集采集，编码，组播，推流和流媒体RTSP服务于一身大屏展示投屏互联网直播同屏组件EasyScreenlive播放器使用DXGI采集桌面方法介绍

应用背景

投屏和显示技术的升级，使视频远程控制的功能日益更新，EasyScreenlive广泛应用于大屏显示投屏，无纸化会议同屏演示，课堂同屏等，可以配合全屏显示，反向模拟触控实现远程控制功能（Android控制Windows，Windows控制Android，Windows控制Windows等）

EasyScreenlive支持DXGI采集桌面

之前文章中我们已经提到了通过GDI和D3D来采集windows桌面，通过D3D采集效率已经提高了不少，那么有没有更加高效的方法呢？答案是有的，那就是我们现在要讲的DXGI桌面采集技术。

该技术是基于DirectX技术，所以你需要简单熟悉DirectX技术才能使用DXGI,他通过一系列DX设备的创建和查询各种接口,最终获取到 IDXGIOutputDuplication 接口。

截屏的时候,使用这个接口的AcquireNextFrame 函数获取当前桌面图像, 当然这个接口还提供 GetFrameDirtyRects等函数获取发生了变化的矩形区域。 这应该算是一个比较好的截屏方法,CPU占用也极低,可惜只支持windows 8 以上的平台,而win7,windows xp等系统不支持。

下面我们通过代码简单讲解下采集实现流程，首先，通过DXGI接口获取桌面设备：

    // Get desktop
    DUPL_RETURN Ret;
    HDESK CurrentDesktop = nullptr;
    CurrentDesktop = OpenInputDesktop(0, FALSE, GENERIC_ALL);
    if (!CurrentDesktop)
    {
        // We do not have access to the desktop so request a retry
        SetEvent(TData->ExpectedErrorEvent);
        Ret = DUPL_RETURN_ERROR_EXPECTED;
        goto Exit;
    }

    // Attach desktop to this thread
    bool DesktopAttached = SetThreadDesktop(CurrentDesktop) != 0;
    CloseDesktop(CurrentDesktop);
    CurrentDesktop = nullptr;
    if (!DesktopAttached)
    {
        // We do not have access to the desktop so request a retry
        Ret = DUPL_RETURN_ERROR_EXPECTED;
        goto Exit;
    }
}
    // New display manager
    DispMgr.InitD3D(&TData->DxRes);

    // Obtain handle to sync shared Surface
    HRESULT hr = TData->DxRes.Device->OpenSharedResource(TData->TexSharedHandle, __uuidof(ID3D11Texture2D), reinterpret_cast<void**>(&SharedSurf));
    if (FAILED (hr))
    {
        Ret = ProcessFailure(TData->DxRes.Device, L"Opening shared texture failed", L"Error", hr, SystemTransitionsExpectedErrors);
        goto Exit;
    }

    hr = SharedSurf->QueryInterface(__uuidof(IDXGIKeyedMutex), reinterpret_cast<void**>(&KeyMutex));
    if (FAILED(hr))
    {
        Ret = ProcessFailure(nullptr, L"Failed to get keyed mutex interface in spawned thread", L"Error", hr);
        goto Exit;
    }

    // Make duplication manager
    Ret = DuplMgr.InitDupl(TData->DxRes.Device, TData->Output);
    if (Ret != DUPL_RETURN_SUCCESS)
    {
        goto Exit;
    }

    // Get output description
    DXGI_OUTPUT_DESC DesktopDesc;
    RtlZeroMemory(&DesktopDesc, sizeof(DXGI_OUTPUT_DESC));
    DuplMgr.GetOutputDesc(&DesktopDesc);

然后，通过大循环GetFrame采集桌面图像数据源，实现代码如下：

    while ((WaitForSingleObjectEx(TData->TerminateThreadsEvent, 0, FALSE) == WAIT_TIMEOUT))
    {
        if (!WaitToProcessCurrentFrame)
        {
            // Get new frame from desktop duplication
            bool TimeOut;
            Ret = DuplMgr.GetFrame(&CurrentData, &TimeOut);
            if (Ret != DUPL_RETURN_SUCCESS)
            {
                // An error occurred getting the next frame drop out of loop which
                // will check if it was expected or not
                break;
            }

            // Check for timeout
            if (TimeOut)
            {
                // No new frame at the moment
                continue;
            }
        }

        // We have a new frame so try and process it
        // Try to acquire keyed mutex in order to access shared surface
        hr = KeyMutex->AcquireSync(0, 1000);
        if (hr == static_cast<HRESULT>(WAIT_TIMEOUT))
        {
            // Can't use shared surface right now, try again later
            WaitToProcessCurrentFrame = true;
            continue;
        }
        else if (FAILED(hr))
        {
            // Generic unknown failure
            Ret = ProcessFailure(TData->DxRes.Device, L"Unexpected error acquiring KeyMutex", L"Error", hr, SystemTransitionsExpectedErrors);
            DuplMgr.DoneWithFrame();
            break;
        }

        // We can now process the current frame
        WaitToProcessCurrentFrame = false;

        // Get mouse info
        Ret = DuplMgr.GetMouse(TData->PtrInfo, &(CurrentData.FrameInfo), TData->OffsetX, TData->OffsetY);
        if (Ret != DUPL_RETURN_SUCCESS)
        {
            DuplMgr.DoneWithFrame();
            KeyMutex->ReleaseSync(1);
            break;
        }

        // Process new frame
        Ret = DispMgr.ProcessFrame(&CurrentData, SharedSurf, TData->OffsetX, TData->OffsetY, &DesktopDesc);
        if (Ret != DUPL_RETURN_SUCCESS)
        {
            DuplMgr.DoneWithFrame();
            KeyMutex->ReleaseSync(1);
            break;
        }

        // Release acquired keyed mutex
        hr = KeyMutex->ReleaseSync(1);
        if (FAILED(hr))
        {
            Ret = ProcessFailure(TData->DxRes.Device, L"Unexpected error releasing the keyed mutex", L"Error", hr, SystemTransitionsExpectedErrors);
            DuplMgr.DoneWithFrame();
            break;
        }

        // Release frame back to desktop duplication
        Ret = DuplMgr.DoneWithFrame();
        if (Ret != DUPL_RETURN_SUCCESS)
        {
            break;
        }
  }