/contrib/freetype-1.3.1/docs/apirefx.txt

                        The FreeType Engine



                    Extension Library Reference





                -----------------------------------





  Table of Contents:



    I. Engine extensions

      1. kerning (ftxkern)

      2. PostScript names (ftxpost)

      3. TrueType Open (ftxopen)

         a. The `BASE' table (baseline data)

         b. The `GDEF' table (glyph definitions)

         c. The `GPOS' table (glyph positions)

         d. The `GSUB' table (glyph substitions)

         e. The `JSTF' table (justification data)

         f. auxiliary functions

      4. embedded bitmaps (ftxsbit)



    II. API extensions

      1. cmap iteration (ftxcmap)

      2. internationalized error messages (ftxerr18)

      3. access to the `gasp' table (ftxgasp)

      4. fast retrieval of glyph widths and heights (ftxwidth)



    III. Error codes





                        --------------------





Please read the file  `user.txt' for an introduction into FreeType's

extension  mechanism  and  the  difference between  engine  and  API

extensions.





I. Engine extensions

====================



To use  engine extensions you have  to compile the  library with the

macro TT_CONFIG_OPTION_EXTEND_ENGINE.  By default, this macro is set

and all engine extensions are linked to the FreeType library.





 1. kerning (ftxkern)

 --------------------



  TT_Init_Kerning_Extension( TT_Engine  engine )



    Initializes the kerning extension for a given engine.  This must

    be called  just after the  engine creation, and before  any face

    object allocation.  Example:



      TT_Init_FreeType( &engine );

      TT_Init_Kerning_Extension( engine );



  ..................................................................



  TT_Get_Kerning_Directory( TT_Face      face,

                            TT_Kerning*  directory )



    Queries the  kerning directory  found in a  face object.   If no

    kerning  table  is  found   in  the  TrueType  file,  the  error

    TT_Err_Table_Is_Missing will be returned.



    You  can  access  the  subtables  through the  pointers  of  the

    directory.  However, by default, the directory is only loaded if

    a  face object  is created.   You must  load the  subtables that

    interest you with a call to TT_Load_Kerning_Table().



    The  layout of  all kerning  structures is  defined in  the file

    `lib/extend/ftxkern.h'.   Formats 0  and  2 (as  defined in  the

    Microsoft TrueType specification) are exposed by this API.



    NOTE:



      This function  must be called after the  kerning extension has

      been initialized.



  ..................................................................



  TT_Load_Kerning_Table( TT_Face    face,

                         TT_UShort  kernIndex )



    Loads the kerning subtable number `kern_index' into memory.  The

    subtable can  be accessed through  the pointers provided  by the

    kerning  directory,  obtained  from   a  call  to  the  function

    TT_Get_Kerning_Directory().



    Note that the interpretation of  the kerning data is left to the

    client  application.  Read the  TrueType specification  for more

    information on kerning encoding.



    NOTE 1:



      This function must be  called after the kerning extension were

      initialized.



    NOTE 2:



      An example can be found in the file `test/ftstrtto.c'.





====================================================================





 2. PostScript names (ftxpost)

 -----------------------------



  TT_Init_Post_Extension( TT_Engine  engine )



    Initializes the PostScript name extension to load the PostScript

    glyph names given in the `post' table.  This must be called just

    after  creation  of  the  engine,  and before  any  face  object

    allocation.  See description of TT_Get_PS_Name() for an example.



  ..................................................................



  TT_Load_PS_Names( TT_Face   face,

                    TT_Post*  post )



    Loads the PostScript glyph names into memory.  This must be done

    before  TT_Get_PS_Name() is  called.  In  case of  error, either

    TT_Err_Invalid_Post_Table or TT_Err_Invalid_Post_Table_Format is

    returned.  See description of TT_Get_PS_Name() for an example.



  ..................................................................



  TT_Get_PS_Name( TT_Face      face,

                  TT_UShort    index,

                  TT_String**  PSname )



    Get  the PostScript  glyph  name  for a  given  glyph index.   A

    pointer to the name is returned in `PSname'.  Example:



      ...

      TT_Post  post;

      char*    PSname;



      ...

      TT_Init_Post_Extension( engine );

      TT_Load_PS_Names( face, &post );



      ...

      TT_Get_PS_Name( face, index, &PSname );





    NOTE:



      You must  not alter the PostScript glyph  name string returned

      in `PSname'.





====================================================================





 3. TrueType Open (ftxopen)

 --------------------------



  Please note that TrueType Open specific error codes have the

  prefix `TTO_Err_' instead of `TT_Err_'.



  a. The `BASE' table (baseline data)



    Not yet supported.



  b. The `GDEF' table (glyph definitions)



    TT_Init_GDEF_Extension( TT_Engine  engine )



      Initializes the  GDEF extension  to load the  glyph definition

      data  given in  the `GDEF'  table.  This  must be  called just

      after  creation of  the  engine, and  before  any face  object

      allocation.  See the file `ftstrtto.c' for an example.



    ................................................................



    TT_Load_GDEF_Table( TT_Face          face,

                        TTO_GDEFHeader*  gdef )



      Loads  the GDEF  table into  `gdef' for  a given  face `face'.

      This must  be done before  any queries about  glyph properties

      with TT_GSUB_Get_Property().   Returns TT_Err_Table_Missing if

      there is no GDEF table in the font.



    ................................................................



    TT_GDEF_Get_Glyph_Property( TTO_GDEFHeader*  gdef,

                                TT_UShort        glyphID,

                                TT_UShort*       property )



      Use  this function  to get  glyph properties  in  the variable

      `property' for  the glyph with  index `glyphID' stored  in the

      `gdef'  table.   This data  is  essential  for  many fonts  to

      correctly apply contextual  substitution (both GSUB and GPOS).

      As a special case, zero is assigned to `property' if `gdef' is

      NULL or  the glyph has  no special glyph property  assigned to

      it.   The  other return  values  of  `property' are  TTO_BASE,

      TTO_LIGATURE,  TTO_MARK, and  TTO_COMPONENT; you  can directly

      apply the `LookupFlag' mask to check for certain properties:



        TTO_GDEFHeader*  gdef;

        TTO_Lookup*      lo;

        TT_UShort        glyph_ID;

        TT_UShort        p;      





        TT_GDEF_Get_Property( gdef, glyph_ID, &p );



        if ( p & lo->LookupFlag )

          return TTO_Err_Not_Covered;



      Usually, you  don't need to  take care of glyph  properties by

      yourself since TT_GSUB_Apply_String() will  do this for you by

      calling TT_GDEF_Get_Property().



      Some  fonts need  GDEF-like  data  even if  no  GDEF table  is

      provided  (for example,  the Arabic  script  needs information

      which glyphs are  base glyphs and which are  mark glyphs).  In

      such cases, you  should use TT_GDEF_Build_ClassDefinition() to

      build the necessary  structures so that TT_GDEF_Get_Property()

      returns meaningful values.



      See also TT_Load_GSUB_Table() and TT_Load_GPOS_Table().



    ................................................................



    TT_GDEF_Build_ClassDefinition( TTO_GDEFHeader*  gdef,

                                   TT_UShort        num_glyphs,

                                   TT_UShort        glyph_count,

                                   TT_UShort*       glyph_array,

                                   TT_UShort*       class_array )



      Fills    a    `gdef'    structure    with   data    to    make

      TT_GDEF_Get_Property()   work  in  case   no  GDEF   table  is

      available.  `num_glyphs' is the  number of glyphs in the font.



      `glyph_count' is the number  of glyphs resp.  class values (as

      specified  in  the GDEF  specification)  given  in the  arrays

      `glyph_array'  and  `class_array',  respectively.   The  glyph

      indices in  `glyph_array' must be all different  and sorted in

      ascending  order;  the   function  expects  that  glyph  index

      `glyph_array[n]' has its class value in `class_array[n]'.



      Note that mark  attach classes as defined in  OpenType 1.2 are

      not supported for constructed GDEF tables.



      See `arabic.c' for an example.





  c. The `GPOS' table (glyph positions)



    Not yet supported.





  d. The `GSUB' table (glyph substitions)



    For glyph substitution, a  string object of type TTO_GSUB_String

    is used.   The field  `length' holds the  length of  the string,

    `pos' points to the actual position in the glyph string `string'

    (for  input strings)  resp. the  position where  the substituted

    glyphs should be placed at (for output strings).



    Within the  `properties' array (which must always  have the same

    length as `string' if set), you can define properties for glyphs

    -- `string[n]' is associated  with `properties[n]'.  The idea is

    that  some  features  apply  to  specific glyphs  only.   As  an

    example, the  `fina' feature for  Arabic applies only  to glyphs

    which  appear at  the end  of  a word  (strictly speaking,  this

    feature is used  only for glyphs which have  a `final' property;

    such glyphs can occur in the middle of a word also under certain

    circumstances which  is dependent on Arabic  script rules).  The

    relationship between properties and  features can be set up with

    the function  TT_GSUB_Add_Feature().  If `properties'  is set to

    NULL, all  selected features  apply to all  glyphs in  the given

    string object.  If `properties' is non-NULL, the elements of the

    array  are treated as  bit fields.   A set  flag means  that the

    corresponding  feature (as  set  with the  TT_GSUB_Add_Feature()

    function) should not  be applied to the particular  glyph.  As a

    consequence,  a zero  value for  these  16 bits  means that  all

    features should be  applied, and a value of  0xFFFF implies that

    no feature at all should be used for the glyph.



    The field `allocated'  is for internal use only  and must not be

    modified.   If its  value is  larger than  zero, you  should use

    free()  to   deallocate  the   memory  used  by   `string'  (and

    `properties'   if  set)   in  case   you  want   to   destroy  a

    TTO_GSUB_String object (memory  for `string' and `properties' is

    allocated  automatically  e.g.   by  TT_GSUB_Apply_String()  for

    output string objects).



      struct  TTO_GSUB_String_

      {

        TT_ULong    length;

        TT_ULong    pos;

        TT_ULong    allocated;

        TT_UShort*  string;

        TT_UShort*  properties;

      };



      typedef struct TTO_GSUB_String_  TTO_GSUB_String;



    Note  that the `string'  field must  contain glyph  indices, not

    character codes.



    For  initializing an  input string  object, you  should  set the

    `length', `string',  and `properties' fields (the  last one only

    if necessary) to appropriate values.  `pos' has to be set to the

    position  where the substitution  lookups should  start (usually

    zero).  The `allocated' field will be ignored.



    For  initializing an  output string  object, all  fields (except

    `length' which  will be  ignored) must be  set to zero.   If you

    want to  reuse the object, set  `pos' to the  position where the

    substituted glyphs should be placed at (usually zero), but don't

    touch the `allocated', `string', and `properties' fields.



    ................................................................



    TT_Init_GSUB_Extension( TT_Engine  engine )



      Initializes the GSUB extension  to load the glyph substitution

      data  given in  the `GSUB'  table.  This  must be  called just

      after  creation of  the  engine, and  before  any face  object

      allocation.   See the  files `ftstrtto.c'  and  `ftdump.c' for

      detailed examples.



    ................................................................



    TT_Load_GSUB_Table( TT_Face          face,

                        TTO_GSUBHeader*  gsub,

                        TTO_GDEFHeader*  gdef )



      Loads  the GSUB  table into  `gsub' for  a given  face `face'.

      This must  be done  before any queries  about or  selection of

      scripts,      languages,      and      features.       Returns

      TT_Err_Table_Missing if there is no GSUB table in the font.



      `gdef' should  contain a pointer to an  associated GDEF table,

      either  a  native  one  loaded  with  TT_Load_GDEF_Table()  or

      emulated  with TT_GDEF_Build_ClassDefinition().  If  `gdef' is

      set to NULL, no GDEF data will be used.



    ................................................................



    TT_GSUB_Select_Script( TTO_GSUBHeader*  gsub,

                           TT_ULong         script_tag,

                           TT_UShort*       script_index )



      This  function sets  the script  index of  a given  script tag

      `script_tag' in the variable `script_index' for the GSUB table

      `gsub'.  Returns TTO_Err_Not_Covered  if the script tag cannot

      be found.  The  available script tags can be  queried with the

      function TT_GSUB_Query_Scripts().



    ................................................................



    TT_GSUB_Select_Language( TTO_GSUBHeader*  gsub,

                             TT_ULong         language_tag,

                             TT_UShort        script_index,

                             TT_UShort*       language_index,

                             TT_UShort*       req_feature_index )



      This function sets the language  index of a given language tag

      `language_tag' and script index `script_index' in the variable

      `language_index'   for  the   GSUB   table  `gsub'.    Returns

      TTO_Err_Not_Covered if the language  tag cannot be found.  The

      available  language  tags can  be  queried  with the  function

      TT_GSUB_Query_Languages().



      Additionally,  the  index of  the  required  feature for  this

      language system is returned in `req_feature_index'; it must be

      later registered for use with TT_GSUB_Add_Feature().



    ................................................................



    TT_GSUB_Select_Feature( TTO_GSUBHeader*  gsub,

                            TT_ULong         feature_tag,

                            TT_UShort        script_index,

                            TT_UShort        language_index,

                            TT_UShort*       feature_index )



      This  function  sets  the  feature  index  of  a  feature  tag

      `feature_tag', script index `script_index', and language index

      `language_index' in the  variable `feature_index' for the GSUB

      table `gsub'.  Returns  TTO_Err_Not_Covered if the feature tag

      cannot be  found.  The available  feature tags can  be queried

      with    the   function    TT_GSUB_Query_Features().    Setting

      language_index to 0xFFFF selects the default language system.



    ................................................................



    TT_GSUB_Query_Scripts( TTO_GSUBHeader*  gsub,

                           TT_ULong**       script_tag_list )



      Returns  the available  script  tags for  a  given GSUB  table

      `gsub' in the array `script_tag_list'.  The array can be later

      deallocated with free().



    ................................................................



    TT_GSUB_Query_Languages( TTO_GSUBHeader*  gsub,

                             TT_UShort        script_index,

                             TT_ULong**       language_tag_list )



      Returns  the available language  tags for  a given  GSUB table

      `gsub'   and  script   index  `script_index'   in   the  array

      `language_tag_list'.  The array  can be later deallocated with

      free().



    ................................................................



    TT_GSUB_Query_Features( TTO_GSUBHeader*  gsub,

                            TT_UShort        script_index,

                            TT_UShort        language_index,

                            TT_ULong**       feature_tag_list )



      Returns  the available  feature tags  for a  given  GSUB table

      `gsub',  script  index   `script_index',  and  language  index

      `language_index' in the array `feature_tag_list'.  If language

      index is  set to 0xFFFF,  the values for the  default language

      system are returned.  The  array can be later deallocated with

      free().



    ................................................................



    TT_GSUB_Add_Feature( TTO_GSUBHeader*  gsub,

                         TT_UShort        feature_index,

                         TT_UShort        property )



      To  prepare  a  call  to TT_GSUB_Apply_String()  which  should

      process  a given  feature with  index `feature_index'  and the

      property `property', you must  use this function.  Its task is

      to  mark the  lookup tables  used by  the feature  for further

      processing.



      `property'  defines a  relationship between  the  input string

      object and the specific  feature.  The client must handle this

      variable as a bit field, i.e., up to 16 user properties can be

      defined.  If `property' is set to ALL_GLYPHS (0xFFFF, the only

      predefined value),  or if the  input string object has  no set

      bits  in the `properties'  field, the  feature applies  to all

      glyphs.  If bit `x' is  set in `property', the feature applies

      only  to  glyphs  which  have  bit  `x'  not  set  in  glyph's

      `properties'   field  in   the  input   string   object.   See

      TT_GSUB_Apply_String() for an example.



      Returns TT_Err_Invalid_Argument in case of error.



    ................................................................



    TT_GSUB_Clear_Features( TTO_GSUBHeader*  gsub )



      Clears the  list of used  features and properties.   No lookup

      tables will be processed.



    ................................................................



    TT_GSUB_Register_Alternate_Function( TTO_GSUBHeader*  gsub,

                                         TTO_AltFunction  alt,

                                         void*            data )



      Installs   a    callback   function   to    handle   alternate

      substitutions.  `data' is a  generic pointer to a user-defined

      structure  which will  be  completely ignored  by the  ftxopen

      extension.  `alt' is a function pointer defined as



        typedef TT_UShort

                (*TTO_AltFunction)(TT_ULong    pos,

                                   TT_UShort   glyphID,

                                   TT_UShort   num_alternates,

                                   TT_UShort*  alternates,

                                   void*       data );



      If TT_GSUB_Apply_String() encounters an alternate lookup while

      processing the  input string, it will call  the function `alt'

      to find out which alternate  glyph it should use.  `pos' gives

      the  position in  the string,  `glyphID' the  glyph ID  of the

      glyph   to  be   replaced   with  an   alternate  glyph,   and

      `num_alternates'  the  number   of  alternate  glyphs  in  the

      `alternates'  array.   A pointer  to  the user-defined  `data'

      structure is also available.   `alt' must return an index into

      `alternates'.



      If  `alt' is NULL  or if  this function  isn't called  at all,

      TT_GSUB_Apply_String()  will always  use  the first  alternate

      glyph.



      Please note that theoretically  an alternate lookup can happen

      during any other lookup!  For example, a lookup chain like



        single subst -> alternate subst -> ligature subst



      *is* possible  (albeit rather unlikely).  Thus  be warned that

      `pos' does not necessarily reflect  the position of a glyph to

      be  displayed at  all, nor  does `glyphID'  specifies  a glyph

      which will be in the final output string.



    ................................................................



    TT_GSUB_Apply_String( TTO_GSUBHeader*   gsub,

                          TTO_GSUB_String*  in,

                          TTO_GSUB_String*  out )



      This  is the  very function  which handles  glyph substitution

      according to  the features set  up with TT_GSUB_Add_Feature(),

      using   both   GSUB  and   GDEF   data   (if  defined).    Two

      TTO_GSUB_String  objects `in' and  `out' (as  described above)

      are taken  for input and output;  after successful excecution,

      the  converted  glyph string  can  been  found  in `out',  and

      `out.length'  gives the  actual  length of  the output  string

      (counted from the begin of the array).



      Example:



        /* We assume that the feature `xxxx' has index 5, and  */

        /* feature `yyyy' has index 8, applying only to glyphs */

        /* with the property `FINAL_GLYPHS' set (0x1000 is an  */

        /* ad-hoc value just for this example).                */



        /* The order of calls to TT_GSUB_Add_Feature() is not  */

        /* significant.                                        */



        #define FINAL_GLYPHS  0x1000



        TT_GSUB_Clear_Features( &gsub );

        TT_GSUB_Add_Feature( &gsub, 8, FINAL_GLYPHS );

        TT_GSUB_Add_Feature( &gsub, 5, ALL_GLYPHS );



        TT_GSUB_Apply_String( &gsub, &in, &out );



      You must initialize both `in' and `out' structures; allocation

      necessary for the `out' object will be handled automatically.



      In  case you  don't register  a function  to  handle alternate

      substitutions  (GSUB  lookup 3),  always  the first  alternate

      glyph will be used.  See TT_GSUB_Register_Alternate_Function()

      above for more details.





  e. The `JSTF' table (justification data)



    Not yet supported.





  f. auxiliary functions



    TT_GSUB_Add_String( TTO_GSUB_String*  in,

                        TT_UShort         num_in,

                        TTO_GSUB_String*  out,

                        TT_UShort         num_out,

                        TT_UShort*        data )



      This function copies `num_out'  elements from `data' to `out',

      advancing the array pointer  `in.pos' by `num_in' elements and

      `out.pos'  by `num_out'  elements.  If  the string  (resp. the

      properties) array in `out' is empty or too small, it allocates

      resp.    reallocates  the   string  (and   properties)  array.

      Finally, it sets `out.length' equal to `out.pos'.



      The  properties for  all replaced  glyphs are  taken  from the

      glyph at position `in->pos'.



      TT_GSUB_Add_String()       is      normally       used      in

      TT_GSUB_Apply_String(); you will need  it for the special case

      to skip some glyphs (i.e.,  copy glyphs directly from the `in'

      to the `out' object), bypassing a possible GSUB substitution.



      Here an example which copies one glyph:



        TT_GSUB_Add_String( in, 1,

                            out, 1,

                            &in->string[in->pos] );





====================================================================



 

 4. embedded bitmaps (ftxsbit)

 -----------------------------



  TT_Init_SBit_Extension( TT_Engine  engine )



    Initializes  the embedded  bitmap extension  to load  the bitmap

    glyphs given in the various sbit tables: `EBLC', `bloc', `EBDT',

    and `bdat'  (`bloc' and `bdat'  tables are only in  Apple fonts;

    the  former is equivalent  to `EBLC',  the latter  equivalent to

    `EBDT').  This must be called just after creation of the engine,

    and  before  any face  object  allocation.   See description  of

    TT_Load_Glyph_Bitmap() for an example.



  ..................................................................



  TT_Get_Face_Bitmaps( TT_Face   face,

                       TT_EBLC*  eblc_table )



    Loads the `EBLC' (resp. `bloc')  table from a font file into the

    `eblc_table' structure.   Use this function  for testing whether

    embedded bitmaps are available or not.



    This function returns  TT_Err_Table_Missing if the font contains

    no embedded  bitmaps.  All fields  in `eblc_table' will  then be

    set to 0.



  ..................................................................



  TT_New_SBit_Image( TT_SBit_Image**  image )



    Allocates  a  new  embedded  bitmap  container,  pointed  to  by

    `image'.



  ..................................................................



  void  TT_Done_SBit_Image( TT_SBit_Image*  image )

  ^^^^



    Releases the embedded bitmap container `image'.



  ..................................................................



  TT_Get_SBit_Strike( TT_Face          face,

                      TT_Instance      instance,

                      TT_SBit_Strike*  strike )



    Loads a  suitable strike (i.e.  bitmap sizetable)  for the given

    instance.  Will return TT_Err_Invalid_PPem if there is no strike

    for the current x_ppem and y_ppem values.



  ..................................................................



  TT_Load_Glyph_Bitmap( TT_Face         face,

                        TT_Instance     instance,

                        TT_UShort       glyph_index,

                        TT_SBit_Image*  bitmap );



    Loads a glyph  bitmap for a given glyph  index `glyph_index' (in

    face `face'  and instance  `instance') into `bitmap'.   It calls

    TT_Get_SBit_Strike() internally for  checking the current x_ppem

    and y_ppem values.



    This function  returns an error  if there is no  embedded bitmap

    for the glyph at the given instance.



    Example (omitting the error handling):



      ...

      TT_SBit_Image*  bitmap;



      ...

      TT_Init_SBit_Extension( engine );

      TT_New_SBit_Image( &bitmap );

      ...

      TT_Load_Glyph_Bitmap( face, instance, glyph_index, bitmap );







--------------------------------------------------------------------

--------------------------------------------------------------------







II. API extensions

==================



To use  API extensions, simply  compile the specific  extension file

and  link  it to  the  library or  your  program.   By default,  all

extensions described below are linked to the library.





 1. cmap iteration (ftxcmap)

 ---------------------------



  TT_Long  TT_CharMap_First( TT_CharMap  charMap,

  ^^^^^^^                    TT_UShort*  glyph_index )





    Returns the first valid character  code in a given character map

    `charMap'.  Also  returns the corresponding glyph  index (in the

    parameter `*glyph_index').  In case  of failure, -1 is returned,

    and `*glyph_index' is undefined.



  ..................................................................



  TT_Long  TT_CharMap_Next( TT_CharMap  charMap,

  ^^^^^^^                   TT_UShort   last_char,

                            TT_UShort*  glyph_index )



    Returns the next  valid character code in a  given character map

    `charMap'   which  follows   `last_char'.    Also  returns   the

    corresponding glyph index (in the parameter `*glyph_index').  In

    case of failure, -1 is returned, and `glyph_index' is undefined.



  ..................................................................



  TT_Long  TT_CharMap_Last( TT_CharMap  charMap,

  ^^^^^^^                   TT_UShort*  glyph_index )





    Returns the last  valid character code in a  given character map

    `charMap'.  Also  returns the corresponding glyph  index (in the

    parameter `*glyph_index').  In case  of failure, -1 is returned,

    and `*glyph_index' is undefined.





====================================================================





 2. internationalized error messages (ftxerr18)

 ----------------------------------------------



  This extension  provides internationalized error  strings from the

  various  error  messages.   It   uses  the  `gettext'  package  if

  available  or  returns English/American  message  strings if  not.

  Currently,  the gettext  package  is only  available on  UNIX-like

  systems  like Linux;  this  means that  for  other platforms  only

  English error strings are returned.



  If  the gettext  package is  found on  your system,  the configure

  script  automatically includes it  by default.  In case  you don't

  want to use  it, or if you encounter  some problems compiling this

  file,  try to  disable nls  support by  configuring  FreeType with

  `./configure --disable-nls'.



  Please read the gettext info files for more information how to set

  up   your  system   for  internationalized   messages.    A  short

  introduction is also given in the file `i18n.txt'.





  TT_String*  TT_ErrToString18( TT_Error  i )

  ^^^^^^^^^^



    This function  returns an  error string for  a given  error code

    `i'.   The  type `TT_String'  usually  defaults  to `char';  see

    apiref.txt for more details.



    An  example how  to use  this function  (in connection  with the

    gettext interface) is given e.g. in test/ftdump.c.





====================================================================





 3. access to the `gasp' table (ftxgasp)

 ---------------------------------------



  The `gasp' table  is currently loaded by the  core engine, but the

  standard API doesn't give access to it.





  TT_Get_Face_Gasp_Flags( TT_Face    face,

                          TT_UShort  point_size,

                          TT_Bool*   grid_fit,

                          TT_Bool*   smooth_font )



    This function returns for a given `point_size' the values of the

    gasp  flags `grid_fit' and  `smooth_font'.  The  returned values

    are booleans (where 0 = NO, and 1 = YES).



    Note that this function  will return TT_Err_Table_Missing if the

    font file doesn't contain any gasp table.





====================================================================





 4. fast retrieval of glyph widths and heights (ftxwidth)

 --------------------------------------------------------



  This extension  is used  to parse the  `glyf' table of  a TrueType

  file in  order to  extract the  bounding box of  a given  range of

  glyphs.



  The  bounding box  is  then used  to  build font  unit widths  and

  heights that are returned in two parallel arrays.



  This extension is needed by the FreeType/2 OS/2 Font Driver.





  TT_Get_Face_Widths( TT_Face     face,

                      TT_UShort   first_glyph,

                      TT_UShort   last_glyph,

                      TT_UShort*  widths,

                      TT_UShort*  heights )



    Returns  the widths (in  array `widths')  and heights  (in array

    `heights') of  a glyph range  which starts at  `first_glyph' and

    ends at `last_glyph'.  All  returned values are returned in font

    units.   If  either `widths'  or  `heights'  is  set to  a  NULL

    pointer, no data will be returned for that particular array.



    Note: TT_Get_Face_Widths() does *not* allocate the two arrays!







--------------------------------------------------------------------

--------------------------------------------------------------------







III. Error Messages

===================



  Most functions return an error  code, typed to TT_Error.  A return

  value of zero indicates no error.  The error values are defined in

  the  various  extension header  files  (e.g.  ftxkern.h).  In  the

  following  table, the prefix  `TT_Err_' is  omitted, e.g.  `Ok' ->

  `TT_Err_Ok'.





  Error   Unprefixed               Error

  Code    Macro Name               Description

  ------------------------------------------------------------------



  0x0A00  Invalid_Kerning_Table_Format

                                   An invalid kerning subtable

                                   format was found in this font.



  0x0A01  Invalid_Kerning_Table    A kerning table contains illegal

                                   glyph indices.



  0x0B00  Invalid_Post_Table_Format

                                   The post table format specified

                                   in the font is invalid.



  0x0B01  Invalid_Post_Table       The post table contains illegal

                                   entries.





  Here the TrueType  Open error codes.  In the  following table, the

  prefix `TTO_Err_' is omitted.





  Error   Unprefixed               Error

  Code    Macro Name               Description

  ------------------------------------------------------------------

  0x1000  Invalid_SubTable_Format  The TrueType Open subtable format

                                   specified in the font is invalid.



  0x1001  Invalid_SubTable         A TrueType Open subtable contains

                                   illegal entries.



  0x1002  Not_Covered              The requested feature, glyph,

                                   etc. isn't covered by the actual

                                   function.



  0x1010  Invalid_GSUB_SubTable_Format

                                   The GSUB subtable format

                                   specified in the font is invalid.



  0x1011  Invalid_GSUB_SubTable    The GSUB subtable contains

                                   illegal entries.



  0x1020  Invalid_GPOS_SubTable_Format

                                   The GPOS subtable format

                                   specified in the font is invalid.



  0x1021  Invalid_GPOS_SubTable    The GPOS subtable contains

                                   illegal entries.





--- end of apirefx.txt ---