使用“RDP 编码器镜像驱动程序”捕获屏幕

引言

我的代码片段使用“RDP 编码器镜像驱动程序”截取屏幕。使用镜像驱动程序截取屏幕是一种高性能的方法，但依赖于镜像驱动程序。“RDP 编码器镜像驱动程序”包含在 Windows 7 中，使用它截取屏幕无需安装其他镜像驱动程序。 

背景

当我进行驱动 LED 显示屏的工作时，我需要截取屏幕并将位图数据通过 UDP 发送到与计算机通信的硬件。使用 GDI API 截取屏幕很容易，但性能较差。我知道使用镜像驱动程序是个好主意，并开发了自己的镜像驱动程序。当我编写一个测试程序来列出所有显示设备时，我发现了“RDP 编码器镜像驱动程序”。经过测试，“RDP 编码器镜像驱动程序”运行良好。

Using the Code

首先，我们需要检测“RDP 编码器镜像驱动程序”是否存在。如果“RDP 编码器镜像驱动程序”存在，就可以使用它来截取屏幕。

int Detect_MirrorDriver(vector<DISPLAY_DEVICE>& devices,map<int,DEVMODE>& settings)
{
	CString all_mirror_divers[2] = {
					_T("RDP Encoder Mirror Driver"),//included in windows 7
					_T("LEDXXX Mirror Driver")//my own mirror driver, used in Windows XP
									};
	DISPLAY_DEVICE dd;
	ZeroMemory(&dd, sizeof(dd));
	dd.cb = sizeof(dd);
	int n = 0;
	while(EnumDisplayDevices(NULL, n, &dd, EDD_GET_DEVICE_INTERFACE_NAME))
	{
		n++;
		devices.push_back(dd);
	}
	for(int i=0;i<(int)devices.size();i++)
	{
		DEVMODE dm;
		ZeroMemory(&dm, sizeof(DEVMODE));
		dm.dmSize = sizeof(DEVMODE);
		dm.dmDriverExtra = 0;
		if(EnumDisplaySettingsEx(devices[i].DeviceName,ENUM_CURRENT_SETTINGS,&dm,EDS_ROTATEDMODE))
		{
			settings.insert(map<int,DEVMODE>::value_type(i,dm));
		}
	}
	for(int m =0;m<2;m++)
	{
		for(int i=0;i<(int)devices.size();i++)
		{
			CString drv(devices[i].DeviceString);
			if(drv == all_mirror_divers[m])
			{
				return m;
			}
		}
	}
	return -1;//can not use any mirror driver
} 

使用“RDP 编码器镜像驱动程序”截取屏幕非常简单

class RDPCapture
{
	int mw;
	int mh;
	int mx0;
	int my0;
	DEVMODE myDM;
	DISPLAY_DEVICE myDev;
	HDC m_driverDC;
	CDC m_cdc;
	BITMAPINFO	m_BmpInfo;
	HBITMAP	m_Bitmap;
	HBITMAP	Old_bitmap;
	DEVMODE oldDM;
public:
	RDPCapture(){}
	RDPCapture(DISPLAY_DEVICE dev,DEVMODE dm)
	{
		myDev = dev;
		myDM = dm;
		oldDM = dm;
		m_driverDC = NULL;
	}
	~RDPCapture()
	{
		SelectObject(m_cdc,Old_bitmap);
		DeleteObject(m_Bitmap);
		m_cdc.DeleteDC();
		if(m_driverDC != NULL) DeleteDC(m_driverDC);
		oldDM.dmDeviceName[0] = 0;
		ChangeDisplaySettingsEx(myDev.DeviceName,&oldDM, 0, 0, 0);
	}
	virtual bool Init(int x0,int y0,int width,int height)
	{
		mx0 = x0;
		my0 = y0;
		mw = (width + 3)&0xFFFC;
		mh = height;

		DEVMODE dm;
		dm = myDM;
		WORD drvExtraSaved = dm.dmDriverExtra;
		memset(&dm, 0, sizeof(DEVMODE));
		dm.dmSize = sizeof(DEVMODE);
		dm.dmDriverExtra = drvExtraSaved;
		dm.dmPelsWidth = 2048;
		dm.dmPelsHeight = 1280;
		dm.dmBitsPerPel = 24;
		dm.dmPosition.x = 0;
		dm.dmPosition.y = 0;
		dm.dmDeviceName[0] = '\0';
		dm.dmFields = DM_BITSPERPEL | DM_PELSWIDTH |
                      DM_PELSHEIGHT | DM_POSITION;
		if(ChangeDisplaySettingsEx(myDev.DeviceName, &dm, 0, CDS_UPDATEREGISTRY, 0))
		{
			ChangeDisplaySettingsEx(myDev.DeviceName, &dm, 0, 0, 0);
		}
		//------------------------------------------------
		ZeroMemory(&m_BmpInfo, sizeof(BITMAPINFO));
		m_BmpInfo.bmiHeader.biSize = sizeof(BITMAPINFOHEADER);
		m_BmpInfo.bmiHeader.biBitCount = 24;
		m_BmpInfo.bmiHeader.biCompression = BI_RGB;
		m_BmpInfo.bmiHeader.biPlanes = 1;
		m_BmpInfo.bmiHeader.biWidth = mw;
		m_BmpInfo.bmiHeader.biHeight = -mh;
		m_BmpInfo.bmiHeader.biSizeImage= mw*mh*3;	
		HDC Top = ::GetDC(GetDesktopWindow());
		m_cdc.CreateCompatibleDC(NULL);//兼容设备上下文环境
		m_Bitmap = CreateCompatibleBitmap(Top, mw,mh);//Bitmap,画布
		Old_bitmap = (HBITMAP)SelectObject(m_cdc, m_Bitmap);//画布与设备上下文环境关联
		::ReleaseDC(GetDesktopWindow(),Top);
		m_driverDC = CreateDC(myDev.DeviceName, 0, 0, 0);
		return true;
	};
	virtual bool GetData(unsigned char *buf)
	{
		BitBlt(m_cdc,0,0,mw,mh,m_driverDC,mx0,my0,SRCCOPY|CAPTUREBLT);		
		GetDIBits(m_cdc,m_Bitmap,0,mh,buf, &m_BmpInfo, DIB_RGB_COLORS);
		return true;
	};
}; 

要使用类“RDPCapture”，您可以编写如下代码

RDPCapture* rdp_capture = NULL;
vector<DISPLAY_DEVICE> devices;
map<int,DEVMODE>& settings;
int res = Detect_MirrorDriver(devices,settings);
if(res ==0)
{
	rdp_capture = new RDPCapture(devices[0],settings[0]);
}

关注点

当我写这篇文章时，我发现使用镜像驱动程序与 GDI API 结合使用很有趣。

历史

• 2014/1/27 首次版本
• 2014/1/27 移除 RDPCapture 的基类