[Fontinst] Latin Modern fonts: small caps and accents

[Lars Hellström]

cfrees at imapmail.org skrev:
> On Mon 24th May, 2010 at 17:41, Lars Hellström seems to have written:
> 
>> cfrees at imapmail.org skrev:
>>> On Mon 24th May, 2010 at 12:19, Lars Hellström seems to have written:
>>>
>> [snip]
>>>> Any idea about what tool produced the AFMs? I can imagine e.g. 
>>>> Fontforge being "smart" enough to know about TeX fontdimens and 
>>>> trying to compute proper values for them, whereas I think the 
>>>> lmodern fonts were generated using a MetaPost-based tool that may 
>>>> well have a separate TFM-generation capability. In that case, the 
>>>> TFMs may actually be closer to the designers' intentions.
>>>>
>>> MetaType1 is used to generate the fonts, AFMs etc. Here are the
>>> relevant parts of the various files.
>>> --- lmr10.afm ---
>>> StartFontMetrics 2.0
>>> Comment Generated by MetaType1 (a MetaPost-based engine)
>>
>> Curiouser and curiouser. Seems the designers are actively 
>> contradicting themselves, then. This might well be reason for a bug 
>> report. However...  the reason the maxheight and acccapheight are 
>> different between AFM and TFM _could_ be that these in the AFM are 
>> computed for the full glyph compement but in the TFM only for the 
>> subset of glyphs which occur in that encoding. Vietnamese letters with 
>> double accents would probably be higher than all glyphs covered by the 
>> T1 encoding.
>>
> But surely that would not be limited to the small caps fonts? I'd have
> thought in that case I'd see misplaced accents in all cases and not
> just when using small caps.

The misplaced accents are due to differences in xheight (fontdimen 5), 
and for that the AFM comments agree with the TFM (whereas the AFM 
XHeight value that fontinst uses does not). The cases where AFM 
comments and TFM did not agree were acccapheight (fontdimen 10) and 
maxheight (fontdimen 12), but those aren't involved in accent placement 
(unless you use a macro package which queries \fontdimen explicitly).

>> [snip]
>>> If the TFMs supplied with Latin Modern are a better guide than the
>>> AFMs - which surely seems correct given the placement of accents in
>>> typeset documents - what is the best way of (1) determining which
>>> elements of the AFMs to override;
>>
>> That ultimately comes down to trial and error, I'm afraid.
>>
>>> and (2) actually overriding them? I
>>> was experimenting by manually adjusting the value of xheight for the
>>> small caps font using an additional metrics file, but I'm not sure
>>> whether that's a good way to go about things.
>>> --- change-xheight-sc-shapes.mtx ---
>>> \relax
>>> \metrics
>>> \setint{xheight}{431}
>>> \endmetrics
>>> --- lines for fontinst ---
>>> ...
>>>     
>>> \transformfont{lmcsc8ttl10}{\reencodefont{t1-clm}{\fromafm{lmcsc10}}}
>>>     \transformfont{lmr8ttl10}{\reencodefont{t1-clm}{\fromafm{lmr10}}}
>>> ...
>>>         
>>> \installfont{clmr8t10}{lmr8ttl10,newlatin}{t1-clm}{T1}{clm}{m}{n}{<9.5-11>} 
>>>
>>>         
>>> \installfont{clmcsc8t10}{change-xheight-sc-shapes,lmcsc8ttl10,newlatin}{t1-clm}{T1}{clm}{m}{sc}{} 
>>
>>
>> An easier method to set just the one fontdimen is to use \metrics 
>> inline the \installfont, like so:
>>
>> \installfont{clmcsc8t10}{%
>>   \metrics \setint{xheight}{431},lmcsc8ttl10,newlatin%
>> }{t1-clm}{T1}{clm}{m}{sc}{}
>>
>> To take all fontdimens but nothing else from ec-lmcsc10, a classical 
>> trick would be to go
>>
>> \installfont{clmcsc8t10}{%
>>   glyphoff,kernoff,ec-lmcsc10,kernon,glyphon,%
>>   lmcsc8ttl10,newlatin%
>> }{t1-clm}{T1}{clm}{m}{sc}{}
>>
> Ah. That looks very useful - I've never been sure what those commands
> were really for. Although in this case, it may be easier to use a
> separate mtx file as I can use it in all of the relevant fontinst
> lines which might involve marginally less typing!
> 
>> but an alternative can be
>>
>> \installfont{clmcsc8t10}{%
>>   ec-lmcsc10 encoding txtfdmns,lmcsc8ttl10,newlatin%
>> }{t1-clm}{T1}{clm}{m}{sc}{}
>>
>> The idea here is that txtfdmns.etx declares fontdimens but no slots, 
>> so ec-lmcsc10-txtfdmns.mtx will not contain anything which requires 
>> glyph names (which is the case with \setrawglyph and \setkern). All 
>> you get is \setint commands.
> 
> Am I right to think that this would ignore all the fontdimens given in
> lmcsc8ttl10 and use those given in ec-lmcsc10 instead?

Yes.

> That sounds like
> it might be the ideal way to go. What format would I need ec-lmcsc10 in
> for that to work? Will the PL file (from the TFM) work?

Yes. (The encoding modifier excludes AFM and MTX files from 
consideration.)

>>
>>
>>> --- end ---
>>> Given that other dimensions also seem to differ between the AFM and TFM
>>> files supplied with the fonts - and not just in the case of the small
>>> caps shaps - I don't know what's important and what isn't (since I am
>>> long out of my depth here).
>>
>> Actually, most of them seem to match between AFM comment and supplied 
>> TFM. If the differences are only for max/min type fontdimens, then 
>> that could indeed be use to these maxes and mins being computed over 
>> different sets of glyphs.
> 
> Still seems weird it would create a problem for the small caps but not
> the other shapes. I was thinking that some of the other values looked
> to be different but can't remember what I was thinking of now. Except
> for fontdimen 10 which is mysteriously set at zero in the TFMs. (At
> least, it is mysterious to me...)

Indeed it is! That's probably a bug in the TFMs. And the AFM value is 
probably greater than what is correct for this set of glyphs. Your best 
bet might be to let fontinst use its heuristic (\height{Aring}), then:

\installfont{clmcsc8t10}{%
   ec-lmcsc10 encoding txtfdmns,lmcsc8ttl10,%
   \metrics\unsetint{acccapheight},newlatin%
}{t1-clm}{T1}{clm}{m}{sc}{}

Lars Hellström