Enable applying GSUB/GPOS features in multiple segments

Fixes https://bugzilla.mozilla.org/show_bug.cgi?id=644184
among others.

Shapers now can request segmented feature application by calling
add_gsub_pause() or add_gpos_pause().  They can also provide a
callback to be called at the pause.  Currently the Arabic shaper
uses pauses to enforce certain feature application.  The Indic
shaper can use the same facility to pause and do reordering in the
callback.

src/hb-ot-map-private.hh

@@ -44,6 +44,9 @@ struct hb_ot_map_t
 
   public:
 
+  typedef void (*gsub_pause_func_t) (const hb_ot_map_t *map, hb_face_t *face, hb_buffer_t *buffer, void *user_data);
+  typedef void (*gpos_pause_func_t) (const hb_ot_map_t *map, hb_font_t *font, hb_buffer_t *buffer, void *user_data);
+
   inline hb_mask_t get_global_mask (void) const { return global_mask; }
 
   inline hb_mask_t get_mask (hb_tag_t tag, unsigned int *shift = NULL) const {
@@ -57,27 +60,23 @@ struct hb_ot_map_t
     return map ? map->_1_mask : 0;
   }
 
-  inline void substitute (hb_face_t *face, hb_buffer_t *buffer) const {
-    for (unsigned int i = 0; i < lookups[0].len; i++)
-      hb_ot_layout_substitute_lookup (face, buffer, lookups[0][i].index, lookups[0][i].mask);
-  }
-
-  inline void position (hb_font_t *font, hb_buffer_t *buffer) const {
-    for (unsigned int i = 0; i < lookups[1].len; i++)
-      hb_ot_layout_position_lookup (font, buffer, lookups[1][i].index, lookups[1][i].mask);
-  }
+  HB_INTERNAL void substitute (hb_face_t *face, hb_buffer_t *buffer) const;
+  HB_INTERNAL void position (hb_font_t *font, hb_buffer_t *buffer) const;
 
   inline void finish (void) {
     features.finish ();
     lookups[0].finish ();
     lookups[1].finish ();
+    pauses[0].finish ();
+    pauses[1].finish ();
   }
 
   private:
 
   struct feature_map_t {
     hb_tag_t tag; /* should be first for our bsearch to work */
-    unsigned int index[2]; /* GSUB, GPOS */
+    unsigned int index[2]; /* GSUB/GPOS */
+    unsigned int stage[2]; /* GSUB/GPOS */
     unsigned int shift;
     hb_mask_t mask;
     hb_mask_t _1_mask; /* mask for value=1, for quick access */
@@ -94,6 +93,21 @@ struct hb_ot_map_t
     { return a->index < b->index ? -1 : a->index > b->index ? 1 : 0; }
   };
 
+  typedef union {
+    void *p;
+    gsub_pause_func_t gsub;
+    gpos_pause_func_t gpos;
+  } pause_func_t;
+  typedef struct {
+    pause_func_t func;
+    void *user_data;
+  } pause_callback_t;
+
+  struct pause_map_t {
+    unsigned int num_lookups; /* Cumulative */
+    pause_callback_t callback;
+  };
+
   HB_INTERNAL void add_lookups (hb_face_t    *face,
 				unsigned int  table_index,
 				unsigned int  feature_index,
@@ -104,6 +118,7 @@ struct hb_ot_map_t
 
   hb_prealloced_array_t<feature_map_t, 8> features;
   hb_prealloced_array_t<lookup_map_t, 32> lookups[2]; /* GSUB/GPOS */
+  hb_prealloced_array_t<pause_map_t, 1> pauses[2]; /* GSUB/GPOS */
 };
 
 
@@ -116,12 +131,17 @@ struct hb_ot_map_builder_t
   inline void add_bool_feature (hb_tag_t tag, bool global = true)
   { add_feature (tag, 1, global); }
 
+  HB_INTERNAL void add_gsub_pause (hb_ot_map_t::gsub_pause_func_t pause_func, void *user_data);
+  HB_INTERNAL void add_gpos_pause (hb_ot_map_t::gpos_pause_func_t pause_func, void *user_data);
+
   HB_INTERNAL void compile (hb_face_t *face,
 			    const hb_segment_properties_t *props,
 			    struct hb_ot_map_t &m);
 
   inline void finish (void) {
     feature_infos.finish ();
+    pauses[0].finish ();
+    pauses[1].finish ();
   }
 
   private:
@@ -132,12 +152,20 @@ struct hb_ot_map_builder_t
     unsigned int max_value;
     bool global; /* whether the feature applies value to every glyph in the buffer */
     unsigned int default_value; /* for non-global features, what should the unset glyphs take */
+    unsigned int stage[2]; /* GSUB/GPOS */
 
     static int cmp (const feature_info_t *a, const feature_info_t *b)
     { return (a->tag != b->tag) ?  (a->tag < b->tag ? -1 : 1) : (a->seq < b->seq ? -1 : 1); }
   };
 
-  hb_prealloced_array_t<feature_info_t,16> feature_infos; /* used before compile() only */
+  struct pause_info_t {
+    unsigned int stage;
+    hb_ot_map_t::pause_callback_t callback;
+  };
+
+  unsigned int current_stage[2]; /* GSUB/GPOS */
+  hb_prealloced_array_t<feature_info_t,16> feature_infos;
+  hb_prealloced_array_t<pause_info_t, 1> pauses[2]; /* GSUB/GPOS */
 };
 
 

src/hb-ot-map.cc

@@ -73,6 +73,76 @@ void hb_ot_map_builder_t::add_feature (hb_tag_t tag, unsigned int value, bool gl
   info->max_value = value;
   info->global = global;
   info->default_value = global ? value : 0;
+  info->stage[0] = current_stage[0];
+  info->stage[1] = current_stage[1];
+}
+
+
+void hb_ot_map_t::substitute (hb_face_t *face, hb_buffer_t *buffer) const {
+  unsigned int table_index = 0;
+  unsigned int i = 0;
+
+  for (unsigned int pause_index = 0; pause_index < pauses[table_index].len; pause_index++) {
+    const pause_map_t *pause = &pauses[table_index][pause_index];
+    for (; i < pause->num_lookups; i++)
+      hb_ot_layout_substitute_lookup (face, buffer, lookups[table_index][i].index, lookups[table_index][i].mask);
+
+    pause->callback.func.gsub (this, face, buffer, pause->callback.user_data);
+  }
+
+  for (; i < lookups[table_index].len; i++)
+    hb_ot_layout_substitute_lookup (face, buffer, lookups[table_index][i].index, lookups[table_index][i].mask);
+}
+
+void hb_ot_map_t::position (hb_font_t *font, hb_buffer_t *buffer) const {
+  unsigned int table_index = 1;
+  unsigned int i = 0;
+
+  for (unsigned int pause_index = 0; pause_index < pauses[table_index].len; pause_index++) {
+    const pause_map_t *pause = &pauses[table_index][pause_index];
+    for (; i < pause->num_lookups; i++)
+      hb_ot_layout_position_lookup (font, buffer, lookups[table_index][i].index, lookups[table_index][i].mask);
+
+    pause->callback.func.gpos (this, font, buffer, pause->callback.user_data);
+  }
+
+  for (; i < lookups[table_index].len; i++)
+    hb_ot_layout_position_lookup (font, buffer, lookups[table_index][i].index, lookups[table_index][i].mask);
+}
+
+
+/* TODO refactor the following two functions */
+
+void hb_ot_map_builder_t::add_gsub_pause (hb_ot_map_t::gsub_pause_func_t pause_func, void *user_data)
+{
+  unsigned int table_index = 0;
+
+  if (pause_func) {
+    pause_info_t *p = pauses[table_index].push ();
+    if (likely (p)) {
+      p->stage = current_stage[table_index];
+      p->callback.func.gsub = pause_func;
+      p->callback.user_data = user_data;
+    }
+  }
+
+  current_stage[table_index]++;
+}
+
+void hb_ot_map_builder_t::add_gpos_pause (hb_ot_map_t::gpos_pause_func_t pause_func, void *user_data)
+{
+  unsigned int table_index = 1;
+
+  if (pause_func) {
+    pause_info_t *p = pauses[table_index].push ();
+    if (likely (p)) {
+      p->stage = current_stage[table_index];
+      p->callback.func.gpos = pause_func;
+      p->callback.user_data = user_data;
+    }
+  }
+
+  current_stage[table_index]++;
 }
 
 void
@@ -111,13 +181,17 @@ hb_ot_map_builder_t::compile (hb_face_t *face,
       if (feature_infos[i].tag != feature_infos[j].tag)
 	feature_infos[++j] = feature_infos[i];
       else {
-	if (feature_infos[i].global)
-	  feature_infos[j] = feature_infos[i];
-	else {
+	if (feature_infos[i].global) {
+	  feature_infos[j].global = true;
+	  feature_infos[j].max_value = feature_infos[i].max_value;
+	  feature_infos[j].default_value = feature_infos[i].default_value;
+	} else {
 	  feature_infos[j].global = false;
 	  feature_infos[j].max_value = MAX (feature_infos[j].max_value, feature_infos[i].max_value);
-	  /* Inherit default_value from j */
 	}
+	feature_infos[j].stage[0] = MIN (feature_infos[j].stage[0], feature_infos[i].stage[0]);
+	feature_infos[j].stage[1] = MIN (feature_infos[j].stage[1], feature_infos[i].stage[1]);
+	/* Inherit default_value from j */
       }
     feature_infos.shrink (j + 1);
   }
@@ -160,6 +234,8 @@ hb_ot_map_builder_t::compile (hb_face_t *face,
     map->tag = info->tag;
     map->index[0] = feature_index[0];
     map->index[1] = feature_index[1];
+    map->stage[0] = info->stage[0];
+    map->stage[1] = info->stage[1];
     if (info->global && info->max_value == 1) {
       /* Uses the global bit */
       map->shift = 0;
@@ -177,6 +253,9 @@ hb_ot_map_builder_t::compile (hb_face_t *face,
   feature_infos.shrink (0); /* Done with these */
 
 
+  add_gsub_pause (NULL, NULL);
+  add_gpos_pause (NULL, NULL);
+
   for (unsigned int table_index = 0; table_index < 2; table_index++) {
     hb_tag_t table_tag = table_tags[table_index];
 
@@ -190,20 +269,39 @@ hb_ot_map_builder_t::compile (hb_face_t *face,
 							  &required_feature_index))
       m.add_lookups (face, table_index, required_feature_index, 1);
 
-    for (unsigned i = 0; i < m.features.len; i++)
-      m.add_lookups (face, table_index, m.features[i].index[table_index], m.features[i].mask);
-
-    /* Sort lookups and merge duplicates */
-    m.lookups[table_index].sort ();
-    if (m.lookups[table_index].len)
+    unsigned int pause_index = 0;
+    unsigned int last_num_lookups = 0;
+    for (unsigned stage = 0; stage < current_stage[table_index]; stage++)
     {
-      unsigned int j = 0;
-      for (unsigned int i = 1; i < m.lookups[table_index].len; i++)
-	if (m.lookups[table_index][i].index != m.lookups[table_index][j].index)
-	  m.lookups[table_index][++j] = m.lookups[table_index][i];
-	else
-	  m.lookups[table_index][j].mask |= m.lookups[table_index][i].mask;
-      m.lookups[table_index].shrink (j + 1);
+      for (unsigned i = 0; i < m.features.len; i++)
+        if (m.features[i].stage[table_index] == stage)
+	  m.add_lookups (face, table_index, m.features[i].index[table_index], m.features[i].mask);
+
+      /* Sort lookups and merge duplicates */
+      if (last_num_lookups < m.lookups[table_index].len)
+      {
+	m.lookups[table_index].sort (last_num_lookups, m.lookups[table_index].len);
+
+	unsigned int j = last_num_lookups;
+	for (unsigned int i = j + 1; i < m.lookups[table_index].len; i++)
+	  if (m.lookups[table_index][i].index != m.lookups[table_index][j].index)
+	    m.lookups[table_index][++j] = m.lookups[table_index][i];
+	  else
+	    m.lookups[table_index][j].mask |= m.lookups[table_index][i].mask;
+	m.lookups[table_index].shrink (j + 1);
+      }
+
+      last_num_lookups = m.lookups[table_index].len;
+
+      if (pause_index < pauses[table_index].len && pauses[table_index][pause_index].stage == stage) {
+	hb_ot_map_t::pause_map_t *pause_map = m.pauses[table_index].push ();
+	if (likely (pause_map)) {
+	  pause_map->num_lookups = last_num_lookups;
+	  pause_map->callback = pauses[table_index][pause_index].callback;
+	}
+
+	pause_index++;
+      }
     }
   }
 }

src/hb-ot-shape-complex-arabic.cc

@@ -153,12 +153,32 @@ static const struct arabic_state_table_entry {
 void
 _hb_ot_shape_complex_collect_features_arabic (hb_ot_shape_planner_t *planner, const hb_segment_properties_t  *props)
 {
-  /* ArabicOT spec enables 'cswh' for Arabic where as for basic shaper it's disabled by default. */
-  planner->map.add_bool_feature (HB_TAG('c','s','w','h'));
+  /* For Language forms (in ArabicOT speak), we do the iso/fina/medi/init together,
+   * then rlig and calt each in their own stage.  This makes IranNastaliq's ALLAH
+   * ligature work correctly. It's unfortunate though...
+   *
+   * This also makes Arial Bold in Windows7 work.  See:
+   * https://bugzilla.mozilla.org/show_bug.cgi?id=644184
+   *
+   * TODO: Add test cases for these two.
+   */
+
+  planner->map.add_gsub_pause (NULL, NULL);
 
   unsigned int num_features = props->script == HB_SCRIPT_SYRIAC ? SYRIAC_NUM_FEATURES : COMMON_NUM_FEATURES;
   for (unsigned int i = 0; i < num_features; i++)
     planner->map.add_bool_feature (arabic_syriac_features[i], false);
+
+  planner->map.add_gsub_pause (NULL, NULL);
+
+  planner->map.add_bool_feature (HB_TAG('r','l','i','g'));
+  planner->map.add_gsub_pause (NULL, NULL);
+
+  planner->map.add_bool_feature (HB_TAG('c','a','l','t'));
+  planner->map.add_gsub_pause (NULL, NULL);
+
+  /* ArabicOT spec enables 'cswh' for Arabic where as for basic shaper it's disabled by default. */
+  planner->map.add_bool_feature (HB_TAG('c','s','w','h'));
 }
 
 void

src/hb-private.hh

@@ -304,6 +304,11 @@ struct hb_prealloced_array_t {
     qsort (array, len, sizeof (Type), (hb_compare_func_t) Type::cmp);
   }
 
+  inline void sort (unsigned int start, unsigned int end)
+  {
+    qsort (array + start, end - start, sizeof (Type), (hb_compare_func_t) Type::cmp);
+  }
+
   template <typename T>
   inline Type *bsearch (T *key)
   {