From 1b78e04c78338266c200226bccb21188355046ca Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Fri, 10 Dec 2021 12:45:43 -0700
Subject: [PATCH] [buffer] Add ::reverse_groups()

---
 src/hb-buffer.cc | 23 -----------------------
 src/hb-buffer.hh | 26 +++++++++++++++++++++++++-
 2 files changed, 25 insertions(+), 24 deletions(-)

diff --git a/src/hb-buffer.cc b/src/hb-buffer.cc
index 63c1e5cfa..be3161a54 100644
--- a/src/hb-buffer.cc
+++ b/src/hb-buffer.cc
@@ -395,29 +395,6 @@ hb_buffer_t::set_masks (hb_mask_t    value,
       info[i].mask = (info[i].mask & not_mask) | value;
 }
 
-void
-hb_buffer_t::reverse_clusters ()
-{
-  unsigned int i, start, count, last_cluster;
-
-  if (unlikely (!len))
-    return;
-
-  reverse ();
-
-  count = len;
-  start = 0;
-  last_cluster = info[0].cluster;
-  for (i = 1; i < count; i++) {
-    if (last_cluster != info[i].cluster) {
-      reverse_range (start, i);
-      start = i;
-      last_cluster = info[i].cluster;
-    }
-  }
-  reverse_range (start, i);
-}
-
 void
 hb_buffer_t::merge_clusters_impl (unsigned int start,
 				  unsigned int end)
diff --git a/src/hb-buffer.hh b/src/hb-buffer.hh
index 61c40ec31..06b923f22 100644
--- a/src/hb-buffer.hh
+++ b/src/hb-buffer.hh
@@ -209,7 +209,31 @@ struct hb_buffer_t
   }
   void reverse () { reverse_range (0, len); }
 
-  HB_INTERNAL void reverse_clusters ();
+  template <typename FuncType>
+  void reverse_groups (const FuncType& group)
+  {
+    if (unlikely (!len))
+      return;
+
+    reverse ();
+
+    unsigned count = len;
+    unsigned start = 0;
+    unsigned i;
+    for (i = 1; i < count; i++)
+    {
+      if (!group (info[i - 1], info[i]))
+      {
+	reverse_range (start, i);
+	start = i;
+      }
+    }
+    reverse_range (start, i);
+  }
+
+  void reverse_clusters ()
+  { reverse_groups ([] (const hb_glyph_info_t& a, const hb_glyph_info_t& b) -> bool { return a.cluster == b.cluster; }); }
+
   HB_INTERNAL void guess_segment_properties ();
 
   HB_INTERNAL void swap_buffers ();