From 05c17787c4fc5283925920b546952ccca0ba4a00 Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Mon, 12 Jul 2021 16:55:08 -0600
Subject: [PATCH 1/9] [buffer] Rewind cursor in clear_output()

---
 src/hb-buffer.cc | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/hb-buffer.cc b/src/hb-buffer.cc
index 7aa37eaf0..7ca988dbc 100644
--- a/src/hb-buffer.cc
+++ b/src/hb-buffer.cc
@@ -297,6 +297,7 @@ hb_buffer_t::clear_output ()
   have_output = true;
   have_positions = false;
 
+  idx = 0;
   out_len = 0;
   out_info = info;
 }

From a623446a34a4a388f86afc97ed9c5a74792d5420 Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Mon, 12 Jul 2021 16:55:54 -0600
Subject: [PATCH 2/9] [shape] Remove stray clear_output() call in hb_shape()

---
 src/hb-ot-shape.cc | 2 --
 1 file changed, 2 deletions(-)

diff --git a/src/hb-ot-shape.cc b/src/hb-ot-shape.cc
index b70dece91..246936db3 100644
--- a/src/hb-ot-shape.cc
+++ b/src/hb-ot-shape.cc
@@ -1158,8 +1158,6 @@ hb_ot_shape_internal (hb_ot_shape_context_t *c)
 
   _hb_buffer_allocate_unicode_vars (c->buffer);
 
-  c->buffer->clear_output ();
-
   hb_ot_shape_initialize_masks (c);
   hb_set_unicode_props (c->buffer);
   hb_insert_dotted_circle (c->buffer, c->font);

From 431f164003d1d92b657b3facf984c8bbe342418b Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Mon, 12 Jul 2021 16:57:25 -0600
Subject: [PATCH 3/9] [layout] Don't call clear_output() before pause-func

---
 src/hb-ot-layout.cc | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/src/hb-ot-layout.cc b/src/hb-ot-layout.cc
index 257cc916e..379d92e6a 100644
--- a/src/hb-ot-layout.cc
+++ b/src/hb-ot-layout.cc
@@ -1942,10 +1942,7 @@ inline void hb_ot_map_t::apply (const Proxy &proxy,
     }
 
     if (stage->pause_func)
-    {
-      buffer->clear_output ();
       stage->pause_func (plan, font, buffer);
-    }
   }
 }
 

From 62b441e6ff798f1d551d290a2a4970482254dbe2 Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Mon, 12 Jul 2021 16:59:34 -0600
Subject: [PATCH 4/9] [layout] Use Proxy::inplace instead of table index check

Equivalent.
---
 src/hb-ot-layout.cc | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/src/hb-ot-layout.cc b/src/hb-ot-layout.cc
index 379d92e6a..340c95f7f 100644
--- a/src/hb-ot-layout.cc
+++ b/src/hb-ot-layout.cc
@@ -1886,8 +1886,9 @@ apply_string (OT::hb_ot_apply_context_t *c,
   if (likely (!lookup.is_reverse ()))
   {
     /* in/out forward substitution/positioning */
-    if (Proxy::table_index == 0u)
+    if (!Proxy::inplace)
       buffer->clear_output ();
+
     buffer->idx = 0;
 
     bool ret;

From a7f4c985a8080797482c971a7b6275636fe5be62 Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Mon, 12 Jul 2021 17:00:46 -0600
Subject: [PATCH 5/9] [ot-layout] Always swap_buffers() even if no
 substitutions happened

---
 src/hb-ot-layout.cc | 14 +++++---------
 1 file changed, 5 insertions(+), 9 deletions(-)

diff --git a/src/hb-ot-layout.cc b/src/hb-ot-layout.cc
index 340c95f7f..85795556f 100644
--- a/src/hb-ot-layout.cc
+++ b/src/hb-ot-layout.cc
@@ -1890,16 +1890,12 @@ apply_string (OT::hb_ot_apply_context_t *c,
       buffer->clear_output ();
 
     buffer->idx = 0;
+    apply_forward (c, accel);
 
-    bool ret;
-    ret = apply_forward (c, accel);
-    if (ret)
-    {
-      if (!Proxy::inplace)
-	buffer->swap_buffers ();
-      else
-	assert (!buffer->has_separate_output ());
-    }
+    if (!Proxy::inplace)
+      buffer->swap_buffers ();
+    else
+      assert (!buffer->has_separate_output ());
   }
   else
   {

From 10a9960f0af9d6fb93ff3d234b2a989f9bc00b21 Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Mon, 12 Jul 2021 17:09:03 -0600
Subject: [PATCH 6/9] [buffer] Restructure swap_buffers()

Is more of a "commit" operation now. Will rename when ready.
---
 src/hb-buffer.cc | 20 +++++++-------------
 1 file changed, 7 insertions(+), 13 deletions(-)

diff --git a/src/hb-buffer.cc b/src/hb-buffer.cc
index 7ca988dbc..583137a58 100644
--- a/src/hb-buffer.cc
+++ b/src/hb-buffer.cc
@@ -317,29 +317,23 @@ hb_buffer_t::clear_positions ()
 void
 hb_buffer_t::swap_buffers ()
 {
-  if (unlikely (!successful)) return;
+  assert (have_output);
 
   assert (idx <= len);
-  if (unlikely (!next_glyphs (len - idx))) return;
 
-  assert (have_output);
-  have_output = false;
+  if (unlikely (!successful || !next_glyphs (len - idx)))
+    goto reset;
 
   if (out_info != info)
   {
-    hb_glyph_info_t *tmp;
-    tmp = info;
+    pos = (hb_glyph_position_t *) info;
     info = out_info;
-    out_info = tmp;
-
-    pos = (hb_glyph_position_t *) out_info;
   }
-
-  unsigned int tmp;
-  tmp = len;
   len = out_len;
-  out_len = tmp;
 
+reset:
+  have_output = false;
+  out_len = 0;
   idx = 0;
 }
 

From 3807061d634b60bd6235d6e1d8c47a034377f924 Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Mon, 12 Jul 2021 17:02:03 -0600
Subject: [PATCH 7/9] [ot-layout] Don't remove_output() before reverse
 substitution

No need anymore, because of new swap_buffers() semantics.

Just assert instead.
---
 src/hb-buffer.cc    | 10 ----------
 src/hb-buffer.hh    |  1 -
 src/hb-ot-layout.cc |  4 +---
 3 files changed, 1 insertion(+), 14 deletions(-)

diff --git a/src/hb-buffer.cc b/src/hb-buffer.cc
index 583137a58..82aeaae0f 100644
--- a/src/hb-buffer.cc
+++ b/src/hb-buffer.cc
@@ -281,16 +281,6 @@ hb_buffer_t::add_info (const hb_glyph_info_t &glyph_info)
 }
 
 
-void
-hb_buffer_t::remove_output ()
-{
-  have_output = false;
-  have_positions = false;
-
-  out_len = 0;
-  out_info = info;
-}
-
 void
 hb_buffer_t::clear_output ()
 {
diff --git a/src/hb-buffer.hh b/src/hb-buffer.hh
index 33d6e6c66..67429df23 100644
--- a/src/hb-buffer.hh
+++ b/src/hb-buffer.hh
@@ -209,7 +209,6 @@ struct hb_buffer_t
   HB_INTERNAL void guess_segment_properties ();
 
   HB_INTERNAL void swap_buffers ();
-  HB_INTERNAL void remove_output ();
   HB_INTERNAL void clear_output ();
   HB_INTERNAL void clear_positions ();
 
diff --git a/src/hb-ot-layout.cc b/src/hb-ot-layout.cc
index 85795556f..cb428fba8 100644
--- a/src/hb-ot-layout.cc
+++ b/src/hb-ot-layout.cc
@@ -1900,10 +1900,8 @@ apply_string (OT::hb_ot_apply_context_t *c,
   else
   {
     /* in-place backward substitution/positioning */
-    if (Proxy::table_index == 0u)
-      buffer->remove_output ();
+    assert (!buffer->have_output);
     buffer->idx = buffer->len - 1;
-
     apply_backward (c, accel);
   }
 }

From 3e266e5f64b6d078d64fe0f3783f774d7e29472d Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Mon, 12 Jul 2021 17:30:26 -0600
Subject: [PATCH 8/9] [buffer] Update comments

---
 src/hb-buffer.cc | 9 +++++----
 src/hb-buffer.hh | 2 +-
 2 files changed, 6 insertions(+), 5 deletions(-)

diff --git a/src/hb-buffer.cc b/src/hb-buffer.cc
index 82aeaae0f..c147dfcce 100644
--- a/src/hb-buffer.cc
+++ b/src/hb-buffer.cc
@@ -96,14 +96,15 @@ hb_segment_properties_hash (const hb_segment_properties_t *p)
  * As an optimization, both info and out_info may point to the
  * same piece of memory, which is owned by info.  This remains the
  * case as long as out_len doesn't exceed i at any time.
- * In that case, swap_buffers() is no-op and the glyph operations operate
- * mostly in-place.
+ * In that case, swap_buffers() is mostly no-op and the glyph operations
+ * operate mostly in-place.
  *
  * As soon as out_info gets longer than info, out_info is moved over
- * to an alternate buffer (which we reuse the pos buffer for!), and its
+ * to an alternate buffer (which we reuse the pos buffer for), and its
  * current contents (out_len entries) are copied to the new place.
+ *
  * This should all remain transparent to the user.  swap_buffers() then
- * switches info and out_info.
+ * switches info over to out_info and does housekeeping.
  */
 
 
diff --git a/src/hb-buffer.hh b/src/hb-buffer.hh
index 67429df23..1d47a71a7 100644
--- a/src/hb-buffer.hh
+++ b/src/hb-buffer.hh
@@ -107,7 +107,7 @@ struct hb_buffer_t
 
   unsigned int idx; /* Cursor into ->info and ->pos arrays */
   unsigned int len; /* Length of ->info and ->pos arrays */
-  unsigned int out_len; /* Length of ->out array if have_output */
+  unsigned int out_len; /* Length of ->out_info array if have_output */
 
   unsigned int allocated; /* Length of allocated arrays */
   hb_glyph_info_t     *info;

From 95b04f7409e5af6dec97feb4ed18ba0bfae2cd88 Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Mon, 12 Jul 2021 17:35:45 -0600
Subject: [PATCH 9/9] [buffer] Remove unnecessary have_separate_output()

---
 src/hb-buffer.hh    | 5 +----
 src/hb-ot-layout.cc | 2 --
 2 files changed, 1 insertion(+), 6 deletions(-)

diff --git a/src/hb-buffer.hh b/src/hb-buffer.hh
index 1d47a71a7..8635ebd35 100644
--- a/src/hb-buffer.hh
+++ b/src/hb-buffer.hh
@@ -189,13 +189,10 @@ struct hb_buffer_t
   hb_glyph_info_t &prev ()      { return out_info[out_len ? out_len - 1 : 0]; }
   hb_glyph_info_t prev () const { return out_info[out_len ? out_len - 1 : 0]; }
 
-  HB_NODISCARD bool has_separate_output () const { return info != out_info; }
-
-
   HB_INTERNAL void reset ();
   HB_INTERNAL void clear ();
 
-  unsigned int backtrack_len () const { return have_output? out_len : idx; }
+  unsigned int backtrack_len () const { return have_output ? out_len : idx; }
   unsigned int lookahead_len () const { return len - idx; }
   unsigned int next_serial () { return serial++; }
 
diff --git a/src/hb-ot-layout.cc b/src/hb-ot-layout.cc
index cb428fba8..0454af206 100644
--- a/src/hb-ot-layout.cc
+++ b/src/hb-ot-layout.cc
@@ -1894,8 +1894,6 @@ apply_string (OT::hb_ot_apply_context_t *c,
 
     if (!Proxy::inplace)
       buffer->swap_buffers ();
-    else
-      assert (!buffer->has_separate_output ());
   }
   else
   {