1233 lines
46 KiB
C
1233 lines
46 KiB
C
/****************************************************************************
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*
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* ftdriver.h
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*
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* FreeType API for controlling driver modules (specification only).
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*
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* Copyright (C) 2017-2020 by
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* David Turner, Robert Wilhelm, and Werner Lemberg.
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*
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* This file is part of the FreeType project, and may only be used,
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* modified, and distributed under the terms of the FreeType project
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* license, LICENSE.TXT. By continuing to use, modify, or distribute
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* this file you indicate that you have read the license and
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* understand and accept it fully.
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*
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*/
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#ifndef FTDRIVER_H_
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#define FTDRIVER_H_
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#include <ft2build.h>
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#include FT_FREETYPE_H
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#include FT_PARAMETER_TAGS_H
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#ifdef FREETYPE_H
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#error "freetype.h of FreeType 1 has been loaded!"
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#error "Please fix the directory search order for header files"
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#error "so that freetype.h of FreeType 2 is found first."
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#endif
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FT_BEGIN_HEADER
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/**************************************************************************
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*
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* @section:
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* auto_hinter
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*
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* @title:
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* The auto-hinter
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*
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* @abstract:
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* Controlling the auto-hinting module.
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*
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* @description:
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* While FreeType's auto-hinter doesn't expose API functions by itself,
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* it is possible to control its behaviour with @FT_Property_Set and
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* @FT_Property_Get. The following lists the available properties
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* together with the necessary macros and structures.
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*
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* Note that the auto-hinter's module name is 'autofitter' for historical
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* reasons.
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*
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* Available properties are @increase-x-height, @no-stem-darkening
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* (experimental), @darkening-parameters (experimental), @warping
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* (experimental), @glyph-to-script-map (experimental), @fallback-script
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* (experimental), and @default-script (experimental), as documented in
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* the @properties section.
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*
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*/
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/**************************************************************************
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*
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* @section:
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* cff_driver
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*
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* @title:
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* The CFF driver
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*
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* @abstract:
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* Controlling the CFF driver module.
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*
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* @description:
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* While FreeType's CFF driver doesn't expose API functions by itself, it
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* is possible to control its behaviour with @FT_Property_Set and
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* @FT_Property_Get.
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*
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* The CFF driver's module name is 'cff'.
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*
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* Available properties are @hinting-engine, @no-stem-darkening,
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* @darkening-parameters, and @random-seed, as documented in the
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* @properties section.
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*
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*
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* **Hinting and antialiasing principles of the new engine**
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*
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* The rasterizer is positioning horizontal features (e.g., ascender
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* height & x-height, or crossbars) on the pixel grid and minimizing the
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* amount of antialiasing applied to them, while placing vertical
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* features (vertical stems) on the pixel grid without hinting, thus
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* representing the stem position and weight accurately. Sometimes the
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* vertical stems may be only partially black. In this context,
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* 'antialiasing' means that stems are not positioned exactly on pixel
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* borders, causing a fuzzy appearance.
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*
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* There are two principles behind this approach.
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*
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* 1) No hinting in the horizontal direction: Unlike 'superhinted'
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* TrueType, which changes glyph widths to accommodate regular
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* inter-glyph spacing, Adobe's approach is 'faithful to the design' in
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* representing both the glyph width and the inter-glyph spacing designed
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* for the font. This makes the screen display as close as it can be to
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* the result one would get with infinite resolution, while preserving
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* what is considered the key characteristics of each glyph. Note that
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* the distances between unhinted and grid-fitted positions at small
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* sizes are comparable to kerning values and thus would be noticeable
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* (and distracting) while reading if hinting were applied.
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*
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* One of the reasons to not hint horizontally is antialiasing for LCD
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* screens: The pixel geometry of modern displays supplies three vertical
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* subpixels as the eye moves horizontally across each visible pixel. On
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* devices where we can be certain this characteristic is present a
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* rasterizer can take advantage of the subpixels to add increments of
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* weight. In Western writing systems this turns out to be the more
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* critical direction anyway; the weights and spacing of vertical stems
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* (see above) are central to Armenian, Cyrillic, Greek, and Latin type
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* designs. Even when the rasterizer uses greyscale antialiasing instead
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* of color (a necessary compromise when one doesn't know the screen
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* characteristics), the unhinted vertical features preserve the design's
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* weight and spacing much better than aliased type would.
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*
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* 2) Alignment in the vertical direction: Weights and spacing along the
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* y~axis are less critical; what is much more important is the visual
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* alignment of related features (like cap-height and x-height). The
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* sense of alignment for these is enhanced by the sharpness of grid-fit
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* edges, while the cruder vertical resolution (full pixels instead of
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* 1/3 pixels) is less of a problem.
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*
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* On the technical side, horizontal alignment zones for ascender,
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* x-height, and other important height values (traditionally called
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* 'blue zones') as defined in the font are positioned independently,
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* each being rounded to the nearest pixel edge, taking care of overshoot
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* suppression at small sizes, stem darkening, and scaling.
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*
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* Hstems (this is, hint values defined in the font to help align
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* horizontal features) that fall within a blue zone are said to be
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* 'captured' and are aligned to that zone. Uncaptured stems are moved
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* in one of four ways, top edge up or down, bottom edge up or down.
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* Unless there are conflicting hstems, the smallest movement is taken to
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* minimize distortion.
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*
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*/
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/**************************************************************************
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*
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* @section:
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* pcf_driver
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*
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* @title:
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* The PCF driver
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*
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* @abstract:
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* Controlling the PCF driver module.
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*
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* @description:
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* While FreeType's PCF driver doesn't expose API functions by itself, it
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* is possible to control its behaviour with @FT_Property_Set and
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* @FT_Property_Get. Right now, there is a single property
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* @no-long-family-names available if FreeType is compiled with
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* PCF_CONFIG_OPTION_LONG_FAMILY_NAMES.
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*
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* The PCF driver's module name is 'pcf'.
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*
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*/
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/**************************************************************************
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*
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* @section:
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* t1_cid_driver
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*
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* @title:
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* The Type 1 and CID drivers
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*
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* @abstract:
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* Controlling the Type~1 and CID driver modules.
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*
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* @description:
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* It is possible to control the behaviour of FreeType's Type~1 and
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* Type~1 CID drivers with @FT_Property_Set and @FT_Property_Get.
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*
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* Behind the scenes, both drivers use the Adobe CFF engine for hinting;
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* however, the used properties must be specified separately.
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*
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* The Type~1 driver's module name is 'type1'; the CID driver's module
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* name is 't1cid'.
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*
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* Available properties are @hinting-engine, @no-stem-darkening,
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* @darkening-parameters, and @random-seed, as documented in the
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* @properties section.
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*
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* Please see the @cff_driver section for more details on the new hinting
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* engine.
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*
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*/
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/**************************************************************************
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*
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* @section:
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* tt_driver
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*
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* @title:
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* The TrueType driver
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*
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* @abstract:
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* Controlling the TrueType driver module.
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*
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* @description:
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* While FreeType's TrueType driver doesn't expose API functions by
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* itself, it is possible to control its behaviour with @FT_Property_Set
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* and @FT_Property_Get. The following lists the available properties
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* together with the necessary macros and structures.
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*
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* The TrueType driver's module name is 'truetype'.
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*
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* A single property @interpreter-version is available, as documented in
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* the @properties section.
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*
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* We start with a list of definitions, kindly provided by Greg
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* Hitchcock.
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*
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* _Bi-Level Rendering_
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*
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* Monochromatic rendering, exclusively used in the early days of
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* TrueType by both Apple and Microsoft. Microsoft's GDI interface
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* supported hinting of the right-side bearing point, such that the
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* advance width could be non-linear. Most often this was done to
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* achieve some level of glyph symmetry. To enable reasonable
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* performance (e.g., not having to run hinting on all glyphs just to get
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* the widths) there was a bit in the head table indicating if the side
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* bearing was hinted, and additional tables, 'hdmx' and 'LTSH', to cache
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* hinting widths across multiple sizes and device aspect ratios.
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*
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* _Font Smoothing_
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*
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* Microsoft's GDI implementation of anti-aliasing. Not traditional
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* anti-aliasing as the outlines were hinted before the sampling. The
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* widths matched the bi-level rendering.
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*
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* _ClearType Rendering_
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*
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* Technique that uses physical subpixels to improve rendering on LCD
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* (and other) displays. Because of the higher resolution, many methods
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* of improving symmetry in glyphs through hinting the right-side bearing
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* were no longer necessary. This lead to what GDI calls 'natural
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* widths' ClearType, see
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* http://rastertragedy.com/RTRCh4.htm#Sec21. Since hinting
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* has extra resolution, most non-linearity went away, but it is still
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* possible for hints to change the advance widths in this mode.
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*
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* _ClearType Compatible Widths_
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*
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* One of the earliest challenges with ClearType was allowing the
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* implementation in GDI to be selected without requiring all UI and
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* documents to reflow. To address this, a compatible method of
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* rendering ClearType was added where the font hints are executed once
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* to determine the width in bi-level rendering, and then re-run in
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* ClearType, with the difference in widths being absorbed in the font
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* hints for ClearType (mostly in the white space of hints); see
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* http://rastertragedy.com/RTRCh4.htm#Sec20. Somewhat by
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* definition, compatible width ClearType allows for non-linear widths,
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* but only when the bi-level version has non-linear widths.
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*
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* _ClearType Subpixel Positioning_
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*
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* One of the nice benefits of ClearType is the ability to more crisply
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* display fractional widths; unfortunately, the GDI model of integer
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* bitmaps did not support this. However, the WPF and Direct Write
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* frameworks do support fractional widths. DWrite calls this 'natural
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* mode', not to be confused with GDI's 'natural widths'. Subpixel
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* positioning, in the current implementation of Direct Write,
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* unfortunately does not support hinted advance widths, see
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* http://rastertragedy.com/RTRCh4.htm#Sec22. Note that the
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* TrueType interpreter fully allows the advance width to be adjusted in
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* this mode, just the DWrite client will ignore those changes.
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*
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* _ClearType Backward Compatibility_
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*
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* This is a set of exceptions made in the TrueType interpreter to
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* minimize hinting techniques that were problematic with the extra
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* resolution of ClearType; see
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* http://rastertragedy.com/RTRCh4.htm#Sec1 and
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* https://www.microsoft.com/typography/cleartype/truetypecleartype.aspx.
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* This technique is not to be confused with ClearType compatible widths.
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* ClearType backward compatibility has no direct impact on changing
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* advance widths, but there might be an indirect impact on disabling
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* some deltas. This could be worked around in backward compatibility
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* mode.
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*
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* _Native ClearType Mode_
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*
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* (Not to be confused with 'natural widths'.) This mode removes all the
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* exceptions in the TrueType interpreter when running with ClearType.
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* Any issues on widths would still apply, though.
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*
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*/
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/**************************************************************************
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*
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* @section:
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* properties
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*
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* @title:
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* Driver properties
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*
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* @abstract:
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* Controlling driver modules.
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*
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* @description:
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* Driver modules can be controlled by setting and unsetting properties,
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* using the functions @FT_Property_Set and @FT_Property_Get. This
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* section documents the available properties, together with auxiliary
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* macros and structures.
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*
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*/
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/**************************************************************************
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*
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* @enum:
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* FT_HINTING_XXX
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*
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* @description:
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* A list of constants used for the @hinting-engine property to select
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* the hinting engine for CFF, Type~1, and CID fonts.
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*
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* @values:
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* FT_HINTING_FREETYPE ::
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* Use the old FreeType hinting engine.
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*
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* FT_HINTING_ADOBE ::
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* Use the hinting engine contributed by Adobe.
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*
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* @since:
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* 2.9
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*
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*/
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#define FT_HINTING_FREETYPE 0
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#define FT_HINTING_ADOBE 1
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/* these constants (introduced in 2.4.12) are deprecated */
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#define FT_CFF_HINTING_FREETYPE FT_HINTING_FREETYPE
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#define FT_CFF_HINTING_ADOBE FT_HINTING_ADOBE
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/**************************************************************************
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*
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* @property:
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* hinting-engine
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*
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* @description:
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* Thanks to Adobe, which contributed a new hinting (and parsing) engine,
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* an application can select between 'freetype' and 'adobe' if compiled
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* with `CFF_CONFIG_OPTION_OLD_ENGINE`. If this configuration macro
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* isn't defined, 'hinting-engine' does nothing.
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*
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* The same holds for the Type~1 and CID modules if compiled with
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* `T1_CONFIG_OPTION_OLD_ENGINE`.
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*
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* For the 'cff' module, the default engine is 'freetype' if
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* `CFF_CONFIG_OPTION_OLD_ENGINE` is defined, and 'adobe' otherwise.
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*
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* For both the 'type1' and 't1cid' modules, the default engine is
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* 'freetype' if `T1_CONFIG_OPTION_OLD_ENGINE` is defined, and 'adobe'
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* otherwise.
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*
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* @note:
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* This property can be used with @FT_Property_Get also.
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*
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* This property can be set via the `FREETYPE_PROPERTIES` environment
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* variable (using values 'adobe' or 'freetype').
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*
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* @example:
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* The following example code demonstrates how to select Adobe's hinting
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* engine for the 'cff' module (omitting the error handling).
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*
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* ```
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* FT_Library library;
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* FT_UInt hinting_engine = FT_HINTING_ADOBE;
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*
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*
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* FT_Init_FreeType( &library );
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*
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* FT_Property_Set( library, "cff",
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* "hinting-engine", &hinting_engine );
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* ```
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*
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* @since:
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* 2.4.12 (for 'cff' module)
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*
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* 2.9 (for 'type1' and 't1cid' modules)
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*
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*/
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/**************************************************************************
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*
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* @property:
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* no-stem-darkening
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*
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* @description:
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* All glyphs that pass through the auto-hinter will be emboldened unless
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* this property is set to TRUE. The same is true for the CFF, Type~1,
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* and CID font modules if the 'Adobe' engine is selected (which is the
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* default).
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*
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* Stem darkening emboldens glyphs at smaller sizes to make them more
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* readable on common low-DPI screens when using linear alpha blending
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* and gamma correction, see @FT_Render_Glyph. When not using linear
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* alpha blending and gamma correction, glyphs will appear heavy and
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* fuzzy!
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*
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* Gamma correction essentially lightens fonts since shades of grey are
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* shifted to higher pixel values (=~higher brightness) to match the
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* original intention to the reality of our screens. The side-effect is
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* that glyphs 'thin out'. Mac OS~X and Adobe's proprietary font
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* rendering library implement a counter-measure: stem darkening at
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* smaller sizes where shades of gray dominate. By emboldening a glyph
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* slightly in relation to its pixel size, individual pixels get higher
|
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* coverage of filled-in outlines and are therefore 'blacker'. This
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* counteracts the 'thinning out' of glyphs, making text remain readable
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* at smaller sizes.
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*
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* By default, the Adobe engines for CFF, Type~1, and CID fonts darken
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* stems at smaller sizes, regardless of hinting, to enhance contrast.
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* Setting this property, stem darkening gets switched off.
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*
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* For the auto-hinter, stem-darkening is experimental currently and thus
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* switched off by default (this is, `no-stem-darkening` is set to TRUE
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* by default). Total consistency with the CFF driver is not achieved
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* right now because the emboldening method differs and glyphs must be
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* scaled down on the Y-axis to keep outline points inside their
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* precomputed blue zones. The smaller the size (especially 9ppem and
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* down), the higher the loss of emboldening versus the CFF driver.
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*
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* Note that stem darkening is never applied if @FT_LOAD_NO_SCALE is set.
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*
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* @note:
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* This property can be used with @FT_Property_Get also.
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*
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* This property can be set via the `FREETYPE_PROPERTIES` environment
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* variable (using values 1 and 0 for 'on' and 'off', respectively). It
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* can also be set per face using @FT_Face_Properties with
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* @FT_PARAM_TAG_STEM_DARKENING.
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*
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* @example:
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* ```
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* FT_Library library;
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* FT_Bool no_stem_darkening = TRUE;
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*
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*
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* FT_Init_FreeType( &library );
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*
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* FT_Property_Set( library, "cff",
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* "no-stem-darkening", &no_stem_darkening );
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* ```
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*
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* @since:
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* 2.4.12 (for 'cff' module)
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*
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* 2.6.2 (for 'autofitter' module)
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*
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* 2.9 (for 'type1' and 't1cid' modules)
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*
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*/
|
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|
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/**************************************************************************
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*
|
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* @property:
|
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* darkening-parameters
|
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*
|
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* @description:
|
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* By default, the Adobe hinting engine, as used by the CFF, Type~1, and
|
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* CID font drivers, darkens stems as follows (if the `no-stem-darkening`
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* property isn't set):
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*
|
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* ```
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* stem width <= 0.5px: darkening amount = 0.4px
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* stem width = 1px: darkening amount = 0.275px
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* stem width = 1.667px: darkening amount = 0.275px
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* stem width >= 2.333px: darkening amount = 0px
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* ```
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*
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* and piecewise linear in-between. At configuration time, these four
|
|
* control points can be set with the macro
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|
* `CFF_CONFIG_OPTION_DARKENING_PARAMETERS`; the CFF, Type~1, and CID
|
|
* drivers share these values. At runtime, the control points can be
|
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* changed using the `darkening-parameters` property (see the example
|
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* 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 */
|