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1 ;;; auto-show.el --- perform automatic horizontal scrolling as point moves
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3 ;; This file is in the public domain.
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4
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5 ;; Author: Pete Ware <ware@cis.ohio-state.edu>
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6 ;; Modified by: Ben Wing <wing@666.com>
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7 ;; Maintainer: XEmacs Development Team
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8 ;; Keywords: extensions, internal
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9
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10 ;; This file is part of XEmacs.
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11
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12 ;; XEmacs is free software; you can redistribute it and/or modify it
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13 ;; under the terms of the GNU General Public License as published by
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14 ;; the Free Software Foundation; either version 2, or (at your option)
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15 ;; any later version.
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16
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17 ;; XEmacs is distributed in the hope that it will be useful, but
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18 ;; WITHOUT ANY WARRANTY; without even the implied warranty of
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19 ;; MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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20 ;; General Public License for more details.
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21
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22 ;; You should have received a copy of the GNU General Public License
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23 ;; along with XEmacs; see the file COPYING. If not, write to the Free
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24 ;; Software Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA
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25 ;; 02111-1307, USA.
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26
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27 ;;; Synched up with: Emacs/Mule zeta.
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28
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29 ;;; Commentary:
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30
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31 ;; This file provides functions that
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32 ;; automatically scroll the window horizontally when the point moves
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33 ;; off the left or right side of the window.
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34
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35 ;; Once this library is loaded, automatic horizontal scrolling
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36 ;; occurs whenever long lines are being truncated.
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37 ;; To request truncation of long lines, set the variable
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38 ;; Setting the variable `truncate-lines' to non-nil.
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39 ;; You can do this for all buffers as follows:
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40 ;;
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41 ;; (set-default 'truncate-lines t)
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42
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43 ;; Here is how to do it for C mode only:
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44 ;;
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45 ;; (set-default 'truncate-lines nil) ; this is the original value
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46 ;; (defun my-c-mode-hook ()
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47 ;; "Run when C-mode starts up. Changes ..."
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48 ;; ... set various personal preferences ...
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49 ;; (setq truncate-lines t))
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50 ;; (add-hook 'c-mode-hook 'my-c-mode-hook)
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51 ;;
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52 ;;
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53 ;; As a finer level of control, you can still have truncated lines but
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54 ;; without the automatic horizontal scrolling by setting the buffer
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55 ;; local variable `auto-show-mode' to nil. The default value is t.
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56 ;; The command `auto-show-mode' toggles the value of the variable
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57 ;; `auto-show-mode'.
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58
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59 ;;; Code:
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60
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61 (defvar auto-show-mode t
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62 "*Non-nil enables automatic horizontal scrolling, when lines are truncated.
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63 The default value is t. To change the default, do this:
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64 (set-default 'auto-show-mode nil)
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65 See also command `auto-show-mode'.
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66 This variable has no effect when lines are not being truncated.
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67 This variable is automatically local in each buffer where it is set.")
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68
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69 (make-variable-buffer-local 'auto-show-mode)
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70
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71 (defvar auto-show-shift-amount 8
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72 "*Extra columns to scroll. for automatic horizontal scrolling.")
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73
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74 (defvar auto-show-show-left-margin-threshold 50
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75 "*Threshold column for automatic horizontal scrolling to the right.
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76 If point is before this column, we try to scroll to make the left margin
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77 visible. Setting this to 0 disables this feature.")
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78
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79 (defun auto-show-truncationp ()
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80 "True if line truncation is enabled for the selected window."
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81 ;; XEmacs change (use specifiers)
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82 ;; ### There should be a more straightforward way to do this from elisp.
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83 (or truncate-lines
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84 (and truncate-partial-width-windows
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85 (< (+ (window-width)
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86 (specifier-instance left-margin-width)
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87 (specifier-instance right-margin-width))
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88 (frame-width)))))
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89
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90 (defun auto-show-mode (arg)
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91 "Turn automatic horizontal scroll mode on or off.
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92 With arg, turn auto scrolling on if arg is positive, off otherwise.
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93 This mode is enabled or disabled for each buffer individually.
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94 It takes effect only when `truncate-lines' is non-nil."
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95 (interactive "P")
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96 (setq auto-show-mode
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97 (if (null arg)
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98 (not auto-show-mode)
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99 (> (prefix-numeric-value arg) 0))))
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100
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101 ;; XEmacs addition:
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102 (defvar auto-show-inhibiting-commands
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103 '(scrollbar-char-left
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104 scrollbar-char-right
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105 scrollbar-page-left
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106 scrollbar-page-right
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107 scrollbar-to-left
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108 scrollbar-to-right
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109 scrollbar-horizontal-drag)
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110 "Commands that inhibit auto-show behavior.
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111 This normally includes the horizontal scrollbar commands.")
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112
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113 ;; XEmacs addition:
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114 (defun auto-show-should-take-action-p ()
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115 (and auto-show-mode (auto-show-truncationp)
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116 (equal (window-buffer) (current-buffer))
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117 (not (memq this-command auto-show-inhibiting-commands))))
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118
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119 ;; XEmacs addition:
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120 (defun auto-show-make-region-visible (start end)
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121 "Move point in such a way that the region (START, END) is visible.
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122 This only does anything if auto-show-mode is enabled, and it doesn't
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123 actually do any horizontal scrolling; rather, it just sets things up so
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124 that the region will be visible when `auto-show-make-point-visible'
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125 is next called (this happens after every command)."
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126 (if (auto-show-should-take-action-p)
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127 (let* ((col (current-column)) ;column on line point is at
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128 (scroll (window-hscroll));how far window is scrolled
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129 (w-width (- (window-width)
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130 (if (> scroll 0)
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131 2 1))) ;how wide window is on the screen
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132 (right-col (+ scroll w-width))
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133 (start-col (save-excursion (goto-char start) (current-column)))
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134 (end-col (save-excursion (goto-char end) (current-column))))
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135 (cond ((and (>= start-col scroll)
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136 (<= end-col right-col))
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137 ;; already completely visible
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138 nil)
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139 ((< start-col scroll)
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140 (scroll-right (- scroll start-col)))
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141 (t
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142 (scroll-left (- end-col right-col)))))))
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143
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144 (defun auto-show-make-point-visible (&optional ignore-arg)
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145 "Scroll horizontally to make point visible, if that is enabled.
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146 This function only does something if `auto-show-mode' is non-nil
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147 and longlines are being truncated in the selected window.
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148 See also the command `auto-show-mode'."
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149 (interactive)
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150 ;; XEmacs change
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151 (if (auto-show-should-take-action-p)
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152 (let* ((col (current-column)) ;column on line point is at
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153 (scroll (window-hscroll)) ;how far window is scrolled
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154 (w-width (- (window-width)
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155 (if (> scroll 0)
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156 2 1))) ;how wide window is on the screen
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157 (right-col (+ scroll w-width)))
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158 (if (and (< col auto-show-show-left-margin-threshold)
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159 (< col (window-width))
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160 (> scroll 0))
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161 (scroll-right scroll)
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162 (if (< col scroll) ;to the left of the screen
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163 (scroll-right (+ (- scroll col) auto-show-shift-amount))
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164 (if (or (> col right-col) ;to the right of the screen
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165 (and (= col right-col)
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166 (not (eolp))))
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167 (scroll-left (+ auto-show-shift-amount
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168 (- col (+ scroll w-width))))
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169 )
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170 )
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171 )
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172 )
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173 )
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174 )
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175
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176 ;; XEmacs change:
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177 ;; #### instead of this, we kludgily call it from the C code, to make sure
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178 ;; that it's done after any other things on post-command-hook (which might
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179 ;; move point).
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180 ;; Do auto-scrolling after commands.
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181 ;;(add-hook 'post-command-hook 'auto-show-make-point-visible)
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182
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183 ;; If being dumped, turn it on right away.
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184 (when (boundp 'load-gc)
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185 (auto-show-mode 1))
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186
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187 ;; Do auto-scrolling in comint buffers after process output also.
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188 ; XEmacs -- don't do this now, it messes up comint.
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189 ;(add-hook 'comint-output-filter-functions 'auto-show-make-point-visible t)
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190
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191 (provide 'auto-show)
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192
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193 ;; auto-show.el ends here
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