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On 07/03/08 16:58:16, David J. Peterson wrote:
> Roger:
> <<
> One difficulty with fonts (and the reason I haven't made many) is the 
> 
> problem with ligatures, contextual variations, marks that need glyph 
> 
> positioning tables, etc. I do have an OlaeUni font which follows the 
> 
> CSUR submission (ftp://ftp.io.com/pub/usr/hmiller/fonts/ 
> OLAEUNI_.TTF), although there are a couple of issues with it that  
> would need OpenType features to implement, and OpenType doesn't work 
> 
> with Private Use scripts. Neesklaaz requires complex script  
> processing, even beyond what OpenType tables provide, so my Neesklaaz 
> 
> font only works with SIL Graphite.
>  >>
> 
> Not 100% sure what all that means, but how's this:
> 
> <http://dedalvs.free.fr/writing/ConlangUnicode.ttf>
> 
> I think the characters should show up (they're all in the right
> place).  There are two issues with OlaeUni font:
> 
> (1) There are a lot more characters than I included because you've
> put them in non-private use areas, where other characters from
> other scripts currently sit.  Was that intentional?
> 
> (2) My understand is that these ligature characters don't work
> the way you want them to.  For example, on a Mac, I can "add"
> an acute accent to an "e", but all I'm really doing is typing in a
> code that tells the computer to display the "e-acute" cell.  The
> glyphs you have that display over glyphs already typed should
> work, but I don't *think* Unicode is supposed to be used to,
> say, type an "n", and then type a "g", and then have it automatically
> produce an "ng" ligature.  In order for that ligature to be
> available,
> it must have a codepoint, and currently it doesn't.

Unicode doesn't care a fig about the appearence of glyphs. For 
instance, some high-end fonts contain "fj" or "ffh" ligatures (amongst 
other possible combinations). These characters generally don't occur 
anywhere in the Unicode-addressable part of the font: Not even in the 
Private Use Area.

Instead, the appearence of glyphs is a job for font formats, like Open 
Type. These can contain glyphs that don't actually have any Unicode 
number associated with them. Instead, they will have a property 
associated with them (or with the individual components that make them 
up) that says "if you find the sequence fj, display this glyph over 
here".  

There are two problems here. Firstly, OpenType special features are 
still not available in every program. We're a lot further along than we 
were a couple of years ago, and I think between Macs, Linux, Open 
Office and Microsoft Office 2007, most people will have a program that 
lets you use its special features. (At least, I've *heard* Open Office 
and Microsoft Office 2007 do. But I've never seen it in use.)

The insuperable problem is that unfortunately OpenType, the main modern 
font format, doesn't support all its features everywhere. Automatic 
ligatures apparently don't happen if the unligated characters are in 
the PUA. Another problem is that Latin handwriting fonts can't 
use context-sensitive glyphs the way Arabic fonts do (for instance, my 
cursive p and b are open when a letter follows, but closed when they 
don't --- you can't tell an OpenType font to automatically do that). 

I gather Apple's special font format does support all its features 
everywhere. Unfortunately it only works on Macs, and has different 
features from Open Type.

--
Tristan.