From f5eead04e63e6092fba494471b18016cabe50a15 Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Wed, 28 Jun 2023 15:07:15 -0600
Subject: [PATCH] [glyf/gvar] Optimize getting variable phantom points

Used when there's no HVAR table and get_h_advance().

I see some 10% speedup with a SourceSerifVariable-Roman with
the HVAR table removed.
---
 src/OT/glyf/Glyph.hh        |  3 ++-
 src/hb-ot-var-gvar-table.hh | 30 +++++++++++++++++-------------
 2 files changed, 19 insertions(+), 14 deletions(-)

diff --git a/src/OT/glyf/Glyph.hh b/src/OT/glyf/Glyph.hh
index e5781326a..d7482bbc8 100644
--- a/src/OT/glyf/Glyph.hh
+++ b/src/OT/glyf/Glyph.hh
@@ -373,7 +373,8 @@ struct Glyph
 #ifndef HB_NO_VAR
     glyf_accelerator.gvar->apply_deltas_to_points (gid,
 						   coords,
-						   points.as_array ().sub_array (old_length));
+						   points.as_array ().sub_array (old_length),
+						   phantom_only);
 #endif
 
     // mainly used by CompositeGlyph calculating new X/Y offset value so no need to extend it
diff --git a/src/hb-ot-var-gvar-table.hh b/src/hb-ot-var-gvar-table.hh
index 79b9e3d99..9bc8c1006 100644
--- a/src/hb-ot-var-gvar-table.hh
+++ b/src/hb-ot-var-gvar-table.hh
@@ -291,7 +291,8 @@ struct gvar
     public:
     bool apply_deltas_to_points (hb_codepoint_t glyph,
 				 hb_array_t<int> coords,
-				 const hb_array_t<contour_point_t> points) const
+				 const hb_array_t<contour_point_t> points,
+				 bool phantom_only = false) const
     {
       if (!coords) return true;
 
@@ -322,6 +323,7 @@ struct gvar
       hb_vector_t<unsigned int> private_indices;
       hb_vector_t<int> x_deltas;
       hb_vector_t<int> y_deltas;
+      unsigned count = points.length;
       bool flush = false;
       do
       {
@@ -335,9 +337,10 @@ struct gvar
 
 	if (!deltas)
 	{
-	  if (unlikely (!deltas_vec.resize (points.length, false))) return false;
+	  if (unlikely (!deltas_vec.resize (count, false))) return false;
 	  deltas = deltas_vec.as_array ();
-	  hb_memset (deltas.arrayZ, 0, deltas.get_size ()); // Faster than vector resize
+	  hb_memset (deltas.arrayZ + (phantom_only ? count - 4 : 0), 0,
+		     (phantom_only ? 4 : count) * sizeof (deltas[0]));
 	}
 
 	const HBUINT8 *end = p + length;
@@ -357,7 +360,7 @@ struct gvar
 
 	if (!apply_to_all)
 	{
-	  if (!orig_points)
+	  if (!orig_points && !phantom_only)
 	  {
 	    orig_points_vec.extend (points);
 	    if (unlikely (orig_points_vec.in_error ())) return false;
@@ -366,13 +369,13 @@ struct gvar
 
 	  if (flush)
 	  {
-	    unsigned count = points.length;
-	    for (unsigned int i = 0; i < count; i++)
+	    for (unsigned int i = phantom_only ? count - 4 : 0; i < count; i++)
 	      points.arrayZ[i].translate (deltas.arrayZ[i]);
 	    flush = false;
 
 	  }
-	  hb_memset (deltas.arrayZ, 0, deltas.get_size ());
+	  hb_memset (deltas.arrayZ + (phantom_only ? count - 4 : 0), 0,
+		     (phantom_only ? 4 : count) * sizeof (deltas[0]));
 	}
 
 	if (HB_OPTIMIZE_SIZE_VAL)
@@ -387,6 +390,7 @@ struct gvar
 	      pt_index = indices[i];
 	      if (unlikely (pt_index >= deltas.length)) continue;
 	    }
+	    if (phantom_only && pt_index < count - 4) continue;
 	    auto &delta = deltas.arrayZ[pt_index];
 	    delta.flag = 1;	/* this point is referenced, i.e., explicit deltas specified */
 	    delta.x += x_deltas.arrayZ[i] * scalar;
@@ -399,7 +403,7 @@ struct gvar
 	  if (scalar != 1.0f)
 	  {
 	    if (apply_to_all)
-	      for (unsigned int i = 0; i < num_deltas; i++)
+	      for (unsigned int i = phantom_only ? count - 4 : 0; i < count; i++)
 	      {
 		unsigned int pt_index = i;
 		auto &delta = deltas.arrayZ[pt_index];
@@ -411,6 +415,7 @@ struct gvar
 	      {
 		unsigned int pt_index = indices[i];
 		if (unlikely (pt_index >= deltas.length)) continue;
+		if (phantom_only && pt_index < count - 4) continue;
 		auto &delta = deltas.arrayZ[pt_index];
 		delta.flag = 1;	/* this point is referenced, i.e., explicit deltas specified */
 		delta.x += x_deltas.arrayZ[i] * scalar;
@@ -420,7 +425,7 @@ struct gvar
 	  else
 	  {
 	    if (apply_to_all)
-	      for (unsigned int i = 0; i < num_deltas; i++)
+	      for (unsigned int i = phantom_only ? count - 4 : 0; i < count; i++)
 	      {
 		unsigned int pt_index = i;
 		auto &delta = deltas.arrayZ[pt_index];
@@ -432,6 +437,7 @@ struct gvar
 	      {
 		unsigned int pt_index = indices[i];
 		if (unlikely (pt_index >= deltas.length)) continue;
+		if (phantom_only && pt_index < count - 4) continue;
 		auto &delta = deltas.arrayZ[pt_index];
 		delta.flag = 1;	/* this point is referenced, i.e., explicit deltas specified */
 		delta.x += x_deltas.arrayZ[i];
@@ -441,11 +447,10 @@ struct gvar
 	}
 
 	/* infer deltas for unreferenced points */
-	if (!apply_to_all)
+	if (!apply_to_all && !phantom_only)
 	{
 	  if (!end_points)
 	  {
-	    unsigned count = points.length;
 	    for (unsigned i = 0; i < count; ++i)
 	      if (points.arrayZ[i].is_end_point)
 		end_points.push (i);
@@ -507,8 +512,7 @@ struct gvar
 
       if (flush)
       {
-        unsigned count = points.length;
-	for (unsigned int i = 0; i < count; i++)
+	for (unsigned int i = phantom_only ? count - 4 : 0; i < count; i++)
 	  points.arrayZ[i].translate (deltas.arrayZ[i]);
       }