On Thu, 23 Jul 2015 12:00:06 +0200 Frédéric Grosshans <[email protected]> wrote:
> Le 23/07/2015 00:54, Richard Wordingham a écrit : > > Which means that Ancient Egyptian hieroglyphs are unencoded! Their > > default direction is right-to-left, but that's only the start of the > > trouble. The encoded hieroglyphs aren't Bidi-mirrored, so if I > > embed then in a right-to-left override, I should get retrograde > > characters. > The text of the standard say that they should be mirrored in this > case. The version 7.0.0. has the following comment on Egyptian > hieroglyphs : (p424, p9 of pdf) : > > “When left-to-right directionality is overridden to display > Egyptian hieroglyphic text right to left, the glyphs should be > mirrored from those shown in the code charts.” The UCD may trump the core specification; I'm expecting to be advised not to trust anything in the core specification. > Similar comments are present for other historic script (Italic, > Runic), but also Old North Arabian, which is encoded as RTL but > “Glyphs may be mirrored in lines whenthey have left-to-right > directionality”. This kind of implementation at the font level is > perfectly possible and is indeed done sometimes (see e.g. Andrew > West’s anglo-saxon runic fonts > http://babelstone.co.uk/Fonts/AngloSaxon.html). > The BidiMirrored property is not adapted in this case because, it is > for a few “characters such as parentheses” (Unicode8.0.0, §4.7 > p180=pf 23 of ch04.pdf), and it is thought for a LTR default : it can > in no way consider the case of Old North Arabian. There had been hope until today. > Extending this property for whole scripts would be a lot of work, and > should be more than a Y/N property as currently, since it should > account for cases where the glyph are > > 1. always mirrored (Egyptian, Italic, Runic. Greek ?), > 2. sometimes mirrored (I have examples of both cases in Latin. North > Arabian seems to be in this case too), > 3. never mirrored (Han), > 4. not exactly mirrored ( like for U+2232 CLOCKWISE CONTOUR INTEGRAL > and U+221B CUBE ROOT ) > 5. And also when the behaviour under direction change is undefined (I > have difficulties to guess what it means to have LTR Arabic or > Syriac, or RTL Devanagari. Maybe there are some traditions for > some complex scripts, but it makes no sense to invent a uniform > behaviour for them) > Currently a BidiMirrorred=N can mean anything of the above, and > BidiMirrored=Y means (1. or 4.). To be precise, having reread the Bidi algorithm, in particular L4 and HL6: 1) If resolved directionality is R and Bidi_Mirrored=Yes, mirroring is mandatory. 2) If resolved directionality is L and bidirectional type is not R or AL, mirroring is prohibited. 3) Otherwise, mirroring is optional. It's odd that a font that reverses all the Hebrew letters is compliant with the Unicode standard. So, I was wrong. Not marking hieroglyphs as Bidi_Mirrored didn't stop them being used for Ancient Egyptian in marked up text. > By the way, I think a comment should be added in the §4.7 of the > standard to clarify that the BidiMirrored property is not intended > for cases like hieroglyphs or italic. That is a stupid and dangerous remark. If the hieroglyphs had had the BidiMirrored property corrected to Yes, one could have had, in plain text, once fonts had caught up: <U+132B9 EGYPTIAN HIEROGLYPH R008> for nṯr in normal left-to-right text <U+202B RIGHT-TO-LEFT EMBEDDING, U+132B9, U+202C POP DIRECTIONAL FORMATTING> for nṯr in retrograde left-to-right text and embed whole paragraphs in <U+202B>...<U+202C> for right-to-left text. Once your remark has been adopted in the Unicode Standard, the only way to get consistently oriented Ancient Egyptian in plain text is to: a) Add a complete set of right-to-left hieroglyphs. b) Add the retrograde hieroglyphs to each set. One hopes that Egyptian Hieroglyphs is the only script for which mirroring or not has meaning. Richard.
