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| 1 /***************************************************************************/ | |
| 2 /* */ | |
| 3 /* ftcffdrv.h */ | |
| 4 /* */ | |
| 5 /* FreeType API for controlling the CFF driver (specification only). */ | |
| 6 /* */ | |
| 7 /* Copyright 2013, 2014 by */ | |
| 8 /* David Turner, Robert Wilhelm, and Werner Lemberg. */ | |
| 9 /* */ | |
| 10 /* This file is part of the FreeType project, and may only be used, */ | |
| 11 /* modified, and distributed under the terms of the FreeType project */ | |
| 12 /* license, LICENSE.TXT. By continuing to use, modify, or distribute */ | |
| 13 /* this file you indicate that you have read the license and */ | |
| 14 /* understand and accept it fully. */ | |
| 15 /* */ | |
| 16 /***************************************************************************/ | |
| 17 | |
| 18 | |
| 19 #ifndef __FTCFFDRV_H__ | |
| 20 #define __FTCFFDRV_H__ | |
| 21 | |
| 22 #include <ft2build.h> | |
| 23 #include FT_FREETYPE_H | |
| 24 | |
| 25 #ifdef FREETYPE_H | |
| 26 #error "freetype.h of FreeType 1 has been loaded!" | |
| 27 #error "Please fix the directory search order for header files" | |
| 28 #error "so that freetype.h of FreeType 2 is found first." | |
| 29 #endif | |
| 30 | |
| 31 | |
| 32 FT_BEGIN_HEADER | |
| 33 | |
| 34 | |
| 35 /************************************************************************** | |
| 36 * | |
| 37 * @section: | |
| 38 * cff_driver | |
| 39 * | |
| 40 * @title: | |
| 41 * The CFF driver | |
| 42 * | |
| 43 * @abstract: | |
| 44 * Controlling the CFF driver module. | |
| 45 * | |
| 46 * @description: | |
| 47 * While FreeType's CFF driver doesn't expose API functions by itself, | |
| 48 * it is possible to control its behaviour with @FT_Property_Set and | |
| 49 * @FT_Property_Get. The list below gives the available properties | |
| 50 * together with the necessary macros and structures. | |
| 51 * | |
| 52 * The CFF driver's module name is `cff'. | |
| 53 * | |
| 54 * *Hinting* *and* *antialiasing* *principles* *of* *the* *new* *engine* | |
| 55 * | |
| 56 * The rasterizer is positioning horizontal features (e.g., ascender | |
| 57 * height & x-height, or crossbars) on the pixel grid and minimizing the | |
| 58 * amount of antialiasing applied to them, while placing vertical | |
| 59 * features (vertical stems) on the pixel grid without hinting, thus | |
| 60 * representing the stem position and weight accurately. Sometimes the | |
| 61 * vertical stems may be only partially black. In this context, | |
| 62 * `antialiasing' means that stems are not positioned exactly on pixel | |
| 63 * borders, causing a fuzzy appearance. | |
| 64 * | |
| 65 * There are two principles behind this approach. | |
| 66 * | |
| 67 * 1) No hinting in the horizontal direction: Unlike `superhinted' | |
| 68 * TrueType, which changes glyph widths to accommodate regular | |
| 69 * inter-glyph spacing, Adobe's approach is `faithful to the design' in | |
| 70 * representing both the glyph width and the inter-glyph spacing | |
| 71 * designed for the font. This makes the screen display as close as it | |
| 72 * can be to the result one would get with infinite resolution, while | |
| 73 * preserving what is considered the key characteristics of each glyph. | |
| 74 * Note that the distances between unhinted and grid-fitted positions at | |
| 75 * small sizes are comparable to kerning values and thus would be | |
| 76 * noticeable (and distracting) while reading if hinting were applied. | |
| 77 * | |
| 78 * One of the reasons to not hint horizontally is antialiasing for LCD | |
| 79 * screens: The pixel geometry of modern displays supplies three | |
| 80 * vertical sub-pixels as the eye moves horizontally across each visible | |
| 81 * pixel. On devices where we can be certain this characteristic is | |
| 82 * present a rasterizer can take advantage of the sub-pixels to add | |
| 83 * increments of weight. In Western writing systems this turns out to | |
| 84 * be the more critical direction anyway; the weights and spacing of | |
| 85 * vertical stems (see above) are central to Armenian, Cyrillic, Greek, | |
| 86 * and Latin type designs. Even when the rasterizer uses greyscale | |
| 87 * antialiasing instead of color (a necessary compromise when one | |
| 88 * doesn't know the screen characteristics), the unhinted vertical | |
| 89 * features preserve the design's weight and spacing much better than | |
| 90 * aliased type would. | |
| 91 * | |
| 92 * 2) Aligment in the vertical direction: Weights and spacing along the | |
| 93 * y~axis are less critical; what is much more important is the visual | |
| 94 * alignment of related features (like cap-height and x-height). The | |
| 95 * sense of alignment for these is enhanced by the sharpness of grid-fit | |
| 96 * edges, while the cruder vertical resolution (full pixels instead of | |
| 97 * 1/3 pixels) is less of a problem. | |
| 98 * | |
| 99 * On the technical side, horizontal alignment zones for ascender, | |
| 100 * x-height, and other important height values (traditionally called | |
| 101 * `blue zones') as defined in the font are positioned independently, | |
| 102 * each being rounded to the nearest pixel edge, taking care of | |
| 103 * overshoot suppression at small sizes, stem darkening, and scaling. | |
| 104 * | |
| 105 * Hstems (this is, hint values defined in the font to help align | |
| 106 * horizontal features) that fall within a blue zone are said to be | |
| 107 * `captured' and are aligned to that zone. Uncaptured stems are moved | |
| 108 * in one of four ways, top edge up or down, bottom edge up or down. | |
| 109 * Unless there are conflicting hstems, the smallest movement is taken | |
| 110 * to minimize distortion. | |
| 111 * | |
| 112 * @order: | |
| 113 * hinting-engine | |
| 114 * no-stem-darkening | |
| 115 * darkening-parameters | |
| 116 * | |
| 117 */ | |
| 118 | |
| 119 | |
| 120 /************************************************************************** | |
| 121 * | |
| 122 * @property: | |
| 123 * hinting-engine | |
| 124 * | |
| 125 * @description: | |
| 126 * Thanks to Adobe, which contributed a new hinting (and parsing) | |
| 127 * engine, an application can select between `freetype' and `adobe' if | |
| 128 * compiled with CFF_CONFIG_OPTION_OLD_ENGINE. If this configuration | |
| 129 * macro isn't defined, `hinting-engine' does nothing. | |
| 130 * | |
| 131 * The default engine is `freetype' if CFF_CONFIG_OPTION_OLD_ENGINE is | |
| 132 * defined, and `adobe' otherwise. | |
| 133 * | |
| 134 * The following example code demonstrates how to select Adobe's hinting | |
| 135 * engine (omitting the error handling). | |
| 136 * | |
| 137 * { | |
| 138 * FT_Library library; | |
| 139 * FT_UInt hinting_engine = FT_CFF_HINTING_ADOBE; | |
| 140 * | |
| 141 * | |
| 142 * FT_Init_FreeType( &library ); | |
| 143 * | |
| 144 * FT_Property_Set( library, "cff", | |
| 145 * "hinting-engine", &hinting_engine ); | |
| 146 * } | |
| 147 * | |
| 148 * @note: | |
| 149 * This property can be used with @FT_Property_Get also. | |
| 150 * | |
| 151 */ | |
| 152 | |
| 153 | |
| 154 /************************************************************************** | |
| 155 * | |
| 156 * @enum: | |
| 157 * FT_CFF_HINTING_XXX | |
| 158 * | |
| 159 * @description: | |
| 160 * A list of constants used for the @hinting-engine property to select | |
| 161 * the hinting engine for CFF fonts. | |
| 162 * | |
| 163 * @values: | |
| 164 * FT_CFF_HINTING_FREETYPE :: | |
| 165 * Use the old FreeType hinting engine. | |
| 166 * | |
| 167 * FT_CFF_HINTING_ADOBE :: | |
| 168 * Use the hinting engine contributed by Adobe. | |
| 169 * | |
| 170 */ | |
| 171 #define FT_CFF_HINTING_FREETYPE 0 | |
| 172 #define FT_CFF_HINTING_ADOBE 1 | |
| 173 | |
| 174 | |
| 175 /************************************************************************** | |
| 176 * | |
| 177 * @property: | |
| 178 * no-stem-darkening | |
| 179 * | |
| 180 * @description: | |
| 181 * By default, the Adobe CFF engine darkens stems at smaller sizes, | |
| 182 * regardless of hinting, to enhance contrast. This feature requires | |
| 183 * a rendering system with proper gamma correction. Setting this | |
| 184 * property, stem darkening gets switched off. | |
| 185 * | |
| 186 * Note that stem darkening is never applied if @FT_LOAD_NO_SCALE is set. | |
| 187 * | |
| 188 * { | |
| 189 * FT_Library library; | |
| 190 * FT_Bool no_stem_darkening = TRUE; | |
| 191 * | |
| 192 * | |
| 193 * FT_Init_FreeType( &library ); | |
| 194 * | |
| 195 * FT_Property_Set( library, "cff", | |
| 196 * "no-stem-darkening", &no_stem_darkening ); | |
| 197 * } | |
| 198 * | |
| 199 * @note: | |
| 200 * This property can be used with @FT_Property_Get also. | |
| 201 * | |
| 202 */ | |
| 203 | |
| 204 | |
| 205 /************************************************************************** | |
| 206 * | |
| 207 * @property: | |
| 208 * darkening-parameters | |
| 209 * | |
| 210 * @description: | |
| 211 * By default, the Adobe CFF engine darkens stems as follows (if the | |
| 212 * `no-stem-darkening' property isn't set): | |
| 213 * | |
| 214 * { | |
| 215 * stem width <= 0.5px: darkening amount = 0.4px | |
| 216 * stem width = 1px: darkening amount = 0.275px | |
| 217 * stem width = 1.667px: darkening amount = 0.275px | |
| 218 * stem width >= 2.333px: darkening amount = 0px | |
| 219 * } | |
| 220 * | |
| 221 * and piecewise linear in-between. At configuration time, these four | |
| 222 * control points can be set with the macro | |
| 223 * `CFF_CONFIG_OPTION_DARKENING_PARAMETERS'. At runtime, the control | |
| 224 * points can be changed using the `darkening-parameters' property, as | |
| 225 * the following example demonstrates. | |
| 226 * | |
| 227 * { | |
| 228 * FT_Library library; | |
| 229 * FT_Int darken_params[8] = { 500, 300, // x1, y1 | |
| 230 * 1000, 200, // x2, y2 | |
| 231 * 1500, 100, // x3, y3 | |
| 232 * 2000, 0 }; // x4, y4 | |
| 233 * | |
| 234 * | |
| 235 * FT_Init_FreeType( &library ); | |
| 236 * | |
| 237 * FT_Property_Set( library, "cff", | |
| 238 * "darkening-parameters", darken_params ); | |
| 239 * } | |
| 240 * | |
| 241 * The x~values give the stem width, and the y~values the darkening | |
| 242 * amount. The unit is 1000th of pixels. All coordinate values must be | |
| 243 * positive; the x~values must be monotonically increasing; the | |
| 244 * y~values must be monotonically decreasing and smaller than or | |
| 245 * equal to 500 (corresponding to half a pixel); the slope of each | |
| 246 * linear piece must be shallower than -1 (e.g., -.4). | |
| 247 * | |
| 248 * @note: | |
| 249 * This property can be used with @FT_Property_Get also. | |
| 250 * | |
| 251 */ | |
| 252 | |
| 253 /* */ | |
| 254 | |
| 255 | |
| 256 FT_END_HEADER | |
| 257 | |
| 258 | |
| 259 #endif /* __FTCFFDRV_H__ */ | |
| 260 | |
| 261 | |
| 262 /* END */ | |
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Chromium Code Reviews
Issue 1413673003:
Update bundled freetype to 2.6.1 (Closed)
Base URL: https://pdfium.googlesource.com/pdfium.git@master