Re: [NTG-context] Bug with complex contextual opentype feature

18 Jul 2014


      On 7/18/2014 12:03 PM, Georg Duffner wrote:
...
Hello All,
I’ve recently been experimenting with contextual features in EB Garamond
and LuaTeX’s output is puzzling. As a showcase, I tried to implement the
famous TeX logos with opentype. This is realized in a feature "xtex"
with GSUB and GPOS lookup tables for substituting some glyphs and for
positioning them horizontally and vertically:
##### OT feature code for TeX logos
lookup xtex_sub1 {
     sub X e' T e X by e.xtex2;  # e.xtex2 is a reversed copy of E
     sub X e' L a T e X by e.xtex2;
     sub L a' T e X by a.sc;
     sub T e' X by e.xtex1;      # e.xtex1 is a copy of E
     sub L a.sc T e.xtex1 X [two two.lnum two.taboldstyle two.tablining]
e' by e.xtex3;      # e.xtex3 is a copy of epsilon
} xtex_sub1;
lookup xtex_pos1 {
     pos X e.xtex2' <-130 -180 -320 0> T;
     pos X e.xtex2' <-130 -180 -200 0> L;
     pos X [two two.lnum two.taboldstyle two.tablining] e.xtex3' <0 -180
0 0>;
     pos L a.sc' <-330 210 -490 0> T e.xtex1 X;
     pos T e.xtex1' <-180 -180 -280 0> X;
}xtex_pos1;
feature xtex {
     lookup xtex_sub1;
     lookup xtex_pos1;
} xtex;
#####
LuaTeX only processes the sequence "XeTeX" where it substitutes the
first "e" by e.xtex1 instead of e.xtex2. Then it positions it with
respect to "X" but not to "T". All the other parts of the lookups are
ignored as well. The font file can be downloaded from
http://www.georgduffner.at/ebgaramond/fonts/EBGaramond12-Regular.otf.
The expected output can be seen at the bottom of this page:
http://www.georgduffner.at/ebgaramond/design.html with Firefox and
Chrome/Chromium and in the attached screenshot (from SortsmillEditor).
Like the browsers, XeLaTeX’s output is correct. My LuaTeX and ConTeXt
versions are:
This is LuaTeX, Version beta-0.79.1 (TeX Live 2014/dev) (rev 4972)
ConTeXt  ver: 2014.07.17 13:24 MKIV beta  fmt: 2014.7.17  int:
english/english
%%%%% ConTeXt test
\definefontfeature[xtex]   [default][xtex=yes]
\definefontsynonym[ebg]    [file:EBGaramond12-Regular.otf]
\def\sample{XeTeX LuaLaTeX XeLaTeX TeX LaTeX2e}
\definefontfeature
   [experiment]
   [default]
   [xtex=yes]
\usemodule[fnt-20]
\usemodule[art-01]
\setupbodyfont[dejavu]
\starttext
\startTEXpage
     \hbox{{\definedfont[ebg*default    at 12pt]\sample}
{\definedfont[ebg*default at 12pt]\sample}}\par
     \hbox{{\definedfont[ebg*xtex       at 12pt]\sample}
{\definedfont[ebg*default at 12pt]\feature[+][xtex]\sample}}\par
\stopTEXpage
\def\sample{XeTeX LuaLaTeX XeLaTeX TeX LaTeX2e}
\setvariables
   [otftracker]
   [font=file:EBGaramond12-Regular.otf,
    size=24pt,
    features=experiment,
    title=Feature Check,
    sample=\sample]
\stoptext
%%%%%
fixed

(back and fore were swapped - at some point i merged two handlers as 
there is no conceptual difference between before/current/after and 
fore/names/back apart from some efficiency in the otf file)

thanks for noticing,

Hans

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