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Emacs mode for wrapping visual-line-mode buffers at fill-column.
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README.md

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. If fill-column is too large for the window, the text is wrapped at the window edge.

Installation

visual-fill-column can be installed via Melpa.

Activation

visual-fill-column-mode is primarily intended to be used alongside visual-line-mode. If this is your desired use-case , the way to activate visual-fill-column-mode depends on how you activate visual-line-mode.

If you activate visual-line-mode by using global-visual-line-mode, you can use global-visual-fill-column-mode (either set the user option through Customize, or call it as a function in your init file). global-visual-fill-column-mode turns on visual-fill-column-mode in every buffer that uses visual-line-mode, but only if this buffer is visiting a file.

visual-fill-column-mode can also be turned on in hooks. For example, if you don't use global-visual-line-mode but still prefer to activate visual-fill-column-mode in every buffer that uses visual-line-mode, you can add visual-fill-column-mode to visual-line-mode-hook:

(add-hook 'visual-line-mode-hook #'visual-fill-column-mode)

Both these methods have the effect that visual-fill-column-mode is used in every buffer that uses visual-line-mode. If that's not what you want, you can also use the reverse method: add visual-line-mode to visual-fill-column-mode-hook:

(add-hook 'visual-fill-column-mode-hook #'visual-line-mode)

This way, whenever you activate visual-fill-column-mode (e.g., interactively with M-x visual-fill-column-mode or in a major mode hook), visual-line-mode is also activated, but you can still activate visual-line-mode without using visual-fill-column-mode.

Note that visual-fill-column-mode is not tied to visual-line-mode: it is perfectly possible to use it on its own.

visual-fill-column-mode works by widening the right window margin. This reduces the area that is available for text display, creating the appearance that the text is wrapped at fill-column. The amount by which the right margin is 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).

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.

Widening the margin normally causes the fringes to be pushed inward. Since this is visually less appealing, the fringes are placed outside the margins. You can undo this by setting the variable visual-fill-column-fringes-outside-margins to nil.

Splitting a Window

Emacs won’t vertically split a window (i.e., into two side-by-side windows) that has wide margins. As a result, displaying buffers such as *Help* buffers, *Completion* buffers, etc., won’t split a window vertically, even if there appears to be enough space for a vertical split. This is not problematic, but it may be undesirable. To remedy this, you can set the option split-window-preferred-function to visual-fill-column-split-window-sensibly. This function first unsets the margins and then calls split-window-sensibly to do the actual splitting.

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 (or whatever function you use to adjust the text size) with the function visual-fill-column-adjust:

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

Options

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-fringes-outside-margins: if set to t, put the fringes outside the margins.

All three options are buffer-local, so the values you set through Customize are default values. They can also be set in mode hooks or directory or file local variables in order to customise particular files or file types.

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