Re: Why min-colors 88?

[Bill Wohler]

Eli Zaretskii <address@hidden> writes:

>> Date: Fri, 03 Feb 2006 11:50:46 -0800
>> From: Bill Wohler <address@hidden>
>> 
>> Can anyone explain the magic number 88 to me? Why is this used
>> throughout Emacs? Why is this the default generated when
>> customizing a face (on devices with lots of colors)?
>
> Because there's an 88-color xterm whose color set is rich enough to
> support all the colors we use in Emacs' faces.

Or in other words, Emacs' has 88 faces?

>> An MH-E developer has a device where (device-color-cells) returns 64.
>
> Out of curiosity, what device is that?

Eric?

> In any case, there's no support in Emacs for such devices right now,
> i.e. there's no 64-color set that can be used to map the face colors
> using the tty-colors.el machinery.  So I wonder how does that
> developer use his/her device with Emacs.
>
>> What harm could there be in changing our specifications to use 64
>> instead of 88?
>
> I don't know.  To find out, someone will have to:
>
>   . find out what colors, in terms of RGB values, are defined on that
>     device
>   . map the colors used by Emacs (e.g. in color-name-rgb-alist) into
>     those 64 colors, using tty-color-translate
>   . see how many Emacs colors map to the same color on the 64-color
>     deives, and
>   . draw the conclusions.

Objectively, if the colors that we use do not map to the same color,
we should be OK, right? Subjectively, the MH-E colors should map to a
pleasing set.

>> Finally, why are there a lot of faces with seemingly redundant
>> specifications such as this?
>> 
>>   (defface highlight
>>     '((((class color) (min-colors 88) (background light))
>>        :background "darkseagreen2")
>>       (((class color) (min-colors 88) (background dark))
>>        :background "darkolivegreen")
>>       (((class color) (min-colors 16) (background light))
>>        :background "darkseagreen2")
>>       (((class color) (min-colors 16) (background dark))
>>        :background "darkolivegreen")
>>       (((class color) (min-colors 8))
>>        :background "green" :foreground "black")
>>       (t :inverse-video t))
>>     "Basic face for highlighting."
>>     :group 'basic-faces)
>
> The main reason is to allow an easy modification of the defaults for
> 88-and-up color terminals in the future.  The 88-color support is new
> with Emacs 22, so for now, we just duplicated the old definitions.  We
> expect them to change as user experience is gained when Emacs 22 is
> released.

Thanks, Eli.

-- 
Bill Wohler <address@hidden>  http://www.newt.com/wohler/  GnuPG ID:610BD9AD
Maintainer of comp.mail.mh FAQ and MH-E. Vote Libertarian!
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