1.1 --- /dev/null Thu Jan 01 00:00:00 1970 +0000
1.2 +++ b/modules/freetype2/include/ftcffdrv.h Wed Dec 31 06:09:35 2014 +0100
1.3 @@ -0,0 +1,254 @@
1.4 +/***************************************************************************/
1.5 +/* */
1.6 +/* ftcffdrv.h */
1.7 +/* */
1.8 +/* FreeType API for controlling the CFF driver (specification only). */
1.9 +/* */
1.10 +/* Copyright 2013 by */
1.11 +/* David Turner, Robert Wilhelm, and Werner Lemberg. */
1.12 +/* */
1.13 +/* This file is part of the FreeType project, and may only be used, */
1.14 +/* modified, and distributed under the terms of the FreeType project */
1.15 +/* license, LICENSE.TXT. By continuing to use, modify, or distribute */
1.16 +/* this file you indicate that you have read the license and */
1.17 +/* understand and accept it fully. */
1.18 +/* */
1.19 +/***************************************************************************/
1.20 +
1.21 +
1.22 +#ifndef __FTCFFDRV_H__
1.23 +#define __FTCFFDRV_H__
1.24 +
1.25 +#include <ft2build.h>
1.26 +#include FT_FREETYPE_H
1.27 +
1.28 +#ifdef FREETYPE_H
1.29 +#error "freetype.h of FreeType 1 has been loaded!"
1.30 +#error "Please fix the directory search order for header files"
1.31 +#error "so that freetype.h of FreeType 2 is found first."
1.32 +#endif
1.33 +
1.34 +
1.35 +FT_BEGIN_HEADER
1.36 +
1.37 +
1.38 + /**************************************************************************
1.39 + *
1.40 + * @section:
1.41 + * cff_driver
1.42 + *
1.43 + * @title:
1.44 + * The CFF driver
1.45 + *
1.46 + * @abstract:
1.47 + * Controlling the CFF driver module.
1.48 + *
1.49 + * @description:
1.50 + * While FreeType's CFF driver doesn't expose API functions by itself,
1.51 + * it is possible to control its behaviour with @FT_Property_Set and
1.52 + * @FT_Property_Get. The list below gives the available properties
1.53 + * together with the necessary macros and structures.
1.54 + *
1.55 + * The CFF driver's module name is `cff'.
1.56 + *
1.57 + * *Hinting* *and* *antialiasing* *principles* *of* *the* *new* *engine*
1.58 + *
1.59 + * The rasterizer is positioning horizontal features (e.g., ascender
1.60 + * height & x-height, or crossbars) on the pixel grid and minimizing the
1.61 + * amount of antialiasing applied to them, while placing vertical
1.62 + * features (vertical stems) on the pixel grid without hinting, thus
1.63 + * representing the stem position and weight accurately. Sometimes the
1.64 + * vertical stems may be only partially black. In this context,
1.65 + * `antialiasing' means that stems are not positioned exactly on pixel
1.66 + * borders, causing a fuzzy appearance.
1.67 + *
1.68 + * There are two principles behind this approach.
1.69 + *
1.70 + * 1) No hinting in the horizontal direction: Unlike `superhinted'
1.71 + * TrueType, which changes glyph widths to accommodate regular
1.72 + * inter-glyph spacing, Adobe's approach is `faithful to the design' in
1.73 + * representing both the glyph width and the inter-glyph spacing
1.74 + * designed for the font. This makes the screen display as close as it
1.75 + * can be to the result one would get with infinite resolution, while
1.76 + * preserving what is considered the key characteristics of each glyph.
1.77 + * Note that the distances between unhinted and grid-fitted positions at
1.78 + * small sizes are comparable to kerning values and thus would be
1.79 + * noticeable (and distracting) while reading if hinting were applied.
1.80 + *
1.81 + * One of the reasons to not hint horizontally is antialiasing for LCD
1.82 + * screens: The pixel geometry of modern displays supplies three
1.83 + * vertical sub-pixels as the eye moves horizontally across each visible
1.84 + * pixel. On devices where we can be certain this characteristic is
1.85 + * present a rasterizer can take advantage of the sub-pixels to add
1.86 + * increments of weight. In Western writing systems this turns out to
1.87 + * be the more critical direction anyway; the weights and spacing of
1.88 + * vertical stems (see above) are central to Armenian, Cyrillic, Greek,
1.89 + * and Latin type designs. Even when the rasterizer uses greyscale
1.90 + * antialiasing instead of color (a necessary compromise when one
1.91 + * doesn't know the screen characteristics), the unhinted vertical
1.92 + * features preserve the design's weight and spacing much better than
1.93 + * aliased type would.
1.94 + *
1.95 + * 2) Aligment in the vertical direction: Weights and spacing along the
1.96 + * y~axis are less critical; what is much more important is the visual
1.97 + * alignment of related features (like cap-height and x-height). The
1.98 + * sense of alignment for these is enhanced by the sharpness of grid-fit
1.99 + * edges, while the cruder vertical resolution (full pixels instead of
1.100 + * 1/3 pixels) is less of a problem.
1.101 + *
1.102 + * On the technical side, horizontal alignment zones for ascender,
1.103 + * x-height, and other important height values (traditionally called
1.104 + * `blue zones') as defined in the font are positioned independently,
1.105 + * each being rounded to the nearest pixel edge, taking care of
1.106 + * overshoot suppression at small sizes, stem darkening, and scaling.
1.107 + *
1.108 + * Hstems (this is, hint values defined in the font to help align
1.109 + * horizontal features) that fall within a blue zone are said to be
1.110 + * `captured' and are aligned to that zone. Uncaptured stems are moved
1.111 + * in one of four ways, top edge up or down, bottom edge up or down.
1.112 + * Unless there are conflicting hstems, the smallest movement is taken
1.113 + * to minimize distortion.
1.114 + */
1.115 +
1.116 +
1.117 + /**************************************************************************
1.118 + *
1.119 + * @property:
1.120 + * hinting-engine
1.121 + *
1.122 + * @description:
1.123 + * Thanks to Adobe, which contributed a new hinting (and parsing)
1.124 + * engine, an application can select between `freetype' and `adobe' if
1.125 + * compiled with CFF_CONFIG_OPTION_OLD_ENGINE. If this configuration
1.126 + * macro isn't defined, `hinting-engine' does nothing.
1.127 + *
1.128 + * The default engine is `freetype' if CFF_CONFIG_OPTION_OLD_ENGINE is
1.129 + * defined, and `adobe' otherwise.
1.130 + *
1.131 + * The following example code demonstrates how to select Adobe's hinting
1.132 + * engine (omitting the error handling).
1.133 + *
1.134 + * {
1.135 + * FT_Library library;
1.136 + * FT_UInt hinting_engine = FT_CFF_HINTING_ADOBE;
1.137 + *
1.138 + *
1.139 + * FT_Init_FreeType( &library );
1.140 + *
1.141 + * FT_Property_Set( library, "cff",
1.142 + * "hinting-engine", &hinting_engine );
1.143 + * }
1.144 + *
1.145 + * @note:
1.146 + * This property can be used with @FT_Property_Get also.
1.147 + *
1.148 + */
1.149 +
1.150 +
1.151 + /**************************************************************************
1.152 + *
1.153 + * @enum:
1.154 + * FT_CFF_HINTING_XXX
1.155 + *
1.156 + * @description:
1.157 + * A list of constants used for the @hinting-engine property to select
1.158 + * the hinting engine for CFF fonts.
1.159 + *
1.160 + * @values:
1.161 + * FT_CFF_HINTING_FREETYPE ::
1.162 + * Use the old FreeType hinting engine.
1.163 + *
1.164 + * FT_CFF_HINTING_ADOBE ::
1.165 + * Use the hinting engine contributed by Adobe.
1.166 + *
1.167 + */
1.168 +#define FT_CFF_HINTING_FREETYPE 0
1.169 +#define FT_CFF_HINTING_ADOBE 1
1.170 +
1.171 +
1.172 + /**************************************************************************
1.173 + *
1.174 + * @property:
1.175 + * no-stem-darkening
1.176 + *
1.177 + * @description:
1.178 + * By default, the Adobe CFF engine darkens stems at smaller sizes,
1.179 + * regardless of hinting, to enhance contrast. This feature requires
1.180 + * a rendering system with proper gamma correction. Setting this
1.181 + * property, stem darkening gets switched off.
1.182 + *
1.183 + * Note that stem darkening is never applied if @FT_LOAD_NO_SCALE is set.
1.184 + *
1.185 + * {
1.186 + * FT_Library library;
1.187 + * FT_Bool no_stem_darkening = TRUE;
1.188 + *
1.189 + *
1.190 + * FT_Init_FreeType( &library );
1.191 + *
1.192 + * FT_Property_Set( library, "cff",
1.193 + * "no-stem-darkening", &no_stem_darkening );
1.194 + * }
1.195 + *
1.196 + * @note:
1.197 + * This property can be used with @FT_Property_Get also.
1.198 + *
1.199 + */
1.200 +
1.201 +
1.202 + /**************************************************************************
1.203 + *
1.204 + * @property:
1.205 + * darkening-parameters
1.206 + *
1.207 + * @description:
1.208 + * By default, the Adobe CFF engine darkens stems as follows (if the
1.209 + * `no-stem-darkening' property isn't set):
1.210 + *
1.211 + * {
1.212 + * stem width <= 0.5px: darkening amount = 0.4px
1.213 + * stem width = 1px: darkening amount = 0.275px
1.214 + * stem width = 1.667px: darkening amount = 0.275px
1.215 + * stem width >= 2.333px: darkening amount = 0px
1.216 + * }
1.217 + *
1.218 + * and piecewise linear in-between. Using the `darkening-parameters'
1.219 + * property, these four control points can be changed, as the following
1.220 + * example demonstrates.
1.221 + *
1.222 + * {
1.223 + * FT_Library library;
1.224 + * FT_Int darken_params[8] = { 500, 300, // x1, y1
1.225 + * 1000, 200, // x2, y2
1.226 + * 1500, 100, // x3, y3
1.227 + * 2000, 0 }; // x4, y4
1.228 + *
1.229 + *
1.230 + * FT_Init_FreeType( &library );
1.231 + *
1.232 + * FT_Property_Set( library, "cff",
1.233 + * "darkening-parameters", darken_params );
1.234 + * }
1.235 + *
1.236 + * The x~values give the stem width, and the y~values the darkening
1.237 + * amount. The unit is 1000th of pixels. All coordinate values must be
1.238 + * positive; the x~values must be monotonically increasing; the
1.239 + * y~values must be monotonically decreasing and smaller than or
1.240 + * equal to 500 (corresponding to half a pixel); the slope of each
1.241 + * linear piece must be shallower than -1 (e.g., -.4).
1.242 + *
1.243 + * @note:
1.244 + * This property can be used with @FT_Property_Get also.
1.245 + *
1.246 + */
1.247 +
1.248 +
1.249 + /* */
1.250 +
1.251 +FT_END_HEADER
1.252 +
1.253 +
1.254 +#endif /* __FTCFFDRV_H__ */
1.255 +
1.256 +
1.257 +/* END */
