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ftgasp.h (4138B)

      1 /****************************************************************************
      2 *
      3 * ftgasp.h
      4 *
      5 *   Access of TrueType's 'gasp' table (specification).
      6 *
      7 * Copyright (C) 2007-2025 by
      8 * David Turner, Robert Wilhelm, and Werner Lemberg.
      9 *
     10 * This file is part of the FreeType project, and may only be used,
     11 * modified, and distributed under the terms of the FreeType project
     12 * license, LICENSE.TXT.  By continuing to use, modify, or distribute
     13 * this file you indicate that you have read the license and
     14 * understand and accept it fully.
     15 *
     16 */
     17 
     18 
     19 #ifndef FTGASP_H_
     20 #define FTGASP_H_
     21 
     22 #include <freetype/freetype.h>
     23 
     24 #ifdef FREETYPE_H
     25 #error "freetype.h of FreeType 1 has been loaded!"
     26 #error "Please fix the directory search order for header files"
     27 #error "so that freetype.h of FreeType 2 is found first."
     28 #endif
     29 
     30 
     31 FT_BEGIN_HEADER
     32 
     33 
     34  /**************************************************************************
     35   *
     36   * @section:
     37   *   gasp_table
     38   *
     39   * @title:
     40   *   Gasp Table
     41   *
     42   * @abstract:
     43   *   Retrieving TrueType 'gasp' table entries.
     44   *
     45   * @description:
     46   *   The function @FT_Get_Gasp can be used to query a TrueType or OpenType
     47   *   font for specific entries in its 'gasp' table, if any.  This is mainly
     48   *   useful when implementing native TrueType hinting with the bytecode
     49   *   interpreter to duplicate the Windows text rendering results.
     50   */
     51 
     52  /**************************************************************************
     53   *
     54   * @enum:
     55   *   FT_GASP_XXX
     56   *
     57   * @description:
     58   *   A list of values and/or bit-flags returned by the @FT_Get_Gasp
     59   *   function.
     60   *
     61   * @values:
     62   *   FT_GASP_NO_TABLE ::
     63   *     This special value means that there is no GASP table in this face.
     64   *     It is up to the client to decide what to do.
     65   *
     66   *   FT_GASP_DO_GRIDFIT ::
     67   *     Grid-fitting and hinting should be performed at the specified ppem.
     68   *     This **really** means TrueType bytecode interpretation.  If this bit
     69   *     is not set, no hinting gets applied.
     70   *
     71   *   FT_GASP_DO_GRAY ::
     72   *     Anti-aliased rendering should be performed at the specified ppem.
     73   *     If not set, do monochrome rendering.
     74   *
     75   *   FT_GASP_SYMMETRIC_SMOOTHING ::
     76   *     If set, smoothing along multiple axes must be used with ClearType.
     77   *
     78   *   FT_GASP_SYMMETRIC_GRIDFIT ::
     79   *     Grid-fitting must be used with ClearType's symmetric smoothing.
     80   *
     81   * @note:
     82   *   The bit-flags `FT_GASP_DO_GRIDFIT` and `FT_GASP_DO_GRAY` are to be
     83   *   used for standard font rasterization only.  Independently of that,
     84   *   `FT_GASP_SYMMETRIC_SMOOTHING` and `FT_GASP_SYMMETRIC_GRIDFIT` are to
     85   *   be used if ClearType is enabled (and `FT_GASP_DO_GRIDFIT` and
     86   *   `FT_GASP_DO_GRAY` are consequently ignored).
     87   *
     88   *   'ClearType' is Microsoft's implementation of LCD rendering, partly
     89   *   protected by patents.
     90   *
     91   * @since:
     92   *   2.3.0
     93   */
     94 #define FT_GASP_NO_TABLE               -1
     95 #define FT_GASP_DO_GRIDFIT           0x01
     96 #define FT_GASP_DO_GRAY              0x02
     97 #define FT_GASP_SYMMETRIC_GRIDFIT    0x04
     98 #define FT_GASP_SYMMETRIC_SMOOTHING  0x08
     99 
    100 
    101  /**************************************************************************
    102   *
    103   * @function:
    104   *   FT_Get_Gasp
    105   *
    106   * @description:
    107   *   For a TrueType or OpenType font file, return the rasterizer behaviour
    108   *   flags from the font's 'gasp' table corresponding to a given character
    109   *   pixel size.
    110   *
    111   * @input:
    112   *   face ::
    113   *     The source face handle.
    114   *
    115   *   ppem ::
    116   *     The vertical character pixel size.
    117   *
    118   * @return:
    119   *   Bit flags (see @FT_GASP_XXX), or @FT_GASP_NO_TABLE if there is no
    120   *   'gasp' table in the face.
    121   *
    122   * @note:
    123   *   If you want to use the MM functionality of OpenType variation fonts
    124   *   (i.e., using @FT_Set_Var_Design_Coordinates and friends), call this
    125   *   function **after** setting an instance since the return values can
    126   *   change.
    127   *
    128   * @since:
    129   *   2.3.0
    130   */
    131  FT_EXPORT( FT_Int )
    132  FT_Get_Gasp( FT_Face  face,
    133               FT_UInt  ppem );
    134 
    135  /* */
    136 
    137 
    138 FT_END_HEADER
    139 
    140 #endif /* FTGASP_H_ */
    141 
    142 
    143 /* END */