Merge to XFA: Update bundled freetype to 2.6.1

third_party/freetype/include/freetype/ftttdrv.h

Index: third_party/freetype/include/freetype/ftttdrv.h
diff --git a/third_party/freetype/include/freetype/ftttdrv.h b/third_party/freetype/include/freetype/ftttdrv.h
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index 0000000000000000000000000000000000000000..dc0081a0b9620c84e2cb6252b48daa07f668a21b
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+/***************************************************************************/
+/*                                                                         */
+/*  ftttdrv.h                                                              */
+/*                                                                         */
+/*    FreeType API for controlling the TrueType driver                     */
+/*    (specification only).                                                */
+/*                                                                         */
+/*  Copyright 2013-2015 by                                                 */
+/*  David Turner, Robert Wilhelm, and Werner Lemberg.                      */
+/*                                                                         */
+/*  This file is part of the FreeType project, and may only be used,       */
+/*  modified, and distributed under the terms of the FreeType project      */
+/*  license, LICENSE.TXT.  By continuing to use, modify, or distribute     */
+/*  this file you indicate that you have read the license and              */
+/*  understand and accept it fully.                                        */
+/*                                                                         */
+/***************************************************************************/
+
+
+#ifndef __FTTTDRV_H__
+#define __FTTTDRV_H__
+
+#include <ft2build.h>
+#include FT_FREETYPE_H
+
+#ifdef FREETYPE_H
+#error "freetype.h of FreeType 1 has been loaded!"
+#error "Please fix the directory search order for header files"
+#error "so that freetype.h of FreeType 2 is found first."
+#endif
+
+
+FT_BEGIN_HEADER
+
+
+  /**************************************************************************
+   *
+   * @section:
+   *   tt_driver
+   *
+   * @title:
+   *   The TrueType driver
+   *
+   * @abstract:
+   *   Controlling the TrueType driver module.
+   *
+   * @description:
+   *   While FreeType's TrueType driver doesn't expose API functions by
+   *   itself, it is possible to control its behaviour with @FT_Property_Set
+   *   and @FT_Property_Get.  The following lists the available properties
+   *   together with the necessary macros and structures.
+   *
+   *   The TrueType driver's module name is `truetype'.
+   *
+   *   We start with a list of definitions, kindly provided by Greg
+   *   Hitchcock.
+   *
+   *   _Bi-Level_ _Rendering_
+   *
+   *   Monochromatic rendering, exclusively used in the early days of
+   *   TrueType by both Apple and Microsoft.  Microsoft's GDI interface
+   *   supported hinting of the right-side bearing point, such that the
+   *   advance width could be non-linear.  Most often this was done to
+   *   achieve some level of glyph symmetry.  To enable reasonable
+   *   performance (e.g., not having to run hinting on all glyphs just to
+   *   get the widths) there was a bit in the head table indicating if the
+   *   side bearing was hinted, and additional tables, `hdmx' and `LTSH', to
+   *   cache hinting widths across multiple sizes and device aspect ratios.
+   *
+   *   _Font_ _Smoothing_
+   *
+   *   Microsoft's GDI implementation of anti-aliasing.  Not traditional
+   *   anti-aliasing as the outlines were hinted before the sampling.  The
+   *   widths matched the bi-level rendering.
+   *
+   *   _ClearType_ _Rendering_
+   *
+   *   Technique that uses physical subpixels to improve rendering on LCD
+   *   (and other) displays.  Because of the higher resolution, many methods
+   *   of improving symmetry in glyphs through hinting the right-side
+   *   bearing were no longer necessary.  This lead to what GDI calls
+   *   `natural widths' ClearType, see
+   *   http://www.beatstamm.com/typography/RTRCh4.htm#Sec21.  Since hinting
+   *   has extra resolution, most non-linearity went away, but it is still
+   *   possible for hints to change the advance widths in this mode.
+   *
+   *   _ClearType_ _Compatible_ _Widths_
+   *
+   *   One of the earliest challenges with ClearType was allowing the
+   *   implementation in GDI to be selected without requiring all UI and
+   *   documents to reflow.  To address this, a compatible method of
+   *   rendering ClearType was added where the font hints are executed once
+   *   to determine the width in bi-level rendering, and then re-run in
+   *   ClearType, with the difference in widths being absorbed in the font
+   *   hints for ClearType (mostly in the white space of hints); see
+   *   http://www.beatstamm.com/typography/RTRCh4.htm#Sec20.  Somewhat by
+   *   definition, compatible width ClearType allows for non-linear widths,
+   *   but only when the bi-level version has non-linear widths.
+   *
+   *   _ClearType_ _Subpixel_ _Positioning_
+   *
+   *   One of the nice benefits of ClearType is the ability to more crisply
+   *   display fractional widths; unfortunately, the GDI model of integer
+   *   bitmaps did not support this.  However, the WPF and Direct Write
+   *   frameworks do support fractional widths.  DWrite calls this `natural
+   *   mode', not to be confused with GDI's `natural widths'.  Subpixel
+   *   positioning, in the current implementation of Direct Write,
+   *   unfortunately does not support hinted advance widths, see
+   *   http://www.beatstamm.com/typography/RTRCh4.htm#Sec22.  Note that the
+   *   TrueType interpreter fully allows the advance width to be adjusted in
+   *   this mode, just the DWrite client will ignore those changes.
+   *
+   *   _ClearType_ _Backwards_ _Compatibility_
+   *
+   *   This is a set of exceptions made in the TrueType interpreter to
+   *   minimize hinting techniques that were problematic with the extra
+   *   resolution of ClearType; see
+   *   http://www.beatstamm.com/typography/RTRCh4.htm#Sec1 and
+   *   http://www.microsoft.com/typography/cleartype/truetypecleartype.aspx.
+   *   This technique is not to be confused with ClearType compatible
+   *   widths.  ClearType backwards compatibility has no direct impact on
+   *   changing advance widths, but there might be an indirect impact on
+   *   disabling some deltas.  This could be worked around in backwards
+   *   compatibility mode.
+   *
+   *   _Native_ _ClearType_ _Mode_
+   *
+   *   (Not to be confused with `natural widths'.)  This mode removes all
+   *   the exceptions in the TrueType interpreter when running with
+   *   ClearType.  Any issues on widths would still apply, though.
+   *
+   */
+
+
+  /**************************************************************************
+   *
+   * @property:
+   *   interpreter-version
+   *
+   * @description:
+   *   Currently, two versions are available, representing the bytecode
+   *   interpreter with and without subpixel hinting support,
+   *   respectively.  The default is subpixel support if
+   *   TT_CONFIG_OPTION_SUBPIXEL_HINTING is defined, and no subpixel
+   *   support otherwise (since it isn't available then).
+   *
+   *   If subpixel hinting is on, many TrueType bytecode instructions behave
+   *   differently compared to B/W or grayscale rendering (except if `native
+   *   ClearType' is selected by the font).  The main idea is to render at a
+   *   much increased horizontal resolution, then sampling down the created
+   *   output to subpixel precision.  However, many older fonts are not
+   *   suited to this and must be specially taken care of by applying
+   *   (hardcoded) font-specific tweaks.
+   *
+   *   Details on subpixel hinting and some of the necessary tweaks can be
+   *   found in Greg Hitchcock's whitepaper at
+   *   `http://www.microsoft.com/typography/cleartype/truetypecleartype.aspx'.
+   *
+   *   The following example code demonstrates how to activate subpixel
+   *   hinting (omitting the error handling).
+   *
+   *   {
+   *     FT_Library  library;
+   *     FT_Face     face;
+   *     FT_UInt     interpreter_version = TT_INTERPRETER_VERSION_38;
+   *
+   *
+   *     FT_Init_FreeType( &library );
+   *
+   *     FT_Property_Set( library, "truetype",
+   *                               "interpreter-version",
+   *                               &interpreter_version );
+   *   }
+   *
+   * @note:
+   *   This property can be used with @FT_Property_Get also.
+   *
+   */
+
+
+  /**************************************************************************
+   *
+   * @enum:
+   *   TT_INTERPRETER_VERSION_XXX
+   *
+   * @description:
+   *   A list of constants used for the @interpreter-version property to
+   *   select the hinting engine for Truetype fonts.
+   *
+   *   The numeric value in the constant names represents the version
+   *   number as returned by the `GETINFO' bytecode instruction.
+   *
+   * @values:
+   *   TT_INTERPRETER_VERSION_35 ::
+   *     Version~35 corresponds to MS rasterizer v.1.7 as used e.g. in
+   *     Windows~98; only grayscale and B/W rasterizing is supported.
+   *
+   *   TT_INTERPRETER_VERSION_38 ::
+   *     Version~38 corresponds to MS rasterizer v.1.9; it is roughly
+   *     equivalent to the hinting provided by DirectWrite ClearType (as
+   *     can be found, for example, in the Internet Explorer~9 running on
+   *     Windows~7).
+   *
+   * @note:
+   *   This property controls the behaviour of the bytecode interpreter
+   *   and thus how outlines get hinted.  It does *not* control how glyph
+   *   get rasterized!  In particular, it does not control subpixel color
+   *   filtering.
+   *
+   *   If FreeType has not been compiled with configuration option
+   *   FT_CONFIG_OPTION_SUBPIXEL_HINTING, selecting version~38 causes an
+   *   `FT_Err_Unimplemented_Feature' error.
+   *
+   *   Depending on the graphics framework, Microsoft uses different
+   *   bytecode and rendering engines.  As a consequence, the version
+   *   numbers returned by a call to the `GETINFO' bytecode instruction are
+   *   more convoluted than desired.
+   *
+   *   Here are two tables that try to shed some light on the possible
+   *   values for the MS rasterizer engine, together with the additional
+   *   features introduced by it.
+   *
+   *   {
+   *     GETINFO framework               version feature
+   *     -------------------------------------------------------------------
+   *         3   GDI (Win 3.1),            v1.0  16-bit, first version
+   *             TrueImage
+   *        33   GDI (Win NT 3.1),         v1.5  32-bit
+   *             HP Laserjet
+   *        34   GDI (Win 95)              v1.6  font smoothing,
+   *                                             new SCANTYPE opcode
+   *        35   GDI (Win 98/2000)         v1.7  (UN)SCALED_COMPONENT_OFFSET
+   *                                               bits in composite glyphs
+   *        36   MGDI (Win CE 2)           v1.6+ classic ClearType
+   *        37   GDI (XP and later),       v1.8  ClearType
+   *             GDI+ old (before Vista)
+   *        38   GDI+ old (Vista, Win 7),  v1.9  subpixel ClearType,
+   *             WPF                             Y-direction ClearType,
+   *                                             additional error checking
+   *        39   DWrite (before Win 8)     v2.0  subpixel ClearType flags
+   *                                               in GETINFO opcode,
+   *                                             bug fixes
+   *        40   GDI+ (after Win 7),       v2.1  Y-direction ClearType flag
+   *             DWrite (Win 8)                    in GETINFO opcode,
+   *                                             Gray ClearType
+   *   }
+   *
+   *   The `version' field gives a rough orientation only, since some
+   *   applications provided certain features much earlier (as an example,
+   *   Microsoft Reader used subpixel and Y-direction ClearType already in
+   *   Windows 2000).  Similarly, updates to a given framework might include
+   *   improved hinting support.
+   *
+   *   {
+   *      version   sampling          rendering        comment
+   *               x        y       x           y
+   *     --------------------------------------------------------------
+   *       v1.0   normal  normal  B/W           B/W    bi-level
+   *       v1.6   high    high    gray          gray   grayscale
+   *       v1.8   high    normal  color-filter  B/W    (GDI) ClearType
+   *       v1.9   high    high    color-filter  gray   Color ClearType
+   *       v2.1   high    normal  gray          B/W    Gray ClearType
+   *       v2.1   high    high    gray          gray   Gray ClearType
+   *   }
+   *
+   *   Color and Gray ClearType are the two available variants of
+   *   `Y-direction ClearType', meaning grayscale rasterization along the
+   *   Y-direction; the name used in the TrueType specification for this
+   *   feature is `symmetric smoothing'.  `Classic ClearType' is the
+   *   original algorithm used before introducing a modified version in
+   *   Win~XP.  Another name for v1.6's grayscale rendering is `font
+   *   smoothing', and `Color ClearType' is sometimes also called `DWrite
+   *   ClearType'.  To differentiate between today's Color ClearType and the
+   *   earlier ClearType variant with B/W rendering along the vertical axis,
+   *   the latter is sometimes called `GDI ClearType'.
+   *
+   *   `Normal' and `high' sampling describe the (virtual) resolution to
+   *   access the rasterized outline after the hinting process.  `Normal'
+   *   means 1 sample per grid line (i.e., B/W).  In the current Microsoft
+   *   implementation, `high' means an extra virtual resolution of 16x16 (or
+   *   16x1) grid lines per pixel for bytecode instructions like `MIRP'.
+   *   After hinting, these 16 grid lines are mapped to 6x5 (or 6x1) grid
+   *   lines for color filtering if Color ClearType is activated.
+   *
+   *   Note that `Gray ClearType' is essentially the same as v1.6's
+   *   grayscale rendering.  However, the GETINFO instruction handles it
+   *   differently: v1.6 returns bit~12 (hinting for grayscale), while v2.1
+   *   returns bits~13 (hinting for ClearType), 18 (symmetrical smoothing),
+   *   and~19 (Gray ClearType).  Also, this mode respects bits 2 and~3 for
+   *   the version~1 gasp table exclusively (like Color ClearType), while
+   *   v1.6 only respects the values of version~0 (bits 0 and~1).
+   *
+   *   FreeType doesn't provide all capabilities of the most recent
+   *   ClearType incarnation, thus we identify our subpixel support as
+   *   version~38.
+   *
+   */
+#define TT_INTERPRETER_VERSION_35  35
+#define TT_INTERPRETER_VERSION_38  38
+
+ /* */
+
+
+FT_END_HEADER
+
+
+#endif /* __FTTTDRV_H__ */
+
+
+/* END */