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bug#25890: `color-values` gives wrong value

From: Lars Ingebrigtsen
Subject: bug#25890: `color-values` gives wrong value
Date: Sat, 04 Mar 2017 16:44:28 +0100
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.0.50 (gnu/linux)

Eli Zaretskii <eliz@gnu.org> writes:

>> (apply #'color-rgb-to-hex `(,@(color-name-to-rgb "#ffffff") 2))
>>      => "#fefefe"
>> (apply #'color-rgb-to-hex `(,@(color-name-to-rgb "#fff") 2))
>>      => "#efefef"
>> Where I would like both to give back "#ffffff". Does this mean that I
>> have to ensure that input to `color-name-to-rgb' uses 4 digits per
>> component?
> Yes, IMO.  Emacs does all its calculations with color components
> assuming 16 bits per component.  Applications that need to use fewer
> digits and have the missing digits as something other than zero, need
> to do that in application code.

I haven't followed this discussion closely, but you've changed the way
color-rgb-to-rgb works in an incompatible way?  I don't think that makes
much sense -- it's a function we must assume is used by third party code
and that's supposed to return certain values on certain inputs.

If you want to have a function that does something else, I think it
would make more sense to introduce new functions that does this
"something new" (i.e., 16 bit component parsing instead of HTML-like
color parsing, which is what those functions are supposed to do), and
revert the old functions how they used to work.

(domestic pets only, the antidote for overdose, milk.)
   bloggy blog: http://lars.ingebrigtsen.no

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