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annotate libs/ft2static/freetype/ftlcdfil.h @ 0:b2f14e535253

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author John Tsiombikas <nuclear@member.fsf.org>
date Sat, 01 Feb 2014 19:58:19 +0200
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nuclear@0 1 /***************************************************************************/
nuclear@0 2 /* */
nuclear@0 3 /* ftlcdfil.h */
nuclear@0 4 /* */
nuclear@0 5 /* FreeType API for color filtering of subpixel bitmap glyphs */
nuclear@0 6 /* (specification). */
nuclear@0 7 /* */
nuclear@0 8 /* Copyright 2006, 2007, 2008, 2010 by */
nuclear@0 9 /* David Turner, Robert Wilhelm, and Werner Lemberg. */
nuclear@0 10 /* */
nuclear@0 11 /* This file is part of the FreeType project, and may only be used, */
nuclear@0 12 /* modified, and distributed under the terms of the FreeType project */
nuclear@0 13 /* license, LICENSE.TXT. By continuing to use, modify, or distribute */
nuclear@0 14 /* this file you indicate that you have read the license and */
nuclear@0 15 /* understand and accept it fully. */
nuclear@0 16 /* */
nuclear@0 17 /***************************************************************************/
nuclear@0 18
nuclear@0 19
nuclear@0 20 #ifndef __FT_LCD_FILTER_H__
nuclear@0 21 #define __FT_LCD_FILTER_H__
nuclear@0 22
nuclear@0 23 #include <ft2build.h>
nuclear@0 24 #include FT_FREETYPE_H
nuclear@0 25
nuclear@0 26 #ifdef FREETYPE_H
nuclear@0 27 #error "freetype.h of FreeType 1 has been loaded!"
nuclear@0 28 #error "Please fix the directory search order for header files"
nuclear@0 29 #error "so that freetype.h of FreeType 2 is found first."
nuclear@0 30 #endif
nuclear@0 31
nuclear@0 32
nuclear@0 33 FT_BEGIN_HEADER
nuclear@0 34
nuclear@0 35 /***************************************************************************
nuclear@0 36 *
nuclear@0 37 * @section:
nuclear@0 38 * lcd_filtering
nuclear@0 39 *
nuclear@0 40 * @title:
nuclear@0 41 * LCD Filtering
nuclear@0 42 *
nuclear@0 43 * @abstract:
nuclear@0 44 * Reduce color fringes of LCD-optimized bitmaps.
nuclear@0 45 *
nuclear@0 46 * @description:
nuclear@0 47 * The @FT_Library_SetLcdFilter API can be used to specify a low-pass
nuclear@0 48 * filter which is then applied to LCD-optimized bitmaps generated
nuclear@0 49 * through @FT_Render_Glyph. This is useful to reduce color fringes
nuclear@0 50 * which would occur with unfiltered rendering.
nuclear@0 51 *
nuclear@0 52 * Note that no filter is active by default, and that this function is
nuclear@0 53 * *not* implemented in default builds of the library. You need to
nuclear@0 54 * #define FT_CONFIG_OPTION_SUBPIXEL_RENDERING in your `ftoption.h' file
nuclear@0 55 * in order to activate it.
nuclear@0 56 */
nuclear@0 57
nuclear@0 58
nuclear@0 59 /****************************************************************************
nuclear@0 60 *
nuclear@0 61 * @enum:
nuclear@0 62 * FT_LcdFilter
nuclear@0 63 *
nuclear@0 64 * @description:
nuclear@0 65 * A list of values to identify various types of LCD filters.
nuclear@0 66 *
nuclear@0 67 * @values:
nuclear@0 68 * FT_LCD_FILTER_NONE ::
nuclear@0 69 * Do not perform filtering. When used with subpixel rendering, this
nuclear@0 70 * results in sometimes severe color fringes.
nuclear@0 71 *
nuclear@0 72 * FT_LCD_FILTER_DEFAULT ::
nuclear@0 73 * The default filter reduces color fringes considerably, at the cost
nuclear@0 74 * of a slight blurriness in the output.
nuclear@0 75 *
nuclear@0 76 * FT_LCD_FILTER_LIGHT ::
nuclear@0 77 * The light filter is a variant that produces less blurriness at the
nuclear@0 78 * cost of slightly more color fringes than the default one. It might
nuclear@0 79 * be better, depending on taste, your monitor, or your personal vision.
nuclear@0 80 *
nuclear@0 81 * FT_LCD_FILTER_LEGACY ::
nuclear@0 82 * This filter corresponds to the original libXft color filter. It
nuclear@0 83 * provides high contrast output but can exhibit really bad color
nuclear@0 84 * fringes if glyphs are not extremely well hinted to the pixel grid.
nuclear@0 85 * In other words, it only works well if the TrueType bytecode
nuclear@0 86 * interpreter is enabled *and* high-quality hinted fonts are used.
nuclear@0 87 *
nuclear@0 88 * This filter is only provided for comparison purposes, and might be
nuclear@0 89 * disabled or stay unsupported in the future.
nuclear@0 90 *
nuclear@0 91 * @since:
nuclear@0 92 * 2.3.0
nuclear@0 93 */
nuclear@0 94 typedef enum FT_LcdFilter_
nuclear@0 95 {
nuclear@0 96 FT_LCD_FILTER_NONE = 0,
nuclear@0 97 FT_LCD_FILTER_DEFAULT = 1,
nuclear@0 98 FT_LCD_FILTER_LIGHT = 2,
nuclear@0 99 FT_LCD_FILTER_LEGACY = 16,
nuclear@0 100
nuclear@0 101 FT_LCD_FILTER_MAX /* do not remove */
nuclear@0 102
nuclear@0 103 } FT_LcdFilter;
nuclear@0 104
nuclear@0 105
nuclear@0 106 /**************************************************************************
nuclear@0 107 *
nuclear@0 108 * @func:
nuclear@0 109 * FT_Library_SetLcdFilter
nuclear@0 110 *
nuclear@0 111 * @description:
nuclear@0 112 * This function is used to apply color filtering to LCD decimated
nuclear@0 113 * bitmaps, like the ones used when calling @FT_Render_Glyph with
nuclear@0 114 * @FT_RENDER_MODE_LCD or @FT_RENDER_MODE_LCD_V.
nuclear@0 115 *
nuclear@0 116 * @input:
nuclear@0 117 * library ::
nuclear@0 118 * A handle to the target library instance.
nuclear@0 119 *
nuclear@0 120 * filter ::
nuclear@0 121 * The filter type.
nuclear@0 122 *
nuclear@0 123 * You can use @FT_LCD_FILTER_NONE here to disable this feature, or
nuclear@0 124 * @FT_LCD_FILTER_DEFAULT to use a default filter that should work
nuclear@0 125 * well on most LCD screens.
nuclear@0 126 *
nuclear@0 127 * @return:
nuclear@0 128 * FreeType error code. 0~means success.
nuclear@0 129 *
nuclear@0 130 * @note:
nuclear@0 131 * This feature is always disabled by default. Clients must make an
nuclear@0 132 * explicit call to this function with a `filter' value other than
nuclear@0 133 * @FT_LCD_FILTER_NONE in order to enable it.
nuclear@0 134 *
nuclear@0 135 * Due to *PATENTS* covering subpixel rendering, this function doesn't
nuclear@0 136 * do anything except returning `FT_Err_Unimplemented_Feature' if the
nuclear@0 137 * configuration macro FT_CONFIG_OPTION_SUBPIXEL_RENDERING is not
nuclear@0 138 * defined in your build of the library, which should correspond to all
nuclear@0 139 * default builds of FreeType.
nuclear@0 140 *
nuclear@0 141 * The filter affects glyph bitmaps rendered through @FT_Render_Glyph,
nuclear@0 142 * @FT_Outline_Get_Bitmap, @FT_Load_Glyph, and @FT_Load_Char.
nuclear@0 143 *
nuclear@0 144 * It does _not_ affect the output of @FT_Outline_Render and
nuclear@0 145 * @FT_Outline_Get_Bitmap.
nuclear@0 146 *
nuclear@0 147 * If this feature is activated, the dimensions of LCD glyph bitmaps are
nuclear@0 148 * either larger or taller than the dimensions of the corresponding
nuclear@0 149 * outline with regards to the pixel grid. For example, for
nuclear@0 150 * @FT_RENDER_MODE_LCD, the filter adds up to 3~pixels to the left, and
nuclear@0 151 * up to 3~pixels to the right.
nuclear@0 152 *
nuclear@0 153 * The bitmap offset values are adjusted correctly, so clients shouldn't
nuclear@0 154 * need to modify their layout and glyph positioning code when enabling
nuclear@0 155 * the filter.
nuclear@0 156 *
nuclear@0 157 * @since:
nuclear@0 158 * 2.3.0
nuclear@0 159 */
nuclear@0 160 FT_EXPORT( FT_Error )
nuclear@0 161 FT_Library_SetLcdFilter( FT_Library library,
nuclear@0 162 FT_LcdFilter filter );
nuclear@0 163
nuclear@0 164
nuclear@0 165 /**************************************************************************
nuclear@0 166 *
nuclear@0 167 * @func:
nuclear@0 168 * FT_Library_SetLcdFilterWeights
nuclear@0 169 *
nuclear@0 170 * @description:
nuclear@0 171 * Use this function to override the filter weights selected by
nuclear@0 172 * @FT_Library_SetLcdFilter. By default, FreeType uses the quintuple
nuclear@0 173 * (0x00, 0x55, 0x56, 0x55, 0x00) for FT_LCD_FILTER_LIGHT, and (0x10,
nuclear@0 174 * 0x40, 0x70, 0x40, 0x10) for FT_LCD_FILTER_DEFAULT and
nuclear@0 175 * FT_LCD_FILTER_LEGACY.
nuclear@0 176 *
nuclear@0 177 * @input:
nuclear@0 178 * library ::
nuclear@0 179 * A handle to the target library instance.
nuclear@0 180 *
nuclear@0 181 * weights ::
nuclear@0 182 * A pointer to an array; the function copies the first five bytes and
nuclear@0 183 * uses them to specify the filter weights.
nuclear@0 184 *
nuclear@0 185 * @return:
nuclear@0 186 * FreeType error code. 0~means success.
nuclear@0 187 *
nuclear@0 188 * @note:
nuclear@0 189 * Due to *PATENTS* covering subpixel rendering, this function doesn't
nuclear@0 190 * do anything except returning `FT_Err_Unimplemented_Feature' if the
nuclear@0 191 * configuration macro FT_CONFIG_OPTION_SUBPIXEL_RENDERING is not
nuclear@0 192 * defined in your build of the library, which should correspond to all
nuclear@0 193 * default builds of FreeType.
nuclear@0 194 *
nuclear@0 195 * This function must be called after @FT_Library_SetLcdFilter to have
nuclear@0 196 * any effect.
nuclear@0 197 *
nuclear@0 198 * @since:
nuclear@0 199 * 2.4.0
nuclear@0 200 */
nuclear@0 201 FT_EXPORT( FT_Error )
nuclear@0 202 FT_Library_SetLcdFilterWeights( FT_Library library,
nuclear@0 203 unsigned char *weights );
nuclear@0 204
nuclear@0 205 /* */
nuclear@0 206
nuclear@0 207
nuclear@0 208 FT_END_HEADER
nuclear@0 209
nuclear@0 210 #endif /* __FT_LCD_FILTER_H__ */
nuclear@0 211
nuclear@0 212
nuclear@0 213 /* END */