Ligature subtables use virtual links to enforce an ordering constraint between the subtables and the coverage table. Unfortunately this has the sideeffect of prevent the subtables from being shared by another Ligature with a different coverage table since object equality compares all links real and virtual. This change makes virtual links stored separately from real links and updates the equality check to only check real links. If an object is de-duped any virtual links it has are merged into the object that replaces it.
The current CMAP4 implementation uses whatever the current codepoint ranges are and then encodes them as indivudal glyph ids or as a delta if possible. However, it's often possible to save bytes by splitting up existing ranges and encoding parts of them using deltas where the cost of splitting the range is less than encoding each glyph individual.
We implicitly require it for building ragel subproject. This new version
requirement should satisfied in both Fedora 33 and Debian bullseye, and
not be too cutting edge for us.
./subprojects/harfbuzz/src/hb-array.hh:71:25: warning: 'constexpr' non-static member function will not be implicitly 'const' in C++14; add 'const' to avoid a change in behavior [-Wconstexpr-not-const]
constexpr hb_array_t& operator = (const hb_array_t<U> &o)
^
const
../subprojects/harfbuzz/src/hb-array.hh:72:5: warning: use of this statement in a constexpr function is a C++14 extension [-Wc++14-extensions]
{ arrayZ = o.arrayZ; length = o.length; backwards_length = o.backwards_length; return *this; }
^
../subprojects/harfbuzz/src/hb-array.hh:329:32: warning: 'constexpr' non-static member function will not be implicitly 'const' in C++14; add 'const' to avoid a change in behavior [-Wconstexpr-not-const]
constexpr hb_sorted_array_t& operator = (const hb_array_t<U> &o)
^
const
../subprojects/harfbuzz/src/hb-array.hh:330:5: warning: use of this statement in a constexpr function is a C++14 extension [-Wc++14-extensions]
{ hb_array_t<Type> (*this) = o; return *this; }
^
4 warnings generated.
../src/hb-map.hh:44:38: note: non-constexpr constructor 'hb_array_t' cannot be used in a constant expression
static constexpr K INVALID_KEY = kINVALID;
^
Not all impls implement nullptr_t in a way that would automatically
convert to what we were accepting.
In file included from ../src/test-map.cc:27:
../src/hb-map.hh:44:22: error: no viable conversion from 'nullptr_t' to 'const hb_array_t<const char>'
static constexpr K INVALID_KEY = kINVALID;
^ ~~~~~~~~
This line had me confused for a second because
the condition looked like a cast and the if just
looked misplaced. Add a line break to prevent
such confusion.
Though the spec said FeatureRecords are sorted alphabetically by feature
tag, there're font files with unsorted FeatureList. And harfbuzz is not
able to subset these files correctly because we use binary search in
finding featureRecords when collecting lookups. Also
find_duplicate_features needs to be updated to handle this.
In Windows 7 on Chrome if the coverage table comes before any of the LigatureSet or Ligature subtables the font won't load. This changes the packing order to always place the Coverage table last. Virtual links are used to ensure the repacker maintains the desired ordering.
Coincidentally fontTools also does the same thing (a3f988fbf6/Lib/fontTools/ttLib/tables/otTables.py (L1137)) to reduce overflows during packing.
Khaled Hosny
Garret Rieger
Behdad Esfahbod
Qunxin Liu
Matthias Clasen