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comparison: modules/freetype2/include/ftttdrv.h

modules/freetype2/include/ftttdrv.h

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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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