[pango/non-breaking-attrs] itemize: Don't break runs for font_features

[Matthias Clasen <matthiasc src gnome org>]

commit 6eee3c05d948c6012d56c220396a1dc0f5d3ae6d
Author: Matthias Clasen <mclasen redhat com>
Date:   Thu Jul 11 09:59:23 2019 -0400

    itemize: Don't break runs for font_features
    
    We don't need to break runs just because font_features
    changed - we pass those to harfbuzz with the range they
    apply to, after all.
    
    To do this, split the attributes into two lists,
    those that break runs (as before), and those that
    don't. And collect the overlapping attributes from
    the non-breaking list at the end of processing an
    item, when we know the range.
    
    For now, only font_features is considered non-breaking,
    but this can be expanded.
    
    Closes: https://gitlab.gnome.org/GNOME/pango/issues/242

 pango/pango-context.c | 123 ++++++++++++++++++++++++++++++++++++++++++++++----
 1 file changed, 113 insertions(+), 10 deletions(-)
---
diff --git a/pango/pango-context.c b/pango/pango-context.c
index 413119f3..0fc858b5 100644
--- a/pango/pango-context.c
+++ b/pango/pango-context.c
@@ -739,7 +739,10 @@ struct _ItemizeState
   PangoGravity font_desc_gravity;
   gboolean centered_baseline;
 
+  PangoAttrList *attrs;
+  PangoAttrList *non_breaking_attrs;
   PangoAttrIterator *attr_iter;
+  PangoAttrIterator *non_breaking_attr_iter;
   gboolean free_attr_iter;
   const char *attr_end;
   PangoFontDescription *font_desc;
@@ -796,6 +799,7 @@ static void
 update_attr_iterator (ItemizeState *state)
 {
   PangoLanguage *old_lang;
+  PangoFontDescription *old_font_desc;
   PangoAttribute *attr;
   int end_index;
 
@@ -812,8 +816,7 @@ update_attr_iterator (ItemizeState *state)
     }
 
   old_lang = state->lang;
-  if (state->font_desc)
-    pango_font_description_free (state->font_desc);
+  old_font_desc = state->font_desc;
   state->font_desc = pango_font_description_copy_static (state->context->font_desc);
   pango_attr_iterator_get_font (state->attr_iter, state->font_desc,
                                &state->lang, &state->extra_attrs);
@@ -836,9 +839,15 @@ update_attr_iterator (ItemizeState *state)
   attr = find_attribute (state->extra_attrs, PANGO_ATTR_GRAVITY_HINT);
   state->gravity_hint = attr == NULL ? state->context->gravity_hint : (PangoGravityHint)((PangoAttrInt 
*)attr)->value;
 
-  state->changed |= FONT_CHANGED;
+  if (old_font_desc &&
+      !pango_font_description_equal (state->font_desc, old_font_desc))
+    state->changed |= FONT_CHANGED;
+
   if (state->lang != old_lang)
     state->changed |= LANG_CHANGED;
+
+  if (old_font_desc)
+    pango_font_description_free (old_font_desc);
 }
 
 static void
@@ -971,6 +980,23 @@ width_iter_fini (PangoWidthIter* iter)
 {
 }
 
+static gboolean
+is_non_breaking (PangoAttribute *attr,
+                 gpointer        data)
+{
+  gboolean non_breaking;
+
+  non_breaking = attr->klass->type == PANGO_ATTR_FONT_FEATURES;
+  if (data)
+    {
+      gboolean *b = data;
+      *b = *b || non_breaking;
+      return FALSE;
+    }
+  else
+    return non_breaking;
+}
+
 static void
 itemize_state_init (ItemizeState      *state,
                    PangoContext      *context,
@@ -982,7 +1008,6 @@ itemize_state_init (ItemizeState      *state,
                    PangoAttrIterator *cached_iter,
                    const PangoFontDescription *desc)
 {
-
   state->context = context;
   state->text = text;
   state->end = text + start_index + length;
@@ -1001,8 +1026,34 @@ itemize_state_init (ItemizeState      *state,
   state->embedding_end = text + start_index;
   update_embedding_end (state);
 
-  /* Initialize the attribute iterator
+  /* Initialize the attribute iterators
    */
+
+  state->attrs = NULL;
+  state->attr_iter = NULL;
+  state->non_breaking_attrs = NULL;
+  state->non_breaking_attr_iter = NULL;
+  state->free_attr_iter = FALSE;
+
+  if (attrs)
+    {
+      gboolean has_non_breaking = FALSE;
+
+      pango_attr_list_filter (attrs, is_non_breaking, &has_non_breaking);
+
+      if (has_non_breaking)
+        {
+          state->attrs = pango_attr_list_copy (attrs);
+          state->non_breaking_attrs = pango_attr_list_filter (state->attrs, is_non_breaking, NULL);
+
+          state->attr_iter = pango_attr_list_get_iterator (state->attrs);
+          state->non_breaking_attr_iter = pango_attr_list_get_iterator (state->non_breaking_attrs);
+          state->free_attr_iter = TRUE;
+          attrs = NULL;
+          cached_iter = NULL;
+        }
+    }
+
   if (cached_iter)
     {
       state->attr_iter = cached_iter;
@@ -1013,11 +1064,6 @@ itemize_state_init (ItemizeState      *state,
       state->attr_iter = pango_attr_list_get_iterator (attrs);
       state->free_attr_iter = TRUE;
     }
-  else
-    {
-      state->attr_iter = NULL;
-      state->free_attr_iter = FALSE;
-    }
 
   state->emoji_font_desc = NULL;
   if (state->attr_iter)
@@ -1450,6 +1496,53 @@ string_from_script (PangoScript script)
   return value->value_nick;
 }
 
+static int
+compare_attr (gconstpointer p1, gconstpointer p2)
+{
+  if (pango_attribute_equal ((PangoAttribute *)p1, (PangoAttribute *)p2))
+    return 0;
+
+  return 1;
+}
+
+/* Find attributes from the non-breaking attr list that
+ * overlap with the range of the current item, and add
+ * them to the extra_attrs.
+ */
+static void
+collect_non_breaking_attrs (ItemizeState *state)
+{
+  if (state->non_breaking_attr_iter)
+    {
+      int start, end;
+      GSList *attrs = NULL;
+      do
+        {
+          pango_attr_iterator_range (state->non_breaking_attr_iter, &start, &end);
+          if (start >= state->item->offset + state->item->length)
+            break;
+
+          if (end >= state->item->offset)
+            {
+              GSList *list, *l;
+              list = pango_attr_iterator_get_attrs (state->non_breaking_attr_iter);
+              for (l = list; l; l = l->next)
+                {
+                  if (!g_slist_find_custom (attrs, l->data, compare_attr))
+                    attrs = g_slist_prepend (attrs, pango_attribute_copy (l->data));
+                }
+              g_slist_free_full (list, (GDestroyNotify)pango_attribute_destroy);
+            }
+
+          if (end >= state->item->offset + state->item->length)
+            break;
+        }
+      while (pango_attr_iterator_next (state->non_breaking_attr_iter));
+
+      state->item->analysis.extra_attrs = g_slist_concat (state->item->analysis.extra_attrs, attrs);
+    }
+}
+
 static void
 itemize_state_process_run (ItemizeState *state)
 {
@@ -1544,12 +1637,22 @@ G_GNUC_END_IGNORE_DEPRECATIONS
 
       itemize_state_fill_shaper (state, shape_engine, font);
     }
+
+  collect_non_breaking_attrs (state);
+
   state->item = NULL;
 }
 
 static void
 itemize_state_finish (ItemizeState *state)
 {
+  if (state->attrs)
+    pango_attr_list_unref (state->attrs);
+  if (state->non_breaking_attrs)
+    {
+      pango_attr_list_unref (state->non_breaking_attrs);
+      pango_attr_iterator_destroy (state->non_breaking_attr_iter);
+    }
   g_free (state->embedding_levels);
   if (state->free_attr_iter)
     pango_attr_iterator_destroy (state->attr_iter);