[truetype] Support subpixel hinting.

This is the large, famous `Infinality' patch to support ClearType
bytecode which has been available from
http://www.infinality.net/blog/ for some time, and which has been
refined over the last years.  While still experimental, it is now
mature enough to be included directly into FreeType.

Most of the code is based on the ClearType whitepaper written by
Greg Hitchcock

  http://www.microsoft.com/typography/cleartype/truetypecleartype.aspx

which gives a detailed overview of the necessary changes to the
Microsoft rasterizer so that older fonts are supported.  However, a
lot of details are still missing, and this patches provides a
framework to easily handle rendering issues down to the glyph level
of certain fonts.

Note that ClearType support is not completely implemented!  In
particular, full support for the options `compatible_widths',
`symmetrical_smoothing, and `bgr' (via the GETINFO bytecode
instruction) is missing.

* src/truetype/ttsubpix.c: New file, providing code to handle
`tweaks', this is, rules for certain glyphs in certain fonts
(including wildcards) which need a special treatment.

* src/truetype/ttsubpix.h: New file, holding the tweaking rules.

* include/freetype/config/ftoption.h, src/devel/ftoption.h
(TT_CONFIG_OPTION_SUBPIXEL_HINTING): New macro.

* include/freetype/internal/ftobjs.h (FT_PIX_FLOOR_GRID,
FT_PIX_ROUND_GRID, FT_PIX_CEIL_GRID): New macros.

* src/truetype/truetype.c [TT_USE_BYTECODE_INTERPRETER]: Include
`ttsubpix.c'.

* src/truetype/ttgload.c: Include `ttsubpix.h'.
[All changes below are guarded by TT_CONFIG_OPTION_SUBPIXEL_HINTING.]

(tt_get_metrics): Set tweak flags.
(TT_Hint_Glyph): Call `FT_Outline_EmboldenXY' if necessary.
(TT_Process_Simple_Glyph): Compensate emboldening if necessary.
(compute_glyph_metrics): Handle `compatible widths' option.
(tt_loader_init): Handle ClearType GETINFO information bits.

* src/truetype/rules.mk (TT_DRC_SRC): Updated.

* src/truetype/ttinterp.c: Include `ttsubpix.h'.
[Where necessary, changes below are guarded by
TT_CONFIG_OPTION_SUBPIXEL_HINTING.]

(Direct_Move, Direct_Move_X): Extended.
(Round_None, Round_To_Grid, Round_To_Half_Grid, Round_Down_To_Grid,
Round_Up_To_Grid, Round_To_Double_Grid, Round_Super, Round_Super_45,
SetSuperRound): Add parameter to handle the number of grid lines per
pixel.
(SET_SuperRound, ROUND_None, CUR_Func_round): Updated.
(DO_SROUND, DOS45ROUND, DO_ODD, DO_EVEN): Updated.
(DO_ROUND, DO_NROUND): Updated.
(DO_RS): Take care of `Typeman' bytecode patterns.
(Ins_FDEF): Add some debugging code.  Commented out.
(Ins_ENDF): Restore state.
(Ins_CALL, Ins_LOOPCALL): Handle inline delta functions.
(Ins_MD): Handle `Vacuform' rounds.
(Move_Zp2_Point, Ins_SHPIX, Ins_MSIRP, Ins_MDAP, Ins_MIAP,
Ins_MDRP, Ins_MIRP): Handle tweaks.
(Ins_ALIGNRP): Add tweak guard.
(Ins_IUP, Ins_DELTAP): Handle tweaks.
(Ins_GETINFO): Handle new ClearType bits.
(TT_RunIns): Handle tweaks.

* src/truetype/ttinterp.h: Updated.
(SPH_TweakRule, SPH_ScaleRule): New structures for tweaks.
(TT_ExecContextRec): Add members for subpixel hinting support.

* src/truetype/ttobjs.h (TT_DefRecord): Add `inline_delta' member.

1 files changed, 22 insertions, 0 deletions

diff --git a/devel/ftoption.h b/devel/ftoption.h
index ba7db164c..6b2a40f83 100644
--- a/devel/ftoption.h
+++ b/devel/ftoption.h
@@ -560,6 +560,28 @@ 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.                                     */
+  /*                                                                       */
+  /* 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:                                          */
+  /*                                                                       */
+  /*  http://www.microsoft.com/typography/cleartype/truetypecleartype.aspx */
+  /*                                                                       */
+  /* By undefining this, you only compile the code necessary to hint       */
+  /* TrueType glyphs with native TT hinting.                               */
+  /*                                                                       */
+  /*   This option requires TT_CONFIG_OPTION_BYTECODE_INTERPRETER to be    */
+  /*   defined.                                                            */
+  /*                                                                       */
+#define TT_CONFIG_OPTION_SUBPIXEL_HINTING
+
+
+  /*************************************************************************/
+  /*                                                                       */
   /* If you define TT_CONFIG_OPTION_UNPATENTED_HINTING, a special version  */
   /* of the TrueType bytecode interpreter is used that doesn't implement   */
   /* any of the patented opcodes and algorithms.  The patents related to   */