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1 ;;; auto-show.el --- perform automatic horizontal scrolling as point moves
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2 ;;; This file is in the public domain.
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3
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4 ;;; Keywords: scroll display minor-mode
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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: FSF
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8
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9 ;;; Synched up with: FSF 19.30.
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10
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11 ;;; Commentary:
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12
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13 ;;; This file provides functions that
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14 ;;; automatically scroll the window horizontally when the point moves
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15 ;;; off the left or right side of the window.
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16
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17 ;;; Once this library is loaded, automatic horizontal scrolling
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18 ;;; occurs whenever long lines are being truncated.
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19 ;;; To request truncation of long lines, set the variable
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20 ;;; Setting the variable `truncate-lines' to non-nil.
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21 ;;; You can do this for all buffers as follows:
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22 ;;;
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23 ;;; (set-default 'truncate-lines t)
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24
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25 ;;; Here is how to do it for C mode only:
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26 ;;;
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27 ;;; (set-default 'truncate-lines nil) ; this is the original value
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28 ;;; (defun my-c-mode-hook ()
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29 ;;; "Run when C-mode starts up. Changes ..."
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30 ;;; ... set various personal preferences ...
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31 ;;; (setq truncate-lines t))
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32 ;;; (add-hook 'c-mode-hook 'my-c-mode-hook)
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33 ;;;
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34 ;;;
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35 ;;; As a finer level of control, you can still have truncated lines but
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36 ;;; without the automatic horizontal scrolling by setting the buffer
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37 ;;; local variable `auto-show-mode' to nil. The default value is t.
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38 ;;; The command `auto-show-mode' toggles the value of the variable
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39 ;;; `auto-show-mode'.
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40
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41 ;;; Code:
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42
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43 (defvar auto-show-mode t
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44 "*Non-nil enables automatic horizontal scrolling, when lines are truncated.
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45 The default value is t. To change the default, do this:
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46 (set-default 'auto-show-mode nil)
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47 See also command `auto-show-mode'.
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48 This variable has no effect when lines are not being truncated.")
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49
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50 (make-variable-buffer-local 'auto-show-mode)
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51
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52 (defvar auto-show-shift-amount 8
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53 "*Extra columns to scroll. for automatic horizontal scrolling.")
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54
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55 (defvar auto-show-show-left-margin-threshold 50
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56 "*Threshold column for automatic horizontal scrolling to the right.
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57 If point is before this column, we try to scroll to make the left margin
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58 visible. Setting this to 0 disables this feature.")
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59
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60 (defun auto-show-truncationp ()
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61 "True if line truncation is enabled for the selected window."
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62 ;; ### There should be a more straightforward way to do this from elisp.
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63 (or truncate-lines
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64 (and truncate-partial-width-windows
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65 (< (+ (window-width)
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66 (specifier-instance left-margin-width)
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67 (specifier-instance right-margin-width))
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68 (frame-width)))))
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69
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70 (defun auto-show-mode (arg)
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71 "Turn automatic horizontal scroll mode on or off.
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72 With arg, turn auto scrolling on if arg is positive, off otherwise."
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73 (interactive "P")
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74 (setq auto-show-mode
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75 (if (null arg)
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76 (not auto-show-mode)
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77 (> (prefix-numeric-value arg) 0))))
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78
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79 (defvar auto-show-inhibiting-commands
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80 '(scrollbar-char-left
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81 scrollbar-char-right
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82 scrollbar-page-left
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83 scrollbar-page-right
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84 scrollbar-to-left
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85 scrollbar-to-right
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86 scrollbar-horizontal-drag)
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87 "Commands that inhibit auto-show behavior.
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88 This normally includes the horizontal scrollbar commands.")
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89
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90 (defun auto-show-should-take-action-p ()
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91 (and auto-show-mode (auto-show-truncationp)
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92 (equal (window-buffer) (current-buffer))
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93 (not (memq this-command auto-show-inhibiting-commands))))
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94
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95 ;; XEmacs addition:
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96 (defun auto-show-make-region-visible (start end)
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97 "Move point in such a way that the region (START, END) is visible.
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98 This only does anything if auto-show-mode is enabled, and it doesn't
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99 actually do any horizontal scrolling; rather, it just sets things up so
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100 that the region will be visible when `auto-show-make-point-visible'
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101 is next called (this happens after every command)."
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102 (if (auto-show-should-take-action-p)
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103 (let* ((col (current-column)) ;column on line point is at
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104 (scroll (window-hscroll));how far window is scrolled
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105 (w-width (- (window-width)
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106 (if (> scroll 0)
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107 2 1))) ;how wide window is on the screen
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108 (right-col (+ scroll w-width))
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109 (start-col (save-excursion (goto-char start) (current-column)))
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110 (end-col (save-excursion (goto-char end) (current-column))))
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111 (cond ((and (>= start-col scroll)
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112 (<= end-col right-col))
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113 ;; already completely visible
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114 nil)
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115 ((< start-col scroll)
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116 (scroll-right (- scroll start-col)))
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117 (t
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118 (scroll-left (- end-col right-col)))))))
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119
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120 (defun auto-show-make-point-visible (&optional ignore-arg)
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121 "Scroll horizontally to make point visible, if that is enabled.
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122 This function only does something if `auto-show-mode' is non-nil
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123 and longlines are being truncated in the selected window.
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124 See also the command `auto-show-toggle'."
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125 (interactive)
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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 (if (and (< col auto-show-show-left-margin-threshold)
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134 (< col (window-width))
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135 (> scroll 0))
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136 (scroll-right scroll)
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137 (if (< col scroll) ;to the left of the screen
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138 (scroll-right (+ (- scroll col) auto-show-shift-amount))
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139 (if (or (> col right-col) ;to the right of the screen
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140 (and (= col right-col)
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141 (not (eolp))))
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142 (scroll-left (+ auto-show-shift-amount
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143 (- col (+ scroll w-width))))
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144 )
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145 )
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146 )
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147 )
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148 )
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149 )
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150
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151 ;; XEmacs change:
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152 ;; #### instead of this, we kludgily call it from the C code, to make sure
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153 ;; that it's done after any other things on post-command-hook (which might
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154 ;; move point).
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155 ;; Do auto-scrolling after commands.
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156 ;;(add-hook 'post-command-hook 'auto-show-make-point-visible)
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157
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158 ;; If being dumped, turn it on right away.
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159 (and (noninteractive) (auto-show-mode 1))
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160
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161 ;; Do auto-scrolling in comint buffers after process output also.
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162 ; XEmacs -- don't do this now, it messes up comint.
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163 ;(add-hook 'comint-output-filter-functions 'auto-show-make-point-visible t)
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164
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165 (provide 'auto-show)
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166
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167 ;; auto-show.el ends here
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168
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