[freetype2] master 60bf264: [truetype] Make `IUP' gvar deltas do the same as Apple (#50832).

[Werner LEMBERG]

branch: master
commit 60bf264ee25dc08403dddb3e4cd2bf950cda9e90
Author: Behdad Esfahbod <address@hidden>
Commit: Werner Lemberg <address@hidden>

    [truetype] Make `IUP' gvar deltas do the same as Apple (#50832).
    
    When points are not touched by gvar interpolation deltas, FreeType
    gave a slightly different result than Apple's CoreText.
    
    The OpenType working group will update the specification to document
    the following behaviour: If the two points with deltas to the `left'
    and `right' of the untouched point have the same coordinate, then
    the inferred delta for the untouched point should be zero.
    
    * src/truetype/ttgxvar.c (tt_delta_interpolate): Implement new
    behaviour.
---
 ChangeLog              | 15 +++++++++++++++
 src/truetype/ttgxvar.c | 23 +++++------------------
 2 files changed, 20 insertions(+), 18 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 8dd013e..05fd0aa 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,18 @@
+2017-05-02  Behdad Esfahbod  <address@hidden>
+
+       [truetype] Make `IUP' gvar deltas do the same as Apple (#50832).
+
+       When points are not touched by gvar interpolation deltas, FreeType
+       gave a slightly different result than Apple's CoreText.
+
+       The OpenType working group will update the specification to document
+       the following behaviour: If the two points with deltas to the `left'
+       and `right' of the untouched point have the same coordinate, then
+       the inferred delta for the untouched point should be zero.
+
+       * src/truetype/ttgxvar.c (tt_delta_interpolate): Implement new
+       behaviour.
+
 2017-05-02  Werner Lemberg  <address@hidden>
 
        [autofit] Remove `slight' auto-hint mode again.
diff --git a/src/truetype/ttgxvar.c b/src/truetype/ttgxvar.c
index 6d4529b..0cedb6b 100644
--- a/src/truetype/ttgxvar.c
+++ b/src/truetype/ttgxvar.c
@@ -3081,25 +3081,12 @@
       d1   = out1 - in1;
       d2   = out2 - in2;
 
-      if ( out1 == out2 || in1 == in2 )
+      /* If the reference points have the same coordinate but different */
+      /* delta, inferred delta is zero.  Otherwise interpolate.         */
+      if ( in1 != in2 || out1 == out2 )
       {
-        for ( p = p1; p <= p2; p++ )
-        {
-          out = in_points[p].x;
-
-          if ( out <= in1 )
-            out += d1;
-          else if ( out >= in2 )
-            out += d2;
-          else
-            out = out1;
-
-          out_points[p].x = out;
-        }
-      }
-      else
-      {
-        FT_Fixed  scale = FT_DivFix( out2 - out1, in2 - in1 );
+        FT_Fixed  scale = in1 != in2 ? FT_DivFix( out2 - out1, in2 - in1 )
+                                     : 0;
 
 
         for ( p = p1; p <= p2; p++ )