free software: you can redistribute it and/or modify
12 ;; it under the terms of the GNU General Public License as published by
13 ;; the Free Software Foundation, either version 3 of the License, or
14 ;; (at your option) any later version.
16 ;; GNU Emacs is distributed in the hope that it will be useful,
17 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
18 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
19 ;; GNU General Public License for more details.
21 ;; You should have received a copy of the GNU General Public License
22 ;; along with GNU Emacs. If not, see <http://www.gnu.org/licenses/>.
24 ;;; Commentary:
26 ;; Reposition-window makes an entire function definition or comment visible,
27 ;; or, if it is already visible, places it at the top of the window;
28 ;; additional invocations toggle the visibility of comments preceding the
29 ;; code. For the gory details, see the documentation for reposition-window;
30 ;; rather than reading that, you may just want to play with it.
32 ;; This tries pretty hard to do the recentering correctly; the precise
33 ;; action depends on what the buffer looks like. If you find a situation
34 ;; where it doesn't behave well, let me know. This function is modeled
35 ;; after one of the same name in ZMACS, but the code is all-new and the
36 ;; behavior in some situations differs.
38 ;;; Code:
40 ;;;###autoload
41 (defun reposition-window (&optional arg)
42 "Make the current definition and/or comment visible.
43 Further invocations move it to the top of the window or toggle the
44 visibility of comments that precede it.
45 Point is left unchanged unless prefix ARG is supplied.
46 If the definition is fully onscreen, it is moved to the top of the
47 window. If it is partly offscreen, the window is scrolled to get the
48 definition (or as much as will fit) onscreen, unless point is in a comment
49 which is also partly offscreen, in which case the scrolling attempts to get
50 as much of the comment onscreen as possible.
51 Initially `reposition-window' attempts to make both the definition and
52 preceding comments visible. Further invocations toggle the visibility of
53 the comment lines.
54 If ARG is non-nil, point may move in order to make the whole defun
55 visible (if only part could otherwise be made so), to make the defun line
56 visible (if point is in code and it could not be made so, or if only
57 comments, including the first comment line, are visible), or to make the
58 first comment line visible (if point is in a comment)."
59 (interactive "P")
60 (let* (;; (here (line-beginning-position))
61 (here (point))
62 ;; change this name once I've gotten rid of references to ht.
63 ;; this is actually the number of the last screen line
64 (ht (- (window-height (selected-window)) 2))
65 (line (repos-count-screen-lines (window-start) (point)))
66 (comment-height
67 ;; The call to max deals with the case of cursor between defuns.
68 (max 0
69 (repos-count-screen-lines-signed
70 ;; the beginning of the preceding comment
71 (save-excursion
72 (if (not (eobp)) (forward-char 1))
73 (end-of-defun -1)
74 ;; Skip whitespace, newlines, and form feeds.
75 (if (re-search-forward "[^ \t\n\f]" nil t)
76 (backward-char 1))
77 (point))
78 here)))
79 (defun-height
80 (repos-count-screen-lines-signed
81 (save-excursion
82 (end-of-defun 1) ; so comments associate with following defuns
83 (beginning-of-defun 1)
84 (point))
85 here))
86 ;; This must be positive, so don't use the signed version.
87 (defun-depth (repos-count-screen-lines here
88 (save-excursion
89 (end-of-defun 1)
90 (point))))
91 (defun-line-onscreen-p
92 (and (<= defun-height line)
93 (<= (- line defun-height) ht))))
94 (cond ((or (= comment-height line)
95 (and (= line ht)
96 (> comment-height line)
97 ;; if defun line offscreen, we should be in case 4
98 defun-line-onscreen-p))
99 ;; Either first comment line is at top of screen or (point at
100 ;; bottom of screen, defun line onscreen, and first comment line
101 ;; off top of screen). That is, it looks like we just did
102 ;; recenter-definition, trying to fit as much of the comment
103 ;; onscreen as possible. Put defun line at top of screen; that
104 ;; is, show as much code, and as few comments, as possible.
106 (if (and arg (> defun-depth (1+ ht)))
107 ;; Can't fit whole defun onscreen without moving point.
108 (progn (end-of-defun) (beginning-of-defun) (recenter 0))
109 (recenter (max defun-height 0)))
110 ;;(repos-debug-macro "1")
113 ((or (= defun-height line)
114 (= line 0)
115 (and (< line comment-height)
116 (< defun-height 0)))
117 ;; Defun line or cursor at top of screen, OR cursor in comment
118 ;; whose first line is offscreen.
119 ;; Avoid moving definition up even if defun runs offscreen;
120 ;; we care more about getting the comment onscreen.
122 (cond ((= line ht)
123 ;; cursor on last screen line (and so in a comment)
124 (if arg (progn (end-of-defun) (beginning-of-defun)))
125 (recenter 0)
126 ;;(repos-debug-macro "2a")
129 ;; This condition, copied from case 4, may not be quite right
131 ((and arg (< ht comment-height))
132 ;; Can't get first comment line onscreen.
133 ;; Go there and try again.
134 (forward-line (- comment-height))
135 (beginning-of-line)
136 ;; was (reposition-window)
137 (recenter 0)
138 ;;(repos-debug-macro "2b")
141 (recenter (min ht comment-height))
142 ;;(repos-debug-macro "2c")
144 ;; (recenter (min ht comment-height))
147 ((and (> (+ line defun-depth -1) ht)
148 defun-line-onscreen-p)
149 ;; Defun runs off the bottom of the screen and the defun line
150 ;; is onscreen.
151 ;; Move the defun up.
152 (recenter (max 0 (1+ (- ht defun-depth)) defun-height))
153 ;;(repos-debug-macro "3")
157 ;; If on the bottom line and comment start is offscreen
158 ;; then just move all comments offscreen, or at least as
159 ;; far as they'll go.
161 ;; Try to get as much of the comments onscreen as possible.
162 (if (and arg (< ht comment-height))
163 ;; Can't get defun line onscreen; go there and try again.
164 (progn (forward-line (- defun-height))
165 (beginning-of-line)
166 (reposition-window))
167 (recenter (min ht comment-height)))
168 ;;(repos-debug-macro "4")
169 ))))
171 ;;; Auxiliary functions
173 ;; Return number of screen lines between START and END.
174 (defun repos-count-screen-lines (start end)
175 (save-excursion
176 (save-restriction
177 (narrow-to-region start end)
178 (goto-char (point-min))
179 (vertical-motion (- (point-max) (point-min))))))
181 ;; Return number of screen lines between START and END; returns a negative
182 ;; number if END precedes START.
183 (defun repos-count-screen-lines-signed (start end)
184 (let ((lines (repos-count-screen-lines start end)))
185 (if (< start end)
186 lines
187 (- lines))))
189 ;; (defmacro repos-debug-macro (case-no)
190 ;; `(message (concat "Case " ,case-no ": %s %s %s %s %s")
191 ;; ht line comment-height defun-height defun-depth))
193 (provide 'reposition)
195 ;;; reposition.el ends here