C++截图并保存为文件

调用WindowsApi，使用Com组件，我也是借鉴加修改的，因为网上直接复制下来的并不能直接调用（HBITMAP这种东西就比较奇怪），以后当成工具调用就可以了，写了部分注释，就不一句句讲解了。

        GetThumbImage（）是用来调用截图的ScreenCapture类的，可以指定保存的文件名，截图的范围。

TBitmap* __fastcall TForm3::GetThumbImage()
{
	TImage *img = NULL;
	TBitmap *bitmap = new TBitmap();
	HBITMAP hBitmap = NULL;
	LPSTR addr = "ScreenCapture.png";
	hBitmap = ScreenCapture(addr, 32, NULL);
	::GetObject(hBitmap, sizeof(bitmap), (LPSTR)&bitmap);
    bitmap->LoadFromFile(addr);
	return bitmap;
}

HBITMAP TForm3::ScreenCapture(LPSTR filename ,WORD BitCount,LPRECT lpRect)
{
	HBITMAP hBitmap;
	// 显示器屏幕DC
	HDC hScreenDC = CreateDC(L"DISPLAY", NULL, NULL, NULL);
	HDC hmemDC = CreateCompatibleDC(hScreenDC);
	// 显示器屏幕的宽和高
	int ScreenWidth = GetDeviceCaps(hScreenDC, HORZRES);
	int ScreenHeight = GetDeviceCaps(hScreenDC, VERTRES);
	// 旧的BITMAP，用于与所需截取的位置交换
	HBITMAP hOldBM;
	// 保存位图数据
	PVOID lpvpxldata;
	// 截屏获取的长宽及起点
	INT ixStart;
	INT iyStart;
	INT iX;
	INT iY;
	// 位图数据大小
	DWORD dwBitmapArraySize;
	// 几个大小
	DWORD nBitsOffset;
	DWORD lImageSize ;
	DWORD lFileSize ;
	// 位图信息头
	BITMAPINFO bmInfo;
	// 位图文件头
	BITMAPFILEHEADER bmFileHeader;
	// 写文件用
	HANDLE hbmfile;
	DWORD dwWritten;

	// 如果LPRECT 为NULL 截取整个屏幕
	if(lpRect == NULL)
	{
		ixStart = iyStart = 0;
		iX = ScreenWidth;
		iY =ScreenHeight;
	}
	else
	{
		ixStart = lpRect->left;
		iyStart = lpRect->top;
		iX = lpRect->right - lpRect->left;
		iY = lpRect->bottom - lpRect->top;
	}
	// 创建BTIMAP
	hBitmap = CreateCompatibleBitmap(hScreenDC, iX, iY);
	// 将BITMAP选择入内存DC。
	hOldBM = (HBITMAP)SelectObject(hmemDC, hBitmap);
	// BitBlt屏幕DC到内存DC，根据所需截取的获取设置参数
	BitBlt(hmemDC, 0, 0, iX, iY, hScreenDC, ixStart, iyStart, SRCCOPY);
	// 将旧的BITMAP对象选择回内存DC，返回值为被替换的对象，既所截取的位图
	hBitmap = (HBITMAP)SelectObject(hmemDC, hOldBM);
	if(filename == NULL)
	{
		DeleteDC( hScreenDC);
		DeleteDC(hmemDC);
		return hBitmap;
	}
	// 为位图数据申请内存空间
	dwBitmapArraySize = ((((iX*32) + 31) & ~31)>> 3)* iY;
	lpvpxldata = HeapAlloc(GetProcessHeap(),HEAP_NO_SERIALIZE,dwBitmapArraySize);
	ZeroMemory(lpvpxldata,dwBitmapArraySize);

	// 添充 BITMAPINFO 结构
	ZeroMemory(&bmInfo,sizeof(BITMAPINFO));
	bmInfo.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
	bmInfo.bmiHeader.biWidth = iX;
	bmInfo.bmiHeader.biHeight = iY;
	bmInfo.bmiHeader.biPlanes = 1;
	bmInfo.bmiHeader.biBitCount = BitCount;
	bmInfo.bmiHeader.biCompression = BI_RGB;

	// 添充 BITMAPFILEHEADER 结构
	ZeroMemory(&bmFileHeader,sizeof(BITMAPFILEHEADER));
	nBitsOffset = sizeof(BITMAPFILEHEADER) + bmInfo.bmiHeader.biSize;
	lImageSize =
		((((bmInfo.bmiHeader.biWidth * bmInfo.bmiHeader.biBitCount) + 31) & ~31)>> 3)
		* bmInfo.bmiHeader.biHeight;
	lFileSize = nBitsOffset + lImageSize;
	bmFileHeader.bfType = "B"+("M"<<8);
	bmFileHeader.bfSize = lFileSize;
	bmFileHeader.bfOffBits = nBitsOffset;

	// 获取DIB用于写入到文件
	GetDIBits(hmemDC, hBitmap, 0, bmInfo.bmiHeader.biHeight,
		lpvpxldata, &bmInfo, DIB_RGB_COLORS);
	// 写文件
	hbmfile = CreateFileA(filename,
		GENERIC_WRITE,
		FILE_SHARE_WRITE,
		NULL,
		CREATE_ALWAYS,
		FILE_ATTRIBUTE_NORMAL,
		NULL);

	if(hbmfile == INVALID_HANDLE_VALUE)
	{
		MessageBoxA(NULL,"create file error","error",MB_OK);
	}

	WriteFile(hbmfile,&bmFileHeader,sizeof(BITMAPFILEHEADER),&dwWritten,NULL);
	WriteFile(hbmfile,&bmInfo,sizeof(BITMAPINFO),&dwWritten,NULL);
	WriteFile(hbmfile,lpvpxldata,lImageSize,&dwWritten,NULL);
	CloseHandle(hbmfile);
//	MessageBox(NULL,"文件写入成功","error",MB_OK);

	// 释放内存，清除不同的DC。
	// 这里没有删除BITMAP对象，需在显示完成后删除
	HeapFree(GetProcessHeap(),HEAP_NO_SERIALIZE,lpvpxldata);
	ReleaseDC(0, hScreenDC);
	DeleteDC(hmemDC);
	return hBitmap;
}