From e92eefaabbed7aa04fe98214ae43b061d1497735 Mon Sep 17 00:00:00 2001
From: Behdad Esfahbod <behdad@behdad.org>
Date: Sun, 2 Jul 2023 11:35:51 -0600
Subject: [PATCH] [gvar] Cache two values in shared_tuple_active_idx

Speeds up varc-hangul.ttf draw_glyph by 10%.
---
 src/hb-ot-var-common.hh     | 17 ++++++++++++-----
 src/hb-ot-var-gvar-table.hh | 15 +++++++++------
 2 files changed, 21 insertions(+), 11 deletions(-)

diff --git a/src/hb-ot-var-common.hh b/src/hb-ot-var-common.hh
index c28962103..44ec64bc0 100644
--- a/src/hb-ot-var-common.hh
+++ b/src/hb-ot-var-common.hh
@@ -300,12 +300,13 @@ struct TupleVariationHeader
 
   float calculate_scalar (hb_array_t<int> coords, unsigned int coord_count,
                           const hb_array_t<const F2DOT14> shared_tuples,
-			  const hb_vector_t<int> *shared_tuple_active_idx = nullptr) const
+			  const hb_vector_t<hb_pair_t<int,int>> *shared_tuple_active_idx = nullptr) const
   {
     const F2DOT14 *peak_tuple;
 
     unsigned start_idx = 0;
     unsigned end_idx = coord_count;
+    unsigned step = 1;
 
     if (has_peak ())
       peak_tuple = get_peak_tuple (coord_count).arrayZ;
@@ -320,10 +321,16 @@ struct TupleVariationHeader
       {
 	if (unlikely (index >= shared_tuple_active_idx->length))
 	  return 0.f;
-	int v = (*shared_tuple_active_idx).arrayZ[index];
-	if (v != -1)
+	auto _ = (*shared_tuple_active_idx).arrayZ[index];
+	if (_.second != -1)
 	{
-	  start_idx = v;
+	  start_idx = _.first;
+	  end_idx = _.second + 1;
+	  step = _.second - _.first;
+	}
+	else if (_.first != -1)
+	{
+	  start_idx = _.first;
 	  end_idx = start_idx + 1;
 	}
       }
@@ -339,7 +346,7 @@ struct TupleVariationHeader
     }
 
     float scalar = 1.f;
-    for (unsigned int i = start_idx; i < end_idx; i++)
+    for (unsigned int i = start_idx; i < end_idx; i += step)
     {
       int peak = peak_tuple[i].to_int ();
       if (!peak) continue;
diff --git a/src/hb-ot-var-gvar-table.hh b/src/hb-ot-var-gvar-table.hh
index fc8ae2333..b5099ac07 100644
--- a/src/hb-ot-var-gvar-table.hh
+++ b/src/hb-ot-var-gvar-table.hh
@@ -242,21 +242,24 @@ struct gvar
       for (unsigned i = 0; i < count; i++)
       {
 	hb_array_t<const F2DOT14> tuple = shared_tuples.sub_array (axis_count * i, axis_count);
-	int idx = -1;
+	int idx1 = -1, idx2 = -1;
 	for (unsigned j = 0; j < axis_count; j++)
 	{
 	  const F2DOT14 &peak = tuple.arrayZ[j];
 	  if (peak.to_int () != 0)
 	  {
-	    if (idx != -1)
+	    if (idx1 == -1)
+	      idx1 = j;
+	    else if (idx2 == -1)
+	      idx2 = j;
+	    else
 	    {
-	      idx = -1;
+	      idx1 = idx2 = -1;
 	      break;
 	    }
-	    idx = j;
 	  }
 	}
-	shared_tuple_active_idx.arrayZ[i] = idx;
+	shared_tuple_active_idx.arrayZ[i] = {idx1, idx2};
       }
     }
     ~accelerator_t () { table.destroy (); }
@@ -523,7 +526,7 @@ struct gvar
     private:
     hb_blob_ptr_t<gvar> table;
     unsigned glyphCount;
-    hb_vector_t<signed> shared_tuple_active_idx;
+    hb_vector_t<hb_pair_t<int, int>> shared_tuple_active_idx;
   };
 
   protected: