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/src/freetype/include/freetype/internal/autohint.h

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  1/***************************************************************************/
  2/*                                                                         */
  3/*  autohint.h                                                             */
  4/*                                                                         */
  5/*    High-level `autohint' module-specific interface (specification).     */
  6/*                                                                         */
  7/*  Copyright 1996-2001, 2002, 2007 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  /*                 aggressively 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 <ft2build.h>
 74#include FT_FREETYPE_H
 75
 76
 77FT_BEGIN_HEADER
 78
 79
 80  typedef struct FT_AutoHinterRec_  *FT_AutoHinter;
 81
 82
 83  /*************************************************************************/
 84  /*                                                                       */
 85  /* <FuncType>                                                            */
 86  /*    FT_AutoHinter_GlobalGetFunc                                        */
 87  /*                                                                       */
 88  /* <Description>                                                         */
 89  /*    Retrieves the global hints computed for a given face object the    */
 90  /*    resulting data is dissociated from the face and will survive a     */
 91  /*    call to FT_Done_Face().  It must be discarded through the API      */
 92  /*    FT_AutoHinter_GlobalDoneFunc().                                    */
 93  /*                                                                       */
 94  /* <Input>                                                               */
 95  /*    hinter        :: A handle to the source auto-hinter.               */
 96  /*                                                                       */
 97  /*    face          :: A handle to the source face object.               */
 98  /*                                                                       */
 99  /* <Output>                                                              */
100  /*    global_hints  :: A typeless pointer to the global hints.           */
101  /*                                                                       */
102  /*    global_len    :: The size in bytes of the global hints.            */
103  /*                                                                       */
104  typedef void
105  (*FT_AutoHinter_GlobalGetFunc)( FT_AutoHinter  hinter,
106                                  FT_Face        face,
107                                  void**         global_hints,
108                                  long*          global_len );
109
110
111  /*************************************************************************/
112  /*                                                                       */
113  /* <FuncType>                                                            */
114  /*    FT_AutoHinter_GlobalDoneFunc                                       */
115  /*                                                                       */
116  /* <Description>                                                         */
117  /*    Discards the global hints retrieved through                        */
118  /*    FT_AutoHinter_GlobalGetFunc().  This is the only way these hints   */
119  /*    are freed from memory.                                             */
120  /*                                                                       */
121  /* <Input>                                                               */
122  /*    hinter :: A handle to the auto-hinter module.                      */
123  /*                                                                       */
124  /*    global :: A pointer to retrieved global hints to discard.          */
125  /*                                                                       */
126  typedef void
127  (*FT_AutoHinter_GlobalDoneFunc)( FT_AutoHinter  hinter,
128                                   void*          global );
129
130
131  /*************************************************************************/
132  /*                                                                       */
133  /* <FuncType>                                                            */
134  /*    FT_AutoHinter_GlobalResetFunc                                      */
135  /*                                                                       */
136  /* <Description>                                                         */
137  /*    This function is used to recompute the global metrics in a given   */
138  /*    font.  This is useful when global font data changes (e.g. Multiple */
139  /*    Masters fonts where blend coordinates change).                     */
140  /*                                                                       */
141  /* <Input>                                                               */
142  /*    hinter :: A handle to the source auto-hinter.                      */
143  /*                                                                       */
144  /*    face   :: A handle to the face.                                    */
145  /*                                                                       */
146  typedef void
147  (*FT_AutoHinter_GlobalResetFunc)( FT_AutoHinter  hinter,
148                                    FT_Face        face );
149
150
151  /*************************************************************************/
152  /*                                                                       */
153  /* <FuncType>                                                            */
154  /*    FT_AutoHinter_GlyphLoadFunc                                        */
155  /*                                                                       */
156  /* <Description>                                                         */
157  /*    This function is used to load, scale, and automatically hint a     */
158  /*    glyph from a given face.                                           */
159  /*                                                                       */
160  /* <Input>                                                               */
161  /*    face        :: A handle to the face.                               */
162  /*                                                                       */
163  /*    glyph_index :: The glyph index.                                    */
164  /*                                                                       */
165  /*    load_flags  :: The load flags.                                     */
166  /*                                                                       */
167  /* <Note>                                                                */
168  /*    This function is capable of loading composite glyphs by hinting    */
169  /*    each sub-glyph independently (which improves quality).             */
170  /*                                                                       */
171  /*    It will call the font driver with FT_Load_Glyph(), with            */
172  /*    FT_LOAD_NO_SCALE set.                                              */
173  /*                                                                       */
174  typedef FT_Error
175  (*FT_AutoHinter_GlyphLoadFunc)( FT_AutoHinter  hinter,
176                                  FT_GlyphSlot   slot,
177                                  FT_Size        size,
178                                  FT_UInt        glyph_index,
179                                  FT_Int32       load_flags );
180
181
182  /*************************************************************************/
183  /*                                                                       */
184  /* <Struct>                                                              */
185  /*    FT_AutoHinter_ServiceRec                                           */
186  /*                                                                       */
187  /* <Description>                                                         */
188  /*    The auto-hinter module's interface.                                */
189  /*                                                                       */
190  typedef struct  FT_AutoHinter_ServiceRec_
191  {
192    FT_AutoHinter_GlobalResetFunc  reset_face;
193    FT_AutoHinter_GlobalGetFunc    get_global_hints;
194    FT_AutoHinter_GlobalDoneFunc   done_global_hints;
195    FT_AutoHinter_GlyphLoadFunc    load_glyph;
196
197  } FT_AutoHinter_ServiceRec, *FT_AutoHinter_Service;
198
199#ifndef FT_CONFIG_OPTION_PIC
200
201#define FT_DEFINE_AUTOHINTER_SERVICE(class_, reset_face_, get_global_hints_, \
202                                     done_global_hints_, load_glyph_)        \
203  FT_CALLBACK_TABLE_DEF                                                      \
204  const FT_AutoHinter_ServiceRec class_ =                                    \
205  {                                                                          \
206    reset_face_, get_global_hints_, done_global_hints_, load_glyph_          \
207  };
208
209#else /* FT_CONFIG_OPTION_PIC */
210
211#define FT_DEFINE_AUTOHINTER_SERVICE(class_, reset_face_, get_global_hints_, \
212                                     done_global_hints_, load_glyph_)        \
213  void                                                                       \
214  FT_Init_Class_##class_( FT_Library library,                                \
215                          FT_AutoHinter_ServiceRec* clazz)                   \
216  {                                                                          \
217    FT_UNUSED(library);                                                      \
218    clazz->reset_face = reset_face_;                                         \
219    clazz->get_global_hints = get_global_hints_;                             \
220    clazz->done_global_hints = done_global_hints_;                           \
221    clazz->load_glyph = load_glyph_;                                         \
222  }
223
224#endif /* FT_CONFIG_OPTION_PIC */
225
226FT_END_HEADER
227
228#endif /* __AUTOHINT_H__ */
229
230
231/* END */