Rewrite hide_default_ignorables

Separate the loops for the two cases of replacing with space
and deleting.  For deleting, use the out-buffer machinery.

Needed for upcoming cluster merge fix.

src/hb-buffer-private.hh

@@ -151,6 +151,24 @@ struct hb_buffer_t {
 
     idx++;
   }
+  inline void
+  next_glyphs (unsigned int count)
+  {
+    if (have_output)
+    {
+      if (unlikely (out_info != info || out_len != idx)) {
+	if (unlikely (!make_room_for (count, count))) return;
+	{
+	  while (count--)
+	    out_info[out_len++] = info[idx++];
+	  return;
+	}
+      }
+      out_len += count;
+    }
+
+    idx += count;
+  }
 
   /* Advance idx without copying to output. */
   inline void skip_glyph (void) { idx++; }

src/hb-ot-shape.cc

@@ -647,45 +647,58 @@ hb_ot_position (hb_ot_shape_context_t *c)
 static void
 hb_ot_hide_default_ignorables (hb_ot_shape_context_t *c)
 {
-  if (c->buffer->flags & HB_BUFFER_FLAG_PRESERVE_DEFAULT_IGNORABLES)
-    return;
+  hb_buffer_t *buffer = c->buffer;
 
-  hb_codepoint_t space;
-  enum {
-    SPACE_DONT_KNOW,
-    SPACE_AVAILABLE,
-    SPACE_UNAVAILABLE
-  } space_status = SPACE_DONT_KNOW;
+  if (buffer->flags & HB_BUFFER_FLAG_PRESERVE_DEFAULT_IGNORABLES)
+    return;
 
-  unsigned int count = c->buffer->len;
-  hb_glyph_info_t *info = c->buffer->info;
-  hb_glyph_position_t *pos = c->buffer->pos;
-  unsigned int j = 0;
-  for (unsigned int i = 0; i < count; i++)
+  unsigned int count = buffer->len;
+  hb_glyph_info_t *info = buffer->info;
+  hb_glyph_position_t *pos = buffer->pos;
+  unsigned int i = 0;
+  for (i = 0; i < count; i++)
   {
     if (unlikely (!_hb_glyph_info_ligated (&info[i]) &&
 		  _hb_glyph_info_is_default_ignorable (&info[i])))
-    {
-      if (space_status == SPACE_DONT_KNOW)
-	space_status = c->font->get_glyph (' ', 0, &space) ? SPACE_AVAILABLE : SPACE_UNAVAILABLE;
+      break;
+  }
+
+  /* No default-ignorables found; return. */
+  if (i == count)
+    return;
 
-      if (space_status == SPACE_AVAILABLE)
+  hb_codepoint_t space;
+  if (c->font->get_glyph (' ', 0, &space))
+  {
+    /* Replace default-ignorables with a zero-advance space glyph. */
+    for (/*continue*/; i < count; i++)
+    {
+      if (!_hb_glyph_info_ligated (&info[i]) &&
+	   _hb_glyph_info_is_default_ignorable (&info[i]))
       {
 	info[i].codepoint = space;
-	pos[i].x_advance = 0;
-	pos[i].y_advance = 0;
+	pos[i].x_advance = pos[i].y_advance = pos[i].x_offset = pos[i].y_offset = 0;
       }
-      else
-	continue; /* Delete it. XXX Merge clusters? */
     }
-    if (j != i)
+  }
+  else
+  {
+    /* Merge clusters and delete default-ignorables. */
+    buffer->clear_output ();
+    buffer->idx = 0;
+    buffer->next_glyphs (i);
+    while (buffer->idx < buffer->len)
     {
-      info[j] = info[i];
-      pos[j] = pos[i];
+      if (!_hb_glyph_info_ligated (&info[buffer->idx]) &&
+	   _hb_glyph_info_is_default_ignorable (&info[buffer->idx]))
+      {
+        buffer->skip_glyph ();
+	continue;
+      }
+      buffer->next_glyph ();
     }
-    j++;
+    buffer->swap_buffers ();
   }
-  c->buffer->len = j;
 }