Re: [Freefont-bugs] Combining Diacritical Marks (CDMs)

[Primoz PETERLIN]

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Hello,

I apologize for such a late reply - I must have overlooked this mail in the 
flood of email awaiting for me when I returned back from vacation.

V petek 8. avgusta 2003 00:32 Josef W. Segur piše:

> This Unicode range (U+0300 - U+036F) contains non-spacing marks
> meant to be combined with almost any base character to add a
> needed accent or other modification.
> After the base character is drawn, the reference point is moved
> by the width of the character. This implies that the outline of
> a non-spacing mark should have negative horizontal values in
> order to be combined with the base character. The "non-spacing"
> also implies zero advance width for the mark so it does not move
> the reference point.
> TrueType fonts which support most of that range (Arial Unicode MS,
> Caliban, Caslon, Code2000, Lucida Sans Unicode, Thryomanes) code
> the glyphs as above with few exceptions. The Free fonts generally
> don't.

Indeed. I have to admit I don't quite understand the mechanics of composite 
char yet. Is it enough that the combining accents have negative horizontal 
values and zero advance width, or do PfaEdit's "Anchor classes" came into 
play. Do spacing modifier letters (U+02B0 - U+02FF) differ from combining 
diacritical marks (U+0300 - U+036F) by having pozitive horizontal values and 
non-zero advance width?

> It is possible for a text layout engine to ignore those metrics,
> as Microsoft's Uniscribe seems to do for a dozen or so of the CDMs.
> I put together a little test using the first 40 CDMs and showing
> the results with Lucida Sans Unicode and Code2000 on Win95:
> <URL: http://users.westelcom.com/jsegur/cdmtst4.html >
> For comparison, what can be done on my system with Free Serif and
> Uniscribe is in the image:
> <URL: http://users.westelcom.com/jsegur/ubpfserf.png >

I have taken a look. I am assured that the combining letters are an important 
issue and should get fixed soon. I am willing to put my time into it, but I 
am not quite sure if I understand already all the issues connected with it.

With kind regards,
Primoz

- -- 
Primož Peterlin,   Inštitut za biofiziko, Med. fakulteta, Univerza v Ljubljani
Lipičeva 2, SI-1000 Ljubljana, Slovenija.  address@hidden
Tel +386-1-5437632, fax +386-1-4315127,  http://biofiz.mf.uni-lj.si/~peterlin/
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