src/freetype/freetype/internal/autohint.h

   1 /***************************************************************************/
   2 /*                                                                         */
   3 /*  autohint.h                                                             */
   4 /*                                                                         */
   5 /*    High-level `autohint' module-specific interface (specification).     */
   6 /*                                                                         */
   7 /*  Copyright 1996-2000 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   /*************************************************************************/
  20   /*                                                                       */
  21   /* The auto-hinter is used to load and automatically hint glyphs if a    */
  22   /* format-specific hinter isn't available.                               */
  23   /*                                                                       */
  24   /*************************************************************************/
  25
  26
  27 #ifndef AUTOHINT_H
  28 #define AUTOHINT_H
  29
  30
  31   /*************************************************************************/
  32   /*                                                                       */
  33   /* A small technical note regarding automatic hinting in order to        */
  34   /* clarify this module interface.                                        */
  35   /*                                                                       */
  36   /* An automatic hinter might compute two kinds of data for a given face: */
  37   /*                                                                       */
  38   /* - global hints: Usually some metrics that describe global properties  */
  39   /*                 of the face.  It is computed by scanning more or less */
  40   /*                 agressively the glyphs in the face, and thus can be   */
  41   /*                 very slow to compute (even if the size of global      */
  42   /*                 hints is really small).                               */
  43   /*                                                                       */
  44   /* - glyph hints:  These describe some important features of the glyph   */
  45   /*                 outline, as well as how to align them.  They are      */
  46   /*                 generally much faster to compute than global hints.   */
  47   /*                                                                       */
  48   /* The current FreeType auto-hinter does a pretty good job while         */
  49   /* performing fast computations for both global and glyph hints.         */
  50   /* However, we might be interested in introducing more complex and       */
  51   /* powerful algorithms in the future, like the one described in the John */
  52   /* D. Hobby paper, which unfortunately requires a lot more horsepower.   */
  53   /*                                                                       */
  54   /* Because a sufficiently sophisticated font management system would     */
  55   /* typically implement an LRU cache of opened face objects to reduce     */
  56   /* memory usage, it is a good idea to be able to avoid recomputing       */
  57   /* global hints every time the same face is re-opened.                   */
  58   /*                                                                       */
  59   /* We thus provide the ability to cache global hints outside of the face */
  60   /* object, in order to speed up font re-opening time.  Of course, this   */
  61   /* feature is purely optional, so most client programs won't even notice */
  62   /* it.                                                                   */
  63   /*                                                                       */
  64   /* I initially thought that it would be a good idea to cache the glyph   */
  65   /* hints too.  However, my general idea now is that if you really need   */
  66   /* to cache these too, you are simply in need of a new font format,      */
  67   /* where all this information could be stored within the font file and   */
  68   /* decoded on the fly.                                                   */
  69   /*                                                                       */
  70   /*************************************************************************/
  71
  72
  73 #include <freetype/freetype.h>
  74
  75
  76   typedef struct FT_AutoHinterRec_  *FT_AutoHinter;
  77
  78
  79   /*************************************************************************/
  80   /*                                                                       */
  81   /* <FuncType>                                                            */
  82   /*    FT_AutoHinter_Get_Global_Func                                      */
  83   /*                                                                       */
  84   /* <Description>                                                         */
  85   /*    Retrieves the global hints computed for a given face object the    */
  86   /*    resulting data is dissociated from the face and will survive a     */
  87   /*    call to FT_Done_Face(). It must be discarded through the API       */
  88   /*    FT_AutoHinter_Done_Global_Func().                                  */
  89   /*                                                                       */
  90   /* <Input>                                                               */
  91   /*    hinter        :: A handle to the source auto-hinter.               */
  92   /*                                                                       */
  93   /*    face          :: A handle to the source face object.               */
  94   /*                                                                       */
  95   /* <Output>                                                              */
  96   /*    global_hints  :: A typeless pointer to the global hints.           */
  97   /*                                                                       */
  98   /*    global_len    :: The size in bytes of the global hints.            */
  99   /*                                                                       */
 100   typedef void  (*FT_AutoHinter_Get_Global_Func)(
 101                   FT_AutoHinter  hinter,
 102                   FT_Face        face,
 103                   void**         global_hints,
 104                   long*          global_len );
 105
 106
 107   /*************************************************************************/
 108   /*                                                                       */
 109   /* <FuncType>                                                            */
 110   /*    FT_AutoHinter_Done_Global_Func                                     */
 111   /*                                                                       */
 112   /* <Description>                                                         */
 113   /*    Discards the global hints retrieved through                        */
 114   /*    FT_AutoHinter_Get_Global_Func().  This is the only way these hints */
 115   /*    are freed from memory.                                             */
 116   /*                                                                       */
 117   /* <Input>                                                               */
 118   /*    hinter :: A handle to the auto-hinter module.                      */
 119   /*                                                                       */
 120   /*    global :: A pointer to retrieved global hints to discard.          */
 121   /*                                                                       */
 122   typedef void  (*FT_AutoHinter_Done_Global_Func)( FT_AutoHinter  hinter,
 123                                                    void*          global );
 124
 125
 126   /*************************************************************************/
 127   /*                                                                       */
 128   /* <FuncType>                                                            */
 129   /*    FT_AutoHinter_Reset_Func                                           */
 130   /*                                                                       */
 131   /* <Description>                                                         */
 132   /*    This function is used to recompute the global metrics in a given   */
 133   /*    font.  This is useful when global font data changes (e.g. Multiple */
 134   /*    Masters fonts where blend coordinates change).                     */
 135   /*                                                                       */
 136   /* <Input>                                                               */
 137   /*    hinter :: A handle to the source auto-hinter.                      */
 138   /*                                                                       */
 139   /*    face   :: A handle to the face.                                    */
 140   /*                                                                       */
 141   typedef void  (*FT_AutoHinter_Reset_Func)( FT_AutoHinter  hinter,
 142                                              FT_Face        face );
 143
 144
 145   /*************************************************************************/
 146   /*                                                                       */
 147   /* <FuncType>                                                            */
 148   /*    FT_AutoHinter_Load_Func                                            */
 149   /*                                                                       */
 150   /* <Description>                                                         */
 151   /*    This function is used to load, scale, and automatically hint a     */
 152   /*    glyph from a given face.                                           */
 153   /*                                                                       */
 154   /* <Input>                                                               */
 155   /*    face        :: A handle to the face.                               */
 156   /*    glyph_index :: The glyph index.                                    */
 157   /*    load_flags  :: The load flags.                                     */
 158   /*                                                                       */
 159   /* <Note>                                                                */
 160   /*    This function is capable of loading composite glyphs by hinting    */
 161   /*    each sub-glyph independently (which improves quality).             */
 162   /*                                                                       */
 163   /*    It will call the font driver with FT_Load_Glyph(), with            */
 164   /*    FT_LOAD_NO_SCALE set.                                              */
 165   /*                                                                       */
 166   typedef FT_Error  (*FT_AutoHinter_Load_Func)( FT_AutoHinter  hinter,
 167                                                 FT_GlyphSlot   slot,
 168                                                 FT_Size        size,
 169                                                 FT_UInt        glyph_index,
 170                                                 FT_ULong       load_flags );
 171
 172
 173   /*************************************************************************/
 174   /*                                                                       */
 175   /* <Struct>                                                              */
 176   /*    FT_AutoHinter_Interface                                            */
 177   /*                                                                       */
 178   /* <Description>                                                         */
 179   /*    The auto-hinter module's interface.                                */
 180   /*                                                                       */
 181   typedef struct  FT_AutoHinter_Interface
 182   {
 183     FT_AutoHinter_Reset_Func        reset_face;
 184     FT_AutoHinter_Load_Func         load_glyph;
 185
 186     FT_AutoHinter_Get_Global_Func   get_global_hints;
 187     FT_AutoHinter_Done_Global_Func  done_global_hints;
 188
 189   } FT_AutoHinter_Interface;
 190
 191
 192 #endif /* AUTOHINT_H */
 193
 194
 195 /* END */