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Many modern editors and IDEs can graphically indicate the location of the fill column by drawing a thin line (in design parlance, a "rule") down the length of the editing window. Fill-column-indicator implements this facility in Emacs:

Please Note

There is a small incompatibility between this package and the current stable Emacs relase (v24.3). See issue #31 for more information.

Installation and Usage

Put the package file in your load path and put

(require 'fill-column-indicator)

in your .emacs.

To toggle graphical indication of the fill column in a buffer, use the command fci-mode.

Configuration

• By default fci-mode draws a vertical line at the fill column. If you'd like it to be drawn at a different location, set fci-rule-column to the desired column number. (A case in which this might be useful is when you want to fill comments at, for example, column 70, but want a vertical rule at column 80 or 100 to indicate the maximum line length for code.) The default behavior (showing the indicator at the fill column) is specified by setting fci-rule-column to nil. Note that this variable becomes buffer local when set.

• On graphical displays the fill-column rule is drawn using a bitmap image. Its color is controlled by the variable fci-rule-color, whose value can be any valid color name. The rule's width in pixels is determined by the variable fci-rule-width; the default value is 1.

• The rule can be drawn as a solid or dashed line, as specified by the variable fci-rule-use-dashes; the default is nil. The length of the dashes is controlled by fci-dash-pattern, which is the ratio of dash length to line height; the default value is 0.75. (The value should be a number between 0 and 1; values outside that interval are coerced to the nearest endpoint.)

• The image formats fci-mode can use are XPM and PBM. If Emacs has been compiled with the appropriate library it uses XPM images by default; if not it uses PBM images, which are natively supported. You can specify a particular format by setting fci-rule-image-format to either xpm or pbm.

• On character terminals the rule is drawn using the character specified by fci-rule-character; the default is `|' (ascii 124). If fci-rule-character-color is nil, then it is drawn using fci-rule-color (or the closest approximation thereto that the terminal is capable of); if it is a color name, then that color is used instead.

• If you'd like the rule to be drawn using fci-rule-character even on graphical displays, set fci-always-use-textual-rule to a non-nil value.

These variables (as well as those in the next section) can be given buffer-local bindings.

Other Options

When truncate-lines is nil, the effect of drawing a fill-column rule is very odd looking. Indeed, it makes little sense to use a rule to indicate the position of the fill column in that case (the positions at which the fill column falls in the visual display space won't in general be collinear). For this reason, fci-mode sets truncate-lines to t in buffers in which it is enabled and restores it to its previous value when disabled. You can turn this feature off by setting fci-handle-truncate-lines to nil.

If line-move-visual is t, then vertical navigation can behave oddly in several edge cases while fci-mode is enabled (this is due to a bug in Emacs's C code). Accordingly, fci-mode sets line-move-visual to nil in buffers in which it is enabled and restores it to its previous value when disabled. This can be suppressed by setting fci-handle-line-move-visual to nil. (But you shouldn't want to do this. There's no reason to use line-move-visual if truncate-lines is t, and it doesn't make sense to use something like fci-mode when truncate-lines is nil.)

Fci-mode needs free use of two characters (specifically, it needs the use of two characters whose display table entries it can change arbitrarily). By default, it uses the first two characters of the Private Use Area of the Unicode BMP, viz. U+E000 and U+E001. If you need to use those characters for some other purpose, set fci-eol-char and fci-blank-char to different values.

Troubleshooting

• Fci-mode is intended to be used with monospaced fonts. If you're using a monospaced font and the fill-column rule is missing or misaligned on a few lines but otherwise appears normal, then most likely (a) there are non-ascii characters on those lines that are being displayed using a non-monospaced font, or (b) your font-lock settings use bold or italics and those font variants aren't monospaced.

• Fci-mode in not currently compatible with Emacs's show-trailing-whitespace feature (given the way the latter is implemented, such compatilibility is going to be hard to achieve). A workaround is to use whitespace-mode with an appropriate configuration. This will provide the same functionality as show-trailing-whitespace while remaning compatible with fci-mode. The appropriate whitespace setting is:

    (setq whitespace-style '(face trailing))
  

Known Issues

• The indicator extends only to end of the buffer contents (as opposed to running the full length of the editing window).

• When portions of a buffer are invisible, such as when outline mode is used to hide certain lines, the fill-column rule is hidden as well.

• Fci-mode should work smoothly when simultaneously displaying the same buffer on both a graphical display and on a character terminal. It does not currently support simultaneous display of the same buffer on window frames with different default font sizes. (It would be feasible to support this use case, but thus far there seems to be no demand for it.)

• An issue specific to the Mac OS X (NextStep) port, versions 23.0-23.2: Emacs won't, in these particular versions, draw a cursor on top of an image. Thus on graphical displays the cursor will disappear when positioned directly on top of the fill-column rule. The best way to deal with this is to upgrade to v23.3 or v24 (or downgrade to v22). If that isn't practical, a fix is available via the mini-package fci-osx-23-fix.el, which can be downloaded from this page. Directions for its use are given in the file header.

Todo

• Accommodate non-nil values of hl-line-sticky-flag and similar cases.

• Accommodate linum-mode more robustly.

• Compatibility with non-nil show-trailing-whitespace.

Acknowledgements

Thanks to Ami Fischman, Christopher Genovese, Michael Hoffman, José Alfredo Romero L., R. Lange, Joe Lisee, José Lombera, Frank Meffert, Mitchell Peabody, sheijk, and an anonymous BT subscriber for bug reports and suggestions. Special thanks to lomew, David Röthlisberger, and Pär Wieslander for code contributions.