[truetype] New implementation of v38 bytecode interpreter [1/3].

This patch prepares data structures and the like.

See added comments in `ttinterp.h' for more information on this and
the following commits in the series.

* devel/ftoption.h, include/freetype/config/ftoption.h
(TT_CONFIG_OPTION_SUBPIXEL_HINTING): Assign values to differentiate
between subpixel versions.
(TT_SUPPORT_SUBPIXEL_HINTING_INFINALITY,
TT_SUPPORT_SUBPIXEL_HINTING_MINIMAL): New macros.

* include/freetype/ftttdrv.h (TT_INTERPRETER_VERSION_40): New macro.

* include/freetype/internal/tttypes.h (TT_FaceRec): Updated.

* src/truetype/ttinterp.h (TT_ExecContextRec): Define new fields
`subpixel_hinting_lean', `vertical_lcd_lean',
`backwards_compatibility', `iupx_called', iupy_called', and
`grayscale_cleartype' for new hinting mode.

* src/truetype/ttdriver.c (tt_property_set): Handle v38 and v40
interpreters conditionally.

* src/truetype/ttgload.c (TT_Hint_Glyph): Save phantom points unless
in v38 backwards compatibility mode.
Updated.
(compute_glyph_metrics): Add v38 backwards compatibility mode
constraint for adjusting advance widths.
Updated.
(tt_loader_init): Handle new flags `subpixel_hinting_lean',
`grayscale_cleartype', and `vertical_lcd_lean'.
Updated.
(tt_get_metrics, TT_Process_Simple_Glyph, TT_LOADER_SET_PP):
Updated.

* src/truetype/ttobjs.c (tt_driver_init): Conditionally set
default interpreter version number.

* src/truetype/ttsubpix.c, src/truetype/ttsubpix.h: Updated.

1 files changed, 50 insertions, 12 deletions

diff --git a/devel/ftoption.h b/devel/ftoption.h
index b354efdcd..2360ec693 100644
--- a/devel/ftoption.h
+++ b/devel/ftoption.h
@@ -586,23 +586,53 @@ FT_BEGIN_HEADER
   /*************************************************************************/
   /*                                                                       */
   /* Define TT_CONFIG_OPTION_SUBPIXEL_HINTING if you want to compile       */
-  /* EXPERIMENTAL subpixel hinting support into the TrueType driver.  This */
-  /* replaces the native TrueType hinting mechanism when anything but      */
-  /* FT_RENDER_MODE_MONO is requested.                                     */
+  /* subpixel hinting support into the TrueType driver.  This modifies the */
+  /* TrueType hinting mechanism when anything but FT_RENDER_MODE_MONO is   */
+  /* requested.                                                            */
   /*                                                                       */
-  /* Enabling this causes the TrueType driver to ignore instructions under */
-  /* certain conditions.  This is done in accordance with the guide here,  */
-  /* with some minor differences:                                          */
+  /* In particular, it modifies the bytecode interpreter to interpret (or  */
+  /* not) instructions in a certain way so that all TrueType fonts look    */
+  /* like they do in a Windows ClearType (DirectWrite) environment.  See   */
+  /* [1] for a technical overview on what this means.  See `ttinterp.h'    */
+  /* for more details on the LEAN option.                                  */
   /*                                                                       */
-  /*  http://www.microsoft.com/typography/cleartype/truetypecleartype.aspx */
+  /* There are three options.                                              */
   /*                                                                       */
-  /* By undefining this, you only compile the code necessary to hint       */
-  /* TrueType glyphs with native TT hinting.                               */
+  /* 1. This option is associated with the `Infinality' moniker.           */
+  /*    Contributed by an individual nicknamed Infinality with the goal of */
+  /*    making TrueType fonts render better than on Windows.  A high       */
+  /*    amount of configurability and flexibility, down to rules for       */
+  /*    single glyphs in fonts, but also very slow.  Its experimental and  */
+  /*    slow nature and the original developer losing interest meant that  */
+  /*    this option was never enabled in default builds.                   */
   /*                                                                       */
-  /*   This option requires TT_CONFIG_OPTION_BYTECODE_INTERPRETER to be    */
-  /*   defined.                                                            */
+  /* 2. The new default mode for the TrueType driver.  The Infinality code */
+  /*    base was stripped to the bare minimum and all configurability      */
+  /*    removed in the name of speed and simplicity.  The configurability  */
+  /*    was mainly aimed at legacy fonts like Arial, Times New Roman, or   */
+  /*    Courier.  Legacy fonts are fonts that modify vertical stems to     */
+  /*    achieve clean black-and-white bitmaps.  The new mode focuses on    */
+  /*    applying a minimal set of rules to all fonts indiscriminately so   */
+  /*    that modern and web fonts render well while legacy fonts render    */
+  /*    okay.                                                              */
   /*                                                                       */
-#define TT_CONFIG_OPTION_SUBPIXEL_HINTING
+  /* 3. Compile both.                                                      */
+  /*                                                                       */
+  /* By undefining these, you get rendering behavior like on Windows       */
+  /* without ClearType, i.e., Windows XP without ClearType enabled and     */
+  /* Win9x (interpreter version v35).  Or not, depending on how much       */
+  /* hinting blood and testing tears the font designer put into a given    */
+  /* font.  If you define one or both subpixel hinting options, you can    */
+  /* switch between between v35 and the ones you define.                   */
+  /*                                                                       */
+  /* This option requires TT_CONFIG_OPTION_BYTECODE_INTERPRETER to be      */
+  /* defined.                                                              */
+  /*                                                                       */
+  /* [1] http://www.microsoft.com/typography/cleartype/truetypecleartype.aspx */
+  /*                                                                       */
+/* #define TT_CONFIG_OPTION_SUBPIXEL_HINTING  1     */
+/* #define TT_CONFIG_OPTION_SUBPIXEL_HINTING  2     */
+#define TT_CONFIG_OPTION_SUBPIXEL_HINTING     1 | 2
 
 
   /*************************************************************************/
@@ -811,6 +841,14 @@ FT_BEGIN_HEADER
    */
 #ifdef TT_CONFIG_OPTION_BYTECODE_INTERPRETER
 #define  TT_USE_BYTECODE_INTERPRETER
+
+#if TT_CONFIG_OPTION_SUBPIXEL_HINTING & 1
+#define  TT_SUPPORT_SUBPIXEL_HINTING_INFINALITY
+#endif
+
+#if TT_CONFIG_OPTION_SUBPIXEL_HINTING & 2
+#define  TT_SUPPORT_SUBPIXEL_HINTING_MINIMAL
+#endif
 #endif