NonGNU ELPA - visual-fill-column

Visual Fill Column

visual-fill-column-mode is a small Emacs minor mode that mimics the effect of fill-column in visual-line-mode. Instead of wrapping lines at the window edge, which is the standard behaviour of visual-line-mode, it wraps lines at fill-column (or visual-fill-column-width, if set). That is, it turns the view on the left into the view on the right, without changing the contents of the file:

Without visual-fill-column	With visual-fill-column

Installation

visual-fill-column can be installed from NonGNU Elpa. In Emacs versions 28 and above, simply type M-x package-install RET visual-fill-column-mode RET.

Usage

visual-fill-column-mode wraps long lines at fill-column without adding newlines to the buffer. Its primary (though not exclusive) purpose is to soft-wrap text in buffers that use visual-line-mode. The most straightforward way to achieve this is to use the minor mode visual-line-fill-column-mode instead of visual-line-mode. This function activates (and deactivates) visual-line-mode and visual-fill-column-mode in conjunction.

visual-fill-column can also be used independently from visual-line-mode, for example to centre text in a buffer. In this case, use the function visual-fill-column-mode to activate it. This function can be added to mode hooks or called directly with M-x visual-fill-column-mode RET.

Note that if you activate visual-fill-column-mode in a mode hook, though, it will not be deactivated when the hook's mode is deactivated. If, for example, you would add visual-fill-column-mode to visual-line-mode-hook, activating visual-line-mode will activate visual-fill-column-mode, but deactivating visual-line-mode will not deactivate visual-fill-column-mode. Therefore, the use of visual-line-fill-column-mode is preferred.

There is also a globalised mode global-visual-fill-column-mode. This mode turns on visual-fill-column-mode in every buffer that visits a file. Activate it either through Customize or by calling it as a function in your init file. In buffers that do not visit a file, visual-fill-column-mode may be disruptive, so global-visual-fill-column-mode is restricted to file-visiting buffers. (You can, of course still activate visual-fill-column-mode manually or in hooks for such buffers, of course.)

Wrap prefix

In auto-fill-mode, there is an option adaptive-fill-mode, which ensures that if the first line of a paragraph is indented or has, e.g., a mail quote prefix (>), this is applied to the entire paragraph. To get the same effect, you can use the package adaptive-wrap, which is available from GNU Elpa. Like visual-fill-column-mode, its effect is purely visual, the buffer text is not actually modified. The effect of this package is shown in the following two images:

Without adaptive-wrap	With adaptive-wrap

Centering the text

Another use case for visual-fill-column is to centre the text in a window:

This effect is achieved by setting the user option visual-fill-column-center-text. Note that visual-fill-column-mode is not dependent on visual-line-mode, so it can be used to centre text in buffers that use auto-fill-mode or in programming modes.

Note that visual-fill-column-center-text automatically becomes buffer-local when it is set. Therefore, if you wish to make this the default, either use the Customize interface or use setq-default in your init file, rather than setq:

(setq-default visual-fill-column-center-text t)

Note: If you are interested in a fully distraction-free writing environment, that not only centres the text but also removes the window decorations, the mode line etc., take a look at writeroom-mode.

How it works

visual-fill-column-mode works by widening the window margins. This reduces the area that is available for text display, creating the appearance that the text is wrapped at fill-column. In the default configuration, only the right margin is widened, mimicking the effect of auto-fill-mode. In buffers that are explicitly right-to-left (i.e., those where bidi-paragraph-direction is set to right-to-left), the left margin is expanded, so that the text appears at the window’s right side. When visual-fill-column-center-text is set, both margins are widened.

The amount by which the margins are widened depends on the window width and is automatically adjusted when the window’s width changes (e.g., when the window is split in two side-by-side windows).

Splitting a Window

If you have a wide screen (more specifically, if your Emacs frame is wide), visual-fill-column has the unfortunate effect that if you pop up, say, a *Help* or *Completions* buffer or something similar, the popped-up window appears below the active buffer, not next to it, as you might otherwise expect.

This is due to the fact that Emacs uses the width of the text area to determine whether a window can be split into two side-by-side windows, and since visual-fill-column-mode narrows the text area, Emacs thinks there is not enough room to do a side-by-side split and so opts for putting the new window below the current one.

To remedy this situation, you can set the option visual-fill-column-enable-sensible-window-split. When this option is set, the variable split-window-preferred-function is set to the function visual-fill-column-split-window-sensibly, which first removes the margins, widening the text area again, and then calls split-window-sensibly to do the actual splitting.

This option does not affect the ability to split windows manually. Even if you keep visual-fill-column-enable-sensible-window-split unset, you can still split a window into two side-by-side windows by invoking e.g., split-window-right (C-x 3).

Adjusting Text Size

The width of the margins is adjusted for the text size: larger text size means smaller margins. However, interactive adjustments to the text size (e.g., with text-size-adjust) cannot be detected by visual-fill-column-mode, therefore if you adjust the text size while visual-fill-column-mode is active, the margins won't be adjusted. To remedy this, you can force a redisplay, e.g., by switching buffers, by splitting and unsplitting the window or by calling redraw-display.

Alternatively, you can advise the function text-size-adjust with the function visual-fill-column-adjust:

(advice-add 'text-scale-adjust :after #'visual-fill-column-adjust)

Note that this functionality is controlled by the option visual-fill-column-adjust-for-text-scale. If this is set to nil, the margins are not adjusted for the text size.

Customisation

The customisation group visual-fill-column has several options that can be used to customise the package.

The following options are buffer-local, the values you set in your init file are default values:

visual-fill-column-width — Column at which to wrap lines. If set to nil (the default), use the value of fill-column instead.

visual-fill-column-center-text — If set to t, centre the text area in the window. By default, the text is displayed at the window’s (left) edge, mimicking the effect of fill-column.

visual-fill-column-extra-text-width — Extra columns added to the left and right side of the text area. This should be a cons cell of two integers (<left> . <right>). If visual-fill-column-center-text is t, the text area is centred before the extra columns are added. This is currently used by writeroom-mode to add room for line numbers without shifting the text off-centre.

visual-fill-column-fringes-outside-margins — If set to t, put the fringes outside the margins. Widening the margin would normally cause the fringes to be pushed inward, because by default, they appear between the margins and the text. This effect may be visually less appealing, therefore, visual-fill-column-mode places the fringes outside the margins. If you prefer to have the fringes inside the margins, unset this option.

The following options are global, so that they apply to all buffers with visual-fill-column-mode enabled:

visual-fill-column-enable-sensible-window-split — Allow pop-up windows to create a side-by-side window split, if possible. See the discussion above.

visual-fill-column-adjust-for-text-scale — Take text scaling into account when computing the width of the margins.

visual-fill-column-mode-map — Keymap for mouse events in the left and right margins, to make sure that scrolling or clicking on the margins does what you'd expect (rather than cause an "event not bound" error).