vbf_ddsreader.inl

数据压缩的实例

//************************************************************************
//  文件名： VBF_DDS.cpp
//  描述：   读取DDS的实现文件
//  作者：   杜莹 
//  时间：   2005-1-1
//************************************************************************

#ifndef __VBF_DDS_READER_INL__
#define __VBF_DDS_READER_INL__

//---------------------------------------------------------------------------------
// 函数：LoadDDSBuf()
// 描述：从内存DDS数据中获取信息
// 说明：DDS文件可以是压缩格式的，或非压缩格式的
//---------------------------------------------------------------------------------
inline BOOL LoadDDSBuf(int nSizeDDS, BYTE* pDDSBuf, DDSIMAGE* pImage)
{
    ZeroMemory( pImage, sizeof(DDSIMAGE) );

	// 构造内存文件
	CMemFile* pMemFile = new CMemFile(pDDSBuf, nSizeDDS);

	// 确认文件格式
	DWORD dwMagic;
	pMemFile->Read( &dwMagic, sizeof(DWORD) );
	if( dwMagic!=MAKEFOURCC('D','D','S',' ') )	
	{
		pMemFile->Close();
		SAFE_DELETE(pMemFile);
        return FALSE;
	}
   
    // 读取文件头信息 (即表面描述信息)	
	DDS_HEADER ddsHeader; 
	pMemFile->Read( &ddsHeader, sizeof(DDS_HEADER) );
	
	// 判断是否压缩格式
	BOOL bCompressed = FALSE;
	if( ddsHeader.ddpfPixelFormat.dwFlags & DDS_RGB ) // 非压缩格式(RGB/RGBA)
	{
		bCompressed = FALSE;
		switch(ddsHeader.ddpfPixelFormat.dwRGBBitCount)
		{
			case 24: { pImage->format = DDS_RGB;  break; }   // RGB
			case 32: { pImage->format = DDS_RGBA; break; }   // RGBA
			default: { return FALSE; }
		}
	} 
	else if(ddsHeader.ddpfPixelFormat.dwFlags & DDS_FOURCC)  // 压缩格式
	{
		bCompressed = TRUE;
		switch(ddsHeader.ddpfPixelFormat.dwFourCC)
		{
			case FOURCC_DXT1: {	pImage->format = VBF_COMPRESSED_RGBA_S3TC_DXT1_EXT; break; }
			case FOURCC_DXT3: { pImage->format = VBF_COMPRESSED_RGBA_S3TC_DXT3_EXT;	break; }
			case FOURCC_DXT5: { pImage->format = VBF_COMPRESSED_RGBA_S3TC_DXT5_EXT;	break; }
			default: 	      { return FALSE; }
		}
	}		
    
	// 杜莹修改：2004-12-29
	// 计算DDS大小
	// 每个级别的大计算公式为：(参见D3D9帮助：DDS File Layout for Textures)
	// nSizeDDSLevel = max(1, width ÷ 4) x max(1, height ÷ 4) x 8(DXT1) or 16(DXT2-5)
	
	int nSizeBlk = (ddsHeader.ddpfPixelFormat.dwFourCC==FOURCC_DXT1) ? 8 : 16;
	int nLevelWidth  = ddsHeader.dwWidth;
	int nLevelHeight = ddsHeader.dwHeight;

    pImage->nNumComponents = (ddsHeader.ddpfPixelFormat.dwFourCC==FOURCC_DXT1)? 3 : 4;
	pImage->nNumMipmaps    = ddsHeader.dwMipMapCount;
	pImage->pLevelWidth    = new int[pImage->nNumMipmaps];
	pImage->pLevelHeight   = new int[pImage->nNumMipmaps];
	pImage->pLevelBytes    = new int[pImage->nNumMipmaps];
	pImage->nBitsBytes     = 0;

	for(DWORD i=0; i<ddsHeader.dwMipMapCount; i++)
	{
	    if(bCompressed)
			pImage->pLevelBytes[i] = max(1,nLevelWidth/4) * max(1,nLevelHeight/4) * nSizeBlk;
		else 
			pImage->pLevelBytes[i] = nLevelWidth * nLevelHeight * ddsHeader.ddpfPixelFormat.dwRGBBitCount/8;  
		
		pImage->nBitsBytes += pImage->pLevelBytes[i];
		pImage->pLevelWidth[i]  = nLevelWidth;
		pImage->pLevelHeight[i] = nLevelHeight;	
		
		nLevelWidth  >>= 1;
		nLevelHeight >>= 1;		
	}	

	pImage->pBits = new BYTE[pImage->nBitsBytes];
	pMemFile->Read( pImage->pBits, pImage->nBitsBytes );       

	pMemFile->Close();
	SAFE_DELETE(pMemFile);

	return TRUE;
}

//---------------------------------------------------------------------------------
// 函数：ReadDDSFile()
// 描述：读取DDS文件
//---------------------------------------------------------------------------------
inline BOOL ReadDDSFile(const CString& strDDSFn, DDSIMAGE* pImage)
{
    // 打开DDS文件，并确认格式
	CFile file;
	if( !file.Open(strDDSFn, CFile::modeRead|CFile::typeBinary, NULL) ) 
		return FALSE;

	int nSizeDDS = file.GetLength();

	BYTE* pDDSBuf = new BYTE[nSizeDDS];
	file.ReadHuge(pDDSBuf, nSizeDDS);
	file.Close();

	if( !::LoadDDSBuf(nSizeDDS, pDDSBuf, pImage) ) 
		return FALSE;

	SAFE_DELETE(pDDSBuf); 
    
	return TRUE;
}

#endif