How to define a good highlight face

Question

I would like to use global-hl-line-mode, but some of my themes lack a good highlight face. Is there a general way to define one (that's not inverse-color)? I would like to maintain syntax highlighting, which has broken in my attempts.

Answer 1

This is really a matter of opinion, but I have always found that that making the hl-line have a slightly darker background than the default is best.

I would like to maintain syntax highlighting, which has broken in my attempts.

If you want to maintain syntax highlighting, make sure that hl-line face's :foreground attribute is nil, then set the :background attribute to what you want.

Here is what it looks like for me with these settings:

(set-face-attribute 'default nil :background "gray15")
(set-face-attribute 'hl-line nil :foreground nil :background "gray5")

By the sound of it, you don't want hard coded colors because you will be changing themes. You can have emacs automatically set the :background of the hl-line face to a color slightly darker than the current default :background like this:

(require 'color)

(defun set-hl-line-color-based-on-theme ()
  "Sets the hl-line face to have no foregorund and a background
    that is 10% darker than the default face's background."
  (set-face-attribute 'hl-line nil
                      :foreground nil
                      :background (color-darken-name (face-background 'default) 10)))

(add-hook 'global-hl-line-mode-hook 'set-hl-line-color-based-on-theme)

This will set the face's background to a color 10% darker than the default background anytime you enable global-hl-line-mode