Update freetype to 2.5.4.

third_party/freetype/include/ftcffdrv.h

+/***************************************************************************/
+/*                                                                         */
+/*  ftcffdrv.h                                                             */
+/*                                                                         */
+/*    FreeType API for controlling the CFF driver (specification only).    */
+/*                                                                         */
+/*  Copyright 2013, 2014 by                                                */
+/*  David Turner, Robert Wilhelm, and Werner Lemberg.                      */
+/*                                                                         */
+/*  This file is part of the FreeType project, and may only be used,       */
+/*  modified, and distributed under the terms of the FreeType project      */
+/*  license, LICENSE.TXT.  By continuing to use, modify, or distribute     */
+/*  this file you indicate that you have read the license and              */
+/*  understand and accept it fully.                                        */
+/*                                                                         */
+/***************************************************************************/
+
+
+#ifndef __FTCFFDRV_H__
+#define __FTCFFDRV_H__
+
+#include <ft2build.h>
+#include FT_FREETYPE_H
+
+#ifdef FREETYPE_H
+#error "freetype.h of FreeType 1 has been loaded!"
+#error "Please fix the directory search order for header files"
+#error "so that freetype.h of FreeType 2 is found first."
+#endif
+
+
+FT_BEGIN_HEADER
+
+
+  /**************************************************************************
+   *
+   * @section:
+   *   cff_driver
+   *
+   * @title:
+   *   The CFF driver
+   *
+   * @abstract:
+   *   Controlling the CFF driver module.
+   *
+   * @description:
+   *   While FreeType's CFF driver doesn't expose API functions by itself,
+   *   it is possible to control its behaviour with @FT_Property_Set and
+   *   @FT_Property_Get.  The list below gives the available properties
+   *   together with the necessary macros and structures.
+   *
+   *   The CFF driver's module name is `cff'.
+   *
+   *   *Hinting* *and* *antialiasing* *principles* *of* *the* *new* *engine*
+   *
+   *   The rasterizer is positioning horizontal features (e.g., ascender
+   *   height & x-height, or crossbars) on the pixel grid and minimizing the
+   *   amount of antialiasing applied to them, while placing vertical
+   *   features (vertical stems) on the pixel grid without hinting, thus
+   *   representing the stem position and weight accurately.  Sometimes the
+   *   vertical stems may be only partially black.  In this context,
+   *   `antialiasing' means that stems are not positioned exactly on pixel
+   *   borders, causing a fuzzy appearance.
+   *
+   *   There are two principles behind this approach.
+   *
+   *   1) No hinting in the horizontal direction: Unlike `superhinted'
+   *   TrueType, which changes glyph widths to accommodate regular
+   *   inter-glyph spacing, Adobe's approach is `faithful to the design' in
+   *   representing both the glyph width and the inter-glyph spacing
+   *   designed for the font.  This makes the screen display as close as it
+   *   can be to the result one would get with infinite resolution, while
+   *   preserving what is considered the key characteristics of each glyph.
+   *   Note that the distances between unhinted and grid-fitted positions at
+   *   small sizes are comparable to kerning values and thus would be
+   *   noticeable (and distracting) while reading if hinting were applied.
+   *
+   *   One of the reasons to not hint horizontally is antialiasing for LCD
+   *   screens: The pixel geometry of modern displays supplies three
+   *   vertical sub-pixels as the eye moves horizontally across each visible
+   *   pixel.  On devices where we can be certain this characteristic is
+   *   present a rasterizer can take advantage of the sub-pixels to add
+   *   increments of weight.  In Western writing systems this turns out to
+   *   be the more critical direction anyway; the weights and spacing of
+   *   vertical stems (see above) are central to Armenian, Cyrillic, Greek,
+   *   and Latin type designs.  Even when the rasterizer uses greyscale
+   *   antialiasing instead of color (a necessary compromise when one
+   *   doesn't know the screen characteristics), the unhinted vertical
+   *   features preserve the design's weight and spacing much better than
+   *   aliased type would.
+   *
+   *   2) Aligment in the vertical direction: Weights and spacing along the
+   *   y~axis are less critical; what is much more important is the visual
+   *   alignment of related features (like cap-height and x-height).  The
+   *   sense of alignment for these is enhanced by the sharpness of grid-fit
+   *   edges, while the cruder vertical resolution (full pixels instead of
+   *   1/3 pixels) is less of a problem.
+   *
+   *   On the technical side, horizontal alignment zones for ascender,
+   *   x-height, and other important height values (traditionally called
+   *   `blue zones') as defined in the font are positioned independently,
+   *   each being rounded to the nearest pixel edge, taking care of
+   *   overshoot suppression at small sizes, stem darkening, and scaling.
+   *
+   *   Hstems (this is, hint values defined in the font to help align
+   *   horizontal features) that fall within a blue zone are said to be
+   *   `captured' and are aligned to that zone.  Uncaptured stems are moved
+   *   in one of four ways, top edge up or down, bottom edge up or down.
+   *   Unless there are conflicting hstems, the smallest movement is taken
+   *   to minimize distortion.
+   *
+   * @order:
+   *   hinting-engine
+   *   no-stem-darkening
+   *   darkening-parameters
+   *
+   */
+
+
+  /**************************************************************************
+   *
+   * @property:
+   *   hinting-engine
+   *
+   * @description:
+   *   Thanks to Adobe, which contributed a new hinting (and parsing)
+   *   engine, an application can select between `freetype' and `adobe' if
+   *   compiled with CFF_CONFIG_OPTION_OLD_ENGINE.  If this configuration
+   *   macro isn't defined, `hinting-engine' does nothing.
+   *
+   *   The default engine is `freetype' if CFF_CONFIG_OPTION_OLD_ENGINE is
+   *   defined, and `adobe' otherwise.
+   *
+   *   The following example code demonstrates how to select Adobe's hinting
+   *   engine (omitting the error handling).
+   *
+   *   {
+   *     FT_Library  library;
+   *     FT_UInt     hinting_engine = FT_CFF_HINTING_ADOBE;
+   *
+   *
+   *     FT_Init_FreeType( &library );
+   *
+   *     FT_Property_Set( library, "cff",
+   *                               "hinting-engine", &hinting_engine );
+   *   }
+   *
+   * @note:
+   *   This property can be used with @FT_Property_Get also.
+   *
+   */
+
+
+  /**************************************************************************
+   *
+   * @enum:
+   *   FT_CFF_HINTING_XXX
+   *
+   * @description:
+   *   A list of constants used for the @hinting-engine property to select
+   *   the hinting engine for CFF fonts.
+   *
+   * @values:
+   *   FT_CFF_HINTING_FREETYPE ::
+   *     Use the old FreeType hinting engine.
+   *
+   *   FT_CFF_HINTING_ADOBE ::
+   *     Use the hinting engine contributed by Adobe.
+   *
+   */
+#define FT_CFF_HINTING_FREETYPE  0
+#define FT_CFF_HINTING_ADOBE     1
+
+
+  /**************************************************************************
+   *
+   * @property:
+   *   no-stem-darkening
+   *
+   * @description:
+   *   By default, the Adobe CFF engine darkens stems at smaller sizes,
+   *   regardless of hinting, to enhance contrast.  This feature requires
+   *   a rendering system with proper gamma correction.  Setting this
+   *   property, stem darkening gets switched off.
+   *
+   *   Note that stem darkening is never applied if @FT_LOAD_NO_SCALE is set.
+   *
+   *   {
+   *     FT_Library  library;
+   *     FT_Bool     no_stem_darkening = TRUE;
+   *
+   *
+   *     FT_Init_FreeType( &library );
+   *
+   *     FT_Property_Set( library, "cff",
+   *                               "no-stem-darkening", &no_stem_darkening );
+   *   }
+   *
+   * @note:
+   *   This property can be used with @FT_Property_Get also.
+   *
+   */
+
+
+  /**************************************************************************
+   *
+   * @property:
+   *   darkening-parameters
+   *
+   * @description:
+   *   By default, the Adobe CFF engine darkens stems as follows (if the
+   *   `no-stem-darkening' property isn't set):
+   *
+   *   {
+   *     stem width <= 0.5px:   darkening amount = 0.4px
+   *     stem width  = 1px:     darkening amount = 0.275px
+   *     stem width  = 1.667px: darkening amount = 0.275px
+   *     stem width >= 2.333px: darkening amount = 0px
+   *   }
+   *
+   *   and piecewise linear in-between.  At configuration time, these four
+   *   control points can be set with the macro
+   *   `CFF_CONFIG_OPTION_DARKENING_PARAMETERS'.  At runtime, the control
+   *   points can be changed using the `darkening-parameters' property, as
+   *   the following example demonstrates.
+   *
+   *   {
+   *     FT_Library  library;
+   *     FT_Int      darken_params[8] = {  500, 300,   // x1, y1
+   *                                      1000, 200,   // x2, y2
+   *                                      1500, 100,   // x3, y3
+   *                                      2000,   0 }; // x4, y4
+   *
+   *
+   *     FT_Init_FreeType( &library );
+   *
+   *     FT_Property_Set( library, "cff",
+   *                               "darkening-parameters", darken_params );
+   *   }
+   *
+   *   The x~values give the stem width, and the y~values the darkening
+   *   amount.  The unit is 1000th of pixels.  All coordinate values must be
+   *   positive; the x~values must be monotonically increasing; the
+   *   y~values must be monotonically decreasing and smaller than or
+   *   equal to 500 (corresponding to half a pixel); the slope of each
+   *   linear piece must be shallower than -1 (e.g., -.4).
+   *
+   * @note:
+   *   This property can be used with @FT_Property_Get also.
+   *
+   */
+
+  /* */
+
+
+FT_END_HEADER
+
+
+#endif /* __FTCFFDRV_H__ */
+
+
+/* END */