Focus-hook: attenuate colours when losing focus

Question

How can I use the focus hooks to attenuate all colours in visible buffers when the Emacs frame loses focus?

I tried using the following code:

(set-frame-parameter (selected-frame) 'alpha '(100 80))

To make the frame become translucent, but it would flicker when I hit Ctrl (apparently that's because I let GNOME highlight the mouse cursor when I hit Ctrl).

Making the frame transparent isn't what I want anyway. Is it possible to desaturate all colours instead?

EDIT: a less ambitious goal is to change/attenuate the colours of the mode line on focus change and restore them to normal when focus returns. With two monitors I often find myself typing into the void when Emacs is displayed but not focussed, so I need some better visual indicator of focus.

Answer 1

See if auto-dim-other-buffers-mode works for you.

Out of the box it dims frames when they lose focus as well as buffers when they lose current-buffer status.

It's available on MELPA. Source here: https://github.com/mina86/auto-dim-other-buffers.el

Answer 2

Sure. See function doremi-increment-color in library doremi-frm.el.

In this case, you want to use a negative INCREMENT argument and specify s (for saturation) as the COMPONENT argument to increment (decrement, in this case).

You would call doremi-increment-color on any color of any UI feature you like (or on all of them), to calculate a less saturated version of the color. See also function hexrgb-increment-saturation in library hexrgb.el.

You can get an interactive idea of applying this across the board by using command doremi-all-faces-bg+ or doremi-all-frames-bg+ (or the same, with fg+ instead of bg+).

More Do Re Mi color-changing described here.

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With respect to your request about dynamically desaturating and saturating the mode line: See, for example, function 1on1-color-minibuffer-frame-on-setup in library oneonone.el, which does the same kind of thing for a standalone minibuffer frame. It uses function hexrgb-increment-hue, but you would use hexrgb-increment-saturation instead (or doremi-increment-color).

This is the meat of that function:

(set-background-color (hexrgb-increment-hue ; Change bg hue slightly.
                       (frame-parameter nil 'background-color)
                       1on1-color-minibuffer-frame-on-setup-increment))

Answer 3

Different answer based on your edit.

If you just want to change the mode line, check out what the Emacs manual has to say about mode-line-inactive face.

Like mode-line, but used for mode lines of the windows other than the selected one (if mode-line-in-non-selected-windows is non-nil). This face inherits from mode-line, so changes in that face affect mode lines in all windows.

You could make mode-line have a bright red background and mode-line-inactive a bland grey background, for instance.