Proposal to add standardized variation sequences for chess notation

[Richard Wordingham]

On Mon, 3 Apr 2017 14:12:52 +0200
Michael Everson <everson at evertype.com> wrote:

> On 2 Apr 2017, at 18:27, Richard Wordingham
> <richard.wordingham at ntlworld.com> wrote:

> I think you are seriously going the wrong way with this thinking. The
> immediate parallel that comes to mind are things like:
> 
> 1000   MYANMAR LETTER KA
> ⁓ 1000 FE00   dotted form
> 
> where the character can still be read if the variation selector’s
> glyph can’t be shown. Uniform width is a feature of CJK, sure, but
> that’s the nature of the writing system. Chess pieces for setting
> withing in ordinary text do NOT have to be an em wide, and they don’t
> in fonts. Chess pieces on a white square or on a black square do have
> to have a uniform width in order to produced the board matrix.

Nobody said the glyphs for use in ordinary text had to be a fixed width.
What I am saying is that the glyphs for the two new variants you are
proposing need to harmonise with the block elements such as U+2581
LOWER ONE EIGHTH BLOCK.  That requires uniform width *for those
variants*.  That is a key part of the glyph family's essence.  There is
no such requirement on the glyphs for normal text use as at present. 

> > U+00A0 makes a lot of sense as the base character.  
> 
> What? NBSP and SP are whitespace characters, with complex behaviours,
> and chessboards, whether set in lead type or digitally, are sets of
> simple symbol glyphs. NBSP glues two things together. SP separates
> things. Chessboards are not collections of black squares glued
> together by white spaces with white spaces at the alternating ends of
> lines. I reject this analysis. 

If one had a row of squares in flowing text, one would want the row to
act like a word.  One might have to resort to gluing it together using
CGJ or WJ.

> > Also having variants of U+25A1 and U+25A8 that match the game
> > square filter modifiers seems quite legitimate.  
> 
> Um, wait… What are you proposing NBSP for? I'm confused now. If you
> like these two characters (and I am glad you do) there’s no need for
> U+00A0 at all. 

To be pedantic, I said that the proposed variants were legitimate, not
that I liked them.

> > Secondly, the mechanism can only look for a substitute if it knows
> > that the glyph is missing.  

> The macOS does this quite reliably. If Baskerville has no chess
> piece, but Ludus does, then a text in Baskerville wlll usually
> display the Ludus glyph. You can override this by selecting the Ludus
> gyph and forcing it back to Baskerville and then you get a box or
> other substitution glyph. 

I'm talking about looking for a U+2654 glyph for ordinary text when
all the first font tried has is:

2654 FE01; Chesspiece on white; # WHITE CHESS KING
2654 FE02; Chesspiece on black; # WHITE CHESS KING

I must confess I am now wondering what the format 4 cmap should say
about U+2654.  Should it give a glyph for U+2654 or not?  I'm also
wondering about Windows behaviour.   There was a time when Windows 7
only supported variation sequences if they appeared in the cmap 14
subtable.

> > If it's looking for an OpenType font for a glyph of the family
> > <U+82A6, U+E0100>,  
> 
> Or any OpenType substitution string. 

Most won't be recognised as needed.  If the first font lacks a ligature
for <f, i>, fallback won't be used for it.  Grapheme clusters and
variation sequences get special treatment. 

Richard.