reposition.el 7.12 KB
Newer Older
Eric S. Raymond's avatar
Eric S. Raymond committed
1 2
;;; reposition.el --- center a Lisp function or comment on the screen

Paul Eggert's avatar
Paul Eggert committed
3
;; Copyright (C) 1991, 1994, 2001-2020 Free Software Foundation, Inc.
Eric S. Raymond's avatar
Eric S. Raymond committed
4

Eric S. Raymond's avatar
Eric S. Raymond committed
5
;; Author: Michael D. Ernst <mernst@theory.lcs.mit.edu>
6
;; Created: Jan 1991
7
;; Maintainer: emacs-devel@gnu.org
Richard M. Stallman's avatar
Richard M. Stallman committed
8 9 10

;; This file is part of GNU Emacs.

11
;; GNU Emacs is free software: you can redistribute it and/or modify
Richard M. Stallman's avatar
Richard M. Stallman committed
12
;; it under the terms of the GNU General Public License as published by
13 14
;; the Free Software Foundation, either version 3 of the License, or
;; (at your option) any later version.
Richard M. Stallman's avatar
Richard M. Stallman committed
15 16 17 18 19 20 21

;; GNU Emacs is distributed in the hope that it will be useful,
;; but WITHOUT ANY WARRANTY; without even the implied warranty of
;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
;; GNU General Public License for more details.

;; You should have received a copy of the GNU General Public License
22
;; along with GNU Emacs.  If not, see <https://www.gnu.org/licenses/>.
Richard M. Stallman's avatar
Richard M. Stallman committed
23

Eric S. Raymond's avatar
Eric S. Raymond committed
24 25
;;; Commentary:

Erik Naggum's avatar
Erik Naggum committed
26 27 28 29 30 31 32 33 34 35 36
;; Reposition-window makes an entire function definition or comment visible,
;; or, if it is already visible, places it at the top of the window;
;; additional invocations toggle the visibility of comments preceding the
;; code.  For the gory details, see the documentation for reposition-window;
;; rather than reading that, you may just want to play with it.

;; This tries pretty hard to do the recentering correctly; the precise
;; action depends on what the buffer looks like.  If you find a situation
;; where it doesn't behave well, let me know.  This function is modeled
;; after one of the same name in ZMACS, but the code is all-new and the
;; behavior in some situations differs.
Richard M. Stallman's avatar
Richard M. Stallman committed
37

Eric S. Raymond's avatar
Eric S. Raymond committed
38 39
;;; Code:

Roland McGrath's avatar
Roland McGrath committed
40
;;;###autoload
Richard M. Stallman's avatar
Richard M. Stallman committed
41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59
(defun reposition-window (&optional arg)
  "Make the current definition and/or comment visible.
Further invocations move it to the top of the window or toggle the
visibility of comments that precede it.
  Point is left unchanged unless prefix ARG is supplied.
  If the definition is fully onscreen, it is moved to the top of the
window.  If it is partly offscreen, the window is scrolled to get the
definition (or as much as will fit) onscreen, unless point is in a comment
which is also partly offscreen, in which case the scrolling attempts to get
as much of the comment onscreen as possible.
  Initially `reposition-window' attempts to make both the definition and
preceding comments visible.  Further invocations toggle the visibility of
the comment lines.
  If ARG is non-nil, point may move in order to make the whole defun
visible (if only part could otherwise be made so), to make the defun line
visible (if point is in code and it could not be made so, or if only
comments, including the first comment line, are visible), or to make the
first comment line visible (if point is in a comment)."
  (interactive "P")
60
  (let* (;; (here (line-beginning-position))
Richard M. Stallman's avatar
Richard M. Stallman committed
61 62 63
	 (here (point))
	 ;; change this name once I've gotten rid of references to ht.
	 ;; this is actually the number of the last screen line
64
	 (ht (- (window-height) 2))
Richard M. Stallman's avatar
Richard M. Stallman committed
65 66 67 68 69 70 71
	 (line (repos-count-screen-lines (window-start) (point)))
	 (comment-height
	  ;; The call to max deals with the case of cursor between defuns.
	  (max 0
	       (repos-count-screen-lines-signed
		;; the beginning of the preceding comment
		(save-excursion
72
		  (if (not (eobp)) (forward-char 1))
73
		  (end-of-defun -1)
Richard M. Stallman's avatar
Richard M. Stallman committed
74
		  ;; Skip whitespace, newlines, and form feeds.
75 76
		  (if (re-search-forward "[^ \t\n\f]" nil t)
		      (backward-char 1))
Richard M. Stallman's avatar
Richard M. Stallman committed
77 78
		  (point))
		here)))
79
	 (defun-height
Richard M. Stallman's avatar
Richard M. Stallman committed
80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95 96 97 98 99 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120
	   (repos-count-screen-lines-signed
	    (save-excursion
	      (end-of-defun 1) ; so comments associate with following defuns
	      (beginning-of-defun 1)
	      (point))
	    here))
	 ;; This must be positive, so don't use the signed version.
	 (defun-depth (repos-count-screen-lines here
						(save-excursion
						  (end-of-defun 1)
						  (point))))
	 (defun-line-onscreen-p
	   (and (<= defun-height line)
		(<= (- line defun-height) ht))))
    (cond ((or (= comment-height line)
	       (and (= line ht)
		    (> comment-height line)
		    ;; if defun line offscreen, we should be in case 4
		    defun-line-onscreen-p))
	   ;; Either first comment line is at top of screen or (point at
	   ;; bottom of screen, defun line onscreen, and first comment line
	   ;; off top of screen).  That is, it looks like we just did
	   ;; recenter-definition, trying to fit as much of the comment
	   ;; onscreen as possible.  Put defun line at top of screen; that
	   ;; is, show as much code, and as few comments, as possible.

	   (if (and arg (> defun-depth (1+ ht)))
	       ;; Can't fit whole defun onscreen without moving point.
	       (progn (end-of-defun) (beginning-of-defun) (recenter 0))
	     (recenter (max defun-height 0)))
	   ;;(repos-debug-macro "1")
	   )

	  ((or (= defun-height line)
	       (= line 0)
	       (and (< line comment-height)
		    (< defun-height 0)))
	   ;; Defun line or cursor at top of screen, OR cursor in comment
	   ;; whose first line is offscreen.
	   ;; Avoid moving definition up even if defun runs offscreen;
	   ;; we care more about getting the comment onscreen.
121

Richard M. Stallman's avatar
Richard M. Stallman committed
122 123 124 125 126 127
	   (cond ((= line ht)
		  ;; cursor on last screen line (and so in a comment)
		  (if arg (progn (end-of-defun) (beginning-of-defun)))
		  (recenter 0)
		  ;;(repos-debug-macro "2a")
		  )
128

Richard M. Stallman's avatar
Richard M. Stallman committed
129
		 ;; This condition, copied from case 4, may not be quite right
130

Richard M. Stallman's avatar
Richard M. Stallman committed
131 132 133 134 135 136 137 138 139 140 141 142 143 144 145 146 147 148 149 150 151 152 153 154 155 156 157 158 159 160 161 162 163 164 165 166 167 168 169 170 171 172
		 ((and arg (< ht comment-height))
		  ;; Can't get first comment line onscreen.
		  ;; Go there and try again.
		  (forward-line (- comment-height))
		  (beginning-of-line)
		  ;; was (reposition-window)
		  (recenter 0)
		  ;;(repos-debug-macro "2b")
		  )
		 (t
		  (recenter (min ht comment-height))
		  ;;(repos-debug-macro "2c")
		  ))
	   ;; (recenter (min ht comment-height))
	   )

	  ((and (> (+ line defun-depth -1) ht)
		defun-line-onscreen-p)
	   ;; Defun runs off the bottom of the screen and the defun line
	   ;; is onscreen.
	   ;; Move the defun up.
	   (recenter (max 0 (1+ (- ht defun-depth)) defun-height))
	   ;;(repos-debug-macro "3")
	   )

	  (t
	   ;; If on the bottom line and comment start is offscreen
	   ;; then just move all comments offscreen, or at least as
	   ;; far as they'll go.

	   ;; Try to get as much of the comments onscreen as possible.
	   (if (and arg (< ht comment-height))
	       ;; Can't get defun line onscreen; go there and try again.
	       (progn (forward-line (- defun-height))
		      (beginning-of-line)
		      (reposition-window))
	     (recenter (min ht comment-height)))
	   ;;(repos-debug-macro "4")
	   ))))

;;; Auxiliary functions

173

Richard M. Stallman's avatar
Richard M. Stallman committed
174 175 176 177
;; Return number of screen lines between START and END.
(defun repos-count-screen-lines (start end)
  (save-excursion
    (save-restriction
178 179
      (narrow-to-region (point-min) end)
      (goto-char start)
Richard M. Stallman's avatar
Richard M. Stallman committed
180 181 182 183 184 185 186 187 188 189
      (vertical-motion (- (point-max) (point-min))))))

;; Return number of screen lines between START and END; returns a negative
;; number if END precedes START.
(defun repos-count-screen-lines-signed (start end)
  (let ((lines (repos-count-screen-lines start end)))
    (if (< start end)
	lines
      (- lines))))

Richard M. Stallman's avatar
Richard M. Stallman committed
190
;; (defmacro repos-debug-macro (case-no)
191 192
;;   `(message (concat "Case " ,case-no ": %s %s %s %s %s")
;;             ht line comment-height defun-height defun-depth))
Richard M. Stallman's avatar
Richard M. Stallman committed
193 194

(provide 'reposition)
Richard M. Stallman's avatar
Richard M. Stallman committed
195

Eric S. Raymond's avatar
Eric S. Raymond committed
196
;;; reposition.el ends here