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freetype2/include/freetype/ftdriver.h

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/****************************************************************************
*
* ftdriver.h
*
* FreeType API for controlling driver modules (specification only).
*
* Copyright 2017-2018 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 <ft2build.h>
#include FT_FREETYPE_H
#include FT_PARAMETER_TAGS_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), @warping
* (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 antialiasing 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 antialiasing 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,
* 'antialiasing' 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 antialiasing 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 antialiasing 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 (this 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 following lists the available properties
* together with the necessary macros and structures.
*
* The TrueType driver's module name is 'truetype'.
*
* A single property @interpreter-version is available, as documented in
* the @properties section.
*
* 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 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://www.beatstamm.com/typography/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:
* 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 'freetype' if
* `CFF_CONFIG_OPTION_OLD_ENGINE` is defined, and 'adobe' otherwise.
*
* For both the 'type1' and 't1cid' modules, the default engine is
* 'freetype' if `T1_CONFIG_OPTION_OLD_ENGINE` is defined, and 'adobe'
* otherwise.
*
* @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.
*
* By default, the Adobe engines for CFF, Type~1, and CID fonts darken
* stems at smaller sizes, regardless of hinting, to enhance contrast.
* Setting this property, stem darkening gets switched off.
*
* For the auto-hinter, stem-darkening is experimental currently and thus
* switched off by default (this 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 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). It is used in FreeType to select the 'Infinality'
* subpixel hinting code. The code may be removed in a future version.
*
* 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:
* 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:
* **Experimental only**
*
* If FreeType gets compiled with option `AF_CONFIG_OPTION_USE_WARPER` to
* activate the warp hinting code in the auto-hinter, this property
* switches warping on and off.
*
* Warping only works in 'normal' auto-hinting mode replacing it. The
* idea of the code is 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 are aligned (more or less) to the grid. To find
* out a glyph's optimal scaling and shifting value, various parameter
* combinations are tried and scored.
*
* By default, warping is 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).
*
* The warping code can also change advance widths. Have a look at the
* `lsb_delta` and `rsb_delta` fields in the @FT_GlyphSlotRec structure
* for details on improving inter-glyph distances while rendering.
*
* Since warping is a global property of the auto-hinter it is best to
* change its value before rendering any face. Otherwise, you should
* reload all faces that get auto-hinted in 'normal' hinting mode.
*
* @example:
* This example shows how to switch on warping (omitting the error
* handling).
*
* ```
* FT_Library library;
* FT_Bool warping = 1;
*
*
* FT_Init_FreeType( &library );
*
* FT_Property_Set( library, "autofitter", "warping", &warping );
* ```
*
* @since:
* 2.6
*
*/
/* */
FT_END_HEADER
#endif /* FTDRIVER_H_ */
/* END */
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