保存当前屏幕到位图文件CopyScreenToBitmap

//保存屏幕到图像
//用来保存屏幕到图像文件。
void CMainView::SaveScreen() 
{
	CRect rect;
	GetWindowRect(&rect);
	char BASED_CODE szFilter[] = "bmp Files (*.bmp)|*.bmp|";
	CString filename="";
	CString ext = "";
	CFileDialog dlg(false, "bmp",filename, OFN_HIDEREADONLY | OFN_OVERWRITEPROMPT, szFilter);
	HBITMAP hMap =   CopyScreenToBitmap(rect); 
	if(dlg.DoModal() == IDOK)
	{
		filename = dlg.GetPathName();
		SaveBitmapToFile(hMap,filename.GetBuffer(filename.GetLength()+1)); 
	}
}

int CMainView::SaveBitmapToFile(HBITMAP hBitmap, LPSTR lpFileName)
{       //lpFileName 为位图文件名
	HDC      hDC;         
	//设备描述表
	int      iBits;      
	//当前显示分辨率下每个像素所占字节数
	WORD     wBitCount;   
	//位图中每个像素所占字节数
	//定义调色板大小， 位图中像素字节大小 ，   位图文件大小 ， 写入文件字节数
	DWORD            dwPaletteSize=0,dwBmBitsSize,dwDIBSize, dwWritten;
	BITMAP           Bitmap;        
	//位图属性结构
	BITMAPFILEHEADER    bmfHdr;        
	//位图文件头结构
	BITMAPINFOHEADER    bi;            
	//位图信息头结构 
	LPBITMAPINFOHEADER lpbi;          
	//指向位图信息头结构
	HANDLE           fh, hDib, hPal;
	HPALETTE      hOldPal=NULL;
	//定义文件，分配内存句柄，调色板句柄

	//计算位图文件每个像素所占字节数
	hDC = CreateDC("DISPLAY",NULL,NULL,NULL);
	iBits = GetDeviceCaps(hDC, BITSPIXEL) * 
		GetDeviceCaps(hDC, PLANES);
	DeleteDC(hDC);
	if (iBits <= 1)
		wBitCount = 1;
	else if (iBits <= 4)
		wBitCount = 4;
	else if (iBits <= 8)
		wBitCount = 8;
	else if (iBits <= 24)
		wBitCount = 24;
	else
		wBitCount = 32;
	//计算调色板大小
	if (wBitCount <= 8)
		dwPaletteSize=(1<<wBitCount)*sizeof(RGBQUAD);

	//设置位图信息头结构
	GetObject(hBitmap, sizeof(BITMAP), (LPSTR)&Bitmap);
	bi.biSize             = sizeof(BITMAPINFOHEADER);
	bi.biWidth            = Bitmap.bmWidth;
	bi.biHeight           = Bitmap.bmHeight;
	bi.biPlanes           = 1;
	bi.biBitCount          = wBitCount;
	bi.biCompression       = BI_RGB;
	bi.biSizeImage         = 0;
	bi.biXPelsPerMeter      = 0;
	bi.biYPelsPerMeter      = 0;
	bi.biClrUsed          = 0;
	bi.biClrImportant       = 0;

	dwBmBitsSize = ((Bitmap.bmWidth*wBitCount+31)/32)*4*Bitmap.bmHeight;
	//为位图内容分配内存

	hDib   = GlobalAlloc(GHND,dwBmBitsSize+dwPaletteSize+sizeof(BITMAPINFOHEADER));
	lpbi = (LPBITMAPINFOHEADER)GlobalLock(hDib);
	*lpbi = bi;
	// 处理调色板   
	hPal = GetStockObject(DEFAULT_PALETTE);
	if (hPal)
	{
		hDC = ::GetDC(NULL);
		hOldPal=SelectPalette(hDC,(HPALETTE)hPal,FALSE);
		RealizePalette(hDC);
	}
	// 获取该调色板下新的像素值
	GetDIBits(hDC,hBitmap,0,(UINT)Bitmap.bmHeight,(LPSTR)lpbi+sizeof(BITMAPINFOHEADER)+dwPaletteSize, (BITMAPINFO *)lpbi,DIB_RGB_COLORS);
	//恢复调色板   
	if (hOldPal)
	{
		SelectPalette(hDC, hOldPal, TRUE);
		RealizePalette(hDC);
		::ReleaseDC(NULL, hDC);
	}
	//创建位图文件    
	fh=CreateFile(lpFileName, GENERIC_WRITE,0, NULL, CREATE_ALWAYS,FILE_ATTRIBUTE_NORMAL | FILE_FLAG_SEQUENTIAL_SCAN, NULL);
	if (fh==INVALID_HANDLE_VALUE)
		return FALSE;
	// 设置位图文件头
	bmfHdr.bfType = 0x4D42;   // "BM"
	dwDIBSize=sizeof(BITMAPFILEHEADER)+sizeof(BITMAPINFOHEADER)+dwPaletteSize+dwBmBitsSize;  
	bmfHdr.bfSize = dwDIBSize;
	bmfHdr.bfReserved1 = 0;
	bmfHdr.bfReserved2 = 0;
	bmfHdr.bfOffBits = (DWORD)sizeof(BITMAPFILEHEADER)+(DWORD)sizeof(BITMAPINFOHEADER)+dwPaletteSize;
	// 写入位图文件头
	WriteFile(fh, (LPSTR)&bmfHdr, sizeof(BITMAPFILEHEADER), &dwWritten, NULL);
	// 写入位图文件其余内容
	WriteFile(fh, (LPSTR)lpbi, sizeof(BITMAPINFOHEADER)+dwPaletteSize+dwBmBitsSize , &dwWritten, NULL); 
	//清除   
	GlobalUnlock(hDib);
	GlobalFree(hDib);
	CloseHandle(fh);
	return TRUE;
}



HBITMAP CMainView::CopyScreenToBitmap(LPRECT lpRect)
{
	HDC hScrDC, hMemDC;      
	// 屏幕和内存设备描述表
	HBITMAP hBitmap,hOldBitmap;   
	// 位图句柄
	int        nX, nY, nX2, nY2;      
	// 选定区域坐标
	int        nWidth, nHeight;      
	// 位图宽度和高度
	int        xScrn, yScrn;         
	// 屏幕分辨率
	// 确保选定区域不为空矩形
	if (IsRectEmpty(lpRect))
		return NULL;
	//为屏幕创建设备描述表
	hScrDC = CreateDC("DISPLAY", NULL, NULL, NULL);
	//为屏幕设备描述表创建兼容的内存设备描述表
	hMemDC = CreateCompatibleDC(hScrDC);
	// 获得选定区域坐标
	nX = lpRect->left;
	nY = lpRect->top;
	nX2 = lpRect->right;
	nY2 = lpRect->bottom;
	// 获得屏幕分辨率
	xScrn = GetDeviceCaps(hScrDC, HORZRES);
	yScrn = GetDeviceCaps(hScrDC, VERTRES);
	//确保选定区域是可见的
	if (nX < 0)
		nX = 0;
	if (nY < 0)
		nY = 0;
	if (nX2 > xScrn)
		nX2 = xScrn;
	if (nY2 > yScrn)
		nY2 = yScrn;
	nWidth = nX2 - nX;
	nHeight = nY2 - nY;
	// 创建一个与屏幕设备描述表兼容的位图
	hBitmap=CreateCompatibleBitmap(hScrDC,nWidth,nHeight);
	// 把新位图选到内存设备描述表中
	hOldBitmap=(HBITMAP)SelectObject(hMemDC,hBitmap);
	// 把屏幕设备描述表拷贝到内存设备描述表中
	BitBlt(hMemDC,0,0, nWidth,nHeight,hScrDC, nX, nY, SRCCOPY);
	//得到屏幕位图的句柄
	hBitmap=(HBITMAP)SelectObject(hMemDC,hOldBitmap);
	//清除 
	DeleteDC(hScrDC);
	DeleteDC(hMemDC);
	// 返回位图句柄
	return hBitmap;
}