VC下将位图存为BMP文件(Save CBitmap to file)

从The Code Project上找到的代码,也不容易的

代码声明:

/**************************************************
 * CBitmap To File Function
 * 参数:
 * pWnd - 窗体指针
 * cb - 所要存储的CBitmap对象
 * name - 所要存储的文件名
 **************************************************/
BOOL WriteBMPtoFile( CWnd* pWnd, CBitmap& cb,CString name );

//另外两个函数(不需要自己调用)
HANDLE DDBToDIB( CBitmap& bitmap, DWORD dwCompression, CPalette* pPal );
BOOL WriteDIB( LPTSTR szFile, HANDLE hDIB );

具体代码:

/************************************************************************/
// CBitmap转换为.bmp图片函数
/************************************************************************/
BOOL CMyFun::WriteBMPtoFile(CWnd* pWnd, CBitmap& cb,CString name)
{
	// Create logical palette if device support a palette
	CWindowDC* mpScreenDC = new CWindowDC(pWnd);
	CDC dc;
	dc.CreateCompatibleDC(mpScreenDC);
	CPalette pal;
	if( dc.GetDeviceCaps(RASTERCAPS) & RC_PALETTE )
	{
		UINT nSize = sizeof(LOGPALETTE) + (sizeof(PALETTEENTRY) * 256);
		LOGPALETTE *pLP = (LOGPALETTE *) new BYTE[nSize];
		pLP->palVersion = 0x300;

		pLP->palNumEntries =
			GetSystemPaletteEntries(dc , 0, 255, pLP->palPalEntry );

		// Create the palette
		pal.CreatePalette( pLP );

		delete[] pLP;
	}

	// Convert the bitmap to a DIB
	HANDLE hDIB = DDBToDIB(cb, BI_RGB, &pal );

	if( hDIB == NULL )
		return FALSE;

	// Write it to file
	WriteDIB(name.GetBuffer(1), hDIB ); //(LPCTSTR)CString

	// Free the memory allocated by DDBToDIB for the DIB
	GlobalFree( hDIB );
	dc.DeleteDC();
	return TRUE;
}
HANDLE CMyFun::DDBToDIB( CBitmap& bitmap, DWORD dwCompression, CPalette* pPal )
{
	BITMAP			bm;
	BITMAPINFOHEADER	bi;
	LPBITMAPINFOHEADER 	lpbi;
	DWORD			dwLen;
	HANDLE			hDIB;
	HANDLE			handle;
	HDC 			hDC;
	HPALETTE		hPal;


	ASSERT( bitmap.GetSafeHandle() );

	// The function has no arg for bitfields
	if( dwCompression == BI_BITFIELDS )
		return NULL;

	// If a palette has not been supplied use defaul palette
	hPal = (HPALETTE) pPal->GetSafeHandle();
	if (hPal==NULL)
		hPal = (HPALETTE) GetStockObject(DEFAULT_PALETTE);

	// Get bitmap information
	bitmap.GetObject(sizeof(bm),(LPSTR)&bm);

	// Initialize the bitmapinfoheader
	bi.biSize		= sizeof(BITMAPINFOHEADER);
	bi.biWidth		= bm.bmWidth;
	bi.biHeight 		= bm.bmHeight;
	bi.biPlanes 		= 1;
	bi.biBitCount		= bm.bmPlanes * bm.bmBitsPixel;
	bi.biCompression	= dwCompression;
	bi.biSizeImage		= 0;
	bi.biXPelsPerMeter	= 0;
	bi.biYPelsPerMeter	= 0;
	bi.biClrUsed		= 0;
	bi.biClrImportant	= 0;

	// Compute the size of the  infoheader and the color table
	int nColors = (1 << bi.biBitCount);
	if( nColors > 256 )
		nColors = 0;
	dwLen  = bi.biSize + nColors * sizeof(RGBQUAD);

	// We need a device context to get the DIB from
	hDC = ::GetDC(NULL);
	hPal = SelectPalette(hDC,hPal,FALSE);
	RealizePalette(hDC);

	// Allocate enough memory to hold bitmapinfoheader and color table
	hDIB = GlobalAlloc(GMEM_FIXED,dwLen);

	if (!hDIB){
		SelectPalette(hDC,hPal,FALSE);
		::ReleaseDC(NULL,hDC);
		return NULL;
	}

	lpbi = (LPBITMAPINFOHEADER)hDIB;

	*lpbi = bi;

	// Call GetDIBits with a NULL lpBits param, so the device driver 
	// will calculate the biSizeImage field 
	GetDIBits(hDC, (HBITMAP)bitmap.GetSafeHandle(), 0L, (DWORD)bi.biHeight,
			(LPBYTE)NULL, (LPBITMAPINFO)lpbi, (DWORD)DIB_RGB_COLORS);

	bi = *lpbi;

	// If the driver did not fill in the biSizeImage field, then compute it
	// Each scan line of the image is aligned on a DWORD (32bit) boundary
	if (bi.biSizeImage == 0){
		bi.biSizeImage = ((((bi.biWidth * bi.biBitCount) + 31) & ~31) / 8)
						* bi.biHeight;

		// If a compression scheme is used the result may infact be larger
		// Increase the size to account for this.
		if (dwCompression != BI_RGB)
			bi.biSizeImage = (bi.biSizeImage * 3) / 2;
	}

	// Realloc the buffer so that it can hold all the bits
	dwLen += bi.biSizeImage;
	if (handle = GlobalReAlloc(hDIB, dwLen, GMEM_MOVEABLE))
		hDIB = handle;
	else{
		GlobalFree(hDIB);

		// Reselect the original palette
		SelectPalette(hDC,hPal,FALSE);
		::ReleaseDC(NULL,hDC);
		return NULL;
	}

	// Get the bitmap bits
	lpbi = (LPBITMAPINFOHEADER)hDIB;

	// FINALLY get the DIB
	BOOL bGotBits = GetDIBits( hDC, (HBITMAP)bitmap.GetSafeHandle(),
				0L,				// Start scan line
				(DWORD)bi.biHeight,		// # of scan lines
				(LPBYTE)lpbi 			// address for bitmap bits
				+ (bi.biSize + nColors * sizeof(RGBQUAD)),
				(LPBITMAPINFO)lpbi,		// address of bitmapinfo
				(DWORD)DIB_RGB_COLORS);		// Use RGB for color table

	if( !bGotBits )
	{
		GlobalFree(hDIB);

		SelectPalette(hDC,hPal,FALSE);
		::ReleaseDC(NULL,hDC);
		return NULL;
	}

	SelectPalette(hDC,hPal,FALSE);
	::ReleaseDC(NULL,hDC);
	return hDIB;
}

BOOL CMyFun::WriteDIB( LPTSTR szFile, HANDLE hDIB)
{
	BITMAPFILEHEADER	hdr;
	LPBITMAPINFOHEADER	lpbi;

	if (!hDIB)
		return FALSE;

	CFile file;
	if( !file.Open( szFile, CFile::modeWrite|CFile::modeCreate) )
		return FALSE;

	lpbi = (LPBITMAPINFOHEADER)hDIB;

	int nColors = 1 << lpbi->biBitCount;

	// Fill in the fields of the file header 
	hdr.bfType		= ((WORD) ('M' << 8) | 'B');	// is always "BM"
	hdr.bfSize		= GlobalSize (hDIB) + sizeof( hdr );
	hdr.bfReserved1 	= 0;
	hdr.bfReserved2 	= 0;
	hdr.bfOffBits	= (DWORD) (sizeof( hdr ) + lpbi->biSize + nColors * sizeof(RGBQUAD));

	// Write the file header 
	file.Write( &hdr, sizeof(hdr) );

	// Write the DIB header and the bits 
	file.Write( lpbi, GlobalSize(hDIB) );

	return TRUE;
}

调用演示:

CFileDialog fileDialog(
	FALSE,".bmp","MyCatchBmp",OFN_HIDEREADONLY|OFN_OVERWRITEPROMPT,
	"图片文件 (*.bmp)|*.bmp||",this
	);

if(fileDialog.DoModal() == IDOK)
{
	if(m_pBitmap != NULL)
	{
		//存文件
		m_MyFun.WriteBMPtoFile(this,*m_pBitmap,
			fileDialog.GetPathName());
	}
}

其他问题:
在同样的显示效果下,用这种生成的BMP文件比普通生成的BMP文件要大…..(不知为何…文件头比较大?)
如想生成较小的文件,可以使用CxImage开源的类库,还可以转换为其他格式的图形文件

详见:使用CxImage进行图形和格式转换(CBitmap to jpg or png or gif or bmp)