Implement the Unicode Canonical Composition algorithm
[framework/uifw/harfbuzz.git] / src / hb-ot-shape.cc
index 58d1e7f..929a662 100644 (file)
@@ -1,6 +1,6 @@
 /*
- * Copyright (C) 2009,2010  Red Hat, Inc.
- * Copyright (C) 2010  Google, Inc.
+ * Copyright © 2009,2010  Red Hat, Inc.
+ * Copyright © 2010,2011  Google, Inc.
  *
  *  This is part of HarfBuzz, a text shaping library.
  *
  * Google Author(s): Behdad Esfahbod
  */
 
-#include "hb-ot-shape-private.h"
+#include "hb-ot-shape-private.hh"
+#include "hb-ot-shape-complex-private.hh"
 
-#include "hb-open-type-private.hh"
-
-#include "hb-ot-layout.h"
+#include "hb-font-private.hh"
 
 HB_BEGIN_DECLS
 
 
-/* XXX vertical */
-hb_tag_t default_features[] = {
-  HB_TAG('c','a','l','t'),
+hb_tag_t common_features[] = {
   HB_TAG('c','c','m','p'),
-  HB_TAG('c','l','i','g'),
-  HB_TAG('c','s','w','h'),
-  HB_TAG('c','u','r','s'),
-  HB_TAG('k','e','r','n'),
-  HB_TAG('l','i','g','a'),
   HB_TAG('l','o','c','l'),
   HB_TAG('m','a','r','k'),
   HB_TAG('m','k','m','k'),
-  HB_TAG('r','l','i','g')
+  HB_TAG('r','l','i','g'),
 };
 
-struct lookup_map {
-  unsigned int index;
-  hb_mask_t mask;
+hb_tag_t horizontal_features[] = {
+  HB_TAG('c','a','l','t'),
+  HB_TAG('c','l','i','g'),
+  HB_TAG('c','u','r','s'),
+  HB_TAG('k','e','r','n'),
+  HB_TAG('l','i','g','a'),
 };
 
-
-static void
-add_lookups (hb_face_t    *face,
-            hb_tag_t      table_tag,
-            unsigned int  feature_index,
-            hb_mask_t     mask,
-            lookup_map   *lookups,
-            unsigned int *num_lookups,
-            unsigned int  room_lookups)
-{
-  unsigned int i = room_lookups - *num_lookups;
-  lookups += *num_lookups;
-
-  unsigned int *lookup_indices = (unsigned int *) lookups;
-
-  hb_ot_layout_feature_get_lookup_indexes (face, table_tag, feature_index, 0,
-                                          &i,
-                                          lookup_indices);
-
-  *num_lookups += i;
-
-  while (i--) {
-    lookups[i].mask = mask;
-    lookups[i].index = lookup_indices[i];
-  }
-}
-
-static int
-cmp_lookups (const void *p1, const void *p2)
-{
-  const lookup_map *a = (const lookup_map *) p1;
-  const lookup_map *b = (const lookup_map *) p2;
-
-  return a->index - b->index;
-}
-
-
-#define MAX_FEATURES 100 /* FIXME */
-
-struct hb_mask_allocator_t {
-
-  struct feature_info_t {
-    hb_tag_t tag;
-    unsigned int value;
-    unsigned int seq;
-    bool global;
-
-    static int
-    cmp (const void *p1, const void *p2)
-    {
-      const feature_info_t *a = reinterpret_cast<const feature_info_t *>(p1);
-      const feature_info_t *b = reinterpret_cast<const feature_info_t *>(p2);
-
-      if (a->tag != b->tag)
-        return a->tag < b->tag ? -1 : 1;
-
-      return a->seq < b->seq ? -1 : 1;
-    }
-  };
-
-  struct feature_map_t {
-    hb_tag_t tag; /* should be first */
-    unsigned int index;
-    unsigned int shift;
-    hb_mask_t mask;
-
-    static int
-    cmp (const void *p1, const void *p2)
-    {
-      const feature_map_t *a = reinterpret_cast<const feature_map_t *>(p1);
-      const feature_map_t *b = reinterpret_cast<const feature_map_t *>(p2);
-
-      return a->tag < b->tag ? -1 : a->tag > b->tag ? 1 : 0;
-    }
-  };
-
-  hb_mask_allocator_t (void) : count (0) {}
-
-  void add_feature (hb_tag_t tag,
-                   unsigned int value,
-                   bool global)
-  {
-    feature_info_t *info = &infos[count++];
-    info->tag = tag;
-    info->value = value;
-    info->seq = count;
-    info->global = global;
-  }
-
-  void compile (hb_face_t *face,
-               hb_tag_t table_tag,
-               unsigned int script_index,
-               unsigned int language_index)
-  {
-    global_mask = 0;
-    unsigned int next_bit = 1;
-
-    if (!count)
-      return;
-
-    qsort (infos, count, sizeof (infos[0]), feature_info_t::cmp);
-
-    unsigned int j = 0;
-    for (unsigned int i = 1; i < count; i++)
-      if (infos[i].tag != infos[j].tag)
-       infos[++j] = infos[i];
-      else {
-       if (infos[i].global)
-         infos[j] = infos[i];
-       else {
-         infos[j].global = infos[j].global && (infos[j].value == infos[i].value);
-         infos[j].value = MAX (infos[j].value, infos[i].value);
-       }
-      }
-    count = j + 1;
-
-    /* Allocate bits now */
-    j = 0;
-    for (unsigned int i = 0; i < count; i++) {
-      const feature_info_t *info = &infos[i];
-
-      unsigned int bits_needed;
-
-      if (info->global && info->value == 1)
-        /* Uses the global bit */
-        bits_needed = 0;
-      else
-        bits_needed = _hb_bit_storage (info->value);
-
-      if (!info->value || next_bit + bits_needed > 8 * sizeof (hb_mask_t))
-        continue; /* Feature disabled, or not enough bits. */
-
-      unsigned int feature_index;
-      if (!hb_ot_layout_language_find_feature (face, table_tag, script_index, language_index,
-                                              info->tag, &feature_index))
-        continue;
-
-      feature_map_t *map = &maps[j++];
-
-      map->tag = info->tag;
-      map->index = feature_index;
-      if (info->global && info->value == 1) {
-        /* Use the global bit */
-        map->shift = 0;
-       map->mask = 1;
-      } else {
-       map->shift = next_bit;
-       map->mask = (1 << (next_bit + bits_needed)) - (1 << next_bit);
-       next_bit += bits_needed;
-      }
-
-      if (info->global && map->mask != 1)
-        global_mask |= map->mask;
-    }
-    count = j;
-  }
-
-  hb_mask_t get_global_mask (void) { return global_mask; }
-
-  const feature_map_t *get_features (unsigned int *num_features) const {
-    *num_features = count;
-    return maps;
-  }
-
-
-  const feature_map_t *find_feature (hb_tag_t tag) const {
-    static const feature_map_t off_map = { HB_TAG_NONE, Index::NOT_FOUND_INDEX, 0, 0 };
-    const feature_map_t *map = (const feature_map_t *) bsearch (&tag, maps, count, sizeof (maps[0]), feature_map_t::cmp);
-    return map ? map : &off_map;
-  }
-
-
-  private:
-
-  unsigned int count;
-  feature_info_t infos[MAX_FEATURES];
-
-  feature_map_t maps[MAX_FEATURES];
-  hb_mask_t global_mask;
+/* Note:
+ * Technically speaking, vrt2 and vert are mutually exclusive.
+ * According to the spec, valt and vpal are also mutually exclusive.
+ * But we apply them all for now.
+ */
+hb_tag_t vertical_features[] = {
+  HB_TAG('v','a','l','t'),
+  HB_TAG('v','e','r','t'),
+  HB_TAG('v','k','r','n'),
+  HB_TAG('v','p','a','l'),
+  HB_TAG('v','r','t','2'),
 };
 
 static void
-hb_ot_shape_setup_lookups_complex (hb_ot_shape_context_t *c,
-                                  lookup_map            *lookups,
-                                  unsigned int          *num_lookups)
+hb_ot_shape_collect_features (hb_ot_shape_planner_t          *planner,
+                             const hb_segment_properties_t  *props,
+                             const hb_feature_t             *user_features,
+                             unsigned int                    num_user_features)
 {
-  /* XXX */
-}
-
-static void
-hb_ot_shape_setup_lookups (hb_ot_shape_context_t *c,
-                          lookup_map            *lookups,
-                          unsigned int          *num_lookups)
-{
-  unsigned int i, j, script_index, language_index, feature_index, room_lookups;
-
-  room_lookups = *num_lookups;
-  *num_lookups = 0;
-
-  hb_ot_layout_table_choose_script (c->face, c->table_tag,
-                                   hb_ot_tags_from_script (c->buffer->props.script),
-                                   &script_index);
-  hb_ot_layout_script_find_language (c->face, c->table_tag, script_index,
-                                    hb_ot_tag_from_language (c->buffer->props.language),
-                                    &language_index);
-
-
-  hb_mask_allocator_t allocator;
-
-  switch (c->original_direction) {
+  switch (props->direction) {
     case HB_DIRECTION_LTR:
-      allocator.add_feature (HB_TAG ('l','t','r','a'), 1, true);
-      allocator.add_feature (HB_TAG ('l','t','r','m'), 1, true);
+      planner->map.add_bool_feature (HB_TAG ('l','t','r','a'));
+      planner->map.add_bool_feature (HB_TAG ('l','t','r','m'));
       break;
     case HB_DIRECTION_RTL:
-      allocator.add_feature (HB_TAG ('r','t','l','a'), 1, true);
-      allocator.add_feature (HB_TAG ('r','t','l','m'), 1, false);
+      planner->map.add_bool_feature (HB_TAG ('r','t','l','a'));
+      planner->map.add_bool_feature (HB_TAG ('r','t','l','m'), false);
       break;
     case HB_DIRECTION_TTB:
     case HB_DIRECTION_BTT:
+    case HB_DIRECTION_INVALID:
     default:
       break;
   }
 
-  for (i = 0; i < ARRAY_LENGTH (default_features); i++)
-    allocator.add_feature (default_features[i], 1, true);
-
-  hb_ot_shape_setup_lookups_complex (c, lookups, num_lookups);
-
-  for (unsigned int i = 0; i < c->num_features; i++) {
-    const hb_feature_t *feature = &c->features[i];
-    allocator.add_feature (feature->tag, feature->value, (feature->start == 0 && feature->end == (unsigned int) -1));
-  }
-
-
-  /* Compile features */
-  allocator.compile (c->face, c->table_tag, script_index, language_index);
+#define ADD_FEATURES(array) \
+  HB_STMT_START { \
+    for (unsigned int i = 0; i < ARRAY_LENGTH (array); i++) \
+      planner->map.add_bool_feature (array[i]); \
+  } HB_STMT_END
 
+  hb_ot_shape_complex_collect_features (planner->shaper, &planner->map, props);
 
-  /* Gather lookup indices for features */
+  ADD_FEATURES (common_features);
 
-  if (hb_ot_layout_language_get_required_feature_index (c->face, c->table_tag, script_index, language_index,
-                                                       &feature_index))
-    add_lookups (c->face, c->table_tag, feature_index, 1, lookups, num_lookups, room_lookups);
+  if (HB_DIRECTION_IS_HORIZONTAL (props->direction))
+    ADD_FEATURES (horizontal_features);
+  else
+    ADD_FEATURES (vertical_features);
 
-  const hb_mask_allocator_t::feature_map_t *map;
-  unsigned int num_features;
+#undef ADD_FEATURES
 
-  map = allocator.get_features (&num_features);
-  for (i = 0; i < num_features; i++)
-    add_lookups (c->face, c->table_tag, map[i].index, map[i].mask, lookups, num_lookups, room_lookups);
-
-  /* Sort lookups and merge duplicates */
-
-  qsort (lookups, *num_lookups, sizeof (lookups[0]), cmp_lookups);
-
-  if (*num_lookups)
-  {
-    for (i = 1, j = 0; i < *num_lookups; i++)
-      if (lookups[i].index != lookups[j].index)
-       lookups[++j] = lookups[i];
-      else
-        lookups[j].mask |= lookups[i].mask;
-    j++;
-    *num_lookups = j;
+  for (unsigned int i = 0; i < num_user_features; i++) {
+    const hb_feature_t *feature = &user_features[i];
+    planner->map.add_feature (feature->tag, feature->value, (feature->start == 0 && feature->end == (unsigned int) -1));
   }
+}
+
 
+static void
+hb_ot_shape_setup_masks (hb_ot_shape_context_t *c)
+{
+  hb_mask_t global_mask = c->plan->map.get_global_mask ();
+  c->buffer->reset_masks (global_mask);
 
-  /* Set masks in buffer */
+  hb_ot_shape_complex_setup_masks (c->plan->shaper, &c->plan->map, c->buffer); /* BUFFER: Clobbers var2 */
 
-  for (i = 0; i < c->num_features; i++)
+  for (unsigned int i = 0; i < c->num_user_features; i++)
   {
-    hb_feature_t *feature = &c->features[i];
-    map = allocator.find_feature (feature->tag);
-    if (!(feature->start == 0 && feature->end == (unsigned int)-1))
-      c->buffer->set_masks (feature->value << map->shift, map->mask, feature->start, feature->end);
+    const hb_feature_t *feature = &c->user_features[i];
+    if (!(feature->start == 0 && feature->end == (unsigned int)-1)) {
+      unsigned int shift;
+      hb_mask_t mask = c->plan->map.get_mask (feature->tag, &shift);
+      c->buffer->set_masks (feature->value << shift, mask, feature->start, feature->end);
+    }
   }
-
-  hb_mask_t global_mask = allocator.get_global_mask ();
-  if (global_mask)
-    c->buffer->set_masks (global_mask, global_mask, 0, (unsigned int) -1);
 }
 
 
 static void
 hb_ot_substitute_complex (hb_ot_shape_context_t *c)
 {
-  lookup_map lookups[1000]; /* FIXME */
-  unsigned int num_lookups = ARRAY_LENGTH (lookups);
-  unsigned int i;
-
   if (!hb_ot_layout_has_substitution (c->face))
     return;
 
-  c->table_tag = HB_OT_TAG_GSUB;
-
-  hb_ot_shape_setup_lookups (c, lookups, &num_lookups);
-
-  for (i = 0; i < num_lookups; i++)
-    hb_ot_layout_substitute_lookup (c->face, c->buffer, lookups[i].index, lookups[i].mask);
+  c->plan->map.substitute (c->face, c->buffer);
 
   c->applied_substitute_complex = TRUE;
   return;
@@ -363,21 +144,28 @@ hb_ot_substitute_complex (hb_ot_shape_context_t *c)
 static void
 hb_ot_position_complex (hb_ot_shape_context_t *c)
 {
-  lookup_map lookups[1000]; /* FIXME */
-  unsigned int num_lookups = ARRAY_LENGTH (lookups);
-  unsigned int i;
 
   if (!hb_ot_layout_has_positioning (c->face))
     return;
 
-  c->table_tag = HB_OT_TAG_GPOS;
+  unsigned int count = c->buffer->len;
+  for (unsigned int i = 0; i < count; i++) {
+    hb_font_add_glyph_origin_for_direction (c->font, c->buffer->info[i].codepoint,
+                                           HB_DIRECTION_LTR,
+                                           &c->buffer->pos[i].x_offset,
+                                           &c->buffer->pos[i].y_offset);
+  }
 
-  hb_ot_shape_setup_lookups (c, lookups, &num_lookups);
+  c->plan->map.position (c->font, c->buffer);
 
-  for (i = 0; i < num_lookups; i++)
-    hb_ot_layout_position_lookup (c->font, c->face, c->buffer, lookups[i].index, lookups[i].mask);
+  for (unsigned int i = 0; i < count; i++) {
+    hb_font_subtract_glyph_origin_for_direction (c->font, c->buffer->info[i].codepoint,
+                                                HB_DIRECTION_LTR,
+                                                &c->buffer->pos[i].x_offset,
+                                                &c->buffer->pos[i].y_offset);
+  }
 
-  hb_ot_layout_position_finish (c->font, c->face, c->buffer);
+  hb_ot_layout_position_finish (c->buffer);
 
   c->applied_position_complex = TRUE;
   return;
@@ -388,12 +176,12 @@ hb_ot_position_complex (hb_ot_shape_context_t *c)
 
 /* Prepare */
 
-static inline hb_bool_t
-is_variation_selector (hb_codepoint_t unicode)
+void
+_hb_set_unicode_props (hb_buffer_t *buffer)
 {
-  return unlikely ((unicode >=  0x180B && unicode <=  0x180D) || /* MONGOLIAN FREE VARIATION SELECTOR ONE..THREE */
-                  (unicode >=  0xFE00 && unicode <=  0xFE0F) || /* VARIATION SELECTOR-1..16 */
-                  (unicode >= 0xE0100 && unicode <= 0xE01EF));  /* VARIATION SELECTOR-17..256 */
+  unsigned int count = buffer->len;
+  for (unsigned int i = 1; i < count; i++)
+    hb_glyph_info_set_unicode_props (&buffer->info[i], buffer->unicode);
 }
 
 static void
@@ -401,7 +189,10 @@ hb_form_clusters (hb_buffer_t *buffer)
 {
   unsigned int count = buffer->len;
   for (unsigned int i = 1; i < count; i++)
-    if (buffer->unicode->v.get_general_category (buffer->info[i].codepoint) == HB_CATEGORY_NON_SPACING_MARK)
+    if (FLAG (buffer->info[i].general_category()) &
+       (FLAG (HB_UNICODE_GENERAL_CATEGORY_SPACING_MARK) |
+        FLAG (HB_UNICODE_GENERAL_CATEGORY_ENCLOSING_MARK) |
+        FLAG (HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK)))
       buffer->info[i].cluster = buffer->info[i - 1].cluster;
 }
 
@@ -410,65 +201,82 @@ hb_ensure_native_direction (hb_buffer_t *buffer)
 {
   hb_direction_t direction = buffer->props.direction;
 
-  /* TODO vertical */
-  if (HB_DIRECTION_IS_HORIZONTAL (direction) &&
-      direction != _hb_script_get_horizontal_direction (buffer->props.script))
+  /* TODO vertical:
+   * The only BTT vertical script is Ogham, but it's not clear to me whether OpenType
+   * Ogham fonts are supposed to be implemented BTT or not.  Need to research that
+   * first. */
+  if ((HB_DIRECTION_IS_HORIZONTAL (direction) && direction != hb_script_get_horizontal_direction (buffer->props.script)) ||
+      (HB_DIRECTION_IS_VERTICAL   (direction) && direction != HB_DIRECTION_TTB))
   {
     hb_buffer_reverse_clusters (buffer);
     buffer->props.direction = HB_DIRECTION_REVERSE (buffer->props.direction);
   }
 }
 
+static void
+hb_reset_glyph_infos (hb_buffer_t *buffer)
+{
+  unsigned int count = buffer->len;
+  for (unsigned int i = 0; i < count; i++)
+    buffer->info[i].var1.u32 = buffer->info[i].var2.u32 = 0;
+}
+
 
 /* Substitute */
 
 static void
-hb_mirror_chars (hb_buffer_t *buffer)
+hb_mirror_chars (hb_ot_shape_context_t *c)
 {
-  hb_unicode_get_mirroring_func_t get_mirroring = buffer->unicode->v.get_mirroring;
+  hb_unicode_funcs_t *unicode = c->buffer->unicode;
 
-  if (HB_DIRECTION_IS_FORWARD (buffer->props.direction))
+  if (HB_DIRECTION_IS_FORWARD (c->target_direction))
     return;
 
-//  map = allocator.find_feature (HB_TAG ('r','t','l','m'));
+  hb_mask_t rtlm_mask = c->plan->map.get_1_mask (HB_TAG ('r','t','l','m'));
 
-  unsigned int count = buffer->len;
+  unsigned int count = c->buffer->len;
   for (unsigned int i = 0; i < count; i++) {
-    hb_codepoint_t codepoint = get_mirroring (buffer->info[i].codepoint);
-    if (likely (codepoint == buffer->info[i].codepoint))
-;//      buffer->info[i].mask |= map->mask;
+    hb_codepoint_t codepoint = hb_unicode_mirroring (unicode, c->buffer->info[i].codepoint);
+    if (likely (codepoint == c->buffer->info[i].codepoint))
+      c->buffer->info[i].mask |= rtlm_mask; /* XXX this should be moved to before setting user-feature masks */
     else
-      buffer->info[i].codepoint = codepoint;
+      c->buffer->info[i].codepoint = codepoint;
   }
 }
 
 static void
 hb_map_glyphs (hb_font_t    *font,
-              hb_face_t    *face,
               hb_buffer_t  *buffer)
 {
+  hb_codepoint_t glyph;
+
   if (unlikely (!buffer->len))
     return;
 
   buffer->clear_output ();
+
   unsigned int count = buffer->len - 1;
-  for (buffer->i = 0; buffer->i < count;) {
-    if (unlikely (is_variation_selector (buffer->info[buffer->i + 1].codepoint))) {
-      buffer->add_output_glyph (hb_font_get_glyph (font, face, buffer->info[buffer->i].codepoint, buffer->info[buffer->i + 1].codepoint));
-      buffer->i++;
+  for (buffer->idx = 0; buffer->idx < count;) {
+    if (unlikely (is_variation_selector (buffer->info[buffer->idx + 1].codepoint))) {
+      hb_font_get_glyph (font, buffer->info[buffer->idx].codepoint, buffer->info[buffer->idx + 1].codepoint, &glyph);
+      buffer->replace_glyph (glyph);
+      buffer->skip_glyph ();
     } else {
-      buffer->add_output_glyph (hb_font_get_glyph (font, face, buffer->info[buffer->i].codepoint, 0));
+      hb_font_get_glyph (font, buffer->info[buffer->idx].codepoint, 0, &glyph);
+      buffer->replace_glyph (glyph);
     }
   }
-  if (likely (buffer->i < buffer->len))
-    buffer->add_output_glyph (hb_font_get_glyph (font, face, buffer->info[buffer->i].codepoint, 0));
-  buffer->swap ();
+  if (likely (buffer->idx < buffer->len)) {
+    hb_font_get_glyph (font, buffer->info[buffer->idx].codepoint, 0, &glyph);
+    buffer->replace_glyph (glyph);
+  }
+  buffer->swap_buffers ();
 }
 
 static void
 hb_substitute_default (hb_ot_shape_context_t *c)
 {
-  hb_map_glyphs (c->font, c->face, c->buffer);
+  hb_map_glyphs (c->font, c->buffer);
 }
 
 static void
@@ -483,14 +291,18 @@ hb_substitute_complex_fallback (hb_ot_shape_context_t *c HB_UNUSED)
 static void
 hb_position_default (hb_ot_shape_context_t *c)
 {
-  hb_buffer_clear_positions (c->buffer);
+  hb_ot_layout_position_start (c->buffer);
 
   unsigned int count = c->buffer->len;
   for (unsigned int i = 0; i < count; i++) {
-    hb_glyph_metrics_t metrics;
-    hb_font_get_glyph_metrics (c->font, c->face, c->buffer->info[i].codepoint, &metrics);
-    c->buffer->pos[i].x_advance = metrics.x_advance;
-    c->buffer->pos[i].y_advance = metrics.y_advance;
+    hb_font_get_glyph_advance_for_direction (c->font, c->buffer->info[i].codepoint,
+                                            c->buffer->props.direction,
+                                            &c->buffer->pos[i].x_advance,
+                                            &c->buffer->pos[i].y_advance);
+    hb_font_subtract_glyph_origin_for_direction (c->font, c->buffer->info[i].codepoint,
+                                                c->buffer->props.direction,
+                                                &c->buffer->pos[i].x_offset,
+                                                &c->buffer->pos[i].y_offset);
   }
 }
 
@@ -506,13 +318,23 @@ hb_truetype_kern (hb_ot_shape_context_t *c)
   /* TODO Check for kern=0 */
   unsigned int count = c->buffer->len;
   for (unsigned int i = 1; i < count; i++) {
-    hb_position_t kern, kern1, kern2;
-    kern = hb_font_get_kerning (c->font, c->face, c->buffer->info[i - 1].codepoint, c->buffer->info[i].codepoint);
-    kern1 = kern >> 1;
-    kern2 = kern - kern1;
+    hb_position_t x_kern, y_kern, kern1, kern2;
+    hb_font_get_glyph_kerning_for_direction (c->font,
+                                            c->buffer->info[i - 1].codepoint, c->buffer->info[i].codepoint,
+                                            c->buffer->props.direction,
+                                            &x_kern, &y_kern);
+
+    kern1 = x_kern >> 1;
+    kern2 = x_kern - kern1;
     c->buffer->pos[i - 1].x_advance += kern1;
     c->buffer->pos[i].x_advance += kern2;
     c->buffer->pos[i].x_offset += kern2;
+
+    kern1 = y_kern >> 1;
+    kern2 = y_kern - kern1;
+    c->buffer->pos[i - 1].y_advance += kern1;
+    c->buffer->pos[i].y_advance += kern2;
+    c->buffer->pos[i].y_offset += kern2;
   }
 }
 
@@ -526,18 +348,26 @@ hb_position_complex_fallback_visual (hb_ot_shape_context_t *c)
 /* Do it! */
 
 static void
-hb_ot_shape_internal (hb_ot_shape_context_t *c)
+hb_ot_shape_execute_internal (hb_ot_shape_context_t *c)
 {
+  /* Save the original direction, we use it later. */
+  c->target_direction = c->buffer->props.direction;
+
+  hb_reset_glyph_infos (c->buffer); /* BUFFER: Clear buffer var1 and var2 */
+
+  _hb_set_unicode_props (c->buffer); /* BUFFER: Set general_category and combining_class in var1 */
+
   hb_form_clusters (c->buffer);
 
-  /* SUBSTITUTE */
-  {
-    c->buffer->clear_masks ();
+  hb_ensure_native_direction (c->buffer);
+
+  _hb_ot_shape_normalize (c);
 
-    /* Mirroring needs to see the original direction */
-    hb_mirror_chars (c->buffer);
+  hb_ot_shape_setup_masks (c); /* BUFFER: Clobbers var2 */
 
-    hb_ensure_native_direction (c->buffer);
+  /* SUBSTITUTE */
+  {
+    hb_mirror_chars (c);
 
     hb_substitute_default (c);
 
@@ -549,8 +379,6 @@ hb_ot_shape_internal (hb_ot_shape_context_t *c)
 
   /* POSITION */
   {
-    c->buffer->clear_masks ();
-
     hb_position_default (c);
 
     hb_ot_position_complex (c);
@@ -566,22 +394,46 @@ hb_ot_shape_internal (hb_ot_shape_context_t *c)
       hb_position_complex_fallback_visual (c);
   }
 
-  c->buffer->props.direction = c->original_direction;
+  c->buffer->props.direction = c->target_direction;
 }
 
-void
-hb_ot_shape (hb_font_t    *font,
-            hb_face_t    *face,
-            hb_buffer_t  *buffer,
-            hb_feature_t *features,
-            unsigned int  num_features)
+static void
+hb_ot_shape_plan_internal (hb_ot_shape_plan_t       *plan,
+                          hb_face_t                *face,
+                          const hb_segment_properties_t  *props,
+                          const hb_feature_t       *user_features,
+                          unsigned int              num_user_features)
 {
-  hb_ot_shape_context_t c = {font, face, buffer, features, num_features};
+  hb_ot_shape_planner_t planner;
+
+  planner.shaper = hb_ot_shape_complex_categorize (props);
 
-  /* Setup transient context members */
-  c.original_direction = buffer->props.direction;
+  hb_ot_shape_collect_features (&planner, props, user_features, num_user_features);
+
+  planner.compile (face, props, *plan);
+}
+
+static void
+hb_ot_shape_execute (hb_ot_shape_plan_t *plan,
+                    hb_font_t          *font,
+                    hb_buffer_t        *buffer,
+                    const hb_feature_t *user_features,
+                    unsigned int        num_user_features)
+{
+  hb_ot_shape_context_t c = {plan, font, font->face, buffer, user_features, num_user_features};
+  hb_ot_shape_execute_internal (&c);
+}
+
+void
+hb_ot_shape (hb_font_t          *font,
+            hb_buffer_t        *buffer,
+            const hb_feature_t *features,
+            unsigned int        num_features)
+{
+  hb_ot_shape_plan_t plan;
 
-  hb_ot_shape_internal (&c);
+  hb_ot_shape_plan_internal (&plan, font->face, &buffer->props, features, num_features);
+  hb_ot_shape_execute (&plan, font, buffer, features, num_features);
 }