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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, 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 */ | |
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