Edit
kc3-lang/freetype/include/ftttdrv.h
Werner Lemberg
- include/ftttdrv.h
-
/***************************************************************************/ /* */ /* ftttdrv.h */ /* */ /* FreeType API for controlling the TrueType driver */ /* (specification only). */ /* */ /* Copyright 2013-2015 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 __FTTTDRV_H__ #define __FTTTDRV_H__ #include <ft2build.h> #include FT_FREETYPE_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: * tt_driver * * @title: * The TrueType driver * * @abstract: * Controlling the TrueType driver module. * * @description: * While FreeType's TrueType driver doesn't expose API functions by * itself, it is possible to control its behaviour with @FT_Property_Set * and @FT_Property_Get. The following lists the available properties * together with the necessary macros and structures. * * The TrueType driver's module name is `truetype'. * */ /************************************************************************** * * @property: * interpreter-version * * @description: * Currently, two versions are available, representing the bytecode * interpreter with and without subpixel hinting support, * 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. The * 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) font-specific * tweaks. * * Details on subpixel hinting and some of the necessary tweaks can be * found in Greg Hitchcock's whitepaper at * `http://www.microsoft.com/typography/cleartype/truetypecleartype.aspx'. * * The following example code demonstrates how to activate subpixel * hinting (omitting the error handling). * * { * FT_Library library; * FT_Face face; * FT_UInt interpreter_version = TT_INTERPRETER_VERSION_38; * * * FT_Init_FreeType( &library ); * * FT_Property_Set( library, "truetype", * "interpreter-version", * &interpreter_version ); * } * * @note: * This property can be used with @FT_Property_Get also. * */ /************************************************************************** * * @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). * * @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 configuration option * FT_CONFIG_OPTION_SUBPIXEL_HINTING, selecting version~38 causes an * `FT_Err_Unimplemented_Feature' error. * * Depending on the graphics framework, Microsoft uses different * bytecode engines. As a consequence, the version numbers returned by * a call to the `GETINFO[1]' bytecode instruction are more convoluted * than desired. * * { * framework Windows version result of GETINFO[1] * ---------------------------------------------------- * GDI before XP 35 * GDI XP and later 37 * GDI+ old before Vista 37 * GDI+ old Vista, 7 38 * GDI+ after 7 40 * DWrite before 8 39 * DWrite 8 and later 40 * } * * Since FreeType doesn't provide all capabilities of DWrite ClearType, * using version~38 seems justified. * */ #define TT_INTERPRETER_VERSION_35 35 #define TT_INTERPRETER_VERSION_38 38 /* */ FT_END_HEADER #endif /* __FTTTDRV_H__ */ /* END */