ftcache.h

奇趣公司比较新的qt/emd版本

/***************************************************************************/
/*                                                                         */
/*  ftcache.h                                                              */
/*                                                                         */
/*    FreeType Cache subsystem (specification).                            */
/*                                                                         */
/*  Copyright 1996-2001, 2002, 2003, 2004, 2005, 2006 by                   */
/*  David Turner, Robert Wilhelm, and Werner Lemberg.                      */
/*                                                                         */
/*  This file is part of the FreeType project, and may only be used,       */
/*  modified, and distributed under the terms of the FreeType project      */
/*  license, LICENSE.TXT.  By continuing to use, modify, or distribute     */
/*  this file you indicate that you have read the license and              */
/*  understand and accept it fully.                                        */
/*                                                                         */
/***************************************************************************/


#ifndef __FTCACHE_H__
#define __FTCACHE_H__


#include <ft2build.h>
#include FT_GLYPH_H


FT_BEGIN_HEADER


  /*************************************************************************
   *
   * <Section>
   *    cache_subsystem
   *
   * <Title>
   *    Cache Sub-System
   *
   * <Abstract>
   *    How to cache face, size, and glyph data with FreeType 2.
   *
   * <Description>
   *   This section describes the FreeType 2 cache sub-system, which is used
   *   to limit the number of concurrently opened @FT_Face and @FT_Size
   *   objects, as well as caching information like character maps and glyph
   *   images while limiting their maximum memory usage.
   *
   *   Note that all types and functions begin with the `FTC_' prefix.
   *
   *   The cache is highly portable and thus doesn't know anything about the
   *   fonts installed on your system, or how to access them.  This implies
   *   the following scheme:
   *
   *   First, available or installed font faces are uniquely identified by
   *   @FTC_FaceID values, provided to the cache by the client.  Note that
   *   the cache only stores and compares these values, and doesn't try to
   *   interpret them in any way.
   *
   *   Second, the cache calls, only when needed, a client-provided function
   *   to convert a @FTC_FaceID into a new @FT_Face object.  The latter is
   *   then completely managed by the cache, including its termination
   *   through @FT_Done_Face.
   *
   *   Clients are free to map face IDs to anything else.  The most simple
   *   usage is to associate them to a (pathname,face_index) pair that is
   *   used to call @FT_New_Face.  However, more complex schemes are also
   *   possible.
   *
   *   Note that for the cache to work correctly, the face ID values must be
   *   *persistent*, which means that the contents they point to should not
   *   change at runtime, or that their value should not become invalid.
   *
   *   If this is unavoidable (e.g., when a font is uninstalled at runtime),
   *   you should call @FTC_Manager_RemoveFaceID as soon as possible, to let
   *   the cache get rid of any references to the old @FTC_FaceID it may
   *   keep internally.  Failure to do so will lead to incorrect behaviour
   *   or even crashes.
   *
   *   To use the cache, start with calling @FTC_Manager_New to create a new
   *   @FTC_Manager object, which models a single cache instance.  You can
   *   then look up @FT_Face and @FT_Size objects with
   *   @FTC_Manager_LookupFace and @FTC_Manager_LookupSize, respectively.
   *
   *   If you want to use the charmap caching, call @FTC_CMapCache_New, then
   *   later use @FTC_CMapCache_Lookup to perform the equivalent of
   *   @FT_Get_Char_Index, only much faster.
   *
   *   If you want to use the @FT_Glyph caching, call @FTC_ImageCache, then
   *   later use @FTC_ImageCache_Lookup to retrieve the corresponding
   *   @FT_Glyph objects from the cache.
   *
   *   If you need lots of small bitmaps, it is much more memory efficient
   *   to call @FTC_SBitCache_New followed by @FTC_SBitCache_Lookup.  This
   *   returns @FTC_SBitRec structures, which are used to store small
   *   bitmaps directly.  (A small bitmap is one whose metrics and
   *   dimensions all fit into 8-bit integers).
   *
   *   We hope to also provide a kerning cache in the near future.
   *
   *
   * <Order>
   *   FTC_Manager
   *   FTC_FaceID
   *   FTC_Face_Requester
   *
   *   FTC_Manager_New
   *   FTC_Manager_Reset
   *   FTC_Manager_Done
   *   FTC_Manager_LookupFace
   *   FTC_Manager_LookupSize
   *   FTC_Manager_RemoveFaceID
   *
   *   FTC_Node
   *   FTC_Node_Unref
   *
   *   FTC_ImageCache
   *   FTC_ImageCache_New
   *   FTC_ImageCache_Lookup
   *
   *   FTC_SBit
   *   FTC_SBitCache
   *   FTC_SBitCache_New
   *   FTC_SBitCache_Lookup
   *
   *   FTC_CMapCache
   *   FTC_CMapCache_New
   *   FTC_CMapCache_Lookup
   *
   *************************************************************************/


  /*************************************************************************/
  /*************************************************************************/
  /*************************************************************************/
  /*****                                                               *****/
  /*****                    BASIC TYPE DEFINITIONS                     *****/
  /*****                                                               *****/
  /*************************************************************************/
  /*************************************************************************/
  /*************************************************************************/


  /*************************************************************************
   *
   * @type: FTC_FaceID
   *
   * @description:
   *   An opaque pointer type that is used to identity face objects.  The
   *   contents of such objects is application-dependent.
   *
   *   These pointers are typically used to point to a user-defined
   *   structure containing a font file path, and face index.
   *
   * @note:
   *   Never use NULL as a valid @FTC_FaceID.
   *
   *   Face IDs are passed by the client to the cache manager, which calls,
   *   when needed, the @FTC_Face_Requester to translate them into new
   *   @FT_Face objects.
   *
   *   If the content of a given face ID changes at runtime, or if the value
   *   becomes invalid (e.g., when uninstalling a font), you should
   *   immediately call @FTC_Manager_RemoveFaceID before any other cache
   *   function.
   *
   *   Failure to do so will result in incorrect behaviour or even
   *   memory leaks and crashes.
   */
  typedef struct FTC_FaceIDRec_*  FTC_FaceID;


  /************************************************************************
   *
   * @functype:
   *   FTC_Face_Requester
   *
   * @description:
   *   A callback function provided by client applications.  It is used by
   *   the cache manager to translate a given @FTC_FaceID into a new valid
   *   @FT_Face object, on demand.
   *
   * <Input>
   *   face_id ::
   *     The face ID to resolve.
   *
   *   library ::
   *     A handle to a FreeType library object.
   *
   *   req_data ::
   *     Application-provided request data (see note below).
   *
   * <Output>
   *   aface ::
   *     A new @FT_Face handle.
   *
   * <Return>
   *   FreeType error code.  0 means success.
   *
   * <Note>
   *   The third parameter `req_data' is the same as the one passed by the
   *   client when @FTC_Manager_New is called.
   *
   *   The face requester should not perform funny things on the returned
   *   face object, like creating a new @FT_Size for it, or setting a
   *   transformation through @FT_Set_Transform!
   */
  typedef FT_Error
  (*FTC_Face_Requester)( FTC_FaceID  face_id,
                         FT_Library  library,
                         FT_Pointer  request_data,
                         FT_Face*    aface );

 /* */

#define FT_POINTER_TO_ULONG( p )  ( (FT_ULong)(FT_Pointer)(p) )

#define FTC_FACE_ID_HASH( i )                                \
          ((FT_UInt32)(( FT_POINTER_TO_ULONG( i ) >> 3 ) ^   \
                       ( FT_POINTER_TO_ULONG( i ) << 7 ) ) )


  /*************************************************************************/
  /*************************************************************************/
  /*************************************************************************/
  /*****                                                               *****/
  /*****                      CACHE MANAGER OBJECT                     *****/
  /*****                                                               *****/
  /*************************************************************************/
  /*************************************************************************/
  /*************************************************************************/


  /*************************************************************************/
  /*                                                                       */
  /* <Type>                                                                */
  /*    FTC_Manager                                                        */
  /*                                                                       */
  /* <Description>                                                         */
  /*    This object corresponds to one instance of the cache-subsystem.    */
  /*    It is used to cache one or more @FT_Face objects, along with       */
  /*    corresponding @FT_Size objects.                                    */
  /*                                                                       */
  /*    The manager intentionally limits the total number of opened        */
  /*    @FT_Face and @FT_Size objects to control memory usage.  See the    */
  /*    `max_faces' and `max_sizes' parameters of @FTC_Manager_New.        */
  /*                                                                       */
  /*    The manager is also used to cache `nodes' of various types while   */
  /*    limiting their total memory usage.                                 */
  /*                                                                       */
  /*    All limitations are enforced by keeping lists of managed objects   */
  /*    in most-recently-used order, and flushing old nodes to make room   */
  /*    for new ones.                                                      */