Re: Proposal to add standardized variation sequences for chess notation

On Mon, Apr 3, 2017 at 4:47 PM, Richard Wordingham <
richard.wordingham_at_ntlworld.com> wrote:

> On Mon, 3 Apr 2017 23:35:52 +0100
> Michael Everson <everson_at_evertype.com> wrote:
>
> > On 3 Apr 2017, at 22:03, Richard Wordingham
> > <richard.wordingham_at_ntlworld.com> wrote:
>
> The relevant text before was,
>
> "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"
>
> > > Should it give a glyph for U+2654 or not?
>
> > Of course. Why wouldn't it? It’s a graphic character.
>
> What my conceptual example font has is not the sort of glyph one would
> want for sentences like "Alice ♙ d4 meets White Queen ♕ (with shawl)".
>
> > I don’t see how anything you’re saying either identifies or tried to
> > solve any actual problem with the proposal. The proposal says “put
> > some substitution tables into your chess font to display a particular
> > glyph” and some apps do that and some don’t. You can’t use VS with
> > apps that don't.
>
> I'm trying to work out whether we need a variation sequence for
> "chesspiece in a sentence". We need the advice of someone who's worked
> on font fallback.
>
> You don't need substitution tables to be executed if your application
> can just look up glyphs for variation sequences.
>

I haven't worked on font fallback but maybe I can add something to this.

Honestly, I'm not sure we need to make a distinction between
piece-on-light-square and piece-in-notation at the SVS level.

Currently, chess fonts can be (roughly) divided into "diagram fonts" and
"notation fonts". A diagram font:
- Is fixed-width (at least for the chess figurines themselves)
- Centers each figurine in the character cell
- Has a means of producing dark squares and on-dark-square equivalents of
the figurines, either through separate allocation or a "combining dark
square background" mechanism (usually a negative kerning hack)
- Usually has board border elements, and may have decimal digits and a
subset of the lowercase Basic Latin alphabet for labeling ranks and files

A notation font:
- May be proportional
- Has figurines sitting on the baseline
(Neither is *required* for figurine notation. They just look nice.)

None of the features required for a diagram font are unacceptable in
figurine notation: they are either irrelevant (dark squares, border
elements) or acceptable visual variation (fixed width, vertical centering).
Most chess fonts are of the diagram type, and figurines from diagram fonts
may be (and frequently are) used in figurine notation. A font with
figurines sitting on the baseline would not be illegible in diagrams, just
a bit clumsy-looking. A proportional-width font would be unacceptable for
proper typesetting of a diagram since board spaces would not line up
properly, but would likely still be readable.

In addition, when figurines for notation and for diagrams are
distinguished, they are distinguished above the character level, in runs of
like type: rows of a diagram, or lines of figurine notation. This is not
unlike proportional vs. tabular digits. A font that supported both could
default to fixed-width figurines (the "safer" option) and provide
proportional figurines through a stylistic set.
Received on Tue Apr 04 2017 - 21:41:56 CDT