windows抓屏(截屏)实现方法

         在windows系统中，抓取当前桌面的屏幕有很多方法，比较常用的是GDI和mirror两种方式，除此以外，利用ddraw和dxgi（windows7以上系统支持）方式也可以抓取屏幕。由于mirror的方式牵扯到驱动，并且也不是所有系统都支持，本文不会介绍这种抓屏方式，这里将着重介绍GDI， DDRAW和DXGI这三种抓屏方式，并给出其相应的实现代码。

        GDI抓屏

        这种方式比较通用，所有的windows版本都支持此方式抓屏，而且不依赖其他API，仅仅使用user32中的API即可完成抓屏；但是这种抓屏方式相对比较慢，抓取一帧1080p的桌面需要5~8ms左右的时间。单纯的从抓屏来说，这个时间还是可以接受的，但是抓屏后往往需要进行很多图像处理，所以这个用时就显得不那么友好了。而且在Vista以后的系统上，如果启用Aero特效的话，抓取一帧的用时会增加到300~500ms，基本上属于不可用的级别。

       下面给出实现代码：

HDC               m_hMemDC, m_hRootDC;HBITMAP           m_hBitmapMem;DEVMODE           m_origDevMode;BITMAPINFO        m_bitmapInfo;void             *m_pvBits;int               m_iWidth = 1920,m_iHeight = 1080;BOOL InitBitmapInfo(void){ 	if (m_hRootDC)	{		return FALSE;	}	m_hRootDC = CreateDC(("DISPLAY"), NULL, NULL, NULL);	if (!m_hRootDC)	{		return FALSE;	}	m_hMemDC = CreateCompatibleDC(m_hRootDC);        if (!m_hMemDC)	{               return FALSE;        }        m_hBitmapMem = CreateCompatibleBitmap(m_hRootDC, m_iWidth, m_iHeight);        if (!m_hBitmapMem)	{            return FALSE;        }        return TRUE;}BOOL CreateDIBBuffers(void){	m_bitmapInfo.bmiHeader.biSize     = sizeof(BITMAPINFOHEADER);        m_bitmapInfo.bmiHeader.biBitCount = 0;        if (GetDIBits(m_hMemDC, m_hBitmapMem, 0, 1, NULL, &m_bitmapInfo, DIB_RGB_COLORS) == 0)	{               return FALSE;        }	m_bitmapInfo.bmiHeader.biComPRession = BI_RGB;	m_bitmapInfo.bmiHeader.biHeight      = -abs(m_bitmapInfo.bmiHeader.biHeight);  // 因为抓取的图片是上下颠倒的，所以这里需要将高度颠倒一下        HBITMAP hBitmapTmp = CreateDIBSection(m_hMemDC, &m_bitmapInfo, DIB_RGB_COLORS, &m_pvBits, NULL, 0);        if (!hBitmapTmp)	{               ("Can not use fast blit!/n");	}        if (m_hBitmapMem != NULL)	{              DeleteObject(m_hBitmapMem);              m_hBitmapMem = NULL;        }	m_hBitmapMem = hBitmapTmp;        return TRUE;}void  ByteAlign(RECT &rect){	int nWidth = rect.right - rect.left;	int nHeight = rect.bottom - rect.top;	//	// 对齐4字节边界	// 因为GDI的原因，分辨率必须要是4字节的边界，否则抓出来的图像重新渲染的话，	// 会出现花屏现象，这里处理的目的就是为了保证是4字节的边界。——yshen on 2012-11-25	//	int nMod = nWidth % 4;	if (nMod)	{		rect.left  += (nMod / 2);		rect.right -= (nMod / 2);	}	nMod = nHeight % 4;	if (nMod)	{		rect.top    += (nMod / 2);		rect.bottom -= (nMod / 2);	}}int CaptureScreen(const RECT &rect){       	ByteAlign(rect);	// 检测和启动时的分辨率是否一致，如果不一致，则停止抓屏	INT nWidth  = GetSystemMetrics(SM_CXSCREEN);        INT nHeight = GetSystemMetrics(SM_CYSCREEN);	if ((m_iWidth != nWidth) && (m_iHeight != nHeight))	{		return -1;	}	GdiFlush();	HBITMAP hOldBitmap = (HBITMAP)SelectObject(m_hMemDC, m_hBitmapMem);	if (hOldBitmap)	{		BitBlt(m_hMemDC, rect.left, rect.top, rect.right - rect.left, rect.bottom - rect.top, m_hRootDC, rect.left, rect.top, SRCCOPY | CAPTUREBLT);		SelectObject(m_hMemDC, hOldBitmap);	}	return 0;}BOOL Init(void){	if (!InitBitmapInfo())	{            return FALSE;        }        if (!CreateDIBBuffers())	{            return FALSE;        }    return TRUE;}
调用示例：
  // 初始化抓屏     init();     // 抓取一帧     RECT rect(0, 0, 1920, 1080);    CaptureScreen(rect);
   DDRAW抓屏
    这种方式抓屏速度比GDI要快一些，抓取一帧图像大概需要4~5ms左右，但是缺点也和GDI一样，如果启用了特效，速度也非常慢，基本也在400ms以上。
    实现代码：
LPDIRECTDRAW        m_lpDDraw;LPDIRECTDRAWSURFACE m_lpDDSPrime;LPDIRECTDRAWSURFACE m_lpDDSBack;DDSURFACEDESC       m_DDSdesc;BOOL Init(){	HMODULE hDll = LoadLibrary("ddraw.dll");	if (hDll == NULL)	{		("无法载入ddraw.dll/n");		return FALSE;	}	// 载入ddraw的导入函数	PFN_DirectDrawCreate DirectDrawCreateFunc = (PFN_DirectDrawCreate)GetProcAddress(hDll, "DirectDrawCreate");	if (DirectDrawCreateFunc == NULL)	{		("无法找到访问点：DirectDrawCreate/n");		return FALSE;	}	HRESULT hr = DirectDrawCreateFunc(NULL, &m_lpDDraw, NULL);	if (FAILED(hr))	{		("DirectDrawCreate失败/n");		return FALSE;	}	hr = m_lpDDraw->SetCoOperativeLevel(NULL, DDSCL_NORMAL);	if (FAILED(hr))	{		("SetCooperativeLevel失败/n");		return FALSE; 	}	DDSURFACEDESC DDSdesc;	ZeroMemory(&DDSdesc, sizeof(DDSdesc));	DDSdesc.dwSize         = sizeof(DDSdesc);	DDSdesc.dwFlags        = DDSD_CAPS;	DDSdesc.ddsCaps.dwCaps = DDSCAPS_PRIMARYSURFACE;	hr = m_lpDDraw->CreateSurface(&DDSdesc, &m_lpDDSPrime, NULL);	if (FAILED(hr))	{		("CreateSurface 主表面失败/n");		return FALSE; 	}	ZeroMemory(&DDSdesc, sizeof(DDSdesc));	DDSdesc.dwSize  = sizeof(DDSdesc);	DDSdesc.dwFlags = DDSD_ALL;	hr = m_lpDDSPrime->GetSurfaceDesc(&DDSdesc);	if (FAILED(hr))	{		("GetSurfaceDesc失败/n");		return FALSE;	}	// 备份描述信息	memcpy(&m_DDSdesc, &DDSdesc, sizeof(DDSdesc));	DDSdesc.dwFlags        = DDSD_CAPS | DDSD_HEIGHT |DDSD_WIDTH; 	DDSdesc.ddsCaps.dwCaps = DDSCAPS_OFFSCREENPLAIN;	hr = m_lpDDraw->CreateSurface(&DDSdesc, &m_lpDDSBack, 0);	if (FAILED(hr))	{		("CreateSurface 后备表面失败/n");		return FALSE;	}	return TRUE;}BOOL CaptureImage(RECT &rect, void *pData, INT &nLen){	if (m_lpDDSBack == NULL)	{		("DDraw对象未初始化/n");		return FALSE;	}	HRESULT hr = m_lpDDSBack->BltFast(rect.left, rect.top, m_lpDDSPrime, &rect, DDBLTFAST_NOCOLORKEY | DDBLTFAST_WAIT);	if (FAILED(hr))	{		("BltFast失败/n");		return FALSE;	}	DDSURFACEDESC surfDesc;	ZeroMemory(&surfDesc, sizeof(surfDesc)); 	surfDesc.dwSize = sizeof(surfDesc);	hr = m_lpDDSBack->Lock(&rect, &surfDesc, DDLOCK_READONLY | DDLOCK_WAIT | DDLOCK_SURFACEMEMORYPTR , NULL);	if (FAILED(hr))	{		("Lock失败/n");		return FALSE;	}	// 这里拷贝的是32位数据	memcpy(pBuf, (BYTE*)surfDesc.lpSurface, surfDesc.dwWidth * surfDesc.dwHeight * surfDesc.ddpfPixelFormat.dwRGBBitCount / 8);	 m_lpDDSBack->Unlock(surfDesc.lpSurface);	return TRUE;}
  DXGI抓屏
     这种抓屏方式，速度非常快，通常一帧图像能够在2~3ms内完成，而且即使启用了Aero特效，抓屏效率也一样。尤其在windows10以后的系统上，当桌面没有变化时，你是抓取不到任何图像的，只有在桌面有变化时，你才能抓取到图像。这会带来更高的抓屏效率和更少的系统开销。当然，它也不是完美的，它只能在vista以上的系统上才可以使用，老旧的xp是不支持这种新技术的。
     实现代码：
ID3D11Device           *m_hDevice;ID3D11DeviceContext    *m_hContext;IDXGIOutputDuplication *m_hDeskDupl;DXGI_OUTPUT_DESC        m_dxgiOutDesc;BOOL Init(){	HRESULT hr = S_OK;	// Driver types supported	D3D_DRIVER_TYPE DriverTypes[] =	{		D3D_DRIVER_TYPE_HARDWARE,		D3D_DRIVER_TYPE_WARP,		D3D_DRIVER_TYPE_REFERENCE,	};	UINT NumDriverTypes = ARRAYSIZE(DriverTypes);	// Feature levels supported	D3D_FEATURE_LEVEL FeatureLevels[] =	{		D3D_FEATURE_LEVEL_11_0,		D3D_FEATURE_LEVEL_10_1,		D3D_FEATURE_LEVEL_10_0,		D3D_FEATURE_LEVEL_9_1	};	UINT NumFeatureLevels = ARRAYSIZE(FeatureLevels);	D3D_FEATURE_LEVEL FeatureLevel;	//	// Create D3D device	//	for (UINT DriverTypeIndex = 0; DriverTypeIndex < NumDriverTypes; ++DriverTypeIndex)	{		hr = D3D11CreateDevice(NULL, DriverTypes[DriverTypeIndex], NULL, 0, FeatureLevels, NumFeatureLevels, D3D11_SDK_VERSION, &m_hDevice, &FeatureLevel, &m_hContext);		if (SUCCEEDED(hr))		{			break;		}	}	if (FAILED(hr))	{		return FALSE;	}	//	// Get DXGI device	//	IDXGIDevice *hDxgiDevice = NULL;	hr = m_hDevice->QueryInterface(__uuidof(IDXGIDevice), reinterpret_cast<void**>(&hDxgiDevice));	if (FAILED(hr))	{		return FALSE;	}	//	// Get DXGI adapter	//	IDXGIAdapter *hDxgiAdapter = NULL;	hr = hDxgiDevice->GetParent(__uuidof(IDXGIAdapter), reinterpret_cast<void**>(&hDxgiAdapter));	RESET_OBJECT(hDxgiDevice);	if (FAILED(hr))	{		return FALSE;	}	//	// Get output	//	INT nOutput = 0;	IDXGIOutput *hDxgiOutput = NULL;	hr = hDxgiAdapter->EnumOutputs(nOutput, &hDxgiOutput);	RESET_OBJECT(hDxgiAdapter);	if (FAILED(hr))	{		return FALSE;	}	//	// get output description struct	//	hDxgiOutput->GetDesc(&m_dxgiOutDesc);		//	// QI for Output 1	//	IDXGIOutput1 *hDxgiOutput1 = NULL;	hr = hDxgiOutput->QueryInterface(__uuidof(hDxgiOutput1), reinterpret_cast<void**>(&hDxgiOutput1));	RESET_OBJECT(hDxgiOutput);	if (FAILED(hr))	{		return FALSE;	}	//	// Create desktop duplication	//	hr = hDxgiOutput1->DuplicateOutput(m_hDevice, &m_hDeskDupl);	RESET_OBJECT(hDxgiOutput1);	if (FAILED(hr))	{		return FALSE;	}	return TRUE;}BOOL AttatchToThread(VOID){		HDESK hCurrentDesktop = OpenInputDesktop(0, FALSE, GENERIC_ALL);	if (!hCurrentDesktop)	{		return FALSE;	}	// Attach desktop to this thread	BOOL bDesktopAttached = SetThreadDesktop(hCurrentDesktop);	CloseDesktop(hCurrentDesktop);	hCurrentDesktop = NULL;	return bDesktopAttached;}BOOL VideoDXGICaptor::QueryFrame(void *pImgData, INT &nImgSize){	if (!AttatchToThread())	{		return FALSE;	}	nImgSize = 0;	IDXGIResource *hDesktopResource = NULL;	DXGI_OUTDUPL_FRAME_INFO FrameInfo;	HRESULT hr = m_hDeskDupl->AcquireNextFrame(500, &FrameInfo, &hDesktopResource);	if (FAILED(hr))	{		//		// 在一些win10的系统上,如果桌面没有变化的情况下，		// 这里会发生超时现象，但是这并不是发生了错误，而是系统优化了刷新动作导致的。		// 所以，这里没必要返回FALSE，返回不带任何数据的TRUE即可		//		return TRUE;	}	//	// query next frame staging buffer	//	ID3D11Texture2D *hAcquiredDesktopImage = NULL;	hr = hDesktopResource->QueryInterface(__uuidof(ID3D11Texture2D), reinterpret_cast<void **>(&hAcquiredDesktopImage));	RESET_OBJECT(hDesktopResource);	if (FAILED(hr))	{		return FALSE;	}	//	// copy old description	//	D3D11_TEXTURE2D_DESC frameDescriptor;	hAcquiredDesktopImage->GetDesc(&frameDescriptor);	//	// create a new staging buffer for fill frame image	//	ID3D11Texture2D *hNewDesktopImage = NULL;	frameDescriptor.Usage = D3D11_USAGE_STAGING;	frameDescriptor.CPUaccessFlags = D3D11_CPU_ACCESS_READ;	frameDescriptor.BindFlags = 0;	frameDescriptor.MiscFlags = 0;	frameDescriptor.MipLevels = 1;	frameDescriptor.ArraySize = 1;	frameDescriptor.SampleDesc.Count = 1;	hr = m_hDevice->CreateTexture2D(&frameDescriptor, NULL, &hNewDesktopImage);	if (FAILED(hr))	{		RESET_OBJECT(hAcquiredDesktopImage);		m_hDeskDupl->ReleaseFrame();		return FALSE;	}	//	// copy next staging buffer to new staging buffer	//	m_hContext->CopyResource(hNewDesktopImage, hAcquiredDesktopImage);	RESET_OBJECT(hAcquiredDesktopImage);	m_hDeskDupl->ReleaseFrame();	//	// create staging buffer for map bits	//	IDXGISurface *hStagingSurf = NULL;	hr = hNewDesktopImage->QueryInterface(__uuidof(IDXGISurface), (void **)(&hStagingSurf));	RESET_OBJECT(hNewDesktopImage);	if (FAILED(hr))	{		return FALSE;	}	//	// copy bits to user space	//	DXGI_MAPPED_RECT mappedRect;	hr = hStagingSurf->Map(&mappedRect, DXGI_MAP_READ);	if (SUCCEEDED(hr))	{		nImgSize = GetWidth() * GetHeight() * 3;		PrepareBGR24From32(mappedRect.pBits, (BYTE*)pImgData, m_dxgiOutDesc.DesktopCoordinates);		hStagingSurf->Unmap();	}	RESET_OBJECT(hStagingSurf);	return SUCCEEDED(hr);}DXGI只能使用vs2012以上的IDE才可以编译。