1 /***************************************************************************/ 2 /* */ 3 /* ftttdrv.h */ 4 /* */ 5 /* FreeType API for controlling the TrueType driver */ 6 /* (specification only). */ 7 /* */ 8 /* Copyright 2013 by */ 9 /* David Turner, Robert Wilhelm, and Werner Lemberg. */ 10 /* */ 11 /* This file is part of the FreeType project, and may only be used, */ 12 /* modified, and distributed under the terms of the FreeType project */ 13 /* license, LICENSE.TXT. By continuing to use, modify, or distribute */ 14 /* this file you indicate that you have read the license and */ 15 /* understand and accept it fully. */ 16 /* */ 17 /***************************************************************************/ 18 19 20 #ifndef __FTTTDRV_H__ 21 #define __FTTTDRV_H__ 22 23 #include <ft2build.h> 24 #include FT_FREETYPE_H 25 26 #ifdef FREETYPE_H 27 #error "freetype.h of FreeType 1 has been loaded!" 28 #error "Please fix the directory search order for header files" 29 #error "so that freetype.h of FreeType 2 is found first." 30 #endif 31 32 33 FT_BEGIN_HEADER 34 35 36 /************************************************************************** 37 * 38 * @section: 39 * tt_driver 40 * 41 * @title: 42 * The TrueType driver 43 * 44 * @abstract: 45 * Controlling the TrueType driver module. 46 * 47 * @description: 48 * While FreeType's TrueType driver doesn't expose API functions by 49 * itself, it is possible to control its behaviour with @FT_Property_Set 50 * and @FT_Property_Get. The following lists the available properties 51 * together with the necessary macros and structures. 52 * 53 * The TrueType driver's module name is `truetype'. 54 * 55 */ 56 57 58 /************************************************************************** 59 * 60 * @property: 61 * interpreter-version 62 * 63 * @description: 64 * Currently, two versions are available, representing the bytecode 65 * interpreter with and without subpixel hinting support, 66 * respectively. The default is subpixel support if 67 * TT_CONFIG_OPTION_SUBPIXEL_HINTING is defined, and no subpixel 68 * support otherwise (since it isn't available then). 69 * 70 * If subpixel hinting is on, many TrueType bytecode instructions 71 * behave differently compared to B/W or grayscale rendering. The 72 * main idea is to render at a much increased horizontal resolution, 73 * then sampling down the created output to subpixel precision. 74 * However, many older fonts are not suited to this and must be 75 * specially taken care of by applying (hardcoded) font-specific 76 * tweaks. 77 * 78 * Details on subpixel hinting and some of the necessary tweaks can be 79 * found in Greg Hitchcock's whitepaper at 80 * `http://www.microsoft.com/typography/cleartype/truetypecleartype.aspx'. 81 * 82 * The following example code demonstrates how to activate subpixel 83 * hinting (omitting the error handling). 84 * 85 * { 86 * FT_Library library; 87 * FT_Face face; 88 * FT_UInt interpreter_version = TT_INTERPRETER_VERSION_38; 89 * 90 * 91 * FT_Init_FreeType( &library ); 92 * 93 * FT_Property_Set( library, "truetype", 94 * "interpreter-version", 95 * &interpreter_version ); 96 * } 97 * 98 * @note: 99 * This property can be used with @FT_Property_Get also. 100 * 101 */ 102 103 104 /************************************************************************** 105 * 106 * @enum: 107 * TT_INTERPRETER_VERSION_XXX 108 * 109 * @description: 110 * A list of constants used for the @interpreter-version property to 111 * select the hinting engine for Truetype fonts. 112 * 113 * The numeric value in the constant names represents the version 114 * number as returned by the `GETINFO' bytecode instruction. 115 * 116 * @values: 117 * TT_INTERPRETER_VERSION_35 :: 118 * Version~35 corresponds to MS rasterizer v.1.7 as used e.g. in 119 * Windows~98; only grayscale and B/W rasterizing is supported. 120 * 121 * TT_INTERPRETER_VERSION_38 :: 122 * Version~38 corresponds to MS rasterizer v.1.9; it is roughly 123 * equivalent to the hinting provided by DirectWrite ClearType (as 124 * can be found, for example, in the Internet Explorer~9 running on 125 * Windows~7). 126 * 127 * @note: 128 * This property controls the behaviour of the bytecode interpreter 129 * and thus how outlines get hinted. It does *not* control how glyph 130 * get rasterized! In particular, it does not control subpixel color 131 * filtering. 132 * 133 * If FreeType has not been compiled with configuration option 134 * FT_CONFIG_OPTION_SUBPIXEL_HINTING, selecting version~38 causes an 135 * `FT_Err_Unimplemented_Feature' error. 136 * 137 * Depending on the graphics framework, Microsoft uses different 138 * bytecode engines. As a consequence, the version numbers returned by 139 * a call to the `GETINFO[1]' bytecode instruction are more convoluted 140 * than desired. 141 * 142 * { 143 * framework Windows version result of GETINFO[1] 144 * ---------------------------------------------------- 145 * GDI before XP 35 146 * GDI XP and later 37 147 * GDI+ old before Vista 37 148 * GDI+ old Vista, 7 38 149 * GDI+ after 7 40 150 * DWrite before 8 39 151 * DWrite 8 and later 40 152 * } 153 * 154 * Since FreeType doesn't provide all capabilities of DWrite ClearType, 155 * using version~38 seems justified. 156 * 157 */ 158 #define TT_INTERPRETER_VERSION_35 35 159 #define TT_INTERPRETER_VERSION_38 38 160 161 162 /* */ 163 164 FT_END_HEADER 165 166 167 #endif /* __FTTTDRV_H__ */ 168 169 170 /* END */ 171
