内存jpeg文件读取程序

本人项目中只需要读，因此没有提供写jpeg的代码。

有C的习惯用法，c++ hard core可能不习惯，欢迎修改。

提到的引擎，要找原始的代码，应可以找到。

主要代码

头文件：jpegReader.h 

 

#define SIG_BYTES_OFFSET  6
#define HEADER_BYTES_TO_CHECK  4

//TODO：

//参考tge/../gBitmap.cc/GBitmap::allocateBitmap封装内存分配部分代码，并按osg2.2/.../Image.cpp/setImage封装设置MstBitmap的函数。

struct MstBitmap

{

     unsigned int width;

     unsigned int height;

     unsigned int pixelFormat;

     unsigned int internalFormat;

     unsigned int dataType;

     unsigned char *data;

};

源文件：jpegReader.cpp

 #include "jpegReader.h"

 #include <assert.h>

#include <GL/gl.h>

 extern "C"

{

     #include "jpeglib.h"

}

//参考ReaderWriterJPEG.cpp (osg2.2/.../jpeg)、bitmapPng.cc (tge/engine/dgl)完成。
//对libjpeg库的修改参考《libjpeg实现内存内位图的压缩及解压缩.mht》一文。不贴了。
MstBitmap * JpegReader::readJpegStream(void* stream,int size)

{

     assert( size != 0);

     assert(NULL != stream);

 

     //检测是否jpeg格式

     char sig[HEADER_BYTES_TO_CHECK];

     strncpy(sig,(char*) stream + SIG_BYTES_OFFSET, HEADER_BYTES_TO_CHECK);

     if( !strcmp(sig, "JFIF") )

         return NULL;

 

    struct jpeg_decompress_struct cinfo;

    jpeg_error_mgr jerr;

 

     int width;

    int height;

    int format ;

     int rowBytes;

 

     unsigned char *data;//解压后数据的指针

 

    cinfo.err = jpeg_std_error(&jerr);   

 

    jpeg_create_decompress(&cinfo);   

 

    //指定数据源

     jpeg_stdio_src(&cinfo,(char*)stream, size);

 

    jpeg_read_header(&cinfo, TRUE);

 

     switch (cinfo.out_color_space)

     {

         case JCS_GRAYSCALE: 

              format = 1; break;

         case JCS_RGB:

              format = 3; break;

         default:

              jpeg_destroy_decompress(&cinfo);

              return NULL;

     }

 

    jpeg_start_decompress(&cinfo);

 

    width = cinfo.output_width;

    height = cinfo.output_height;

     rowBytes = cinfo.output_width * cinfo.output_components;

  

    data = new unsigned char[rowBytes * height];

 

    //创建每一行数据的指针

    unsigned char** row_p = new unsigned char*[height];

    for (int i = 0; i < height; i++)

        row_p[i] = &data[rowBytes*i];

 

    //读取像素数据

     for (unsigned int i = 0; i < height; i++)

       jpeg_read_scanlines(&cinfo,&row_p[i], 1);

 

    delete[] row_p;

 

     jpeg_finish_decompress(&cinfo);

 

   // Release JPEG decompression object

   // This is an important step since it will release a good deal of memory.

     jpeg_destroy_decompress(&cinfo);

 

     unsigned int internalFormat =

         format == 1 ? GL_LUMINANCE :

         format == 2 ? GL_LUMINANCE_ALPHA :

         format == 3 ? GL_RGB :

         format == 4 ? GL_RGBA : (GLenum)-1;

 

     unsigned int pixelFormat =

         format == 1 ? GL_LUMINANCE :

         format == 2 ? GL_LUMINANCE_ALPHA :

         format == 3 ? GL_RGB :

         format == 4 ? GL_RGBA : (GLenum)-1;

 

     unsigned int dataType = GL_UNSIGNED_BYTE;

 

     MstBitmap *pbi = (MstBitmap*)malloc(sizeof(MstBitmap));

 

     if(NULL != pbi)

     {

         pbi->width   = width;

         pbi->height   = height;

         pbi->pixelFormat = pixelFormat;

         pbi->internalFormat = internalFormat;

         pbi->dataType = dataType;

         pbi->data = data;

     }

    return pbi;

}

btw：

(csdn编辑系统貌似比较烂，所见非所得，反复弄几次，

也就这种乱七八糟的样子，有合适的就换)