Re: CSS contrast (#30295) (was Re: Heads-up: Emacs 26.1 RC1)

[Richard Copley <rcopley@gmail.com>]

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On 21 March 2018 at 13:32, Eli Zaretskii <eliz@gnu.org> wrote:

> > From: Richard Copley <rcopley@gmail.com>
> > Date: Wed, 21 Mar 2018 13:22:37 +0000
> > Cc: John Wiegley <johnw@gnu.org>, Tom Tromey <tom@tromey.com>,
> >       Emacs Development <emacs-devel@gnu.org>
> >
> >  We do something very similar in frame-set-background-mode and in
> >  tty-color-approximate.
> >
> > I don't see it. You're talking about this?
> >
> >           ((>= (apply '+ (color-values bg-color frame))
> >                ;; Just looking at the screen, colors whose
> >                ;; values add up to .6 of the white total
> >                ;; still look dark to me.
> >                (* (apply '+ (color-values "white" frame)) .6))
>
> That's the first example, yes.
>
> > It's this particular way of using color-distance that we appear to
> > have invented.
>
> Not according to the article from which the implementation of
> color-distance was taken.


???

> If we didn't then we took it from
> > somewhere else, and someone (Tom?) should know where.
>
> The comments in the sources of color-distance tell where we took it
> from.
>

The comments, and the article, say where the colour distance formula itself
comes from.
The article doesn't support our usage of the formula at all.

It says:
>> This distance will only be used in comparisons, to verify whether one
colour, *A*, is closer to colour *B* or to colour *C*.
That's what my patch 1 does. It's nothing like what the current code does.

> I don't believe the concept of a sphere centred on black is a useful one
> in this context, or that allowing the
> > user to vary its radius makes it any better.
>
> I suggest to read the original article mentioned above.
>

I suggest you re-read it.

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