Let HarfBuzz inject its function pointers into FreeType

CMakeLists.txt

@@ -205,6 +205,9 @@ option(FT_DISABLE_HARFBUZZ
 cmake_dependent_option(FT_DYNAMIC_HARFBUZZ
   "Load HarfBuzz library dynamically at runtime, if possible." ON
   "NOT FT_DISABLE_HARFBUZZ" OFF)
+cmake_dependent_option(FT_USE_HARFBUZZ_CALLBACKS
+  "Let HarfBuzz library inject callback methods at runtime." OFF
+  "NOT FT_DISABLE_HARFBUZZ;NOT FT_DYNAMIC_HARFBUZZ" OFF)
 cmake_dependent_option(FT_REQUIRE_HARFBUZZ
   "Require HarfBuzz for improving auto-hinting of OpenType fonts." OFF
   "NOT FT_DISABLE_HARFBUZZ" OFF)
@@ -272,10 +275,14 @@ if (NOT FT_DISABLE_HARFBUZZ)
         endif()
       endif()
     endif()
+  elseif(FT_USE_HARFBUZZ_CALLBACKS)
+    set(FT_HARFBUZZ_CALLBACKS_ENABLED TRUE)
   endif()
 
   if (FT_DYNAMIC_HARFBUZZ_ENABLED)
     message(STATUS "Enabled dynamic loading of HarfBuzz library at runtime.")
+  elseif (FT_HARFBUZZ_CALLBACKS_ENABLED)
+    message(STATUS "Enable HarfBuzz to inject callbacks into FreeType.")
   elseif (FT_REQUIRE_HARFBUZZ)
     find_package(HarfBuzz ${HARFBUZZ_MIN_VERSION} REQUIRED)
   else ()
@@ -373,7 +380,7 @@ if (PNG_FOUND)
     "/\\* +(#define +FT_CONFIG_OPTION_USE_PNG) +\\*/" "\\1"
     FTOPTION_H "${FTOPTION_H}")
 endif ()
-if (HARFBUZZ_FOUND OR FT_DYNAMIC_HARFBUZZ_ENABLED)
+if (HARFBUZZ_FOUND OR FT_DYNAMIC_HARFBUZZ_ENABLED OR FT_HARFBUZZ_CALLBACKS_ENABLED)
   string(REGEX REPLACE
     "/\\* +(#define +FT_CONFIG_OPTION_USE_HARFBUZZ) +\\*/" "\\1"
     FTOPTION_H "${FTOPTION_H}")
@@ -381,6 +388,10 @@ if (HARFBUZZ_FOUND OR FT_DYNAMIC_HARFBUZZ_ENABLED)
     string(REGEX REPLACE
       "/\\* +(#define +FT_CONFIG_OPTION_USE_HARFBUZZ_DYNAMIC) +\\*/" "\\1"
       FTOPTION_H "${FTOPTION_H}")
+  elseif (FT_HARFBUZZ_CALLBACKS_ENABLED)
+    string(REGEX REPLACE
+      "/\\* +(#define +FT_CONFIG_OPTION_USE_HARFBUZZ_CALLBACKS) +\\*/" "\\1"
+      FTOPTION_H "${FTOPTION_H}")
   endif ()
 endif ()
 if (BROTLIDEC_FOUND)
@@ -572,7 +583,7 @@ if (FT_DYNAMIC_HARFBUZZ_ENABLED AND FT_NEED_LIBDL)
   target_link_libraries(freetype PRIVATE dl)
   list(APPEND PKGCONFIG_LIBS_PRIVATE " -ldl")
 endif ()
-if (HarfBuzz_FOUND AND (NOT FT_DYNAMIC_HARFBUZZ_ENABLED))
+if (HarfBuzz_FOUND AND (NOT FT_DYNAMIC_HARFBUZZ_ENABLED) AND (NOT FT_HARFBUZZ_CALLBACKS_ENABLED))
   target_link_libraries(freetype PRIVATE HarfBuzz::HarfBuzz)
   list(APPEND PKGCONFIG_REQUIRES_PRIVATE "harfbuzz >= ${HARFBUZZ_MIN_VERSION}")
 endif ()

builds/unix/configure.raw

@@ -441,7 +441,7 @@ fi
 # check for system libharfbuzz
 
 AC_ARG_WITH([harfbuzz],
-  [AS_HELP_STRING([--with-harfbuzz=@<:@yes|dynamic|no|auto@:>@],
+  [AS_HELP_STRING([--with-harfbuzz=@<:@yes|dynamic|no|callbacks|auto@:>@],
                   [improve auto-hinting of OpenType fonts @<:@default=auto@:>@])],
   [], [with_harfbuzz=auto])
 
@@ -505,6 +505,14 @@ if test x"$have_harfbuzz" = xno; then
       ;;
     esac
   fi
+
+
+have_harfbuzz_callbacks=no
+if test x"$have_harfbuzz" = xno; then
+  if test x"$with_harfbuzz" = xcallbacks; then
+    have_harfbuzz_callbacks=yes
+    have_harfbuzz="yes (callbacks)"
+  fi
 fi
 
 if test x"$have_harfbuzz" = xno; then
@@ -1165,6 +1173,11 @@ if test "$have_harfbuzz_dynamic" != no; then
 else
   ftoption_unset FT_CONFIG_OPTION_USE_HARFBUZZ_DYNAMIC
 fi
+if test "$have_harfbuzz_callbacks" != no; then
+  ftoption_set FT_CONFIG_OPTION_USE_HARFBUZZ_CALLBACKS
+else
+  ftoption_unset FT_CONFIG_OPTION_USE_HARFBUZZ_CALLBACKS
+fi
 if test "$have_brotli" != no; then
   CFLAGS="$CFLAGS $BROTLI_CFLAGS"
   LDFLAGS="$LDFLAGS $BROTLI_LIBS"

include/freetype/config/ftoption.h

@@ -317,6 +317,26 @@ FT_BEGIN_HEADER
    */
 /* #define FT_CONFIG_OPTION_USE_HARFBUZZ_DYNAMIC */
 
+  /**************************************************************************
+   *
+   * HarfBuzz callbacks support.
+   *
+   *   Define this macro if you want the HarfBuzz library to inject callback
+   *   functions to FreeType
+   *
+   *   This option has no effect if `FT_CONFIG_OPTION_USE_HARFBUZZ` is not
+   *   defined.
+   *
+   *   When this option is enabled, FreeType will not load or link to the 
+   *   HarfBuzz library. Instead, the HarfBuzz library is expected to set
+   *   use property 'harfbuzz-callbacks' to pass callback functions into 
+   *   FreeType.
+   *
+   *   If you use a build system like cmake or the `configure` script,
+   *   options set by those programs have precedence, overwriting the value
+   *   here with the configured one.
+   */
+/* #define FT_CONFIG_OPTION_USE_HARFBUZZ_CALLBACKS */
 
   /**************************************************************************
    *

meson.build

@@ -388,6 +388,13 @@ if not harfbuzz_dep.found() and \
   endif
 endif
 
+if harfbuzz_opt == 'callbacks'
+  ftoption_command += [
+      '--enable=FT_CONFIG_OPTION_USE_HARFBUZZ',
+      '--enable=FT_CONFIG_OPTION_USE_HARFBUZZ_CALLBACKS',
+    ]
+endif
+
 if harfbuzz_opt == 'disabled' or harfbuzz_opt == 'auto'
   harfbuzz_opt = 'NO'
 endif

meson_options.txt

@@ -24,7 +24,7 @@ option('bzip2',
 
 option('harfbuzz',
   type: 'combo',
-  choices: ['auto', 'enabled', 'dynamic', 'disabled'],
+  choices: ['auto', 'enabled', 'dynamic', 'disabled', 'callbacks'],
   value: 'auto',
   description: 'Use Harfbuzz library to improve auto-hinting;'
                + ' if available, many glyphs not directly addressable'

src/autofit/afmodule.c

@@ -275,7 +275,16 @@
 
       return error;
     }
-
+#if defined( FT_CONFIG_OPTION_USE_HARFBUZZ )           && \
+    defined( FT_CONFIG_OPTION_USE_HARFBUZZ_CALLBACKS )
+#if defined ( FT_CONFIG_OPTION_USE_HARFBUZZ_DYNAMIC )
+#error "Can not set both dynamic harfbuzz and injected harfbuzz callbacks"
+#endif
+    else if ( !ft_strcmp( property_name, "harfbuzz-callbacks" ) )
+    {
+      module->hb_funcs = (ft_hb_funcs_t*)value;
+    }
+#endif
     FT_TRACE2(( "af_property_set: missing property `%s'\n",
                 property_name ));
     return FT_THROW( Missing_Property );
@@ -362,7 +371,17 @@
 
       return error;
     }
-
+#if defined( FT_CONFIG_OPTION_USE_HARFBUZZ )           && \
+    defined( FT_CONFIG_OPTION_USE_HARFBUZZ_CALLBACKS )
+#if defined ( FT_CONFIG_OPTION_USE_HARFBUZZ_DYNAMIC )
+#error "Can not set both dynamic harfbuzz and injected harfbuzz callbacks"
+#endif
+    else if ( !ft_strcmp( property_name, "harfbuzz-callbacks" ) )
+    {
+      ft_hb_funcs_t **val               = (ft_hb_funcs_t **)value;
+      *val = module->hb_funcs;
+    }
+#endif
     FT_TRACE2(( "af_property_get: missing property `%s'\n",
                 property_name ));
     return FT_THROW( Missing_Property );

src/autofit/afmodule.h

@@ -41,8 +41,9 @@ FT_BEGIN_HEADER
     FT_Bool       no_stem_darkening;
     FT_Int        darken_params[8];
 
-#if defined( FT_CONFIG_OPTION_USE_HARFBUZZ )         && \
-    defined( FT_CONFIG_OPTION_USE_HARFBUZZ_DYNAMIC )
+#if defined( FT_CONFIG_OPTION_USE_HARFBUZZ )               && \
+    ( defined( FT_CONFIG_OPTION_USE_HARFBUZZ_DYNAMIC )     || \
+      defined( FT_CONFIG_OPTION_USE_HARFBUZZ_CALLBACKS ) )
     ft_hb_funcs_t*  hb_funcs;
 #endif
 

src/autofit/ft-hb.c

@@ -179,6 +179,14 @@
 
 #else /* !FT_CONFIG_OPTION_USE_HARFBUZZ_DYNAMIC */
 
+#if defined( FT_CONFIG_OPTION_USE_HARFBUZZ )         && \
+    defined( FT_CONFIG_OPTION_USE_HARFBUZZ_CALLBACKS )
+  FT_LOCAL_DEF( FT_Bool )
+  ft_hb_enabled( struct AF_FaceGlobalsRec_  *globals )
+  {
+    return globals->module->hb_funcs != NULL;
+  }
+#else /* !FT_CONFIG_OPTION_USE_HARFBUZZ_CALLBACKS*/
   FT_LOCAL_DEF( FT_Bool )
   ft_hb_enabled( struct AF_FaceGlobalsRec_  *globals )
   {
@@ -191,6 +199,8 @@
 #endif
   }
 
+#endif /* !FT_CONFIG_OPTION_USE_HARFBUZZ_CALLBACKS */
+
 #endif /* !FT_CONFIG_OPTION_USE_HARFBUZZ_DYNAMIC */
 
 

src/autofit/ft-hb.h

@@ -29,7 +29,8 @@ FT_BEGIN_HEADER
 
 #  include "ft-hb-types.h"
 
-#  ifdef FT_CONFIG_OPTION_USE_HARFBUZZ_DYNAMIC
+#  if defined( FT_CONFIG_OPTION_USE_HARFBUZZ_DYNAMIC )   || \
+      defined( FT_CONFIG_OPTION_USE_HARFBUZZ_CALLBACKS )
 
 #    define HB_EXTERN( ret, name, args ) \
               typedef ret (*ft_ ## name ## _func_t) args;
@@ -44,6 +45,8 @@ FT_BEGIN_HEADER
 #    undef HB_EXTERN
   } ft_hb_funcs_t;
 
+#  ifdef FT_CONFIG_OPTION_USE_HARFBUZZ_DYNAMIC
+
   struct  AF_ModuleRec_;
 
   FT_LOCAL( void )
@@ -52,9 +55,11 @@ FT_BEGIN_HEADER
   FT_LOCAL( void )
   ft_hb_funcs_done( struct AF_ModuleRec_  *af_module );
 
+#  endif /* !FT_CONFIG_OPTION_USE_HARFBUZZ_DYNAMIC */
+
 #    define hb( x )  globals->module->hb_funcs->hb_ ## x
 
-#  else /* !FT_CONFIG_OPTION_USE_HARFBUZZ_DYNAMIC */
+#  else /* !FT_CONFIG_OPTION_USE_HARFBUZZ_DYNAMIC && !FT_CONFIG_OPTION_USE_HARFBUZZ_CALLBACKS*/
 
 #    define HB_EXTERN( ret, name, args ) \
               ret name args;