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Diffstat (limited to 'include/ftttdrv.h')
| -rw-r--r-- | include/ftttdrv.h | 170 |
1 files changed, 170 insertions, 0 deletions
diff --git a/include/ftttdrv.h b/include/ftttdrv.h new file mode 100644 index 0000000..70ad3d5 --- /dev/null +++ b/include/ftttdrv.h @@ -0,0 +1,170 @@ +/***************************************************************************/ +/* */ +/* ftttdrv.h */ +/* */ +/* FreeType API for controlling the TrueType driver */ +/* (specification only). */ +/* */ +/* Copyright 2013 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 */ |