Hi,
I was playing with the variable font support of ConTeXt's font loader
and noticed some issues.
1. While parsing the LocalSubRS and GlobalSubRS Indices, ConTeXt tries
to use 16bit count fields as in CFF(1) instead of 32bit fields as in
CFF2, reducing the number of found subroutines by a factor of 65536.
Effectivly this suppressed all subroutines in the fonts I tested.
2. For fonts where the Top DICT does not contain an FDSelect entry,
ConTeXt tries to read the Private dictionary offset from the Top
dictionary as in name-keyed CFF1 fonts. This is not the expected
behavior for CFF2, where the Top dictionary never contains the Privte
offset.
Instead, a missing FDSelect means that exactly one entry exists in
FDArray which should be used for all CIDs. This caused problems
when ConTeXt tried to find the Private directory in order to find
local subroutines.
A test font demonstrating both issues is "SourceCode Variable"
https://github.com/adobe-fonts/source-code-pro/releases:
The document
\definefontfeature
[light]
[default]
[axis={weight=200}]
\definefont
[sourcelight]
[file:SourceCodeVariable-Roman.otf*light]
\starttext
\sourcelight Hallo
\stoptext
generates
[...]
otf reader > cff > unknown local call 14, case 2 : [] n=0
otf reader > cff > unknown local call 11, case 2 : [] n=0
otf reader > cff > unknown local call 138, case 2 : [] n=0
otf reader > cff > unknown local call 314, case 2 : [300 -12] n=2
otf reader > cff > unknown local call 607, case 2 : [-99 -66 99 174]
n=4
otf reader > fatal error in file 'SourceCodeVariable-Roman.otf':
...e0dde776fb1556f32e/formats/luametatex/font-cff-macro.lua:1517: attempt to
perform arithmetic on a nil value (local 'v')
stack traceback:
...e0dde776fb1556f32e/formats/luametatex/font-otr-macro.lua:2339: in
metamethod 'add'
...e0dde776fb1556f32e/formats/luametatex/font-cff-macro.lua:1517: in
local 'a'
...e0dde776fb1556f32e/formats/luametatex/font-cff-macro.lua:1980: in
upvalue 'process'
[...]
A possible fix for both issues would be
diff --git a/tex/context/base/mkiv/font-cff.lua
b/tex/context/base/mkiv/font-cff.lua
index c2cf0e699..d00637b8e 100644
--- a/tex/context/base/mkiv/font-cff.lua
+++ b/tex/context/base/mkiv/font-cff.lua
@@ -2265,8 +2265,8 @@ do
end
-local function readglobals(f,data)
-local routines = readlengths(f)
+local function readglobals(f,data,version)
+local routines = readlengths(f,version == "cff2")
for i=1,#routines do
routines[i] = readbytetable(f,routines[i])
end
@@ -2324,14 +2324,14 @@ local function readprivates(f,data)
end
end
-local function readlocals(f,data,dictionary)
+local function readlocals(f,data,dictionary,version)
local header = data.header
local private = dictionary.private
if private then
local subroutineoffset = private.data.subroutines
if subroutineoffset ~= 0 then
setposition(f,header.offset+private.offset+subroutineoffset)
-local subroutines = readlengths(f)
+local subroutines = readlengths(f,version=="cff2")
for i=1,#subroutines do
subroutines[i] = readbytetable(f,subroutines[i])
end
@@ -2394,7 +2394,7 @@ readers.parsecharstrings = parsecharstrings -- used in
font-onr.lua (type 1)
local function readnoselect(f,fontdata,data,glyphs,doshapes,version,streams)
local dictionaries = data.dictionaries
local dictionary = dictionaries[1]
-readglobals(f,data)
+readglobals(f,data,version)
readcharstrings(f,data,version)
if version == "cff2" then
dictionary.charset = nil
@@ -2402,9 +2402,19 @@ local function
readnoselect(f,fontdata,data,glyphs,doshapes,version,streams)
readencodings(f,data)
readcharsets(f,data,dictionary)
end
+local cid = dictionary.cid
+local fdarray = cid and cid.fdarray
+if fdarray and not dictionary.private then
+setposition(f,data.header.offset+fdarray)
+local dictionaries = readlengths(f,version=="cff2")
+assert(#dictionaries == 1)
+dictionaries[1] = readstring(f,dictionaries[1])
+parsedictionaries(data,dictionaries)
+dictionary.private = dictionaries[1].private
+end
readprivates(f,data)
parseprivates(data,data.dictionaries)
-readlocals(f,data,dictionary)
+readlocals(f,data,dictionary,version)
startparsing(fontdata,data,streams)
parsecharstrings(fontdata,data,glyphs,doshapes,version,streams)
stopparsing(fontdata,data)
@@ -2416,7 +2426,7 @@ local function
readfdselect(f,fontdata,data,glyphs,doshapes,version,streams)
local dictionary = dictionaries[1]
local cid = dictionary.cid
local cidselect= cid and cid.fdselect
-readglobals(f,data)
+readglobals(f,data,version)
readcharstrings(f,data,version)
