Add harfbuzzjs build configuration (#1636)

CMakeLists.txt

@@ -85,6 +85,10 @@ if (HB_CHECK)
   endif ()
 endif ()
 
+# https://github.com/harfbuzz/harfbuzzjs/
+# emcmake cmake -Bwasmbuild -H. -GNinja -DHB_HARFBUZZJS=1 && ninja -Cwasmbuild
+option(HB_HARFBUZZJS "Enable our opinionated harfbuzzjs related build optimization" OFF)
+
 include_directories(AFTER
   ${PROJECT_SOURCE_DIR}/src
   ${PROJECT_BINARY_DIR}/src
@@ -295,6 +299,16 @@ if (HB_HAVE_GRAPHITE2)
   mark_as_advanced(GRAPHITE2_INCLUDE_DIR GRAPHITE2_LIBRARY)
 endif ()
 
+if (HB_HARFBUZZJS)
+  # we won't need multithread support in harfbuzzjs
+  add_definitions(-DHB_NO_MT)
+
+  add_definitions(-DHB_NO_OPTIONS -DHB_NO_OT_FONT_CFF -DHB_NO_NAME_TABLE_AAT
+    -DHB_NO_OT_FONT_BITMAP -DHB_NO_OT_SHAPE_COMPLEX_HEBREW_FALLBACK
+    -DHB_NO_OT_SHAPE_FALLBACK -DHB_NO_OT_SHAPE_COMPLEX_THAI_FALLBACK
+    -DHB_NO_OT_LAYOUT_BLACKLIST -DHB_NO_OT_SHAPE_COMPLEX_VOWEL_CONSTRAINTS)
+endif ()
+
 if (HB_BUILTIN_UCDN)
   include_directories(src/hb-ucdn)
   add_definitions(-DHAVE_UCDN)
@@ -538,6 +552,27 @@ endif ()
 add_library(harfbuzz ${project_sources} ${project_extra_sources} ${project_headers})
 target_link_libraries(harfbuzz ${THIRD_PARTY_LIBS})
 
+if (HB_HARFBUZZJS)
+  set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -std=c++11 -s MODULARIZE=1 \
+    -s NO_FILESYSTEM=1 -s ALLOW_MEMORY_GROWTH=1 -s NO_EXIT_RUNTIME=1 -s STRICT=1 \
+    -Oz --closure 1")
+
+  # add_definitions("-DHB_EXTERN=__attribute__((used))")
+  # Alternatively, only the needed calls
+  set (CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -s \"EXPORTED_FUNCTIONS=['_hb_version_string', \
+    '_malloc', '_hb_blob_create', '_hb_face_create', '_hb_font_create', \
+    '_hb_buffer_create', '_hb_buffer_add_utf8', '_hb_buffer_guess_segment_properties', \
+    '_hb_buffer_set_direction', '_hb_shape', '_hb_buffer_serialize_glyphs', \
+    '_hb_buffer_get_length', '_hb_buffer_serialize_glyphs', '_hb_buffer_destroy', \
+    '_hb_font_destroy', '_hb_face_destroy', '_hb_blob_destroy', '_hb_blob_get_length', \
+    '_hb_direction_from_string', '_free']\"")
+
+  # Trick emscripten to create js/wasm from a library
+  add_executable(harfbuzzjs /dev/null)
+
+  target_link_libraries(harfbuzzjs harfbuzz)
+endif ()
+
 ## Define harfbuzz-subset library
 if (HB_BUILD_SUBSET)
   add_library(harfbuzz-subset ${subset_project_sources} ${subset_project_headers})