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Add feature detection to automatically use new subsetting api. (flutter/engine#28026)

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In the upcoming version of harfbuzz (3.0.0) the subsetting api is being declared stable. With this there are some changes to the API. This prepares flutter to start automatically using the new API once harfbuzz 3.0.0 is rolled into flutter.
This commit is contained in:
Garret Rieger 2021-08-26 14:34:39 -06:00 committed by GitHub
parent 8e7f83d912
commit 0aa51f6464
1 changed files with 34 additions and 2 deletions
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36
engine/src/flutter/tools/font-subset/main.cc
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@ -49,6 +49,37 @@ void Usage() {
<< std::endl;
}
template <typename...>
using void_t = void;
template <typename T, typename = void>
struct HarfBuzzSubset {
// This is the HarfBuzz 3.0 interface.
static HarfbuzzWrappers::HbFacePtr Make(hb_face_t* face, T input) {
// The prior version of harfbuzz automatically dropped layout tables,
// but in the new version they are kept by default. So re-add them to the
// drop list to retain the same behaviour.
hb_set_add(hb_subset_input_drop_tables_set(input),
HB_TAG('G', 'S', 'U', 'B'));
hb_set_add(hb_subset_input_drop_tables_set(input),
HB_TAG('G', 'P', 'O', 'S'));
hb_set_add(hb_subset_input_drop_tables_set(input),
HB_TAG('G', 'D', 'E', 'F'));
return HarfbuzzWrappers::HbFacePtr(hb_subset_or_fail(face, input));
}
};
template <typename T>
struct HarfBuzzSubset<T,
void_t<decltype(hb_subset(std::declval<hb_face_t*>(),
std::declval<T>()))>> {
// This is the HarfBuzz 2.0 (non-public) interface, used if it exists.
// This code should be removed as soon as all users are migrated to the newer
// API.
static HarfbuzzWrappers::HbFacePtr Make(hb_face_t* face, T input) {
return HarfbuzzWrappers::HbFacePtr(hb_subset(face, input));
}
};
int main(int argc, char** argv) {
if (argc != 3) {
Usage();
@ -104,9 +135,10 @@ int main(int argc, char** argv) {
}
}
HarfbuzzWrappers::HbFacePtr new_face(hb_subset(font_face.get(), input.get()));
HarfbuzzWrappers::HbFacePtr new_face =
HarfBuzzSubset<hb_subset_input_t*>::Make(font_face.get(), input.get());
if (new_face.get() == hb_face_get_empty()) {
if (!new_face || new_face.get() == hb_face_get_empty()) {
std::cerr
<< "Failed to subset font; aborting. This error normally indicates "
"the current version of Harfbuzz is unable to process it."