d5d048bbfe
The existing documentation comments on `FT_Stream_IoFunc` hinted at the dual seek/read behavior required for custom stream implementations to work, but it didn't explicitly explain it. Without looking at the internals of FreeType, it was easy for someone to assume their implementation should handle both seek and read operations all the time. If this is done, you get a variety of errors, but mostly just `Unknown_File_Format` (error code 0x02).
359 lines
8.6 KiB
C
359 lines
8.6 KiB
C
/****************************************************************************
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*
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* ftsystem.h
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*
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* FreeType low-level system interface definition (specification).
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*
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* Copyright (C) 1996-2022 by
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* David Turner, Robert Wilhelm, and Werner Lemberg.
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*
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* This file is part of the FreeType project, and may only be used,
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* modified, and distributed under the terms of the FreeType project
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* license, LICENSE.TXT. By continuing to use, modify, or distribute
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* this file you indicate that you have read the license and
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* understand and accept it fully.
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*
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*/
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#ifndef FTSYSTEM_H_
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#define FTSYSTEM_H_
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FT_BEGIN_HEADER
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/**************************************************************************
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*
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* @section:
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* system_interface
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*
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* @title:
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* System Interface
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*
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* @abstract:
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* How FreeType manages memory and i/o.
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*
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* @description:
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* This section contains various definitions related to memory management
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* and i/o access. You need to understand this information if you want to
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* use a custom memory manager or you own i/o streams.
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*
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*/
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/**************************************************************************
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*
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* M E M O R Y M A N A G E M E N T
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*
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*/
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/**************************************************************************
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*
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* @type:
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* FT_Memory
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*
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* @description:
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* A handle to a given memory manager object, defined with an
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* @FT_MemoryRec structure.
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*
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*/
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typedef struct FT_MemoryRec_* FT_Memory;
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/**************************************************************************
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*
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* @functype:
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* FT_Alloc_Func
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*
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* @description:
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* A function used to allocate `size` bytes from `memory`.
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*
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* @input:
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* memory ::
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* A handle to the source memory manager.
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*
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* size ::
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* The size in bytes to allocate.
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*
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* @return:
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* Address of new memory block. 0~in case of failure.
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*
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*/
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typedef void*
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(*FT_Alloc_Func)( FT_Memory memory,
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long size );
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/**************************************************************************
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*
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* @functype:
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* FT_Free_Func
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*
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* @description:
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* A function used to release a given block of memory.
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*
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* @input:
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* memory ::
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* A handle to the source memory manager.
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*
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* block ::
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* The address of the target memory block.
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*
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*/
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typedef void
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(*FT_Free_Func)( FT_Memory memory,
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void* block );
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/**************************************************************************
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*
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* @functype:
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* FT_Realloc_Func
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*
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* @description:
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* A function used to re-allocate a given block of memory.
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*
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* @input:
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* memory ::
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* A handle to the source memory manager.
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*
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* cur_size ::
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* The block's current size in bytes.
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*
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* new_size ::
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* The block's requested new size.
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*
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* block ::
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* The block's current address.
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*
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* @return:
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* New block address. 0~in case of memory shortage.
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*
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* @note:
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* In case of error, the old block must still be available.
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*
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*/
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typedef void*
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(*FT_Realloc_Func)( FT_Memory memory,
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long cur_size,
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long new_size,
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void* block );
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/**************************************************************************
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*
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* @struct:
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* FT_MemoryRec
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*
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* @description:
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* A structure used to describe a given memory manager to FreeType~2.
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*
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* @fields:
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* user ::
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* A generic typeless pointer for user data.
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*
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* alloc ::
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* A pointer type to an allocation function.
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*
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* free ::
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* A pointer type to an memory freeing function.
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*
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* realloc ::
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* A pointer type to a reallocation function.
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*
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*/
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struct FT_MemoryRec_
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{
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void* user;
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FT_Alloc_Func alloc;
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FT_Free_Func free;
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FT_Realloc_Func realloc;
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};
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/**************************************************************************
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*
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* I / O M A N A G E M E N T
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*
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*/
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/**************************************************************************
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*
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* @type:
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* FT_Stream
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*
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* @description:
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* A handle to an input stream.
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*
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* @also:
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* See @FT_StreamRec for the publicly accessible fields of a given stream
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* object.
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*
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*/
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typedef struct FT_StreamRec_* FT_Stream;
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/**************************************************************************
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*
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* @struct:
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* FT_StreamDesc
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*
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* @description:
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* A union type used to store either a long or a pointer. This is used
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* to store a file descriptor or a `FILE*` in an input stream.
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*
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*/
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typedef union FT_StreamDesc_
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{
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long value;
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void* pointer;
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} FT_StreamDesc;
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/**************************************************************************
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*
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* @functype:
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* FT_Stream_IoFunc
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*
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* @description:
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* A function used to seek and read data from a given input stream.
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*
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* @input:
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* stream ::
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* A handle to the source stream.
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*
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* offset ::
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* The offset from the start of the stream to seek to if this is a seek
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* operation (see note).
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*
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* buffer ::
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* The address of the read buffer.
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*
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* count ::
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* The number of bytes to read from the stream.
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*
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* @return:
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* The number of bytes effectively read by the stream.
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*
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* @note:
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* This function performs a seek *or* a read operation depending on the
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* argument values. If `count` is zero, the operation is a seek to
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* `offset` bytes. If `count` is >~0, the operation is a read of `count`
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* bytes from the current position in the stream, and the `offset` value
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* should be ignored.
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*
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* For seek operations, a non-zero return value indicates an error.
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*
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*/
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typedef unsigned long
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(*FT_Stream_IoFunc)( FT_Stream stream,
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unsigned long offset,
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unsigned char* buffer,
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unsigned long count );
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/**************************************************************************
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*
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* @functype:
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* FT_Stream_CloseFunc
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*
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* @description:
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* A function used to close a given input stream.
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*
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* @input:
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* stream ::
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* A handle to the target stream.
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*
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*/
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typedef void
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(*FT_Stream_CloseFunc)( FT_Stream stream );
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/**************************************************************************
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*
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* @struct:
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* FT_StreamRec
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*
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* @description:
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* A structure used to describe an input stream.
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*
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* @input:
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* base ::
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* For memory-based streams, this is the address of the first stream
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* byte in memory. This field should always be set to `NULL` for
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* disk-based streams.
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*
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* size ::
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* The stream size in bytes.
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*
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* In case of compressed streams where the size is unknown before
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* actually doing the decompression, the value is set to 0x7FFFFFFF.
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* (Note that this size value can occur for normal streams also; it is
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* thus just a hint.)
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*
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* pos ::
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* The current position within the stream.
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*
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* descriptor ::
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* This field is a union that can hold an integer or a pointer. It is
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* used by stream implementations to store file descriptors or `FILE*`
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* pointers.
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*
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* pathname ::
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* This field is completely ignored by FreeType. However, it is often
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* useful during debugging to use it to store the stream's filename
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* (where available).
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*
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* read ::
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* The stream's input function.
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*
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* close ::
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* The stream's close function.
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*
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* memory ::
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* The memory manager to use to preload frames. This is set internally
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* by FreeType and shouldn't be touched by stream implementations.
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*
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* cursor ::
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* This field is set and used internally by FreeType when parsing
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* frames. In particular, the `FT_GET_XXX` macros use this instead of
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* the `pos` field.
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*
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* limit ::
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* This field is set and used internally by FreeType when parsing
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* frames.
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*
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*/
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typedef struct FT_StreamRec_
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{
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unsigned char* base;
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unsigned long size;
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unsigned long pos;
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FT_StreamDesc descriptor;
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FT_StreamDesc pathname;
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FT_Stream_IoFunc read;
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FT_Stream_CloseFunc close;
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FT_Memory memory;
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unsigned char* cursor;
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unsigned char* limit;
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} FT_StreamRec;
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/* */
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FT_END_HEADER
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#endif /* FTSYSTEM_H_ */
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/* END */
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