[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

1 files changed, 10 insertions, 4 deletions

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" ));