Re: 'kern': TrueType table and GPOS lookup feature

[Hans Hagen <pragma@wxs.nl>]

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On 11/30/2012 10:58 AM, Steve White wrote:

> 2) I understood that ConTeXt only uses the old-style TrueType 'kern'
> table, rather than the OpenType 'kern' GPOS lookup.  If that is the
> case, I would suggest that you consider to change the  logic to first
> use the OpenType lookup, and if it doesn't exist, fall back to the
> TrueType table. Several applications are already complaining that both
> exist; the plan is to drop support for the TrueType table in FreeFont.

I has always supported both but the user does not show the difference.


> 3) In most applications, the script of a run of text is determined from
> the Unicode.  This is the assumption made in FreeFont.  The GNU FreeFont
> policy starts from its essence as a Unicode font, in which no particular
> script is default. (Some generic features that are not specific to any
> script, are in {dflt,dflt}.)
>
> There was a suggestion that Latin kerns should be activated by
> {script,lang}={dflt,dflt}.  Let me ask, should Devanagari kerns also be
> activated by {dflt, dflt}?  If not, why?

because one text can contain multiple scripts

> It appears that there maybe some conflict her with TeX implementaions.
> I don't completely understand this.  Maybe we can find a solution.

If you have context installed and running, you can do this:

\usemodule[fnt-20,art-01]

\starttext

\definefontfeature
   [freeserif-default]
   [default]
   [script=latn]

\setvariables
   [otftracker]
   [font=file:freeserif.ttf,
    size=24pt,
    figure=,
    features=freeserif-default,
    title=Feature Check,
    sample={dadedidodufafefifofufrflftlale}]

\setvariables
   [otftracker]
   [font=file:freeserif.ttf,
    size=24pt,
    figure=,
    features=freeserif-default,
    title=Feature Check,
    sample={lilolutatetitotu}]

\stoptext

This gives insight in the stepwise processing of features (something 
that is handy for relatively complex fonts, for instance those dealign 
with arabic).

> 4) I have written something like Pablo's test using XeTeX and fontspec.
> Kerning works very well with GNU FreeFont.  Find attached.

maybe xetex defaults to latn

> 5) There was also a report that OpenType kerning doesn't work in some
> E-Book readers (I know this isn't the forum for that, but ...) .  My
> iriver Story kerns very nicely text in FreeSerif.  Can I get an example
> of an E-reader for which kerning fails?  (I really don't doubt that they
> exist!)

Natively I suppose? If a pdf file is viewed on an ebook reader it's not 
the ereader's issue.

Hans

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\usemodule[fnt-20,art-01]

\starttext

\definefontfeature
  [freeserif-default]
  [default]
  [script=latn]

\setvariables
  [otftracker]
  [font=file:freeserif.ttf,
   size=24pt,
   figure=,
   features=freeserif-default,
   title=Feature Check,
   sample={dadedidodufafefifofufrflftlale}]

\setvariables
  [otftracker]
  [font=file:freeserif.ttf,
   size=24pt,
   figure=,
   features=freeserif-default,
   title=Feature Check,
   sample={lilolutatetitotu}]

\stoptext

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