2017-04-02 11:57 GMT+02:00 Michael Everson <ever...@evertype.com>: > I’m not using E0100. And I’m not using CJK character 芦. I did not propose > sequences for unqualified chess pieces because I didn’t see any reason why > there should be a benefit for it. If there is some genuine benefit, > obviously the sequences in my proposal could be altered from > > 2654 FE00; Chesspiece on white; # WHITE CHESS KING > 2654 FE01; Chesspiece on black; # WHITE CHESS KING > > (that is: > > sub uni2654 uniFE00 by uni2654FE00 ; > sub uni2654 uniFE01 by uni2654FE01 ;) > > to > > 2654 FE00; Unqualified chesspiece; # WHITE CHESS KING > 2654 FE01; Chesspiece on white; # WHITE CHESS KING > 2654 FE02; Chesspiece on black; # WHITE CHESS KING > > (that is: > > sub uni2654 uniFE00 by uni2654 ; > sub uni2654 uniFE01 by uni2654FE02 ; > sub uni2654 uniFE02 by uni2654FE01 ;) > > But I didn’t see any need for that, since 2654 is already the unqualified > chesspiece. If there’s a formal need for triplets rather than couplets > here, I’ll conform to it, but that seems to be incidental to the robustness > of the proposal. > > > 2) <U+82A6, U+E0100> is not catered for. If one needs to be sure of > having its distinctive form, another font must be used. > > > > If I have understood the intended use correctly, then we need another > variation sequence to explicitly specify a glyph of U+2656 suitable for use > in plain-looking running text, analogous to <U+0032, FE0E> for a text-style > '2'. A renderer can then ask whether a font supports plain text white > rooks, as opposed to providing one dimensioned for assembling chess boards. > > If a font doesn’t support a glyph or a sequence, then operating systems > substitute other glyphs or the .notdef glyph or whatever, no? > > Semantically, using variation selectors for this usage seems a bit strange for me: you are adding a semantic for the "on a <color> cell" which also affects the metrics and placement of the piece (to center it within the checkboard cell). What is represented is then BOTH a chess piece (such as 2654), AND a checkboard cell (in your example you took 25A1 WHITE SQUARE but if its metrics is appropriate for use in plain text, its margins are inappropriate for use in a checkboard where cells should be touching without any margin).
There's still no reliable way to represent the empty cells except by adding a variation selector on the 25A1 WHITE SQUARE to transform it into a true cell. Then how to add the chess piece in it ? in Unicode we traditionally use joinder controls to suggest a ligature. This would then produce something like: <25A1, VS-1, ZWJ, 2654>, the first part before ZWJ for the cell itself. You are promoting a simpler encoding using pairs by encoding separate variants of the pieces themselves (two variants for the "on white cell" and "on black cell") but this is still not consistant for the empty cells: do you accept 00A0 NBSP to represent the absence of piece so that <00A0 FE00> and <00A0 FE01> will correctly represent the colored cells ?
