minhngoc25a
/
freetype2
mirror of git://git.savannah.gnu.org/freetype/freetype2.git
2
1
Fork 2
Code Issues 4 Releases Wiki Activity
freetype2/include/freetype/ftdriver.h

1226 lines
47 KiB
C
Raw Blame History

/***************************************************************************/
/* */
/* 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.
*
* 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_CFF_HINTING_ADOBE;
*
*
* FT_Init_FreeType( &library );
*
* FT_Property_Set( library, "cff",
* "hinting-engine", &hinting_engine );
* }
*
* @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').
*
* @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.
*
* {
* FT_Library library;
* FT_Bool no_stem_darkening = TRUE;
*
*
* FT_Init_FreeType( &library );
*
* FT_Property_Set( library, "cff",
* "no-stem-darkening", &no_stem_darkening );
* }
*
* @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.
*
* @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, as the following
* example demonstrates for the Type~1 driver.
*
* {
* 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 );
* }
*
* 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
* }
*
* @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.
*
* {
* 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 );
* }
*
* @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).
*
* @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.
*
* 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 );
* }
*
* @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').
*
* @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.
*
* 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.
*
* {
* FT_Library library;
* FT_UInt fallback_script = FT_AUTOHINTER_SCRIPT_NONE;
*
*
* FT_Init_FreeType( &library );
*
* FT_Property_Set( library, "autofitter",
* "fallback-script", &fallback_script );
* }
*
* @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.
*
* @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.
*
* {
* FT_Library library;
* FT_UInt default_script = FT_AUTOHINTER_SCRIPT_NONE;
*
*
* FT_Init_FreeType( &library );
*
* FT_Property_Set( library, "autofitter",
* "default-script", &default_script );
* }
*
* @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.
*
* @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.
*
* {
* 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 );
* }
*
* @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).
*
* @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. The example below 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 );
* }
*
* @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.
*
* @since:
* 2.6
*
*/
/* */
FT_END_HEADER
#endif /* FTDRIVER_H_ */
/* END */
Reference in New Issue View Git Blame Copy Permalink