[sfnt, truetype] Add `size_reset` to `MetricsVariations`.

This is a generalization of commit

```
commit e6699596af5c5d6f0ae0ea06e19df87dce088df8
Author: Werner Lemberg <wl@gnu.org>
Date:   Thu Feb 2 11:38:04 2017 +0100

    [truetype] Fix MVAR post-action handling.
```

It is also possible for plain `CFF ` style fonts to contain an `fvar` and
`MVAR` table and use `cff_metrics_adjust`.  `tt_size_reset` should only be
called with `TT_Size` and never with `CFF_Size`.

Allow the "metrics-variations" service to specify the correct function (if
any) to reset `FT_Size`s after adjusting metrics.

* src/truetype/ttobjs.c (tt_size_reset): Split off some functionality
into...
(tt_size_reset_height): ... this new function.

* src/truetype/ttdriver.c (tt_service_metrics_variations): Add
`size_reset`.
(tt_size_select, tt_size_request): Updated.

* src/truetype/ttobjs.h: Updated.

* include/freetype/internal/services/svmetric.h (MetricsVariations): Add
`size_reset`.
(FT_DEFINE_SERVICE_METRICSVARIATIONSREC): Updated.

* include/freetype/internal/tttypes.h (TT_FaceRec_): Rename `var` to
`tt_var` and add `face_var`.

* src/cff/cffdrivr.c (cff_service_metrics_variations): Add `size_reset`.
(cff_hadvance_adjust, cff_metrics_adjust): Updated.

* src/cff/cffobjs.c (cff_face_init): Use `face_var`.

* src/sfnt/sfobjs.c (sfnt_init_face): Initialize `face_var`.

* src/sfnt/ttmtx.c (tt_face_get_metrics): Use `tt_var`.

* src/truetype/ttgxvar.c (tt_size_reset_iterator): Renamed to...
(ft_size_reset_iterator): ... this new function.
Call `size_reset`.
(tt_apply_mvar): Pass `size_reset` to `ft_size_reset_iterator`.

Fixes #1211

10 files changed, 93 insertions, 56 deletions

diff --git a/include/freetype/internal/services/svmetric.h b/include/freetype/internal/services/svmetric.h
index e588ea487..d067dc977 100644
--- a/include/freetype/internal/services/svmetric.h
+++ b/include/freetype/internal/services/svmetric.h
@@ -77,6 +77,9 @@ FT_BEGIN_HEADER
   typedef void
   (*FT_Metrics_Adjust_Func)( FT_Face  face );
 
+  typedef void
+  (*FT_Size_Reset_Func)( FT_Size  size );
+
 
   FT_DEFINE_SERVICE( MetricsVariations )
   {
@@ -90,6 +93,7 @@ FT_BEGIN_HEADER
     FT_VOrg_Adjust_Func      vorg_adjust;
 
     FT_Metrics_Adjust_Func   metrics_adjust;
+    FT_Size_Reset_Func       size_reset;
   };
 
 
@@ -101,7 +105,8 @@ FT_BEGIN_HEADER
                                                 tsb_adjust_,       \
                                                 bsb_adjust_,       \
                                                 vorg_adjust_,      \
-                                                metrics_adjust_  ) \
+                                                metrics_adjust_,   \
+                                                size_reset_      ) \
   static const FT_Service_MetricsVariationsRec  class_ =           \
   {                                                                \
     hadvance_adjust_,                                              \
@@ -111,7 +116,8 @@ FT_BEGIN_HEADER
     tsb_adjust_,                                                   \
     bsb_adjust_,                                                   \
     vorg_adjust_,                                                  \
-    metrics_adjust_                                                \
+    metrics_adjust_,                                               \
+    size_reset_                                                    \
   };
 
   /* */
diff --git a/include/freetype/internal/tttypes.h b/include/freetype/internal/tttypes.h
index dc790f932..d257d05bd 100644
--- a/include/freetype/internal/tttypes.h
+++ b/include/freetype/internal/tttypes.h
@@ -1455,8 +1455,14 @@ FT_BEGIN_HEADER
     void*                 mm;
 
     /* a typeless pointer to the FT_Service_MetricsVariationsRec table */
-    /* used to handle the HVAR, VVAR, and MVAR OpenType tables         */
-    void*                 var;
+    /* used to handle the HVAR, VVAR, and MVAR OpenType tables by the  */
+    /* "truetype" driver                                               */
+    void*                 tt_var;
+
+    /* a typeless pointer to the FT_Service_MetricsVariationsRec table */
+    /* used to handle the HVAR, VVAR, and MVAR OpenType tables by this */
+    /* TT_Face's driver                                                */
+    void*                 face_var;
 #endif
 
     /* a typeless pointer to the PostScript Aux service */
diff --git a/src/cff/cffdrivr.c b/src/cff/cffdrivr.c
index 4e2e0e00d..688c4c0b3 100644
--- a/src/cff/cffdrivr.c
+++ b/src/cff/cffdrivr.c
@@ -1046,7 +1046,8 @@
                        FT_UInt   gindex,
                        FT_Int   *avalue )
   {
-    FT_Service_MetricsVariations  var = (FT_Service_MetricsVariations)face->var;
+    FT_Service_MetricsVariations
+      var = (FT_Service_MetricsVariations)face->tt_var;
 
 
     return var->hadvance_adjust( FT_FACE( face ), gindex, avalue );
@@ -1056,7 +1057,8 @@
   static void
   cff_metrics_adjust( CFF_Face  face )
   {
-    FT_Service_MetricsVariations  var = (FT_Service_MetricsVariations)face->var;
+    FT_Service_MetricsVariations
+      var = (FT_Service_MetricsVariations)face->tt_var;
 
 
     var->metrics_adjust( FT_FACE( face ) );
@@ -1075,7 +1077,8 @@
     (FT_BSB_Adjust_Func)     NULL,                   /* bsb_adjust      */
     (FT_VOrg_Adjust_Func)    NULL,                   /* vorg_adjust     */
 
-    (FT_Metrics_Adjust_Func) cff_metrics_adjust      /* metrics_adjust  */
+    (FT_Metrics_Adjust_Func) cff_metrics_adjust,     /* metrics_adjust  */
+    (FT_Size_Reset_Func)     NULL                    /* size_reset      */
   )
 #endif
 
diff --git a/src/cff/cffobjs.c b/src/cff/cffobjs.c
index 3e94a283e..9608a4178 100644
--- a/src/cff/cffobjs.c
+++ b/src/cff/cffobjs.c
@@ -719,8 +719,10 @@
 
 #ifdef TT_CONFIG_OPTION_GX_VAR_SUPPORT
       {
-        FT_Service_MultiMasters       mm  = (FT_Service_MultiMasters)face->mm;
-        FT_Service_MetricsVariations  var = (FT_Service_MetricsVariations)face->var;
+        FT_Service_MultiMasters
+          mm = (FT_Service_MultiMasters)face->mm;
+        FT_Service_MetricsVariations
+          var = (FT_Service_MetricsVariations)face->face_var;
 
         FT_UInt  instance_index = (FT_UInt)face_index >> 16;
 
diff --git a/src/sfnt/sfobjs.c b/src/sfnt/sfobjs.c
index 6469da9ab..13f2f45f4 100644
--- a/src/sfnt/sfobjs.c
+++ b/src/sfnt/sfobjs.c
@@ -534,17 +534,23 @@
                                         0 );
     }
 
-    if ( !face->var )
+    if ( !face->tt_var )
     {
       /* we want the metrics variations interface */
       /* from the `truetype' module only          */
       FT_Module  tt_module = FT_Get_Module( library, "truetype" );
 
 
-      face->var = ft_module_get_service( tt_module,
-                                         FT_SERVICE_ID_METRICS_VARIATIONS,
-                                         0 );
+      face->tt_var = ft_module_get_service( tt_module,
+                                            FT_SERVICE_ID_METRICS_VARIATIONS,
+                                            0 );
     }
+
+    if ( !face->face_var )
+      face->face_var = ft_module_get_service(
+                         &face->root.driver->root,
+                         FT_SERVICE_ID_METRICS_VARIATIONS,
+                         0 );
 #endif
 
     FT_TRACE2(( "SFNT driver\n" ));
diff --git a/src/sfnt/ttmtx.c b/src/sfnt/ttmtx.c
index 5e53e6dd4..38ee9ae72 100644
--- a/src/sfnt/ttmtx.c
+++ b/src/sfnt/ttmtx.c
@@ -239,7 +239,7 @@
 
 #ifdef TT_CONFIG_OPTION_GX_VAR_SUPPORT
     FT_Service_MetricsVariations  var =
-      (FT_Service_MetricsVariations)face->var;
+      (FT_Service_MetricsVariations)face->tt_var;
 #endif
 
 
diff --git a/src/truetype/ttdriver.c b/src/truetype/ttdriver.c
index 4e689e99a..c2e041cd3 100644
--- a/src/truetype/ttdriver.c
+++ b/src/truetype/ttdriver.c
@@ -316,7 +316,7 @@
       /* use the scaled metrics, even when tt_size_reset fails */
       FT_Select_Metrics( size->face, strike_index );
 
-      tt_size_reset( ttsize, 0 ); /* ignore return value */
+      tt_size_reset( ttsize ); /* ignore return value */
     }
     else
     {
@@ -377,7 +377,7 @@
 
     if ( FT_IS_SCALABLE( size->face ) )
     {
-      error = tt_size_reset( ttsize, 0 );
+      error = tt_size_reset( ttsize );
 
 #ifdef TT_USE_BYTECODE_INTERPRETER
       /* for the `MPS' bytecode instruction we need the point size */
@@ -559,7 +559,8 @@
     (FT_BSB_Adjust_Func)     NULL,                   /* bsb_adjust      */
     (FT_VOrg_Adjust_Func)    NULL,                   /* vorg_adjust     */
 
-    (FT_Metrics_Adjust_Func) tt_apply_mvar           /* metrics_adjust  */
+    (FT_Metrics_Adjust_Func) tt_apply_mvar,          /* metrics_adjust  */
+    (FT_Size_Reset_Func)     tt_size_reset_height    /* size_reset      */
   )
 
 #endif /* TT_CONFIG_OPTION_GX_VAR_SUPPORT */
diff --git a/src/truetype/ttgxvar.c b/src/truetype/ttgxvar.c
index 20d27ee42..3af028aac 100644
--- a/src/truetype/ttgxvar.c
+++ b/src/truetype/ttgxvar.c
@@ -1462,15 +1462,14 @@
 
 
   static FT_Error
-  tt_size_reset_iterator( FT_ListNode  node,
+  ft_size_reset_iterator( FT_ListNode  node,
                           void*        user )
   {
-    TT_Size  size = (TT_Size)node->data;
-
-    FT_UNUSED( user );
+    FT_Size                       size = (FT_Size)node->data;
+    FT_Service_MetricsVariations  var  = (FT_Service_MetricsVariations)user;
 
 
-    tt_size_reset( size, 1 );
+    var->size_reset( size );
 
     return FT_Err_Ok;
   }
@@ -1543,6 +1542,9 @@
 
     /* adjust all derived values */
     {
+      FT_Service_MetricsVariations  var =
+        (FT_Service_MetricsVariations)face->face_var;
+
       FT_Face  root = &face->root;
 
       /*
@@ -1584,11 +1586,12 @@
                                   face->postscript.underlineThickness / 2;
       root->underline_thickness = face->postscript.underlineThickness;
 
-      /* iterate over all FT_Size objects and call `tt_size_reset' */
-      /* to propagate the metrics changes                          */
-      FT_List_Iterate( &root->sizes_list,
-                       tt_size_reset_iterator,
-                       NULL );
+      /* iterate over all FT_Size objects and call `var->size_reset' */
+      /* to propagate the metrics changes                            */
+      if ( var && var->size_reset )
+        FT_List_Iterate( &root->sizes_list,
+                         ft_size_reset_iterator,
+                         (void*)var );
     }
   }
 
diff --git a/src/truetype/ttobjs.c b/src/truetype/ttobjs.c
index 4a8873fd8..ee4f3de1b 100644
--- a/src/truetype/ttobjs.c
+++ b/src/truetype/ttobjs.c
@@ -1338,39 +1338,25 @@
   /**************************************************************************
    *
    * @Function:
-   *   tt_size_reset
+   *   tt_size_reset_height
    *
    * @Description:
-   *   Reset a TrueType size when resolutions and character dimensions
-   *   have been changed.
+   *   Recompute a TrueType size's ascender, descender, and height
+   *   when resolutions and character dimensions have been changed.
+   *   Used for variation fonts as an iterator function.
    *
    * @Input:
    *   size ::
    *     A handle to the target size object.
-   *
-   *   only_height ::
-   *     Only recompute ascender, descender, and height;
-   *     this flag is used for variation fonts where
-   *     `tt_size_reset' is used as an iterator function.
    */
   FT_LOCAL_DEF( FT_Error )
-  tt_size_reset( TT_Size  size,
-                 FT_Bool  only_height )
+  tt_size_reset_height( TT_Size  size )
   {
-    TT_Face           face;
-    FT_Size_Metrics*  size_metrics;
-
-
-    face = (TT_Face)size->root.face;
-
-    /* nothing to do for CFF2 */
-    if ( face->is_cff2 )
-      return FT_Err_Ok;
+    TT_Face           face         = (TT_Face)size->root.face;
+    FT_Size_Metrics*  size_metrics = &size->hinted_metrics;
 
     size->ttmetrics.valid = FALSE;
 
-    size_metrics = &size->hinted_metrics;
-
     /* copy the result from base layer */
     *size_metrics = size->root.metrics;
 
@@ -1397,12 +1383,34 @@
 
     size->ttmetrics.valid = TRUE;
 
-    if ( only_height )
-    {
-      /* we must not recompute the scaling values here since       */
-      /* `tt_size_reset' was already called (with only_height = 0) */
-      return FT_Err_Ok;
-    }
+    return FT_Err_Ok;
+  }
+
+
+  /**************************************************************************
+   *
+   * @Function:
+   *   tt_size_reset
+   *
+   * @Description:
+   *   Reset a TrueType size when resolutions and character dimensions
+   *   have been changed.
+   *
+   * @Input:
+   *   size ::
+   *     A handle to the target size object.
+   */
+  FT_LOCAL_DEF( FT_Error )
+  tt_size_reset( TT_Size  size )
+  {
+    FT_Error          error;
+    TT_Face           face         = (TT_Face)size->root.face;
+    FT_Size_Metrics*  size_metrics = &size->hinted_metrics;
+
+
+    error = tt_size_reset_height( size );
+    if ( error )
+      return error;
 
     if ( face->header.Flags & 8 )
     {
diff --git a/src/truetype/ttobjs.h b/src/truetype/ttobjs.h
index bc6fbe7f1..d74264e57 100644
--- a/src/truetype/ttobjs.h
+++ b/src/truetype/ttobjs.h
@@ -391,8 +391,10 @@ FT_BEGIN_HEADER
 #endif /* TT_USE_BYTECODE_INTERPRETER */
 
   FT_LOCAL( FT_Error )
-  tt_size_reset( TT_Size  size,
-                 FT_Bool  only_height );
+  tt_size_reset_height( TT_Size  size );
+
+  FT_LOCAL( FT_Error )
+  tt_size_reset( TT_Size  size );
 
 
   /**************************************************************************