jpeg2000(j2k)图像编码解码:c++实现openjpeg内存流接口(memory stream)

前阵子用libjpeg-turbo实现jpeg图像在内存中编码与解码

参见《libjpeg:实现jpeg内存解压缩塈转换色彩空间/压缩分辨率》，《libjpeg:实现jpeg内存压缩暨error_exit错误异常处理和个性化参数设置》

觉得libjpeg接口用起来挺麻烦的。。。但libjpeg 80以上的版本好歹提供了jpeg_mem_dest/jpeg_mem_src API让我可以直接将实现内存编/解码。
当我开始着手做jpeg2000(j2k)图像的内存压缩的时候，看了openjpeg的接口，人家压根儿没有提供类似libjpeg中jpeg_mem_dest/jpeg_mem_src这样的内存数据IO接口(感觉还是libjpeg厚道些，呵呵)，而是提供了抽象stream接口，openjpeg代码中只实现了文件流(file stream)接口(参见opj_stream_create_default_file_stream代码)
如果使用者想实现内存图像压缩，你得自己实现这stream接口。。。。这对使用者来说好处是非常灵活(可以实现内存流接口，也可以实现网络流接口。。。你想怎么干都成)，麻烦的就是要写好多代码。

openjpeg中file stream的实现

先参考一下openjpeg中file stream的实现：
以下是openjpeg中opj_stream_create_default_file_stream的实现代码

opj_stream_t* OPJ_CALLCONV opj_stream_create_default_file_stream (const char *fname, OPJ_BOOL p_is_read_stream)
{
    return opj_stream_create_file_stream(fname, OPJ_J2K_STREAM_CHUNK_SIZE, p_is_read_stream);
}

opj_stream_t* OPJ_CALLCONV opj_stream_create_file_stream (
        const char *fname, 
        OPJ_SIZE_T p_size, 
        OPJ_BOOL p_is_read_stream)
{
    opj_stream_t* l_stream = 00;
    FILE *p_file;
    const char *mode;

    if (! fname) {
        return NULL;
    }

    if(p_is_read_stream) mode = "rb"; else mode = "wb";

    p_file = fopen(fname, mode);

    if (! p_file) {
        return NULL;
    }

    l_stream = opj_stream_create(p_size,p_is_read_stream);
    if (! l_stream) {
        fclose(p_file);
        return NULL;
    }

    opj_stream_set_user_data(l_stream, p_file, (opj_stream_free_user_data_fn) fclose);
    opj_stream_set_user_data_length(l_stream, opj_get_data_length_from_file(p_file));
    opj_stream_set_read_function(l_stream, (opj_stream_read_fn) opj_read_from_file);
    opj_stream_set_write_function(l_stream, (opj_stream_write_fn) opj_write_from_file);
    opj_stream_set_skip_function(l_stream, (opj_stream_skip_fn) opj_skip_from_file);
    opj_stream_set_seek_function(l_stream, (opj_stream_seek_fn) opj_seek_from_file);

    return l_stream;
}

/* ---------------------------------------------------------------------- */
//下面的代码中实现了对文件流的close,read,write,seek,skip操作，
//其实这里的close,read,write,seek,skip的实现与c标准库中的文件操作函数fclose,fread,fwrite,fseek的接口描述是基本一样的
static OPJ_SIZE_T opj_read_from_file (void * p_buffer, OPJ_SIZE_T p_nb_bytes, FILE * p_file)
{
    OPJ_SIZE_T l_nb_read = fread(p_buffer,1,p_nb_bytes,p_file);
    return l_nb_read ? l_nb_read : (OPJ_SIZE_T)-1;
}
static OPJ_SIZE_T opj_write_from_file (void * p_buffer, OPJ_SIZE_T p_nb_bytes, FILE * p_file)
{
    return fwrite(p_buffer,1,p_nb_bytes,p_file);
}

static OPJ_OFF_T opj_skip_from_file (OPJ_OFF_T p_nb_bytes, FILE * p_user_data)
{
    if (OPJ_FSEEK(p_user_data,p_nb_bytes,SEEK_CUR)) {
        return -1;
    }

    return p_nb_bytes;
}

static OPJ_BOOL opj_seek_from_file (OPJ_OFF_T p_nb_bytes, FILE * p_user_data)
{
    if (OPJ_FSEEK(p_user_data,p_nb_bytes,SEEK_SET)) {
        return OPJ_FALSE;
    }

    return OPJ_TRUE;
}

memory stream接口实现

参考上面opj_stream_create_default_file_stream的实现代码，可以知道，自定义一个类似file stream的流对象只要实现close,read，write,seek,skip这几个函数并保证输入输出的状态与对应的opj_xxx_from_file函数一样，就可以让openjpeg将图像压缩或解压缩到你的stream对象中。

于是，要实现jpeg2000的内存编/解码首先要做的工作就是实现自定义的内存流(memory stream)对象。

#include <vector>
#include <iostream>
#include <algorithm>
#include <utility>
#include <cstring>
#include "openjpeg-2.1/openjpeg.h"
using namespace std;

#define DEFAULT_MEM_STREAM_INIT_SIZE (1024*16)

/* 流(stream)接口 */
struct opj_stream_interface{
// 从stream中读取指定长度的数据,对应opj_read_from_file 
    virtual OPJ_SIZE_T read (void * p_buffer, OPJ_SIZE_T p_nb_bytes)const=0;
// 向stream中写入指定长度的数据,对应opj_write_from_file 
    virtual OPJ_SIZE_T write (void * p_buffer, OPJ_SIZE_T p_nb_bytes)=0;
// 以stream起始位置为参照设置stream的游标(position indicator)到指定的位置，对应opj_seek_from_file
    virtual OPJ_BOOL seek (OPJ_OFF_T p_nb_bytes)const=0;
// 以stream当前位置为参照设置stream的游标(position indicator)到指定的位置，对应opj_skip_from_file
    virtual OPJ_OFF_T skip (OPJ_OFF_T p_nb_bytes)const=0;
// 返回流的长度 
    virtual OPJ_UINT64 stream_length()const=0;
// 返回流内存数据地址
    virtual uint8_t* stream_data()const=0;
// 关闭流，对应fclose()
    virtual void close()=0;
// 为TRUE时stream对象为read only ，否则为只写write only。
    virtual OPJ_BOOL is_read_stream()const=0;
    virtual ~opj_stream_interface()=default;
};
/** abstract memory stream(内存流虚类) 只实现opj_stream_interface中的seek,skip,close,stream_length */
class opj_stream_mem_abstract:public opj_stream_interface{
protected:
    /** pointer to the start of the stream */
    // 内存流数据起始位置
    mutable uint8_t *start;
    /** pointer to the end of the stream */
    // 内存流数据结尾位置
    mutable uint8_t *last;
    /** pointer to the current position */
    // 内存流数据当前游标位置
    mutable uint8_t *cursor;
public:
    virtual OPJ_SIZE_T write (void * p_buffer, OPJ_SIZE_T p_nb_bytes)=0;
    virtual uint8_t* stream_data()const=0;
    virtual OPJ_BOOL is_read_stream()const=0;
    virtual OPJ_SIZE_T read (void * p_buffer, OPJ_SIZE_T p_nb_bytes)const=0;
    virtual OPJ_BOOL seek (OPJ_OFF_T p_nb_bytes)const{
        if(p_nb_bytes>=0){
            cursor=start+p_nb_bytes;
            return OPJ_TRUE;
        }
        return OPJ_FALSE;
    }
    virtual OPJ_OFF_T skip (OPJ_OFF_T p_nb_bytes)const{
        // 这个函数设计是有问题的,当p_nb_bytes为-1时返回会产生歧义，
        // 但openjpeg中opj_skip_from_file就是这么写的
        // opj_stream_skip_fn定义的返回也是bool
        // 所以也只能按其接口要求这么定义
        auto nc=cursor+p_nb_bytes;
        if(nc>=start){
            cursor=nc;
            return p_nb_bytes;
        }
        return (OPJ_OFF_T)-1;
    }
    virtual OPJ_UINT64 stream_length()const{
        return (OPJ_UINT64)(last-start);
    }
    virtual void close(){}
    virtual ~opj_stream_mem_abstract()=default;
};
/** memory output stream(内存输出流) 从std::vector<uint8_t>继承，实现opj_stream_interface中的read,write,stream_data,is_read_stream */
class opj_stream_mem_output:public opj_stream_mem_abstract,private vector<uint8_t>{
    /** pointer to the end of the vector */
    uint8_t *end;
    using base=vector<uint8_t>;
public:
    opj_stream_mem_output():opj_stream_mem_output(DEFAULT_MEM_STREAM_INIT_SIZE){}
    opj_stream_mem_output(size_t init_capacity):base(init_capacity){
        start=stream_data();
        end=stream_data()+size();
        cursor=stream_data();
        last=stream_data();
    }
    virtual OPJ_SIZE_T read (void * p_buffer, OPJ_SIZE_T p_nb_bytes)const{
        // output stream不能读取
        return 0;
    }
    virtual OPJ_SIZE_T write (void * p_buffer, OPJ_SIZE_T p_nb_bytes){
        auto left=(OPJ_SIZE_T)(end-cursor);
        if(p_nb_bytes>left){
            // 容量不足时先扩充(至少扩充1倍)
            auto off_cur=cursor-start;
            auto off_last=last-start;
            try{
                base::resize(base::size()+max(p_nb_bytes-left,(OPJ_SIZE_T)base::size()));
            }catch(...){
            // 处理resize失败抛出的异常
#ifndef NDEBUG
                cerr<<"exception on call vector::resize"<<endl;
#endif
                return 0;
            }
            start=stream_data();
            end=start+base::size();
            last=start+off_last;
            cursor=start+off_cur;
        }
        memcpy(cursor,p_buffer,p_nb_bytes);
        auto old_cursor=cursor;
        cursor+=p_nb_bytes;
        if(cursor>last){
            if(old_cursor>last){
                memset(last,0,old_cursor-last);
            }
            last=cursor;
        }
        return p_nb_bytes;
    }
    virtual uint8_t* stream_data()const{
        return const_cast<uint8_t*>(base::data());
    }
    virtual OPJ_BOOL is_read_stream()const{return 0;}
};

/** memory input stream(内存输入流) 实现opj_stream_interface中的read,write,stream_data,is_read_stream */
class opj_stream_mem_input:public opj_stream_mem_abstract{
    const uint8_t* _data;
    const size_t size;
public:
    opj_stream_mem_input(const void * data,size_t size):_data(reinterpret_cast<const uint8_t*>(data)),size(size){
        if(nullptr==data)
            throw opj_stream_exception("input data is null");
        start=const_cast<uint8_t*>(_data);
        cursor=start;
        last=start+size;
    }
    virtual OPJ_SIZE_T read (void * p_buffer, OPJ_SIZE_T p_nb_bytes)const{
        if(last>cursor){
            auto len=min((OPJ_SIZE_T)(last-cursor),p_nb_bytes);
            if(len){
                memcpy(p_buffer,cursor,len);
                cursor+=len;
                return len;
            }
        }
        return (OPJ_SIZE_T)-1;
    }
    virtual OPJ_SIZE_T write (void * p_buffer, OPJ_SIZE_T p_nb_bytes){
        // input stream不能写入
        return 0;
    }
    virtual uint8_t* stream_data()const{
        return const_cast<uint8_t*>(_data);
    }
    virtual OPJ_BOOL is_read_stream()const{return 1;}
};

create opj_stream_t from memory stream

上面的代码中最终实现了opj_stream_mem_input和opj_stream_mem_output两个流对象(分别用于图像解码和编码)，这两个流对象的外部表现与openjpeg所要求的stream接口完全一致，但它们是c++的对象，不能直接用于c接口，所以还需要做一层封装。
于是，参照上面openjpeg的opj_stream_create_default_file_stream 和opj_stream_create_file_stream 函数，我们实现了memory stream对应的opj_stream_create_default_si和opj_stream_create_si

// 对应opj_stream_create_file_stream
opj_stream_t* opj_stream_create_si(opj_stream_interface& stream, OPJ_SIZE_T p_size) {
    opj_stream_t* l_stream = opj_stream_create(p_size, stream.is_read_stream());
    if (l_stream) {
        opj_stream_set_user_data(l_stream, std::addressof(stream), (opj_stream_free_user_data_fn) (opj_stream_interface_close));
        opj_stream_set_user_data_length(l_stream, stream.stream_length());
        opj_stream_set_read_function(l_stream, (opj_stream_read_fn) (opj_stream_interface_read));
        opj_stream_set_write_function(l_stream, (opj_stream_write_fn) (opj_stream_interface_write));
        opj_stream_set_skip_function(l_stream, (opj_stream_skip_fn) (opj_stream_interface_skip));
        opj_stream_set_seek_function(l_stream, (opj_stream_seek_fn) (opj_stream_interface_seek));
        return l_stream;
    }
    throw opj_exception("fail to ceate stream:opj_stream_create");
}
// 对应 opj_stream_create_default_file_stream
opj_stream_t* opj_stream_create_default_si(opj_stream_interface& stream) {
    return opj_stream_create_si(stream, OPJ_J2K_STREAM_CHUNK_SIZE);
}

// 对应 fclose
void opj_stream_interface_close(opj_stream_interface* stream_instance) {
    stream_instance->close();
}

// 对应opj_read_seek_file 
OPJ_BOOL opj_stream_interface_seek(OPJ_OFF_T p_nb_bytes, opj_stream_interface* stream_instance) {
    return stream_instance->seek(p_nb_bytes);
}
// 对应opj_read_skip_file 
OPJ_OFF_T opj_stream_interface_skip(OPJ_OFF_T p_nb_bytes, opj_stream_interface* stream_instance) {
    return stream_instance->skip(p_nb_bytes);
}
// 对应opj_read_write_file 
OPJ_SIZE_T opj_stream_interface_write(void* p_buffer, OPJ_SIZE_T p_nb_bytes, opj_stream_interface* stream_instance) {
    return stream_instance->write(p_buffer, p_nb_bytes);
}
// 对应opj_read_read_file 
OPJ_SIZE_T opj_stream_interface_read(void* p_buffer, OPJ_SIZE_T p_nb_bytes, opj_stream_interface* stream_instance) {
    return stream_instance->read(p_buffer, p_nb_bytes);
}

所有的准备工作完成，下面要上主菜了–> jpeg2000图像的内存压缩