[freetype2] master f6be927: [truetype] Fix incremental metrics (#59503).

[Werner LEMBERG]

branch: master
commit f6be92767d1d002f5e90a4673ee4e6d4f1e1744f
Author: Chris Liddell <chris.liddell@artifex.com>
Commit: Werner Lemberg <wl@gnu.org>

    [truetype] Fix incremental metrics (#59503).
    
    * src/truetype/ttgload.c (tt_get_metrics, load_truetype_glyph):
    Previously, the code would populate the phantom points before
    calling the `get_glyph_metrics` callback.  For formats like PCL XL
    format 1, class 2 downloaded fonts (where metrics are removed from
    the TTF header), this causes problems when the hinting program uses
    the phantom points (misplaced and distorted glyphs) due to the
    metrics being unset (all zeros).
    (tt_get_metrics_incr_overrides): Renamed to...
    (tt_get_metrics_incremental): ... this.  Updated caller
    
    * include/freetype/ftincrem.h: Update the documentation to make it
    clearer that `get_glyph_metrics` is to retrieve metrics from a
    non-standard source, but *not* for the purpose of imposing custom
    metrics.
---
 ChangeLog                   | 19 +++++++++++++++++++
 include/freetype/ftincrem.h | 15 ++++++++++-----
 src/truetype/ttgload.c      | 33 ++++++++++++++++++---------------
 3 files changed, 47 insertions(+), 20 deletions(-)

diff --git a/ChangeLog b/ChangeLog
index 9a5796e..3c93564 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,3 +1,22 @@
+2020-12-16  Chris Liddell  <chris.liddell@artifex.com>
+
+       [truetype] Fix incremental metrics (#59503).
+
+       * src/truetype/ttgload.c (tt_get_metrics, load_truetype_glyph):
+       Previously, the code would populate the phantom points before
+       calling the `get_glyph_metrics` callback.  For formats like PCL XL
+       format 1, class 2 downloaded fonts (where metrics are removed from
+       the TTF header), this causes problems when the hinting program uses
+       the phantom points (misplaced and distorted glyphs) due to the
+       metrics being unset (all zeros).
+       (tt_get_metrics_incr_overrides): Renamed to...
+       (tt_get_metrics_incremental): ... this.  Updated caller
+
+       * include/freetype/ftincrem.h: Update the documentation to make it
+       clearer that `get_glyph_metrics` is to retrieve metrics from a
+       non-standard source, but *not* for the purpose of imposing custom
+       metrics.
+
 2020-12-14  Werner Lemberg  <wl@gnu.org>
 
        [type42] Pacify static analysis tools (#59682).
diff --git a/include/freetype/ftincrem.h b/include/freetype/ftincrem.h
index f67655e..54145c1 100644
--- a/include/freetype/ftincrem.h
+++ b/include/freetype/ftincrem.h
@@ -213,9 +213,14 @@ FT_BEGIN_HEADER
    *
    * @description:
    *   A function used to retrieve the basic metrics of a given glyph index
-   *   before accessing its data.  This is necessary because, in certain
-   *   formats like TrueType, the metrics are stored in a different place
-   *   from the glyph images proper.
+   *   before accessing its data.  This allows for handling font types such
+   *   as PCL~XL Format~1, Class~2 downloaded TrueType fonts, where the glyph
+   *   metrics (`hmtx` and `vmtx` tables) are permitted to be omitted from
+   *   the font, and the relevant metrics included in the header of the glyph
+   *   outline data.  Importantly, this is not intended to allow custom glyph
+   *   metrics (for example, Postscript Metrics dictionaries), because that
+   *   conflicts with the requirements of outline hinting.  Such custom
+   *   metrics must be handled separately, by the calling application.
    *
    * @input:
    *   incremental ::
@@ -235,7 +240,7 @@ FT_BEGIN_HEADER
    *
    * @output:
    *   ametrics ::
-   *     The replacement glyph metrics in font units.
+   *     The glyph metrics in font units.
    *
    */
   typedef FT_Error
@@ -264,7 +269,7 @@ FT_BEGIN_HEADER
    *
    *   get_glyph_metrics ::
    *     The function to get glyph metrics.  May be null if the font does not
-   *     provide overriding glyph metrics.
+   *     require it.
    *
    */
   typedef struct  FT_Incremental_FuncsRec_
diff --git a/src/truetype/ttgload.c b/src/truetype/ttgload.c
index d08a975..81cecbb 100644
--- a/src/truetype/ttgload.c
+++ b/src/truetype/ttgload.c
@@ -197,10 +197,17 @@
     }
 #endif /* TT_SUPPORT_SUBPIXEL_HINTING_INFINALITY */
 
-    if ( !loader->linear_def )
+#ifdef FT_CONFIG_OPTION_INCREMENTAL
+    /* With the incremental interface, these values are set by  */
+    /* a call to `tt_get_metrics_incremental'.                  */
+    if ( face->root.internal->incremental_interface == NULL )
+#endif
     {
-      loader->linear_def = 1;
-      loader->linear     = advance_width;
+      if ( !loader->linear_def )
+      {
+        loader->linear_def = 1;
+        loader->linear     = advance_width;
+      }
     }
 
     return FT_Err_Ok;
@@ -210,8 +217,8 @@
 #ifdef FT_CONFIG_OPTION_INCREMENTAL
 
   static void
-  tt_get_metrics_incr_overrides( TT_Loader  loader,
-                                 FT_UInt    glyph_index )
+  tt_get_metrics_incremental( TT_Loader  loader,
+                              FT_UInt    glyph_index )
   {
     TT_Face  face = loader->face;
 
@@ -1741,13 +1748,11 @@
 
     if ( loader->byte_len == 0 || loader->n_contours == 0 )
     {
-      /* must initialize points before (possibly) overriding */
-      /* glyph metrics from the incremental interface        */
-      tt_loader_set_pp( loader );
-
 #ifdef FT_CONFIG_OPTION_INCREMENTAL
-      tt_get_metrics_incr_overrides( loader, glyph_index );
+      tt_get_metrics_incremental( loader, glyph_index );
 #endif
+      tt_loader_set_pp( loader );
+
 
 #ifdef TT_CONFIG_OPTION_GX_VAR_SUPPORT
 
@@ -1830,13 +1835,11 @@
       goto Exit;
     }
 
-    /* must initialize phantom points before (possibly) overriding */
-    /* glyph metrics from the incremental interface                */
-    tt_loader_set_pp( loader );
-
 #ifdef FT_CONFIG_OPTION_INCREMENTAL
-    tt_get_metrics_incr_overrides( loader, glyph_index );
+    tt_get_metrics_incremental( loader, glyph_index );
 #endif
+    tt_loader_set_pp( loader );
+
 
     /***********************************************************************/
     /***********************************************************************/