From 763e5466c0a03a7c27020e1e2598e488612529a7 Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Sat, 2 Aug 2014 16:17:44 -0400
Subject: [PATCH] Make it easier to use HB_BUFFER_FLAG_BOT/EOT

Previously, we expected users to provide BOT/EOT flags when the
text *segment* was at paragraph boundaries.  This meant that for
clients that provide full paragraph to HarfBuzz (eg. Pango), they
had code like this:

  hb_buffer_set_flags (hb_buffer,
                       (item_offset == 0 ? HB_BUFFER_FLAG_BOT : 0) |
                       (item_offset + item_length == paragraph_length ?
                        HB_BUFFER_FLAG_EOT : 0));

  hb_buffer_add_utf8 (hb_buffer,
                      paragraph_text, paragraph_length,
                      item_offset, item_length);

After this change such clients can simply say:

  hb_buffer_set_flags (hb_buffer,
                       HB_BUFFER_FLAG_BOT | HB_BUFFER_FLAG_EOT);

  hb_buffer_add_utf8 (hb_buffer,
                      paragraph_text, paragraph_length,
                      item_offset, item_length);

Ie, HarfBuzz itself checks whether the segment is at the beginning/end
of the paragraph.  Clients that only pass item-at-a-time to HarfBuzz
continue not setting any flags whatsoever.

Another way to put it is: if there's pre-context text in the buffer,
HarfBuzz ignores the BOT flag.  If there's post-context, it ignores
EOT flag.
---
 src/hb-ot-shape-complex-arabic.cc | 40 +++++++++++++++----------------
 src/hb-ot-shape.cc                |  1 +
 2 files changed, 20 insertions(+), 21 deletions(-)

diff --git a/src/hb-ot-shape-complex-arabic.cc b/src/hb-ot-shape-complex-arabic.cc
index 9870ba3da..6cf1a7f59 100644
--- a/src/hb-ot-shape-complex-arabic.cc
+++ b/src/hb-ot-shape-complex-arabic.cc
@@ -248,18 +248,17 @@ arabic_joining (hb_buffer_t *buffer)
   unsigned int prev = (unsigned int) -1, state = 0;
 
   /* Check pre-context */
-  if (!(buffer->flags & HB_BUFFER_FLAG_BOT))
-    for (unsigned int i = 0; i < buffer->context_len[0]; i++)
-    {
-      unsigned int this_type = get_joining_type (buffer->context[0][i], buffer->unicode->general_category (buffer->context[0][i]));
+  for (unsigned int i = 0; i < buffer->context_len[0]; i++)
+  {
+    unsigned int this_type = get_joining_type (buffer->context[0][i], buffer->unicode->general_category (buffer->context[0][i]));
 
-      if (unlikely (this_type == JOINING_TYPE_T))
-	continue;
+    if (unlikely (this_type == JOINING_TYPE_T))
+      continue;
 
-      const arabic_state_table_entry *entry = &arabic_state_table[state][this_type];
-      state = entry->next_state;
-      break;
-    }
+    const arabic_state_table_entry *entry = &arabic_state_table[state][this_type];
+    state = entry->next_state;
+    break;
+  }
 
   for (unsigned int i = 0; i < count; i++)
   {
@@ -281,19 +280,18 @@ arabic_joining (hb_buffer_t *buffer)
     state = entry->next_state;
   }
 
-  if (!(buffer->flags & HB_BUFFER_FLAG_EOT))
-    for (unsigned int i = 0; i < buffer->context_len[1]; i++)
-    {
-      unsigned int this_type = get_joining_type (buffer->context[1][i], buffer->unicode->general_category (buffer->context[1][i]));
+  for (unsigned int i = 0; i < buffer->context_len[1]; i++)
+  {
+    unsigned int this_type = get_joining_type (buffer->context[1][i], buffer->unicode->general_category (buffer->context[1][i]));
 
-      if (unlikely (this_type == JOINING_TYPE_T))
-	continue;
+    if (unlikely (this_type == JOINING_TYPE_T))
+      continue;
 
-      const arabic_state_table_entry *entry = &arabic_state_table[state][this_type];
-      if (entry->prev_action != NONE && prev != (unsigned int) -1)
-	info[prev].arabic_shaping_action() = entry->prev_action;
-      break;
-    }
+    const arabic_state_table_entry *entry = &arabic_state_table[state][this_type];
+    if (entry->prev_action != NONE && prev != (unsigned int) -1)
+      info[prev].arabic_shaping_action() = entry->prev_action;
+    break;
+  }
 }
 
 static void
diff --git a/src/hb-ot-shape.cc b/src/hb-ot-shape.cc
index 66846ed34..85f50a6d4 100644
--- a/src/hb-ot-shape.cc
+++ b/src/hb-ot-shape.cc
@@ -236,6 +236,7 @@ static void
 hb_insert_dotted_circle (hb_buffer_t *buffer, hb_font_t *font)
 {
   if (!(buffer->flags & HB_BUFFER_FLAG_BOT) ||
+      buffer->context_len[0] ||
       _hb_glyph_info_get_general_category (&buffer->info[0]) !=
       HB_UNICODE_GENERAL_CATEGORY_NON_SPACING_MARK)
     return;