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Re: [Fontforge-users] Best practice: combining glyphs
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From: Rainer S. <rs...@ba...> - 2014-03-19 15:38:38
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Hi Denis, thank you very much for your kind answer! > No, the combining marks in DejaVu fonts are non-spacing characters. Right, I was looking at mono, and as you explain below, that is a special case. Sorry. > The DejaVu fonts actually don’t have any contextual substitution to > replace a decomposed sequence by a precomposed character, that happens > at the font shaper level (which is a good thing but sometimes not at > all). May I ask for my understanding: this means you can only access the font shaper level-logic within unicode blocks that have well defined rules for combining glyphs? This could never work in PUA? Is there a way to tell a font-shaper via a font how to act? > GPOS anchors should work even on WinXP (with the right version of Uniscribe). Anchors would be lovely for me, but my impression is they are not supported broadly on Windows at all: I tried the following in Windows 8.1 using Wordpad and DejaVu Sans Mono: enter a insert grave U+0300 by copying it from charmap -> they do not combine I do the same thing with DejaVu Sans (non-mono), which uses zero-width left-sided positioning -> They combine! Same thing with more exotical stuff like combining double low line. I have made several experiments with Anchors and other GPOS lookups - and my impression is, that such lookups are only supported by very few applications. Maybe it’s there in uniscribe, but it doesn’t seem to propagate to the odd Application, not even to WordPad, which is MS’ counterpart of Mac's TextEdit. In the free domain, the only program with good support I found so far is BabelPad (even the SIL Editor does not seem to have broad support). I am tempted to ignore the TT-monospace specs and go for left-sided marks. I haven’t noticed in the past, but also haven’t used it a lot. Thanks again and best Rainer On 19 Mar 2014, at 13:52, Denis Jacquerye <mo...@gm...> wrote: > Hi Rainer, > > > On Wed, Mar 19, 2014 at 12:08 PM, Rainer Schuetz <rs...@ba...> wrote: >> Dear All, >> >> I am starting to “assemble” my glyphs and have a basic decision to make: which character width and mark-positioning to use for marks that can both be used as independent character and as combining mark. In DejaVu I observe most, (if not all) combining marks are full-width characters. This is clearly nice when the char is used by itself, and in cases where entering a basechar and the mark in an editor triggers calling a precomposed glyph, which is available as alternative glyph. The precomposed glyph can be created quite easily by linking both base and mark into a new slot. > > No, the combining marks in DejaVu fonts are non-spacing characters. > The precomposed glyphs might be using the spacing marks as components > but that is because that's how Bitstream did it. > If one were to start a font from scratch, I'd strongly recommend using > the non-spacing marks as components. > The DejaVu fonts actually don’t have any contextual substitution to > replace a decomposed sequence by a precomposed character, that happens > at the font shaper level (which is a good thing but sometimes not at > all). > >> But what happens in case no alternative glyph is available? Without any additional measures the mark will display behind the basechar in an editor instead of on top of it (I am talking of chars in the PUA, there is no generic knowledge about how a basechar and an mark should combine). So what is the most broadly, reasonably efficient way to to define that repositioning of the mark (creating an altglyph for each and every possible combination is out of the question for me, I’d end up with many thousands of glyphs)? > > If the precomposed glyphs are non existent, use anchors. They can > position mark-to-base and also mark-to-mark. > You'll have to add a lookup for that. > > Fonts like Source Sans Pro do it in a more efficient way than DejaVu > (something to fix on my todo list). > The anchors are only on single contour glyphs. > The glyphs with components are decomposed into their sequence of > single contour glyphs when followed by a combining diacritic. This > means anchors don't have to be added everywhere, just in the single > contour glyphs. > >> >> - kerning? > > You can do contextual kerning. Good luck! > >> - gpos tables that define a negative offset for all marks in a specific class? I’ve seen something like that in DejaVu, but I don’t fully understand it. > > I think you’re referring to what we do in DejaVu Sans Mono. > We have lookups that remove the advance width and offset the marks. > That is because according to the TrueType specs, in monospace fonts, > all the glyphs must have the same advance width. > >> - or in the end old-style “left-side” negative-positioning of the glyphs? > > Putting the mark outlines in negative offset is a old practice that > made sense back when OpenType GPOS features weren’t well supported. > One would put the mark in the negative to center on the n or o, so it > would still look ok when the application can’t use GPOS anchors. > Obviously this would break if used with narrower or wider base glyphs, > or caps and ascenders. > Since GPOS is well supported these days, there’s no valid reason to > place the marks in negative offset. > >> I like that the same mark could be both fullwidth “standalone” and combining, and positioning marks outside (to the left) of the “charbox” seems untidy, I wouldn’t mind saving some work, but most importantly I’d like to have the font work in as many as possible (even older, say WinXP/Word2000) environments. > > GPOS anchors should work even on WinXP (with the right version of Uniscribe). > >> Thank you for any recommendations and explanations >> >> Best >> Rainer >> ------------------------------------------------------------------------------ >> Learn Graph Databases - Download FREE O'Reilly Book >> "Graph Databases" is the definitive new guide to graph databases and their >> applications. Written by three acclaimed leaders in the field, >> this first edition is now available. Download your free book today! >> http://p.sf.net/sfu/13534_NeoTech >> _______________________________________________ >> Fontforge-users mailing list >> Fon...@li... >> https://lists.sourceforge.net/lists/listinfo/fontforge-users > > > > -- > Denis Moyogo Jacquerye > African Network for Localisation http://www.africanlocalisation.net/ > Nkótá ya Kongó míbalé --- http://info-langues-congo.1sd.org/ > DejaVu fonts --- http://www.dejavu-fonts.org/ > > ------------------------------------------------------------------------------ > Learn Graph Databases - Download FREE O'Reilly Book > "Graph Databases" is the definitive new guide to graph databases and their > applications. Written by three acclaimed leaders in the field, > this first edition is now available. Download your free book today! > http://p.sf.net/sfu/13534_NeoTech > _______________________________________________ > Fontforge-users mailing list > Fon...@li... > https://lists.sourceforge.net/lists/listinfo/fontforge-users |