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/***************************************************************************/
/* */
/* ftttdrv.h */
/* */
/* FreeType API for controlling the TrueType driver */
/* (specification only). */
/* */
/* Copyright 2013 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 __FTTTDRV_H__
#define __FTTTDRV_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:
* tt_driver
*
* @title:
* The TrueType driver
*
* @abstract:
* Controlling the TrueType driver module.
*
* @description:
* While FreeType's TrueType driver doesn't expose API functions by
* itself, it is possible to control its behaviour with @FT_Property_Set
* and @FT_Property_Get. The following lists the available properties
* together with the necessary macros and structures.
*
* The TrueType driver's module name is `truetype'.
*
*/
/**************************************************************************
*
* @property:
* interpreter-version
*
* @description:
* Currently, two versions are available, representing the bytecode
* interpreter with and without subpixel hinting support,
* respectively. The default is subpixel support if
* TT_CONFIG_OPTION_SUBPIXEL_HINTING is defined, and no subpixel
* support otherwise (since it isn't available then).
*
* If subpixel hinting is on, many TrueType bytecode instructions
* behave differently compared to B/W or grayscale rendering. The
* main idea is to render at a much increased horizontal resolution,
* then sampling down the created output to subpixel precision.
* However, many older fonts are not suited to this and must be
* specially taken care of by applying (hardcoded) font-specific
* tweaks.
*
* Details on subpixel hinting and some of the necessary tweaks can be
* found in Greg Hitchcock's whitepaper at
* `http://www.microsoft.com/typography/cleartype/truetypecleartype.aspx'.
*
* The following example code demonstrates how to activate subpixel
* hinting (omitting the error handling).
*
* {
* FT_Library library;
* FT_Face face;
* FT_UInt interpreter_version = TT_INTERPRETER_VERSION_38;
*
*
* FT_Init_FreeType( &library );
*
* FT_Property_Set( library, "truetype",
* "interpreter-version",
* &interpreter_version );
* }
*
* @note:
* This property can be used with @FT_Property_Get also.
*
*/
/**************************************************************************
*
* @enum:
* TT_INTERPRETER_VERSION_XXX
*
* @description:
* A list of constants used for the @interpreter-version property to
* select the hinting engine for Truetype fonts.
*
* The numeric value in the constant names represents the version
* number as returned by the `GETINFO' bytecode instruction.
*
* @values:
* TT_INTERPRETER_VERSION_35 ::
* Version~35 corresponds to MS rasterizer v.1.7 as used e.g. in
* Windows~98; only grayscale and B/W rasterizing is supported.
*
* TT_INTERPRETER_VERSION_38 ::
* Version~38 corresponds to MS rasterizer v.1.9; it is roughly
* equivalent to the hinting provided by DirectWrite ClearType (as
* can be found, for example, in the Internet Explorer~9 running on
* Windows~7).
*
* @note:
* This property controls the behaviour of the bytecode interpreter
* and thus how outlines get hinted. It does *not* control how glyph
* get rasterized! In particular, it does not control subpixel color
* filtering.
*
* If FreeType has not been compiled with configuration option
* FT_CONFIG_OPTION_SUBPIXEL_HINTING, selecting version~38 causes an
* `FT_Err_Unimplemented_Feature' error.
*
* Depending on the graphics framework, Microsoft uses different
* bytecode engines. As a consequence, the version numbers returned by
* a call to the `GETINFO[1]' bytecode instruction are more convoluted
* than desired.
*
* {
* framework Windows version result of GETINFO[1]
* ----------------------------------------------------
* GDI before XP 35
* GDI XP and later 37
* GDI+ old before Vista 37
* GDI+ old Vista, 7 38
* GDI+ after 7 40
* DWrite before 8 39
* DWrite 8 and later 40
* }
*
* Since FreeType doesn't provide all capabilities of DWrite ClearType,
* using version~38 seems justified.
*
*/
#define TT_INTERPRETER_VERSION_35 35
#define TT_INTERPRETER_VERSION_38 38
/* */
FT_END_HEADER
#endif /* __FTTTDRV_H__ */
/* END */
|
