MFC 调用UVC相机

要在MFC应用程序中调用UVC相机，需要使用UVC库提供的API。以下是一个简单的MFC应用程序示例，演示如何使用UVC库访问USB摄像头：

#include "stdafx.h"
#include <dshow.h>
#include <strmif.h>
#include <opencv2/opencv.hpp>

#pragma comment(lib, "strmiids.lib")

void CMyAppDlg::OnBnClickedButtonStart()
{
    HRESULT hr;
    ICreateDevEnum *pDevEnum = NULL;
    IEnumMoniker *pEnum = NULL;
    IMoniker *pMoniker = NULL;
    IBaseFilter *pSrc = NULL;
    ICaptureGraphBuilder2 *pBuild = NULL;
    IGraphBuilder *pGraph = NULL;
    IMediaControl *pControl = NULL;
    IMediaEvent *pEvent = NULL;
    IVideoWindow *pVW = NULL;
    IVMRWindowlessControl *pWC = NULL;

    cv::Mat frame;
    cv::VideoCapture cap;

    // Initialize COM
    hr = CoInitializeEx(NULL, COINIT_APARTMENTTHREADED);
    if (FAILED(hr)) return;

    // Create the system device enumerator
    hr = CoCreateInstance(CLSID_SystemDeviceEnum, NULL, CLSCTX_INPROC_SERVER,
        IID_ICreateDevEnum, (void**)&pDevEnum);
    if (FAILED(hr)) goto done;

    // Create an enumerator for the video capture devices
    hr = pDevEnum->CreateClassEnumerator(CLSID_VideoInputDeviceCategory, &pEnum, 0);
    if (hr == S_OK)
    {
        // Use the first video capture device on the device list
        hr = pEnum->Next(1, &pMoniker, NULL);
        if (hr == S_OK)
        {
            // Bind the selected video capture device to a filter object
            hr = pMoniker->BindToObject(NULL, NULL, IID_IBaseFilter, (void**)&pSrc);
            if (FAILED(hr)) goto done;

            // Create the capture graph builder
            hr = CoCreateInstance(CLSID_CaptureGraphBuilder2, NULL, CLSCTX_INPROC_SERVER,
                IID_ICaptureGraphBuilder2, (void**)&pBuild);
            if (FAILED(hr)) goto done;

            // Create the filter graph manager
            hr = CoCreateInstance(CLSID_FilterGraph, NULL, CLSCTX_INPROC_SERVER,
                IID_IGraphBuilder, (void**)&pGraph);
            if (FAILED(hr)) goto done;

            // Attach the filter graph manager to the capture graph builder
            hr = pBuild->SetFiltergraph(pGraph);
            if (FAILED(hr)) goto done;

            // Add the video capture device filter to the filter graph manager
            hr = pGraph->AddFilter(pSrc, L"Video Capture");
            if (FAILED(hr)) goto done;

            // Render the video stream from the video capture device filter
            hr = pBuild->RenderStream(&PIN_CATEGORY_PREVIEW, &MEDIATYPE_Video,
                pSrc, NULL, NULL);
            if (FAILED(hr)) goto done;

            // Get the media control interface from the filter graph manager
            hr = pGraph->QueryInterface(IID_IMediaControl, (void**)&pControl);
            if (FAILED(hr)) goto done;

            // Get the media event interface from the filter graph manager
            hr = pGraph->QueryInterface(IID_IMediaEvent, (void**)&pEvent);
            if (FAILED(hr)) goto done;

            // Get the video window interface from the filter graph manager
            hr = pGraph->QueryInterface(IID_IVideoWindow, (void**)&pVW);
            if (FAILED(hr)) goto done;

            // Get the VMR windowless control interface from the filter graph manager
            hr = pGraph->QueryInterface(IID_IVMRWindowlessControl, (void**)&pWC);
            if (FAILED(hr)) goto done;

            // Set the video window style and position
            pVW->put_WindowStyle(WS_CHILD | WS_CLIPCHILDREN);
            pVW->put_Owner((OAHWND)m_hWnd);
            pVW->put_MessageDrain((OAHWND)m_hWnd);
            pVW->SetWindowPosition(0, 0, 640, 480);

            // Set the VMR windowless control aspect ratio mode to letterbox
            pWC->SetAspectRatioMode(VMR_ARMODE_LETTER_BOX);
            pWC->SetVideoPosition(NULL, &RECT{ 0, 0, 640, 480 });

            // Start the capture graph
            hr = pControl->Run();
            if (FAILED(hr)) goto done;

            // Start OpenCV video capture
            cap.open(0);
            if (!cap.isOpened()) goto done;

            // Main loop
            for (;;)
            {
                // Get the next video frame from the capture device
                hr = pEvent->WaitForCompletion(INFINITE, NULL);
                if (hr != S_OK) break;

                // Retrieve the video frame from the capture device
                cap >> frame;

                // Display the video frame in the video window
                cv::imshow("Video", frame);
                cv::waitKey(1);

                // Release the video frame
                frame.release();
            }
        }
    }

done:
    // Cleanup
    if (pSrc) pSrc->Release();
    if (pBuild) pBuild->Release();
    if (pGraph) pGraph->Release();
    if (pControl) pControl->Release();
    if (pEvent) pEvent->Release();
    if (pVW) pVW->Release();
    if (pWC) pWC->Release();
    if (pMoniker) pMoniker->Release();
    if (pEnum) pEnum->Release();
    if (pDevEnum) pDevEnum->Release();
    CoUninitialize();
}

在这个示例中，我们使用了DirectShow API来访问UVC相机，并使用OpenCV来显示视频流。具体来说，我们首先使用ICreateDevEnum接口枚举可用的视频捕获设备，然后使用IMoniker接口获取所选设备的过滤器对象。接下来，我们使用ICaptureGraphBuilder2接口创建捕获图形生成器，使用IGraphBuilder接口创建过滤器图形管理器，并将其附加到捕获图形生成器上。我们将视频捕获设备过滤器添加到过滤器图形管理器中，并使用pBuild->RenderStream方法将视频流从过滤器输出端呈现到过滤器输入端。最后，我们使用IMediaControl接口启动过滤器图形管理器，使用OpenCV的cv::VideoCapture类获取视频帧，并使用cv::imshow方法显示视频帧。