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 /****************************************************************************
  *
  * ftdriver.h
  *
  *   FreeType API for controlling driver modules (specification only).
  *
  * Copyright (C) 2017-2023 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 FTDRIVER_H_
 #define FTDRIVER_H_
 
 #include <freetype/freetype.h>
 #include <freetype/ftparams.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:
    *   auto_hinter
    *
    * @title:
    *   The auto-hinter
    *
    * @abstract:
    *   Controlling the auto-hinting module.
    *
    * @description:
    *   While FreeType's auto-hinter 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.
    *
    *   Note that the auto-hinter's module name is 'autofitter' for historical
    *   reasons.
    *
    *   Available properties are @increase-x-height, @no-stem-darkening
    *   (experimental), @darkening-parameters (experimental),
    *   @glyph-to-script-map (experimental), @fallback-script (experimental),
    *   and @default-script (experimental), as documented in the @properties
    *   section.
    *
    */
 
 
   /**************************************************************************
    *
    * @section:
    *   cff_driver
    *
    * @title:
    *   The CFF driver
    *
    * @abstract:
    *   Controlling the CFF driver module.
    *
    * @description:
    *   While FreeType's CFF driver doesn't expose API functions by itself, it
    *   is possible to control its behaviour with @FT_Property_Set and
    *   @FT_Property_Get.
    *
    *   The CFF driver's module name is 'cff'.
    *
    *   Available properties are @hinting-engine, @no-stem-darkening,
    *   @darkening-parameters, and @random-seed, as documented in the
    *   @properties section.
    *
    *
    *   **Hinting and anti-aliasing principles of the new engine**
    *
    *   The rasterizer is positioning horizontal features (e.g., ascender
    *   height & x-height, or crossbars) on the pixel grid and minimizing the
    *   amount of anti-aliasing applied to them, while placing vertical
    *   features (vertical stems) on the pixel grid without hinting, thus
    *   representing the stem position and weight accurately.  Sometimes the
    *   vertical stems may be only partially black.  In this context,
    *   'anti-aliasing' means that stems are not positioned exactly on pixel
    *   borders, causing a fuzzy appearance.
    *
    *   There are two principles behind this approach.
    *
    *   1) No hinting in the horizontal direction: Unlike 'superhinted'
    *   TrueType, which changes glyph widths to accommodate regular
    *   inter-glyph spacing, Adobe's approach is 'faithful to the design' in
    *   representing both the glyph width and the inter-glyph spacing designed
    *   for the font.  This makes the screen display as close as it can be to
    *   the result one would get with infinite resolution, while preserving
    *   what is considered the key characteristics of each glyph.  Note that
    *   the distances between unhinted and grid-fitted positions at small
    *   sizes are comparable to kerning values and thus would be noticeable
    *   (and distracting) while reading if hinting were applied.
    *
    *   One of the reasons to not hint horizontally is anti-aliasing for LCD
    *   screens: The pixel geometry of modern displays supplies three vertical
    *   subpixels as the eye moves horizontally across each visible pixel.  On
    *   devices where we can be certain this characteristic is present a
    *   rasterizer can take advantage of the subpixels to add increments of
    *   weight.  In Western writing systems this turns out to be the more
    *   critical direction anyway; the weights and spacing of vertical stems
    *   (see above) are central to Armenian, Cyrillic, Greek, and Latin type
    *   designs.  Even when the rasterizer uses greyscale anti-aliasing instead
    *   of color (a necessary compromise when one doesn't know the screen
    *   characteristics), the unhinted vertical features preserve the design's
    *   weight and spacing much better than aliased type would.
    *
    *   2) Alignment in the vertical direction: Weights and spacing along the
    *   y~axis are less critical; what is much more important is the visual
    *   alignment of related features (like cap-height and x-height).  The
    *   sense of alignment for these is enhanced by the sharpness of grid-fit
    *   edges, while the cruder vertical resolution (full pixels instead of
    *   1/3 pixels) is less of a problem.
    *
    *   On the technical side, horizontal alignment zones for ascender,
    *   x-height, and other important height values (traditionally called
    *   'blue zones') as defined in the font are positioned independently,
    *   each being rounded to the nearest pixel edge, taking care of overshoot
    *   suppression at small sizes, stem darkening, and scaling.
    *
    *   Hstems (that is, hint values defined in the font to help align
    *   horizontal features) that fall within a blue zone are said to be
    *   'captured' and are aligned to that zone.  Uncaptured stems are moved
    *   in one of four ways, top edge up or down, bottom edge up or down.
    *   Unless there are conflicting hstems, the smallest movement is taken to
    *   minimize distortion.
    *
    */
 
 
   /**************************************************************************
    *
    * @section:
    *   pcf_driver
    *
    * @title:
    *   The PCF driver
    *
    * @abstract:
    *   Controlling the PCF driver module.
    *
    * @description:
    *   While FreeType's PCF driver doesn't expose API functions by itself, it
    *   is possible to control its behaviour with @FT_Property_Set and
    *   @FT_Property_Get.  Right now, there is a single property
    *   @no-long-family-names available if FreeType is compiled with
    *   PCF_CONFIG_OPTION_LONG_FAMILY_NAMES.
    *
    *   The PCF driver's module name is 'pcf'.
    *
    */
 
 
   /**************************************************************************
    *
    * @section:
    *   t1_cid_driver
    *
    * @title:
    *   The Type 1 and CID drivers
    *
    * @abstract:
    *   Controlling the Type~1 and CID driver modules.
    *
    * @description:
    *   It is possible to control the behaviour of FreeType's Type~1 and
    *   Type~1 CID drivers with @FT_Property_Set and @FT_Property_Get.
    *
    *   Behind the scenes, both drivers use the Adobe CFF engine for hinting;
    *   however, the used properties must be specified separately.
    *
    *   The Type~1 driver's module name is 'type1'; the CID driver's module
    *   name is 't1cid'.
    *
    *   Available properties are @hinting-engine, @no-stem-darkening,
    *   @darkening-parameters, and @random-seed, as documented in the
    *   @properties section.
    *
    *   Please see the @cff_driver section for more details on the new hinting
    *   engine.
    *
    */
 
 
   /**************************************************************************
    *
    * @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 TrueType driver's module name is 'truetype'; a single property
    *   @interpreter-version is available, as documented in the @properties
    *   section.
    *
    *   To help understand the differences between interpreter versions, we
    *   introduce 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://rastertragedy.com/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://rastertragedy.com/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://rastertragedy.com/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 Backward 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://rastertragedy.com/RTRCh4.htm#Sec1 and
    *   https://www.microsoft.com/typography/cleartype/truetypecleartype.aspx.
    *   This technique is not to be confused with ClearType compatible widths.
    *   ClearType backward 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 backward 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.
    *
    */
 
 
   /**************************************************************************
    *
    * @section:
    *   ot_svg_driver
    *
    * @title:
    *   The SVG driver
    *
    * @abstract:
    *   Controlling the external rendering of OT-SVG glyphs.
    *
    * @description:
    *   By default, FreeType can only load the 'SVG~' table of OpenType fonts
    *   if configuration macro `FT_CONFIG_OPTION_SVG` is defined.  To make it
    *   render SVG glyphs, an external SVG rendering library is needed.  All
    *   details on the interface between FreeType and the external library
    *   via function hooks can be found in section @svg_fonts.
    *
    *   The OT-SVG driver's module name is 'ot-svg'; it supports a single
    *   property called @svg-hooks, documented below in the @properties
    *   section.
    *
    */
 
 
   /**************************************************************************
    *
    * @section:
    *   properties
    *
    * @title:
    *   Driver properties
    *
    * @abstract:
    *   Controlling driver modules.
    *
    * @description:
    *   Driver modules can be controlled by setting and unsetting properties,
    *   using the functions @FT_Property_Set and @FT_Property_Get.  This
    *   section documents the available properties, together with auxiliary
    *   macros and structures.
    *
    */
 
 
   /**************************************************************************
    *
    * @enum:
    *   FT_HINTING_XXX
    *
    * @description:
    *   A list of constants used for the @hinting-engine property to select
    *   the hinting engine for CFF, Type~1, and CID fonts.
    *
    * @values:
    *   FT_HINTING_FREETYPE ::
    *     Use the old FreeType hinting engine.
    *
    *   FT_HINTING_ADOBE ::
    *     Use the hinting engine contributed by Adobe.
    *
    * @since:
    *   2.9
    *
    */
 #define FT_HINTING_FREETYPE  0
 #define FT_HINTING_ADOBE     1
 
   /* these constants (introduced in 2.4.12) are deprecated */
 #define FT_CFF_HINTING_FREETYPE  FT_HINTING_FREETYPE
 #define FT_CFF_HINTING_ADOBE     FT_HINTING_ADOBE
 
 
   /**************************************************************************
    *
    * @property:
    *   hinting-engine
    *
    * @description:
    *   Thanks to Adobe, which contributed a new hinting (and parsing) engine,
    *   an application can select between 'freetype' and 'adobe' if compiled
    *   with `CFF_CONFIG_OPTION_OLD_ENGINE`.  If this configuration macro
    *   isn't defined, 'hinting-engine' does nothing.
    *
    *   The same holds for the Type~1 and CID modules if compiled with
    *   `T1_CONFIG_OPTION_OLD_ENGINE`.
    *
    *   For the 'cff' module, the default engine is 'adobe'.  For both the
    *   'type1' and 't1cid' modules, the default engine is 'adobe', too.
    *
    * @note:
    *   This property can be used with @FT_Property_Get also.
    *
    *   This property can be set via the `FREETYPE_PROPERTIES` environment
    *   variable (using values 'adobe' or 'freetype').
    *
    * @example:
    *   The following example code demonstrates how to select Adobe's hinting
    *   engine for the 'cff' module (omitting the error handling).
    *
    *   ```
    *     FT_Library  library;
    *     FT_UInt     hinting_engine = FT_HINTING_ADOBE;
    *
    *
    *     FT_Init_FreeType( &library );
    *
    *     FT_Property_Set( library, "cff",
    *                               "hinting-engine", &hinting_engine );
    *   ```
    *
    * @since:
    *   2.4.12 (for 'cff' module)
    *
    *   2.9 (for 'type1' and 't1cid' modules)
    *
    */
 
 
   /**************************************************************************
    *
    * @property:
    *   no-stem-darkening
    *
    * @description:
    *   All glyphs that pass through the auto-hinter will be emboldened unless
    *   this property is set to TRUE.  The same is true for the CFF, Type~1,
    *   and CID font modules if the 'Adobe' engine is selected (which is the
    *   default).
    *
    *   Stem darkening emboldens glyphs at smaller sizes to make them more
    *   readable on common low-DPI screens when using linear alpha blending
    *   and gamma correction, see @FT_Render_Glyph.  When not using linear
    *   alpha blending and gamma correction, glyphs will appear heavy and
    *   fuzzy!
    *
    *   Gamma correction essentially lightens fonts since shades of grey are
    *   shifted to higher pixel values (=~higher brightness) to match the
    *   original intention to the reality of our screens.  The side-effect is
    *   that glyphs 'thin out'.  Mac OS~X and Adobe's proprietary font
    *   rendering library implement a counter-measure: stem darkening at
    *   smaller sizes where shades of gray dominate.  By emboldening a glyph
    *   slightly in relation to its pixel size, individual pixels get higher
    *   coverage of filled-in outlines and are therefore 'blacker'.  This
    *   counteracts the 'thinning out' of glyphs, making text remain readable
    *   at smaller sizes.
    *
    *   For the auto-hinter, stem-darkening is experimental currently and thus
    *   switched off by default (that is, `no-stem-darkening` is set to TRUE
    *   by default).  Total consistency with the CFF driver is not achieved
    *   right now because the emboldening method differs and glyphs must be
    *   scaled down on the Y-axis to keep outline points inside their
    *   precomputed blue zones.  The smaller the size (especially 9ppem and
    *   down), the higher the loss of emboldening versus the CFF driver.
    *
    *   Note that stem darkening is never applied if @FT_LOAD_NO_SCALE is set.
    *
    * @note:
    *   This property can be used with @FT_Property_Get also.
    *
    *   This property can be set via the `FREETYPE_PROPERTIES` environment
    *   variable (using values 1 and 0 for 'on' and 'off', respectively).  It
    *   can also be set per face using @FT_Face_Properties with
    *   @FT_PARAM_TAG_STEM_DARKENING.
    *
    * @example:
    *   ```
    *     FT_Library  library;
    *     FT_Bool     no_stem_darkening = TRUE;
    *
    *
    *     FT_Init_FreeType( &library );
    *
    *     FT_Property_Set( library, "cff",
    *                               "no-stem-darkening", &no_stem_darkening );
    *   ```
    *
    * @since:
    *   2.4.12 (for 'cff' module)
    *
    *   2.6.2 (for 'autofitter' module)
    *
    *   2.9 (for 'type1' and 't1cid' modules)
    *
    */
 
 
   /**************************************************************************
    *
    * @property:
    *   darkening-parameters
    *
    * @description:
    *   By default, the Adobe hinting engine, as used by the CFF, Type~1, and
    *   CID font drivers, darkens stems as follows (if the `no-stem-darkening`
    *   property isn't set):
    *
    *   ```
    *     stem width <= 0.5px:   darkening amount = 0.4px
    *     stem width  = 1px:     darkening amount = 0.275px
    *     stem width  = 1.667px: darkening amount = 0.275px
    *     stem width >= 2.333px: darkening amount = 0px
    *   ```
    *
    *   and piecewise linear in-between.  At configuration time, these four
    *   control points can be set with the macro
    *   `CFF_CONFIG_OPTION_DARKENING_PARAMETERS`; the CFF, Type~1, and CID
    *   drivers share these values.  At runtime, the control points can be
    *   changed using the `darkening-parameters` property (see the example
    *   below that demonstrates this for the Type~1 driver).
    *
    *   The x~values give the stem width, and the y~values the darkening
    *   amount.  The unit is 1000th of pixels.  All coordinate values must be
    *   positive; the x~values must be monotonically increasing; the y~values
    *   must be monotonically decreasing and smaller than or equal to 500
    *   (corresponding to half a pixel); the slope of each linear piece must
    *   be shallower than -1 (e.g., -.4).
    *
    *   The auto-hinter provides this property, too, as an experimental
    *   feature.  See @no-stem-darkening for more.
    *
    * @note:
    *   This property can be used with @FT_Property_Get also.
    *
    *   This property can be set via the `FREETYPE_PROPERTIES` environment
    *   variable, using eight comma-separated integers without spaces.  Here
    *   the above example, using `\` to break the line for readability.
    *
    *   ```
    *     FREETYPE_PROPERTIES=\
    *     type1:darkening-parameters=500,300,1000,200,1500,100,2000,0
    *   ```
    *
    * @example:
    *   ```
    *     FT_Library  library;
    *     FT_Int      darken_params[8] = {  500, 300,   // x1, y1
    *                                      1000, 200,   // x2, y2
    *                                      1500, 100,   // x3, y3
    *                                      2000,   0 }; // x4, y4
    *
    *
    *     FT_Init_FreeType( &library );
    *
    *     FT_Property_Set( library, "type1",
    *                               "darkening-parameters", darken_params );
    *   ```
    *
    * @since:
    *   2.5.1 (for 'cff' module)
    *
    *   2.6.2 (for 'autofitter' module)
    *
    *   2.9 (for 'type1' and 't1cid' modules)
    *
    */
 
 
   /**************************************************************************
    *
    * @property:
    *   random-seed
    *
    * @description:
    *   By default, the seed value for the CFF 'random' operator and the
    *   similar '0 28 callothersubr pop' command for the Type~1 and CID
    *   drivers is set to a random value.  However, mainly for debugging
    *   purposes, it is often necessary to use a known value as a seed so that
    *   the pseudo-random number sequences generated by 'random' are
    *   repeatable.
    *
    *   The `random-seed` property does that.  Its argument is a signed 32bit
    *   integer; if the value is zero or negative, the seed given by the
    *   `intitialRandomSeed` private DICT operator in a CFF file gets used (or
    *   a default value if there is no such operator).  If the value is
    *   positive, use it instead of `initialRandomSeed`, which is consequently
    *   ignored.
    *
    * @note:
    *   This property can be set via the `FREETYPE_PROPERTIES` environment
    *   variable.  It can also be set per face using @FT_Face_Properties with
    *   @FT_PARAM_TAG_RANDOM_SEED.
    *
    * @since:
    *   2.8 (for 'cff' module)
    *
    *   2.9 (for 'type1' and 't1cid' modules)
    *
    */
 
 
   /**************************************************************************
    *
    * @property:
    *   no-long-family-names
    *
    * @description:
    *   If `PCF_CONFIG_OPTION_LONG_FAMILY_NAMES` is active while compiling
    *   FreeType, the PCF driver constructs long family names.
    *
    *   There are many PCF fonts just called 'Fixed' which look completely
    *   different, and which have nothing to do with each other.  When
    *   selecting 'Fixed' in KDE or Gnome one gets results that appear rather
    *   random, the style changes often if one changes the size and one cannot
    *   select some fonts at all.  The improve this situation, the PCF module
    *   prepends the foundry name (plus a space) to the family name.  It also
    *   checks whether there are 'wide' characters; all put together, family
    *   names like 'Sony Fixed' or 'Misc Fixed Wide' are constructed.
    *
    *   If `no-long-family-names` is set, this feature gets switched off.
    *
    * @note:
    *   This property can be used with @FT_Property_Get also.
    *
    *   This property can be set via the `FREETYPE_PROPERTIES` environment
    *   variable (using values 1 and 0 for 'on' and 'off', respectively).
    *
    * @example:
    *   ```
    *     FT_Library  library;
    *     FT_Bool     no_long_family_names = TRUE;
    *
    *
    *     FT_Init_FreeType( &library );
    *
    *     FT_Property_Set( library, "pcf",
    *                               "no-long-family-names",
    *                               &no_long_family_names );
    *   ```
    *
    * @since:
    *   2.8
    */
 
 
   /**************************************************************************
    *
    * @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 is the same Version~40. The original 'Infinality' code is
    *     no longer available.
    *
    *   TT_INTERPRETER_VERSION_40 ::
    *     Version~40 corresponds to MS rasterizer v.2.1; it is roughly
    *     equivalent to the hinting provided by DirectWrite ClearType (as can
    *     be found, for example, in Microsoft's Edge Browser on Windows~10).
    *     It is used in FreeType to select the 'minimal' subpixel hinting
    *     code, a stripped-down and higher performance version of the
    *     'Infinality' code.
    *
    * @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 the configuration option
    *   `TT_CONFIG_OPTION_SUBPIXEL_HINTING`, selecting version~38 or~40 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).
    *
    *   Keep in mind that the features of the above interpreter versions might
    *   not map exactly to FreeType features or behavior because it is a
    *   fundamentally different library with different internals.
    *
    */
 #define TT_INTERPRETER_VERSION_35  35
 #define TT_INTERPRETER_VERSION_38  38
 #define TT_INTERPRETER_VERSION_40  40
 
 
   /**************************************************************************
    *
    * @property:
    *   interpreter-version
    *
    * @description:
    *   Currently, three versions are available, two representing the bytecode
    *   interpreter with subpixel hinting support (old 'Infinality' code and
    *   new stripped-down and higher performance 'minimal' code) and one
    *   without, 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).  Microsoft's 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) tweaks in Microsoft's interpreter.
    *
    *   Details on subpixel hinting and some of the necessary tweaks can be
    *   found in Greg Hitchcock's whitepaper at
    *   'https://www.microsoft.com/typography/cleartype/truetypecleartype.aspx'.
    *   Note that FreeType currently doesn't really 'subpixel hint' (6x1, 6x2,
    *   or 6x5 supersampling) like discussed in the paper.  Depending on the
    *   chosen interpreter, it simply ignores instructions on vertical stems
    *   to arrive at very similar results.
    *
    * @note:
    *   This property can be used with @FT_Property_Get also.
    *
    *   This property can be set via the `FREETYPE_PROPERTIES` environment
    *   variable (using values '35', '38', or '40').
    *
    * @example:
    *   The following example code demonstrates how to deactivate subpixel
    *   hinting (omitting the error handling).
    *
    *   ```
    *     FT_Library  library;
    *     FT_Face     face;
    *     FT_UInt     interpreter_version = TT_INTERPRETER_VERSION_35;
    *
    *
    *     FT_Init_FreeType( &library );
    *
    *     FT_Property_Set( library, "truetype",
    *                               "interpreter-version",
    *                               &interpreter_version );
    *   ```
    *
    * @since:
    *   2.5
    */
 
   /**************************************************************************
    *
    * @property:
    *   svg-hooks
    *
    * @description:
    *   Set up the interface between FreeType and an extern SVG rendering
    *   library like 'librsvg'.  All details on the function hooks can be
    *   found in section @svg_fonts.
    *
    * @example:
    *   The following example code expects that the four hook functions
    *   `svg_*` are defined elsewhere.  Error handling is omitted, too.
    *
    *   ```
    *     FT_Library  library;
    *     SVG_RendererHooks  hooks = {
    *                          (SVG_Lib_Init_Func)svg_init,
    *                          (SVG_Lib_Free_Func)svg_free,
    *                          (SVG_Lib_Render_Func)svg_render,
    *                          (SVG_Lib_Preset_Slot_Func)svg_preset_slot };
    *
    *
    *     FT_Init_FreeType( &library );
    *
    *     FT_Property_Set( library, "ot-svg",
    *                               "svg-hooks", &hooks );
    *   ```
    *
    * @since:
    *   2.12
    */
 
 
   /**************************************************************************
    *
    * @property:
    *   glyph-to-script-map
    *
    * @description:
    *   **Experimental only**
    *
    *   The auto-hinter provides various script modules to hint glyphs.
    *   Examples of supported scripts are Latin or CJK.  Before a glyph is
    *   auto-hinted, the Unicode character map of the font gets examined, and
    *   the script is then determined based on Unicode character ranges, see
    *   below.
    *
    *   OpenType fonts, however, often provide much more glyphs than character
    *   codes (small caps, superscripts, ligatures, swashes, etc.), to be
    *   controlled by so-called 'features'.  Handling OpenType features can be
    *   quite complicated and thus needs a separate library on top of
    *   FreeType.
    *
    *   The mapping between glyph indices and scripts (in the auto-hinter
    *   sense, see the @FT_AUTOHINTER_SCRIPT_XXX values) is stored as an array
    *   with `num_glyphs` elements, as found in the font's @FT_Face structure.
    *   The `glyph-to-script-map` property returns a pointer to this array,
    *   which can be modified as needed.  Note that the modification should
    *   happen before the first glyph gets processed by the auto-hinter so
    *   that the global analysis of the font shapes actually uses the modified
    *   mapping.
    *
    * @example:
    *   The following example code demonstrates how to access it (omitting the
    *   error handling).
    *
    *   ```
    *     FT_Library                library;
    *     FT_Face                   face;
    *     FT_Prop_GlyphToScriptMap  prop;
    *
    *
    *     FT_Init_FreeType( &library );
    *     FT_New_Face( library, "foo.ttf", 0, &face );
    *
    *     prop.face = face;
    *
    *     FT_Property_Get( library, "autofitter",
    *                               "glyph-to-script-map", &prop );
    *
    *     // adjust `prop.map' as needed right here
    *
    *     FT_Load_Glyph( face, ..., FT_LOAD_FORCE_AUTOHINT );
    *   ```
    *
    * @since:
    *   2.4.11
    *
    */
 
 
   /**************************************************************************
    *
    * @enum:
    *   FT_AUTOHINTER_SCRIPT_XXX
    *
    * @description:
    *   **Experimental only**
    *
    *   A list of constants used for the @glyph-to-script-map property to
    *   specify the script submodule the auto-hinter should use for hinting a
    *   particular glyph.
    *
    * @values:
    *   FT_AUTOHINTER_SCRIPT_NONE ::
    *     Don't auto-hint this glyph.
    *
    *   FT_AUTOHINTER_SCRIPT_LATIN ::
    *     Apply the latin auto-hinter.  For the auto-hinter, 'latin' is a very
    *     broad term, including Cyrillic and Greek also since characters from
    *     those scripts share the same design constraints.
    *
    *     By default, characters from the following Unicode ranges are
    *     assigned to this submodule.
    *
    *     ```
    *       U+0020 - U+007F  // Basic Latin (no control characters)
    *       U+00A0 - U+00FF  // Latin-1 Supplement (no control characters)
    *       U+0100 - U+017F  // Latin Extended-A
    *       U+0180 - U+024F  // Latin Extended-B
    *       U+0250 - U+02AF  // IPA Extensions
    *       U+02B0 - U+02FF  // Spacing Modifier Letters
    *       U+0300 - U+036F  // Combining Diacritical Marks
    *       U+0370 - U+03FF  // Greek and Coptic
    *       U+0400 - U+04FF  // Cyrillic
    *       U+0500 - U+052F  // Cyrillic Supplement
    *       U+1D00 - U+1D7F  // Phonetic Extensions
    *       U+1D80 - U+1DBF  // Phonetic Extensions Supplement
    *       U+1DC0 - U+1DFF  // Combining Diacritical Marks Supplement
    *       U+1E00 - U+1EFF  // Latin Extended Additional
    *       U+1F00 - U+1FFF  // Greek Extended
    *       U+2000 - U+206F  // General Punctuation
    *       U+2070 - U+209F  // Superscripts and Subscripts
    *       U+20A0 - U+20CF  // Currency Symbols
    *       U+2150 - U+218F  // Number Forms
    *       U+2460 - U+24FF  // Enclosed Alphanumerics
    *       U+2C60 - U+2C7F  // Latin Extended-C
    *       U+2DE0 - U+2DFF  // Cyrillic Extended-A
    *       U+2E00 - U+2E7F  // Supplemental Punctuation
    *       U+A640 - U+A69F  // Cyrillic Extended-B
    *       U+A720 - U+A7FF  // Latin Extended-D
    *       U+FB00 - U+FB06  // Alphab. Present. Forms (Latin Ligatures)
    *      U+1D400 - U+1D7FF // Mathematical Alphanumeric Symbols
    *      U+1F100 - U+1F1FF // Enclosed Alphanumeric Supplement
    *     ```
    *
    *   FT_AUTOHINTER_SCRIPT_CJK ::
    *     Apply the CJK auto-hinter, covering Chinese, Japanese, Korean, old
    *     Vietnamese, and some other scripts.
    *
    *     By default, characters from the following Unicode ranges are
    *     assigned to this submodule.
    *
    *     ```
    *       U+1100 - U+11FF  // Hangul Jamo
    *       U+2E80 - U+2EFF  // CJK Radicals Supplement
    *       U+2F00 - U+2FDF  // Kangxi Radicals
    *       U+2FF0 - U+2FFF  // Ideographic Description Characters
    *       U+3000 - U+303F  // CJK Symbols and Punctuation
    *       U+3040 - U+309F  // Hiragana
    *       U+30A0 - U+30FF  // Katakana
    *       U+3100 - U+312F  // Bopomofo
    *       U+3130 - U+318F  // Hangul Compatibility Jamo
    *       U+3190 - U+319F  // Kanbun
    *       U+31A0 - U+31BF  // Bopomofo Extended
    *       U+31C0 - U+31EF  // CJK Strokes
    *       U+31F0 - U+31FF  // Katakana Phonetic Extensions
    *       U+3200 - U+32FF  // Enclosed CJK Letters and Months
    *       U+3300 - U+33FF  // CJK Compatibility
    *       U+3400 - U+4DBF  // CJK Unified Ideographs Extension A
    *       U+4DC0 - U+4DFF  // Yijing Hexagram Symbols
    *       U+4E00 - U+9FFF  // CJK Unified Ideographs
    *       U+A960 - U+A97F  // Hangul Jamo Extended-A
    *       U+AC00 - U+D7AF  // Hangul Syllables
    *       U+D7B0 - U+D7FF  // Hangul Jamo Extended-B
    *       U+F900 - U+FAFF  // CJK Compatibility Ideographs
    *       U+FE10 - U+FE1F  // Vertical forms
    *       U+FE30 - U+FE4F  // CJK Compatibility Forms
    *       U+FF00 - U+FFEF  // Halfwidth and Fullwidth Forms
    *      U+1B000 - U+1B0FF // Kana Supplement
    *      U+1D300 - U+1D35F // Tai Xuan Hing Symbols
    *      U+1F200 - U+1F2FF // Enclosed Ideographic Supplement
    *      U+20000 - U+2A6DF // CJK Unified Ideographs Extension B
    *      U+2A700 - U+2B73F // CJK Unified Ideographs Extension C
    *      U+2B740 - U+2B81F // CJK Unified Ideographs Extension D
    *      U+2F800 - U+2FA1F // CJK Compatibility Ideographs Supplement
    *     ```
    *
    *   FT_AUTOHINTER_SCRIPT_INDIC ::
    *     Apply the indic auto-hinter, covering all major scripts from the
    *     Indian sub-continent and some other related scripts like Thai, Lao,
    *     or Tibetan.
    *
    *     By default, characters from the following Unicode ranges are
    *     assigned to this submodule.
    *
    *     ```
    *       U+0900 - U+0DFF  // Indic Range
    *       U+0F00 - U+0FFF  // Tibetan
    *       U+1900 - U+194F  // Limbu
    *       U+1B80 - U+1BBF  // Sundanese
    *       U+A800 - U+A82F  // Syloti Nagri
    *       U+ABC0 - U+ABFF  // Meetei Mayek
    *      U+11800 - U+118DF // Sharada
    *     ```
    *
    *     Note that currently Indic support is rudimentary only, missing blue
    *     zone support.
    *
    * @since:
    *   2.4.11
    *
    */
 #define FT_AUTOHINTER_SCRIPT_NONE   0
 #define FT_AUTOHINTER_SCRIPT_LATIN  1
 #define FT_AUTOHINTER_SCRIPT_CJK    2
 #define FT_AUTOHINTER_SCRIPT_INDIC  3
 
 
   /**************************************************************************
    *
    * @struct:
    *   FT_Prop_GlyphToScriptMap
    *
    * @description:
    *   **Experimental only**
    *
    *   The data exchange structure for the @glyph-to-script-map property.
    *
    * @since:
    *   2.4.11
    *
    */
   typedef struct  FT_Prop_GlyphToScriptMap_
   {
     FT_Face     face;
     FT_UShort*  map;
 
   } FT_Prop_GlyphToScriptMap;
 
 
   /**************************************************************************
    *
    * @property:
    *   fallback-script
    *
    * @description:
    *   **Experimental only**
    *
    *   If no auto-hinter script module can be assigned to a glyph, a fallback
    *   script gets assigned to it (see also the @glyph-to-script-map
    *   property).  By default, this is @FT_AUTOHINTER_SCRIPT_CJK.  Using the
    *   `fallback-script` property, this fallback value can be changed.
    *
    * @note:
    *   This property can be used with @FT_Property_Get also.
    *
    *   It's important to use the right timing for changing this value: The
    *   creation of the glyph-to-script map that eventually uses the fallback
    *   script value gets triggered either by setting or reading a
    *   face-specific property like @glyph-to-script-map, or by auto-hinting
    *   any glyph from that face.  In particular, if you have already created
    *   an @FT_Face structure but not loaded any glyph (using the
    *   auto-hinter), a change of the fallback script will affect this face.
    *
    * @example:
    *   ```
    *     FT_Library  library;
    *     FT_UInt     fallback_script = FT_AUTOHINTER_SCRIPT_NONE;
    *
    *
    *     FT_Init_FreeType( &library );
    *
    *     FT_Property_Set( library, "autofitter",
    *                               "fallback-script", &fallback_script );
    *   ```
    *
    * @since:
    *   2.4.11
    *
    */
 
 
   /**************************************************************************
    *
    * @property:
    *   default-script
    *
    * @description:
    *   **Experimental only**
    *
    *   If FreeType gets compiled with `FT_CONFIG_OPTION_USE_HARFBUZZ` to make
    *   the HarfBuzz library access OpenType features for getting better glyph
    *   coverages, this property sets the (auto-fitter) script to be used for
    *   the default (OpenType) script data of a font's GSUB table.  Features
    *   for the default script are intended for all scripts not explicitly
    *   handled in GSUB; an example is a 'dlig' feature, containing the
    *   combination of the characters 'T', 'E', and 'L' to form a 'TEL'
    *   ligature.
    *
    *   By default, this is @FT_AUTOHINTER_SCRIPT_LATIN.  Using the
    *   `default-script` property, this default value can be changed.
    *
    * @note:
    *   This property can be used with @FT_Property_Get also.
    *
    *   It's important to use the right timing for changing this value: The
    *   creation of the glyph-to-script map that eventually uses the default
    *   script value gets triggered either by setting or reading a
    *   face-specific property like @glyph-to-script-map, or by auto-hinting
    *   any glyph from that face.  In particular, if you have already created
    *   an @FT_Face structure but not loaded any glyph (using the
    *   auto-hinter), a change of the default script will affect this face.
    *
    * @example:
    *   ```
    *     FT_Library  library;
    *     FT_UInt     default_script = FT_AUTOHINTER_SCRIPT_NONE;
    *
    *
    *     FT_Init_FreeType( &library );
    *
    *     FT_Property_Set( library, "autofitter",
    *                               "default-script", &default_script );
    *   ```
    *
    * @since:
    *   2.5.3
    *
    */
 
 
   /**************************************************************************
    *
    * @property:
    *   increase-x-height
    *
    * @description:
    *   For ppem values in the range 6~<= ppem <= `increase-x-height`, round
    *   up the font's x~height much more often than normally.  If the value is
    *   set to~0, which is the default, this feature is switched off.  Use
    *   this property to improve the legibility of small font sizes if
    *   necessary.
    *
    * @note:
    *   This property can be used with @FT_Property_Get also.
    *
    *   Set this value right after calling @FT_Set_Char_Size, but before
    *   loading any glyph (using the auto-hinter).
    *
    * @example:
    *   ```
    *     FT_Library               library;
    *     FT_Face                  face;
    *     FT_Prop_IncreaseXHeight  prop;
    *
    *
    *     FT_Init_FreeType( &library );
    *     FT_New_Face( library, "foo.ttf", 0, &face );
    *     FT_Set_Char_Size( face, 10 * 64, 0, 72, 0 );
    *
    *     prop.face  = face;
    *     prop.limit = 14;
    *
    *     FT_Property_Set( library, "autofitter",
    *                               "increase-x-height", &prop );
    *   ```
    *
    * @since:
    *   2.4.11
    *
    */
 
 
   /**************************************************************************
    *
    * @struct:
    *   FT_Prop_IncreaseXHeight
    *
    * @description:
    *   The data exchange structure for the @increase-x-height property.
    *
    */
   typedef struct  FT_Prop_IncreaseXHeight_
   {
     FT_Face  face;
     FT_UInt  limit;
 
   } FT_Prop_IncreaseXHeight;
 
 
   /**************************************************************************
    *
    * @property:
    *   warping
    *
    * @description:
    *   **Obsolete**
    *
    *   This property was always experimental and probably never worked
    *   correctly.  It was entirely removed from the FreeType~2 sources.  This
    *   entry is only here for historical reference.
    *
    *   Warping only worked in 'normal' auto-hinting mode replacing it.  The
    *   idea of the code was to slightly scale and shift a glyph along the
    *   non-hinted dimension (which is usually the horizontal axis) so that as
    *   much of its segments were aligned (more or less) to the grid.  To find
    *   out a glyph's optimal scaling and shifting value, various parameter
    *   combinations were tried and scored.
    *
    * @since:
    *   2.6
    *
    */
 
 
  /* */
 
 
 FT_END_HEADER
 
 
 #endif /* FTDRIVER_H_ */
 
 
 /* END */

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