From d7b6e947a32b0ed46f1d86ae030f59061c023d15 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Behdad=20Esfahbod=20=28=D8=A8=D9=87=D8=AF=D8=A7=D8=AF=20?=
 =?UTF-8?q?=D8=A7=D8=B3=D9=81=D9=87=D8=A8=D8=AF=29?= <behdad@behdad.org>
Date: Wed, 21 May 2025 01:34:08 -0600
Subject: [PATCH] [gxvar] Cache shared-tuple scalar values.

GoogleSansFlex HB benchmark-font draw results:

  Before:  2.13ms
  After:   1.65ms
  Speedup: 22%

* src/truetype/ttgxvar.h (GX_BlendRec): Add `tuplescalars` field.

* src/truetype/ttgxvar.c (ft_var_load_gvar): Allocate `tuplescalars` array.
  (tt_set_mm_blend): Set its values.
  (TT_Vary_Apply_Glyph_Deltas): Use it.
  (tt_done_blend): Deallocate it.
---
 src/truetype/ttgxvar.c | 37 ++++++++++++++++++++++++++++++++++---
 src/truetype/ttgxvar.h |  5 +++++
 2 files changed, 39 insertions(+), 3 deletions(-)

diff --git a/src/truetype/ttgxvar.c b/src/truetype/ttgxvar.c
index d0626c7b0..681c0cad2 100644
--- a/src/truetype/ttgxvar.c
+++ b/src/truetype/ttgxvar.c
@@ -1831,6 +1831,10 @@
         FT_TRACE5(( "]\n" ));
       }
 
+      if ( FT_NEW_ARRAY( blend->tuplescalars,
+                         gvar_head.globalCoordCount ) )
+        goto Fail2;
+
       blend->tuplecount = gvar_head.globalCoordCount;
 
       FT_TRACE5(( "\n" ));
@@ -2951,6 +2955,9 @@
       }
     }
 
+    for ( i = 0 ; i < blend->tuplecount ; i++ )
+      blend->tuplescalars[i] = (FT_Fixed)-0x20000L;
+
   Exit:
     return error;
   }
@@ -4192,13 +4199,16 @@
     tupleCount &= GX_TC_TUPLE_COUNT_MASK;
     for ( i = 0; i < tupleCount; i++ )
     {
-      FT_UInt   tupleDataSize;
-      FT_UInt   tupleIndex;
-      FT_Fixed  apply;
+      FT_UInt    tupleDataSize;
+      FT_UInt    tupleIndex;
+      FT_Fixed   apply;
+      FT_Fixed*  tupleScalars;
 
 
       FT_TRACE6(( "  tuple %d:\n", i ));
 
+      tupleScalars = blend->tuplescalars;
+
       /* Enter frame for four bytes. */
       if ( stream->limit - stream->cursor < 4 )
       {
@@ -4214,11 +4224,24 @@
       {
         for ( j = 0; j < blend->num_axis; j++ )
           peak_coords[j] = FT_fdot14ToFixed( FT_GET_SHORT() );
+
         tuple_coords = peak_coords;
+        tupleScalars = NULL;
       }
       else if ( ( tupleIndex & GX_TI_TUPLE_INDEX_MASK ) < blend->tuplecount )
+      {
+        FT_Fixed  scalar = tupleScalars[tupleIndex & GX_TI_TUPLE_INDEX_MASK];
+
+
+        if ( scalar != (FT_Fixed)-0x20000 )
+        {
+          apply = scalar;
+          goto apply_found;
+        }
+
         tuple_coords = blend->tuplecoords +
             ( tupleIndex & GX_TI_TUPLE_INDEX_MASK ) * blend->num_axis;
+      }
       else
       {
         FT_TRACE2(( "TT_Vary_Apply_Glyph_Deltas:"
@@ -4234,6 +4257,8 @@
           im_start_coords[j] = FT_fdot14ToFixed( FT_GET_SHORT() );
         for ( j = 0; j < blend->num_axis; j++ )
           im_end_coords[j] = FT_fdot14ToFixed( FT_GET_SHORT() );
+
+        tupleScalars = NULL;
       }
 
       apply = ft_var_apply_tuple( blend,
@@ -4242,6 +4267,11 @@
                                   im_start_coords,
                                   im_end_coords );
 
+      if ( tupleScalars )
+        tupleScalars[tupleIndex & GX_TI_TUPLE_INDEX_MASK] = apply;
+
+    apply_found:
+
       if ( apply == 0 )              /* tuple isn't active for our blend */
       {
         offsetToData += tupleDataSize;
@@ -4624,6 +4654,7 @@
         FT_FREE( blend->mvar_table );
       }
 
+      FT_FREE( blend->tuplescalars );
       FT_FREE( blend->tuplecoords );
       FT_FREE( blend->glyphoffsets );
       FT_FREE( blend );
diff --git a/src/truetype/ttgxvar.h b/src/truetype/ttgxvar.h
index 9326011e3..fe8f1f6b6 100644
--- a/src/truetype/ttgxvar.h
+++ b/src/truetype/ttgxvar.h
@@ -255,6 +255,10 @@ FT_BEGIN_HEADER
    *     A two-dimensional array that holds the shared tuple coordinates
    *     in the `gvar' table.
    *
+   *   tuplescalars ::
+   *     A one-dimensional array that holds the shared tuple
+   *     scalars in the `gvar' table for current face coordinates.
+   *
    *   gv_glyphcnt ::
    *     The number of glyphs handled in the `gvar' table.
    *
@@ -293,6 +297,7 @@ FT_BEGIN_HEADER
 
     FT_UInt         tuplecount;
     FT_Fixed*       tuplecoords;      /* tuplecoords[tuplecount][num_axis] */
+    FT_Fixed*       tuplescalars;     /* tuplescalars[tuplecount]          */
 
     FT_UInt         gv_glyphcnt;
     FT_ULong*       glyphoffsets;         /* glyphoffsets[gv_glyphcnt + 1] */