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Re: About the :distant-foreground face attribute

From: Jan Djärv
Subject: Re: About the :distant-foreground face attribute
Date: Tue, 7 Jan 2014 16:00:14 +0100


7 jan 2014 kl. 13:55 skrev Chong Yidong <address@hidden>:

> What is the purpose of this face attribute, newly introduced for 24.4?

Too lazy to read documentation?

     Alternative foreground color, a string.  This is like `:foreground'
     but the color is only used as a foreground when the background
     color is near to the foreground that would have been used.  This
     is useful for example when marking text (i.e. the region face).
     If the text has a foreground that is visible with the region face,
     that foreground is used.  If the foreground is near the region
     face background, `:distant-foreground' is used instead so the text
     is readable.

> It seems to be unused in Emacs itself.  Is there a concrete example of
> this being needed in external packages or themes?

Too lazy too read the code?


(defface region
  '((((class color) (min-colors 88) (background dark))
     :background "blue3")
    (((class color) (min-colors 88) (background light) (type gtk))
     :distant-foreground "gtk_selection_fg_color"
     :background "gtk_selection_bg_color")
    (((class color) (min-colors 88) (background light) (type ns))
     :distant-foreground "ns_selection_fg_color"
     :background "ns_selection_bg_color")
    (((class color) (min-colors 88) (background light))
     :background "lightgoldenrod2")
    (((class color) (min-colors 16) (background dark))
     :background "blue3")
    (((class color) (min-colors 16) (background light))
     :background "lightgoldenrod2")
    (((class color) (min-colors 8))
     :background "blue" :foreground "white")
    (((type tty) (class mono))
     :inverse-video t)
    (t :background "gray"))
  "Basic face for highlighting the region."
  :version "21.1"
  :group 'basic-faces)

> First of all, the name :distant-foreground is not intuitive.  What does
> "distant" mean in this context?

The same as in any other context, far removed from something else, i.e. the 

> Also, this feature has one ugly consequence.  Previously, the `default'
> face must have all its face attributes specified, but now its
> :distant-foreground face is unspecified.

Default face does not need to have its font specified, so this is not new.

> Besides that, the implementation seems rather incomplete.  The Customize
> interface, `modify-face', `face-spec-reset-face', and other parts of
> Emacs haven't been updated for the existence of this face attribute.

That is on purpose.  It is supposed to be automatically calculated.

> It's unclear what functions like `face-foreground' should now do if
> there's a :distant-foreground.

No it is not.

> This all sounds like an invitation for more bugs.  In my opinion, this
> feature is a bad idea.

All new features invite new bugs, so are you saying we should never add new 
Your opinion is not very interesting, but if you have core for an alternative 
approach that would be interesting.

        Jan D.

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