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128 lines
4.2 KiB
EmacsLisp
128 lines
4.2 KiB
EmacsLisp
;;; auto-show.el --- perform automatic horizontal scrolling as point moves
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;;; This file is in the public domain.
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;;; Keywords: scroll display minor-mode
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;;; Author: Pete Ware <ware@cis.ohio-state.edu>
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;;; Maintainer: FSF
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;;; Commentary:
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;;; This file provides functions that
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;;; automatically scroll the window horizontally when the point moves
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;;; off the left or right side of the window.
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;;; Once this library is loaded, automatic horizontal scrolling
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;;; occurs whenever long lines are being truncated.
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;;; To request truncation of long lines, set the variable
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;;; Setting the variable `truncate-lines' to non-nil.
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;;; You can do this for all buffers as follows:
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;;;
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;;; (set-default 'truncate-lines t)
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;;; Here is how to do it for C mode only:
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;;;
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;;; (set-default 'truncate-lines nil) ; this is the original value
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;;; (defun my-c-mode-hook ()
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;;; "Run when C-mode starts up. Changes ..."
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;;; ... set various personal preferences ...
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;;; (setq truncate-lines t))
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;;; (add-hook 'c-mode-hook 'my-c-mode-hook)
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;;;
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;;;
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;;; As a finer level of control, you can still have truncated lines but
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;;; without the automatic horizontal scrolling by setting the buffer
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;;; local variable `auto-show-mode' to nil. The default value is t.
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;;; The command `auto-show-mode' toggles the value of the variable
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;;; `auto-show-mode'.
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;;; Code:
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(defgroup auto-show nil
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"Perform automatic horizontal scrolling as point moves."
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:group 'editing)
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(defcustom auto-show-mode t
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"*Non-nil enables automatic horizontal scrolling, when lines are truncated.
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The default value is t. To change the default, do this:
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(set-default 'auto-show-mode nil)
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See also command `auto-show-mode'.
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This variable has no effect when lines are not being truncated.
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This variable is automatically local in each buffer where it is set."
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:type 'boolean
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:group 'auto-show)
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(make-variable-buffer-local 'auto-show-mode)
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(defcustom auto-show-shift-amount 8
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"*Extra columns to scroll. for automatic horizontal scrolling."
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:type 'integer
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:group 'auto-show)
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(defcustom auto-show-show-left-margin-threshold 50
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"*Threshold column for automatic horizontal scrolling to the right.
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If point is before this column, we try to scroll to make the left margin
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visible. Setting this to 0 disables this feature."
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:type 'integer
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:group 'auto-show)
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(defun auto-show-truncationp ()
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"True if line truncation is enabled for the selected window."
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(or truncate-lines
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(and truncate-partial-width-windows
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(< (window-width) (frame-width)))))
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;;;###autoload
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(defun auto-show-mode (arg)
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"Turn automatic horizontal scroll mode on or off.
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With arg, turn auto scrolling on if arg is positive, off otherwise.
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This mode is enabled or disabled for each buffer individually.
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It takes effect only when `truncate-lines' is non-nil."
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(interactive "P")
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(setq auto-show-mode
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(if (null arg)
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(not auto-show-mode)
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(> (prefix-numeric-value arg) 0))))
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(defun auto-show-make-point-visible (&optional ignore-arg)
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"Scroll horizontally to make point visible, if that is enabled.
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This function only does something if `auto-show-mode' is non-nil
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and longlines are being truncated in the selected window.
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See also the command `auto-show-mode'."
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(interactive)
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(if (and auto-show-mode (auto-show-truncationp)
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(equal (window-buffer) (current-buffer)))
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(let* ((col (current-column)) ;column on line point is at
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(scroll (window-hscroll)) ;how far window is scrolled
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(w-width (- (window-width)
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(if (> scroll 0)
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2 1))) ;how wide window is on the screen
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(right-col (+ scroll w-width)))
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(if (and (< col auto-show-show-left-margin-threshold)
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(< col (window-width))
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(> scroll 0))
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(scroll-right scroll)
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(if (< col scroll) ;to the left of the screen
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(scroll-right (+ (- scroll col) auto-show-shift-amount))
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(if (or (> col right-col) ;to the right of the screen
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(and (= col right-col)
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(not (eolp))))
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(scroll-left (+ auto-show-shift-amount
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(- col (+ scroll w-width))))
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)
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)
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)
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)
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)
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)
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;; Do auto-scrolling after commands.
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(add-hook 'post-command-hook 'auto-show-make-point-visible)
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;; Do auto-scrolling in comint buffers after process output also.
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(add-hook 'comint-output-filter-functions 'auto-show-make-point-visible t)
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(provide 'auto-show)
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;; auto-show.el ends here
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