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diff --git a/modules/freetype2/include/freetype/ftdriver.h b/modules/freetype2/include/freetype/ftdriver.h new file mode 100644 index 0000000000..f90946fd17 --- /dev/null +++ b/modules/freetype2/include/freetype/ftdriver.h @@ -0,0 +1,1249 @@ +/**************************************************************************** + * + * 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 (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 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 (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: + * 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 */ |