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| 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 which represent 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 */ |
| 138 #define TT_INTERPRETER_VERSION_35 35 |
| 139 #define TT_INTERPRETER_VERSION_38 38 |
| 140 |
| 141 |
| 142 /* */ |
| 143 |
| 144 FT_END_HEADER |
| 145 |
| 146 |
| 147 #endif /* __FTTTDRV_H__ */ |
| 148 |
| 149 |
| 150 /* END */ |
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