freetype2/include/freetype/ftsystem.h

/****************************************************************************
 *
 * ftsystem.h
 *
 *   FreeType low-level system interface definition (specification).
 *
 * Copyright (C) 1996-2020 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 FTSYSTEM_H_
#define FTSYSTEM_H_




FT_BEGIN_HEADER


  /**************************************************************************
   *
   * @section:
   *  system_interface
   *
   * @title:
   *  System Interface
   *
   * @abstract:
   *  How FreeType manages memory and i/o.
   *
   * @description:
   *  This section contains various definitions related to memory management
   *  and i/o access.  You need to understand this information if you want to
   *  use a custom memory manager or you own i/o streams.
   *
   */


  /**************************************************************************
   *
   *                 M E M O R Y   M A N A G E M E N T
   *
   */


  /**************************************************************************
   *
   * @type:
   *   FT_Memory
   *
   * @description:
   *   A handle to a given memory manager object, defined with an
   *   @FT_MemoryRec structure.
   *
   */
  typedef struct FT_MemoryRec_*  FT_Memory;


  /**************************************************************************
   *
   * @functype:
   *   FT_Alloc_Func
   *
   * @description:
   *   A function used to allocate `size` bytes from `memory`.
   *
   * @input:
   *   memory ::
   *     A handle to the source memory manager.
   *
   *   size ::
   *     The size in bytes to allocate.
   *
   * @return:
   *   Address of new memory block.  0~in case of failure.
   *
   */
  typedef void*
  (*FT_Alloc_Func)( FT_Memory  memory,
                    long       size );


  /**************************************************************************
   *
   * @functype:
   *   FT_Free_Func
   *
   * @description:
   *   A function used to release a given block of memory.
   *
   * @input:
   *   memory ::
   *     A handle to the source memory manager.
   *
   *   block ::
   *     The address of the target memory block.
   *
   */
  typedef void
  (*FT_Free_Func)( FT_Memory  memory,
                   void*      block );


  /**************************************************************************
   *
   * @functype:
   *   FT_Realloc_Func
   *
   * @description:
   *   A function used to re-allocate a given block of memory.
   *
   * @input:
   *   memory ::
   *     A handle to the source memory manager.
   *
   *   cur_size ::
   *     The block's current size in bytes.
   *
   *   new_size ::
   *     The block's requested new size.
   *
   *   block ::
   *     The block's current address.
   *
   * @return:
   *   New block address.  0~in case of memory shortage.
   *
   * @note:
   *   In case of error, the old block must still be available.
   *
   */
  typedef void*
  (*FT_Realloc_Func)( FT_Memory  memory,
                      long       cur_size,
                      long       new_size,
                      void*      block );


  /**************************************************************************
   *
   * @struct:
   *   FT_MemoryRec
   *
   * @description:
   *   A structure used to describe a given memory manager to FreeType~2.
   *
   * @fields:
   *   user ::
   *     A generic typeless pointer for user data.
   *
   *   alloc ::
   *     A pointer type to an allocation function.
   *
   *   free ::
   *     A pointer type to an memory freeing function.
   *
   *   realloc ::
   *     A pointer type to a reallocation function.
   *
   */
  struct  FT_MemoryRec_
  {
    void*            user;
    FT_Alloc_Func    alloc;
    FT_Free_Func     free;
    FT_Realloc_Func  realloc;
  };


  /**************************************************************************
   *
   *                      I / O   M A N A G E M E N T
   *
   */


  /**************************************************************************
   *
   * @type:
   *   FT_Stream
   *
   * @description:
   *   A handle to an input stream.
   *
   * @also:
   *   See @FT_StreamRec for the publicly accessible fields of a given stream
   *   object.
   *
   */
  typedef struct FT_StreamRec_*  FT_Stream;


  /**************************************************************************
   *
   * @struct:
   *   FT_StreamDesc
   *
   * @description:
   *   A union type used to store either a long or a pointer.  This is used
   *   to store a file descriptor or a `FILE*` in an input stream.
   *
   */
  typedef union  FT_StreamDesc_
  {
    long   value;
    void*  pointer;

  } FT_StreamDesc;


  /**************************************************************************
   *
   * @functype:
   *   FT_Stream_IoFunc
   *
   * @description:
   *   A function used to seek and read data from a given input stream.
   *
   * @input:
   *   stream ::
   *     A handle to the source stream.
   *
   *   offset ::
   *     The offset of read in stream (always from start).
   *
   *   buffer ::
   *     The address of the read buffer.
   *
   *   count ::
   *     The number of bytes to read from the stream.
   *
   * @return:
   *   The number of bytes effectively read by the stream.
   *
   * @note:
   *   This function might be called to perform a seek or skip operation with
   *   a `count` of~0.  A non-zero return value then indicates an error.
   *
   */
  typedef unsigned long
  (*FT_Stream_IoFunc)( FT_Stream       stream,
                       unsigned long   offset,
                       unsigned char*  buffer,
                       unsigned long   count );


  /**************************************************************************
   *
   * @functype:
   *   FT_Stream_CloseFunc
   *
   * @description:
   *   A function used to close a given input stream.
   *
   * @input:
   *  stream ::
   *    A handle to the target stream.
   *
   */
  typedef void
  (*FT_Stream_CloseFunc)( FT_Stream  stream );


  /**************************************************************************
   *
   * @struct:
   *   FT_StreamRec
   *
   * @description:
   *   A structure used to describe an input stream.
   *
   * @input:
   *   base ::
   *     For memory-based streams, this is the address of the first stream
   *     byte in memory.  This field should always be set to `NULL` for
   *     disk-based streams.
   *
   *   size ::
   *     The stream size in bytes.
   *
   *     In case of compressed streams where the size is unknown before
   *     actually doing the decompression, the value is set to 0x7FFFFFFF.
   *     (Note that this size value can occur for normal streams also; it is
   *     thus just a hint.)
   *
   *   pos ::
   *     The current position within the stream.
   *
   *   descriptor ::
   *     This field is a union that can hold an integer or a pointer.  It is
   *     used by stream implementations to store file descriptors or `FILE*`
   *     pointers.
   *
   *   pathname ::
   *     This field is completely ignored by FreeType.  However, it is often
   *     useful during debugging to use it to store the stream's filename
   *     (where available).
   *
   *   read ::
   *     The stream's input function.
   *
   *   close ::
   *     The stream's close function.
   *
   *   memory ::
   *     The memory manager to use to preload frames.  This is set internally
   *     by FreeType and shouldn't be touched by stream implementations.
   *
   *   cursor ::
   *     This field is set and used internally by FreeType when parsing
   *     frames.  In particular, the `FT_GET_XXX` macros use this instead of
   *     the `pos` field.
   *
   *   limit ::
   *     This field is set and used internally by FreeType when parsing
   *     frames.
   *
   */
  typedef struct  FT_StreamRec_
  {
    unsigned char*       base;
    unsigned long        size;
    unsigned long        pos;

    FT_StreamDesc        descriptor;
    FT_StreamDesc        pathname;
    FT_Stream_IoFunc     read;
    FT_Stream_CloseFunc  close;

    FT_Memory            memory;
    unsigned char*       cursor;
    unsigned char*       limit;

  } FT_StreamRec;

  /* */


FT_END_HEADER

#endif /* FTSYSTEM_H_ */


/* END */