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  1. /***************************************************************************/
  2. /*                                                                         */
  3. /*  ftttdrv.h                                                              */
  4. /*                                                                         */
  5. /*    FreeType API for controlling the TrueType driver                     */
  6. /*    (specification only).                                                */
  7. /*                                                                         */
  8. /*  Copyright 2013 by                                                      */
  9. /*  David Turner, Robert Wilhelm, and Werner Lemberg.                      */
  10. /*                                                                         */
  11. /*  This file is part of the FreeType project, and may only be used,       */
  12. /*  modified, and distributed under the terms of the FreeType project      */
  13. /*  license, LICENSE.TXT.  By continuing to use, modify, or distribute     */
  14. /*  this file you indicate that you have read the license and              */
  15. /*  understand and accept it fully.                                        */
  16. /*                                                                         */
  17. /***************************************************************************/
  18.  
  19.  
  20. #ifndef __FTTTDRV_H__
  21. #define __FTTTDRV_H__
  22.  
  23. #include <ft2build.h>
  24. #include FT_FREETYPE_H
  25.  
  26. #ifdef FREETYPE_H
  27. #error "freetype.h of FreeType 1 has been loaded!"
  28. #error "Please fix the directory search order for header files"
  29. #error "so that freetype.h of FreeType 2 is found first."
  30. #endif
  31.  
  32.  
  33. FT_BEGIN_HEADER
  34.  
  35.  
  36.   /**************************************************************************
  37.    *
  38.    * @section:
  39.    *   tt_driver
  40.    *
  41.    * @title:
  42.    *   The TrueType driver
  43.    *
  44.    * @abstract:
  45.    *   Controlling the TrueType driver module.
  46.    *
  47.    * @description:
  48.    *   While FreeType's TrueType driver doesn't expose API functions by
  49.    *   itself, it is possible to control its behaviour with @FT_Property_Set
  50.    *   and @FT_Property_Get.  The following lists the available properties
  51.    *   together with the necessary macros and structures.
  52.    *
  53.    *   The TrueType driver's module name is `truetype'.
  54.    *
  55.    */
  56.  
  57.  
  58.   /**************************************************************************
  59.    *
  60.    * @property:
  61.    *   interpreter-version
  62.    *
  63.    * @description:
  64.    *   Currently, two versions are available which represent the bytecode
  65.    *   interpreter with and without subpixel hinting support,
  66.    *   respectively.  The default is subpixel support if
  67.    *   TT_CONFIG_OPTION_SUBPIXEL_HINTING is defined, and no subpixel
  68.    *   support otherwise (since it isn't available then).
  69.    *
  70.    *   If subpixel hinting is on, many TrueType bytecode instructions
  71.    *   behave differently compared to B/W or grayscale rendering.  The
  72.    *   main idea is to render at a much increased horizontal resolution,
  73.    *   then sampling down the created output to subpixel precision.
  74.    *   However, many older fonts are not suited to this and must be
  75.    *   specially taken care of by applying (hardcoded) font-specific
  76.    *   tweaks.
  77.    *
  78.    *   Details on subpixel hinting and some of the necessary tweaks can be
  79.    *   found in Greg Hitchcock's whitepaper at
  80.    *   `http://www.microsoft.com/typography/cleartype/truetypecleartype.aspx'.
  81.    *
  82.    *   The following example code demonstrates how to activate subpixel
  83.    *   hinting (omitting the error handling).
  84.    *
  85.    *   {
  86.    *     FT_Library  library;
  87.    *     FT_Face     face;
  88.    *     FT_UInt     interpreter_version = TT_INTERPRETER_VERSION_38;
  89.    *
  90.    *
  91.    *     FT_Init_FreeType( &library );
  92.    *
  93.    *     FT_Property_Set( library, "truetype",
  94.    *                               "interpreter-version",
  95.    *                               &interpreter_version );
  96.    *   }
  97.    *
  98.    * @note:
  99.    *   This property can be used with @FT_Property_Get also.
  100.    *
  101.    */
  102.  
  103.  
  104.   /**************************************************************************
  105.    *
  106.    * @enum:
  107.    *   TT_INTERPRETER_VERSION_XXX
  108.    *
  109.    * @description:
  110.    *   A list of constants used for the @interpreter-version property to
  111.    *   select the hinting engine for Truetype fonts.
  112.    *
  113.    *   The numeric value in the constant names represents the version
  114.    *   number as returned by the `GETINFO' bytecode instruction.
  115.    *
  116.    * @values:
  117.    *   TT_INTERPRETER_VERSION_35 ::
  118.    *     Version~35 corresponds to MS rasterizer v.1.7 as used e.g. in
  119.    *     Windows~98; only grayscale and B/W rasterizing is supported.
  120.    *
  121.    *   TT_INTERPRETER_VERSION_38 ::
  122.    *     Version~38 corresponds to MS rasterizer v.1.9; it is roughly
  123.    *     equivalent to the hinting provided by DirectWrite ClearType (as
  124.    *     can be found, for example, in the Internet Explorer~9 running on
  125.    *     Windows~7).
  126.    *
  127.    * @note:
  128.    *   This property controls the behaviour of the bytecode interpreter
  129.    *   and thus how outlines get hinted.  It does *not* control how glyph
  130.    *   get rasterized!  In particular, it does not control subpixel color
  131.    *   filtering.
  132.    *
  133.    *   If FreeType has not been compiled with configuration option
  134.    *   FT_CONFIG_OPTION_SUBPIXEL_HINTING, selecting version~38 causes an
  135.    *   `FT_Err_Unimplemented_Feature' error.
  136.    *
  137.    */
  138. #define TT_INTERPRETER_VERSION_35  35
  139. #define TT_INTERPRETER_VERSION_38  38
  140.  
  141.  
  142.  /* */
  143.  
  144. FT_END_HEADER
  145.  
  146.  
  147. #endif /* __FTTTDRV_H__ */
  148.  
  149.  
  150. /* END */
  151.