• Home
  • Line#
  • Scopes#
  • Navigate#
  • Raw
  • Download
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 /***************************************************************************/
18 
19 
20 #ifndef __FT_LCD_FILTER_H__
21 #define __FT_LCD_FILTER_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    * @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    */
57 
58 
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,
100 
101     FT_LCD_FILTER_MAX   /* do not remove */
102 
103   } FT_LcdFilter;
104 
105 
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 );
163 
164 
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 );
204 
205   /* */
206 
207 
208 FT_END_HEADER
209 
210 #endif /* __FT_LCD_FILTER_H__ */
211 
212 
213 /* END */
214