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view libs/ft2static/freetype/ftlcdfil.h @ 1:e7ca128b8713
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| author | John Tsiombikas <nuclear@member.fsf.org> |
|---|---|
| date | Sun, 02 Feb 2014 00:35:22 +0200 |
| parents | |
| children |
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1 /***************************************************************************/
2 /* */
3 /* ftlcdfil.h */
4 /* */
5 /* FreeType API for color filtering of subpixel bitmap glyphs */
6 /* (specification). */
7 /* */
8 /* Copyright 2006, 2007, 2008, 2010 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 /***************************************************************************/
20 #ifndef __FT_LCD_FILTER_H__
21 #define __FT_LCD_FILTER_H__
23 #include <ft2build.h>
24 #include FT_FREETYPE_H
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
33 FT_BEGIN_HEADER
35 /***************************************************************************
36 *
37 * @section:
38 * lcd_filtering
39 *
40 * @title:
41 * LCD Filtering
42 *
43 * @abstract:
44 * Reduce color fringes of LCD-optimized bitmaps.
45 *
46 * @description:
47 * The @FT_Library_SetLcdFilter API can be used to specify a low-pass
48 * filter which is then applied to LCD-optimized bitmaps generated
49 * through @FT_Render_Glyph. This is useful to reduce color fringes
50 * which would occur with unfiltered rendering.
51 *
52 * Note that no filter is active by default, and that this function is
53 * *not* implemented in default builds of the library. You need to
54 * #define FT_CONFIG_OPTION_SUBPIXEL_RENDERING in your `ftoption.h' file
55 * in order to activate it.
56 */
59 /****************************************************************************
60 *
61 * @enum:
62 * FT_LcdFilter
63 *
64 * @description:
65 * A list of values to identify various types of LCD filters.
66 *
67 * @values:
68 * FT_LCD_FILTER_NONE ::
69 * Do not perform filtering. When used with subpixel rendering, this
70 * results in sometimes severe color fringes.
71 *
72 * FT_LCD_FILTER_DEFAULT ::
73 * The default filter reduces color fringes considerably, at the cost
74 * of a slight blurriness in the output.
75 *
76 * FT_LCD_FILTER_LIGHT ::
77 * The light filter is a variant that produces less blurriness at the
78 * cost of slightly more color fringes than the default one. It might
79 * be better, depending on taste, your monitor, or your personal vision.
80 *
81 * FT_LCD_FILTER_LEGACY ::
82 * This filter corresponds to the original libXft color filter. It
83 * provides high contrast output but can exhibit really bad color
84 * fringes if glyphs are not extremely well hinted to the pixel grid.
85 * In other words, it only works well if the TrueType bytecode
86 * interpreter is enabled *and* high-quality hinted fonts are used.
87 *
88 * This filter is only provided for comparison purposes, and might be
89 * disabled or stay unsupported in the future.
90 *
91 * @since:
92 * 2.3.0
93 */
94 typedef enum FT_LcdFilter_
95 {
96 FT_LCD_FILTER_NONE = 0,
97 FT_LCD_FILTER_DEFAULT = 1,
98 FT_LCD_FILTER_LIGHT = 2,
99 FT_LCD_FILTER_LEGACY = 16,
101 FT_LCD_FILTER_MAX /* do not remove */
103 } FT_LcdFilter;
106 /**************************************************************************
107 *
108 * @func:
109 * FT_Library_SetLcdFilter
110 *
111 * @description:
112 * This function is used to apply color filtering to LCD decimated
113 * bitmaps, like the ones used when calling @FT_Render_Glyph with
114 * @FT_RENDER_MODE_LCD or @FT_RENDER_MODE_LCD_V.
115 *
116 * @input:
117 * library ::
118 * A handle to the target library instance.
119 *
120 * filter ::
121 * The filter type.
122 *
123 * You can use @FT_LCD_FILTER_NONE here to disable this feature, or
124 * @FT_LCD_FILTER_DEFAULT to use a default filter that should work
125 * well on most LCD screens.
126 *
127 * @return:
128 * FreeType error code. 0~means success.
129 *
130 * @note:
131 * This feature is always disabled by default. Clients must make an
132 * explicit call to this function with a `filter' value other than
133 * @FT_LCD_FILTER_NONE in order to enable it.
134 *
135 * Due to *PATENTS* covering subpixel rendering, this function doesn't
136 * do anything except returning `FT_Err_Unimplemented_Feature' if the
137 * configuration macro FT_CONFIG_OPTION_SUBPIXEL_RENDERING is not
138 * defined in your build of the library, which should correspond to all
139 * default builds of FreeType.
140 *
141 * The filter affects glyph bitmaps rendered through @FT_Render_Glyph,
142 * @FT_Outline_Get_Bitmap, @FT_Load_Glyph, and @FT_Load_Char.
143 *
144 * It does _not_ affect the output of @FT_Outline_Render and
145 * @FT_Outline_Get_Bitmap.
146 *
147 * If this feature is activated, the dimensions of LCD glyph bitmaps are
148 * either larger or taller than the dimensions of the corresponding
149 * outline with regards to the pixel grid. For example, for
150 * @FT_RENDER_MODE_LCD, the filter adds up to 3~pixels to the left, and
151 * up to 3~pixels to the right.
152 *
153 * The bitmap offset values are adjusted correctly, so clients shouldn't
154 * need to modify their layout and glyph positioning code when enabling
155 * the filter.
156 *
157 * @since:
158 * 2.3.0
159 */
160 FT_EXPORT( FT_Error )
161 FT_Library_SetLcdFilter( FT_Library library,
162 FT_LcdFilter filter );
165 /**************************************************************************
166 *
167 * @func:
168 * FT_Library_SetLcdFilterWeights
169 *
170 * @description:
171 * Use this function to override the filter weights selected by
172 * @FT_Library_SetLcdFilter. By default, FreeType uses the quintuple
173 * (0x00, 0x55, 0x56, 0x55, 0x00) for FT_LCD_FILTER_LIGHT, and (0x10,
174 * 0x40, 0x70, 0x40, 0x10) for FT_LCD_FILTER_DEFAULT and
175 * FT_LCD_FILTER_LEGACY.
176 *
177 * @input:
178 * library ::
179 * A handle to the target library instance.
180 *
181 * weights ::
182 * A pointer to an array; the function copies the first five bytes and
183 * uses them to specify the filter weights.
184 *
185 * @return:
186 * FreeType error code. 0~means success.
187 *
188 * @note:
189 * Due to *PATENTS* covering subpixel rendering, this function doesn't
190 * do anything except returning `FT_Err_Unimplemented_Feature' if the
191 * configuration macro FT_CONFIG_OPTION_SUBPIXEL_RENDERING is not
192 * defined in your build of the library, which should correspond to all
193 * default builds of FreeType.
194 *
195 * This function must be called after @FT_Library_SetLcdFilter to have
196 * any effect.
197 *
198 * @since:
199 * 2.4.0
200 */
201 FT_EXPORT( FT_Error )
202 FT_Library_SetLcdFilterWeights( FT_Library library,
203 unsigned char *weights );
205 /* */
208 FT_END_HEADER
210 #endif /* __FT_LCD_FILTER_H__ */
213 /* END */