lisp/reposition.el

   1 ;;; -*- Mode: Emacs-lisp -*-
   2 ;; Copyright (C) 1991 Free Software Foundation, Inc.
   3
   4 ;; This file is part of GNU Emacs.
   5
   6 ;; GNU Emacs is free software; you can redistribute it and/or modify
   7 ;; it under the terms of the GNU General Public License as published by
   8 ;; the Free Software Foundation; either version 1, or (at your option)
   9 ;; any later version.
  10
  11 ;; GNU Emacs is distributed in the hope that it will be useful,
  12 ;; but WITHOUT ANY WARRANTY; without even the implied warranty of
  13 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  14 ;; GNU General Public License for more details.
  15
  16 ;; You should have received a copy of the GNU General Public License
  17 ;; along with GNU Emacs; see the file COPYING.  If not, write to
  18 ;; the Free Software Foundation, 675 Mass Ave, Cambridge, MA 02139, USA.
  19
  20 ;;; Written by Michael D. Ernst, mernst@theory.lcs.mit.edu, 1/26/91
  21
  22 ;;; Reposition-window makes an entire function definition or comment visible,
  23 ;;; or, if it is already visible, places it at the top of the window;
  24 ;;; additional invocations toggle the visibility of comments preceding the
  25 ;;; code.  For the gory details, see the documentation for reposition-window;
  26 ;;; rather than reading that, you may just want to play with it.
  27
  28 ;;; The recommended binding for this function is M-C-r:
  29 ;;;  (global-set-key "\e\C-r" 'reposition-window)
  30
  31 ;;; This tries pretty hard to do the recentering correctly; the precise
  32 ;;; action depends on what the buffer looks like.  If you find a situation
  33 ;;; where it doesn't behave well, let me know.  This function is modeled
  34 ;;; after one of the same name in ZMACS, but the code is all-new and the
  35 ;;; behavior in some situations differs.
  36
  37 (defun reposition-window (&optional arg)
  38   "Make the current definition and/or comment visible.
  39 Further invocations move it to the top of the window or toggle the
  40 visibility of comments that precede it.
  41   Point is left unchanged unless prefix ARG is supplied.
  42   If the definition is fully onscreen, it is moved to the top of the
  43 window.  If it is partly offscreen, the window is scrolled to get the
  44 definition (or as much as will fit) onscreen, unless point is in a comment
  45 which is also partly offscreen, in which case the scrolling attempts to get
  46 as much of the comment onscreen as possible.
  47   Initially `reposition-window' attempts to make both the definition and
  48 preceding comments visible.  Further invocations toggle the visibility of
  49 the comment lines.
  50   If ARG is non-nil, point may move in order to make the whole defun
  51 visible (if only part could otherwise be made so), to make the defun line
  52 visible (if point is in code and it could not be made so, or if only
  53 comments, including the first comment line, are visible), or to make the
  54 first comment line visible (if point is in a comment)."
  55   (interactive "P")
  56   (let* (;; (here (save-excursion (beginning-of-line) (point)))
  57          (here (point))
  58          ;; change this name once I've gotten rid of references to ht.
  59          ;; this is actually the number of the last screen line
  60          (ht (- (window-height (selected-window)) 2))
  61          (line (repos-count-screen-lines (window-start) (point)))
  62          (comment-height
  63           ;; The call to max deals with the case of cursor between defuns.
  64           (max 0
  65                (repos-count-screen-lines-signed
  66                 ;; the beginning of the preceding comment
  67                 (save-excursion
  68                   (forward-char 1) (end-of-defun -1)
  69                   ;; Skip whitespace, newlines, and form feeds.
  70                   (re-search-forward "[^\\s \n\014]")
  71                   (backward-char 1)
  72                   (point))
  73                 here)))
  74          (defun-height
  75            (repos-count-screen-lines-signed
  76             (save-excursion
  77               (end-of-defun 1) ; so comments associate with following defuns
  78               (beginning-of-defun 1)
  79               (point))
  80             here))
  81          ;; This must be positive, so don't use the signed version.
  82          (defun-depth (repos-count-screen-lines here
  83                                                 (save-excursion
  84                                                   (end-of-defun 1)
  85                                                   (point))))
  86          (defun-line-onscreen-p
  87            (and (<= defun-height line)
  88                 (<= (- line defun-height) ht))))
  89     (cond ((or (= comment-height line)
  90                (and (= line ht)
  91                     (> comment-height line)
  92                     ;; if defun line offscreen, we should be in case 4
  93                     defun-line-onscreen-p))
  94            ;; Either first comment line is at top of screen or (point at
  95            ;; bottom of screen, defun line onscreen, and first comment line
  96            ;; off top of screen).  That is, it looks like we just did
  97            ;; recenter-definition, trying to fit as much of the comment
  98            ;; onscreen as possible.  Put defun line at top of screen; that
  99            ;; is, show as much code, and as few comments, as possible.
 100
 101            (if (and arg (> defun-depth (1+ ht)))
 102                ;; Can't fit whole defun onscreen without moving point.
 103                (progn (end-of-defun) (beginning-of-defun) (recenter 0))
 104              (recenter (max defun-height 0)))
 105            ;;(repos-debug-macro "1")
 106            )
 107
 108           ((or (= defun-height line)
 109                (= line 0)
 110                (and (< line comment-height)
 111                     (< defun-height 0)))
 112            ;; Defun line or cursor at top of screen, OR cursor in comment
 113            ;; whose first line is offscreen.
 114            ;; Avoid moving definition up even if defun runs offscreen;
 115            ;; we care more about getting the comment onscreen.
 116
 117            (cond ((= line ht)
 118                   ;; cursor on last screen line (and so in a comment)
 119                   (if arg (progn (end-of-defun) (beginning-of-defun)))
 120                   (recenter 0)
 121                   ;;(repos-debug-macro "2a")
 122                   )
 123
 124                  ;; This condition, copied from case 4, may not be quite right
 125
 126                  ((and arg (< ht comment-height))
 127                   ;; Can't get first comment line onscreen.
 128                   ;; Go there and try again.
 129                   (forward-line (- comment-height))
 130                   (beginning-of-line)
 131                   ;; was (reposition-window)
 132                   (recenter 0)
 133                   ;;(repos-debug-macro "2b")
 134                   )
 135                  (t
 136                   (recenter (min ht comment-height))
 137                   ;;(repos-debug-macro "2c")
 138                   ))
 139            ;; (recenter (min ht comment-height))
 140            )
 141
 142           ((and (> (+ line defun-depth -1) ht)
 143                 defun-line-onscreen-p)
 144            ;; Defun runs off the bottom of the screen and the defun line
 145            ;; is onscreen.
 146            ;; Move the defun up.
 147            (recenter (max 0 (1+ (- ht defun-depth)) defun-height))
 148            ;;(repos-debug-macro "3")
 149            )
 150
 151           (t
 152            ;; If on the bottom line and comment start is offscreen
 153            ;; then just move all comments offscreen, or at least as
 154            ;; far as they'll go.
 155
 156            ;; Try to get as much of the comments onscreen as possible.
 157            (if (and arg (< ht comment-height))
 158                ;; Can't get defun line onscreen; go there and try again.
 159                (progn (forward-line (- defun-height))
 160                       (beginning-of-line)
 161                       (reposition-window))
 162              (recenter (min ht comment-height)))
 163            ;;(repos-debug-macro "4")
 164            ))))
 165
 166 ;;; Auxiliary functions
 167
 168 ;; Return number of screen lines between START and END.
 169 (defun repos-count-screen-lines (start end)
 170   (save-excursion
 171     (save-restriction
 172       (narrow-to-region start end)
 173       (goto-char (point-min))
 174       (vertical-motion (- (point-max) (point-min))))))
 175
 176 ;; Return number of screen lines between START and END; returns a negative
 177 ;; number if END precedes START.
 178 (defun repos-count-screen-lines-signed (start end)
 179   (let ((lines (repos-count-screen-lines start end)))
 180     (if (< start end)
 181         lines
 182       (- lines))))
 183
 184 ; (defmacro repos-debug-macro (case-no)
 185 ;   (` (message
 186 ;       (concat "Case " (, case-no) ": %s %s %s %s %s")
 187 ;       ht line comment-height defun-height defun-depth)))
 188