| 1 | ;;; reposition.el --- center a Lisp function or comment on the screen |
| 2 | |
| 3 | ;; Copyright (C) 1991, 1994, 2001-2014 Free Software Foundation, Inc. |
| 4 | |
| 5 | ;; Author: Michael D. Ernst <mernst@theory.lcs.mit.edu> |
| 6 | ;; Created: Jan 1991 |
| 7 | ;; Maintainer: emacs-devel@gnu.org |
| 8 | |
| 9 | ;; This file is part of GNU Emacs. |
| 10 | |
| 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. |
| 15 | |
| 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. |
| 20 | |
| 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/>. |
| 23 | |
| 24 | ;;; Commentary: |
| 25 | |
| 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. |
| 31 | |
| 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. |
| 37 | |
| 38 | ;;; Code: |
| 39 | |
| 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) 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. |
| 105 | |
| 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") |
| 111 | ) |
| 112 | |
| 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. |
| 121 | |
| 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") |
| 127 | ) |
| 128 | |
| 129 | ;; This condition, copied from case 4, may not be quite right |
| 130 | |
| 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") |
| 139 | ) |
| 140 | (t |
| 141 | (recenter (min ht comment-height)) |
| 142 | ;;(repos-debug-macro "2c") |
| 143 | )) |
| 144 | ;; (recenter (min ht comment-height)) |
| 145 | ) |
| 146 | |
| 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") |
| 154 | ) |
| 155 | |
| 156 | (t |
| 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. |
| 160 | |
| 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 | )))) |
| 170 | |
| 171 | ;;; Auxiliary functions |
| 172 | |
| 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)))))) |
| 180 | |
| 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)))) |
| 188 | |
| 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)) |
| 192 | |
| 193 | (provide 'reposition) |
| 194 | |
| 195 | ;;; reposition.el ends here |