I no longer see where this is going. If there's still some goal, something you think we should agree or discuss, perhaps you could spell that out. Otherwise, I think it' time to quit.
Some random comments: > Date: Mon, 27 Jul 2015 15:32:01 +0100 > From: Richard Wordingham <richard.wording...@ntlworld.com> > Cc: unicode@unicode.org > > > U+2140 DOUBLE-STRUCK N-ARY SUMMATION gets mirrored, but its glyph is > > > not replaced by any other character's glyph. Or are you claiming > > > that left-to-right U+2140 and right-to-left U+2140 are two different > > > characters? > > > > I'm saying that "providing a mirrored glyph" entails coming up with a > > character whose glyph can play that role, AFAIU. > > I'll take that as 'No' - the left-to-right and right-to-left forms are > the same character. (Unicode has no consistency in this matter.) I don't know what is meant by "left-to-right and right-to-left forms" here. To me, a character has only one form. > > If you are saying that the "rendering system" here is the shaping > > engine using the rtlm OTF feature, then you are in fact saying that > > the mirroring of these characters cannot be implemented with most > > fonts in wide use today, and with most shaping engines. That would be > > a very strange claim, IMO, tantamount to saying that those characters > > cannot, or don't need to, be mirrored at all in most use cases. > > OpenType can handle it - feature rtlm effectively provides a > supplementary an RTL cmap, and ltrm an LTR cmap. It's conceivable that > DirectWrite and Uniscribe don't support it, but that's unlikely. Most popular fonts don't, so this support is basically useless, if it turns out to be a must. > The decision to mirror is entirely up to the font. Not at all. A display engine can make those decisions on its own, even if it consults the fonts while making those decisions. > If you still don't believe me, please explain why U+222B INTEGRAL has > Bidi_Mirrored=Yes but Bidi_Mirroring_Glyph=<none>. The explanation is in the file: there's no glyph for that. > > > Because you still seem not to understand the concept of mirroring. > > > > I think you will fare much better, and actually stand a chance of > > convincing you are right, if you assume your opponents do understand > > the issues, and just happen to disagree about their interpretation, or > > misinterpret what you write. > > You won't understand my reasoning unless you accept that Bidi mirroring > can change a glyph's shape rather than substitute the glyph of another > character. Try to convince me in that. > L4 calls for mandatory 'mirroring'. Note that mirroring is not exact > mirroring. My interpretation works for both Arabic and Hebrew. The > UBA Rule L4 calls for some mathematical symbols to take the form > appropriate for a right-to-left context. (HL6 allows this set > to be extended.) However, from what you say this form depends on the > language. For example, the basic integral sign flips for Arabic maths, > but from what you say, I think not for Hebrew maths. Hebrew always typesets math left to right, so no mirroring of math symbols, including U+222B INTEGRAL, is ever necessary. > OpenType can make the mirrored shaped dependent on the language of > the text. The language of the text is not always well defined, alas. > > L4. A character is depicted by a mirrored glyph if and only if (a) > > the resolved directionality of that character is R, and (b) the > > Bidi_Mirrored property value of that character is Yes. > > > > That's normative and unequivocal. > > And therefore applies to U+222B INTEGRAL. Yes, but since there's no glyph, it's a non-issue. > UBA Section 7 "Mirroring" says: > > "Implementing rule L4 calls for mirrored glyphs. These glyphs may not be > exact graphical mirror images. For example, clearly an italic > parenthesis is not an exact mirror image of another— “(” is not the > mirror image of “)”. Instead, mirror glyphs are those acceptable as > mirrors within the normal parameters of the font in which they are > represented." > > This opens up the possibility of the degree of mirroring depending on > the language being supported. My reading of that is that there's some freedom in choosing the shape of the mirrored glyph, but the degree of mirroring is non-negotiable. > > But that just delineates > > the difference between boustrophedon and bidirectional text, the > > latter being subject to the UBA, while the former isn't. > > I didn't say boustrophedon text was subject to the UBA. I said a > boustrophedon renderer may modify the text to be rendered so that the > UBA will layout the text properly. Given the directional overrides, this is a trivium, I think. > > > If there is no higher-level protocol in effect, the 'first strong > > > character' rule (Rules P2 and P3 of the UBA) declares that the > > > paragraph will be a left-to-right paragraph and will look > > > like "(a". Had it been declared a right-to-left paragraph by a > > > higher-level protocol, it would look like "a)". Thus the UBA has a > > > rôle even for unidirectional left-to-right text. > > > Once the paragraph direction is overridden by a higher-level protocol, > > the text is no longer unidirectional. Such overriding is equivalent > > to enclosing the paragraph in RLE..PDF pair, which makes the text > > bidirectional by definition. > > And if it isn't overridden, it is the UBA which makes it > unidirectional. No, it doesn't. > The UBA specifies the appearance of an opening parenthesis. That's bidirectional, not unidirectional.
