171 lines
6.1 KiB
C
171 lines
6.1 KiB
C
/***************************************************************************/
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/* */
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/* ftttdrv.h */
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/* */
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/* FreeType API for controlling the TrueType driver */
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/* (specification only). */
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/* */
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/* Copyright 2013 by */
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/* David Turner, Robert Wilhelm, and Werner Lemberg. */
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/* */
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/* This file is part of the FreeType project, and may only be used, */
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/* modified, and distributed under the terms of the FreeType project */
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/* license, LICENSE.TXT. By continuing to use, modify, or distribute */
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/* this file you indicate that you have read the license and */
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/* understand and accept it fully. */
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/* */
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/***************************************************************************/
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#ifndef __FTTTDRV_H__
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#define __FTTTDRV_H__
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#include <ft2build.h>
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#include FT_FREETYPE_H
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#ifdef FREETYPE_H
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#error "freetype.h of FreeType 1 has been loaded!"
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#error "Please fix the directory search order for header files"
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#error "so that freetype.h of FreeType 2 is found first."
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#endif
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FT_BEGIN_HEADER
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/**************************************************************************
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*
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* @section:
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* tt_driver
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*
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* @title:
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* The TrueType driver
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*
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* @abstract:
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* Controlling the TrueType driver module.
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*
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* @description:
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* While FreeType's TrueType driver doesn't expose API functions by
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* itself, it is possible to control its behaviour with @FT_Property_Set
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* and @FT_Property_Get. The following lists the available properties
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* together with the necessary macros and structures.
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*
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* The TrueType driver's module name is `truetype'.
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*
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*/
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/**************************************************************************
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*
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* @property:
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* interpreter-version
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*
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* @description:
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* Currently, two versions are available, representing the bytecode
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* interpreter with and without subpixel hinting support,
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* respectively. The default is subpixel support if
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* TT_CONFIG_OPTION_SUBPIXEL_HINTING is defined, and no subpixel
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* support otherwise (since it isn't available then).
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*
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* If subpixel hinting is on, many TrueType bytecode instructions
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* behave differently compared to B/W or grayscale rendering. The
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* main idea is to render at a much increased horizontal resolution,
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* then sampling down the created output to subpixel precision.
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* However, many older fonts are not suited to this and must be
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* specially taken care of by applying (hardcoded) font-specific
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* tweaks.
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*
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* Details on subpixel hinting and some of the necessary tweaks can be
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* found in Greg Hitchcock's whitepaper at
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* `http://www.microsoft.com/typography/cleartype/truetypecleartype.aspx'.
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*
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* The following example code demonstrates how to activate subpixel
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* hinting (omitting the error handling).
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*
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* {
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* FT_Library library;
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* FT_Face face;
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* FT_UInt interpreter_version = TT_INTERPRETER_VERSION_38;
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*
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*
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* FT_Init_FreeType( &library );
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*
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* FT_Property_Set( library, "truetype",
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* "interpreter-version",
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* &interpreter_version );
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* }
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*
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* @note:
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* This property can be used with @FT_Property_Get also.
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*
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*/
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/**************************************************************************
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*
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* @enum:
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* TT_INTERPRETER_VERSION_XXX
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*
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* @description:
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* A list of constants used for the @interpreter-version property to
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* select the hinting engine for Truetype fonts.
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*
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* The numeric value in the constant names represents the version
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* number as returned by the `GETINFO' bytecode instruction.
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*
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* @values:
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* TT_INTERPRETER_VERSION_35 ::
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* Version~35 corresponds to MS rasterizer v.1.7 as used e.g. in
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* Windows~98; only grayscale and B/W rasterizing is supported.
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*
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* TT_INTERPRETER_VERSION_38 ::
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* Version~38 corresponds to MS rasterizer v.1.9; it is roughly
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* equivalent to the hinting provided by DirectWrite ClearType (as
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* can be found, for example, in the Internet Explorer~9 running on
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* Windows~7).
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*
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* @note:
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* This property controls the behaviour of the bytecode interpreter
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* and thus how outlines get hinted. It does *not* control how glyph
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* get rasterized! In particular, it does not control subpixel color
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* filtering.
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*
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* If FreeType has not been compiled with configuration option
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* FT_CONFIG_OPTION_SUBPIXEL_HINTING, selecting version~38 causes an
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* `FT_Err_Unimplemented_Feature' error.
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*
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* Depending on the graphics framework, Microsoft uses different
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* bytecode engines. As a consequence, the version numbers returned by
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* a call to the `GETINFO[1]' bytecode instruction are more convoluted
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* than desired.
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*
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* {
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* framework Windows version result of GETINFO[1]
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* ----------------------------------------------------
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* GDI before XP 35
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* GDI XP and later 37
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* GDI+ old before Vista 37
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* GDI+ old Vista, 7 38
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* GDI+ after 7 40
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* DWrite before 8 39
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* DWrite 8 and later 40
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* }
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*
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* Since FreeType doesn't provide all capabilities of DWrite ClearType,
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* using version~38 seems justified.
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*
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*/
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#define TT_INTERPRETER_VERSION_35 35
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#define TT_INTERPRETER_VERSION_38 38
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/* */
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FT_END_HEADER
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#endif /* __FTTTDRV_H__ */
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/* END */
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