在windows cpp 动态库 读取 test.mp4 视频流到 Windows窗口的离屏表面,且要求再调用该函数时不卡UI， 在Qt调用该动态库。完整源码

由于涉及到视频流的读取和渲染，需要使用第三方库来完成，以下是使用OpenCV和DirectX实现的示例代码：

1. Windows动态库代码：

#include <Windows.h>
#include <opencv2/opencv.hpp>
#include <d3d9.h>

#pragma comment(lib, "d3d9.lib")

using namespace cv;

extern "C" __declspec(dllexport) void renderVideo(HWND hwnd)
{
    // 初始化DirectX
    LPDIRECT3D9 d3d = Direct3DCreate9(D3D_SDK_VERSION);
    if (!d3d)
        return;

    D3DPRESENT_PARAMETERS d3dpp;
    ZeroMemory(&d3dpp, sizeof(d3dpp));
    d3dpp.Windowed = TRUE;
    d3dpp.SwapEffect = D3DSWAPEFFECT_DISCARD;

    LPDIRECT3DDEVICE9 d3ddev;
    if (FAILED(d3d->CreateDevice(D3DADAPTER_DEFAULT, D3DDEVTYPE_HAL, hwnd,
        D3DCREATE_SOFTWARE_VERTEXPROCESSING, &d3dpp, &d3ddev)))
    {
        d3d->Release();
        return;
    }

    // 打开视频文件
    VideoCapture cap("test.mp4");
    if (!cap.isOpened())
        return;

    Mat frame;
    while (cap.read(frame))
    {
        // 将图像转换为DirectX纹理
        LPDIRECT3DTEXTURE9 texture;
        if (FAILED(D3DXCreateTexture(d3ddev, frame.cols, frame.rows, 1,
            D3DUSAGE_DYNAMIC, D3DFMT_X8R8G8B8, D3DPOOL_DEFAULT, &texture)))
            continue;

        D3DLOCKED_RECT lockedRect;
        if (FAILED(texture->LockRect(0, &lockedRect, NULL, D3DLOCK_DISCARD)))
        {
            texture->Release();
            continue;
        }

        uchar* srcData = frame.data;
        uchar* dstData = (uchar*)lockedRect.pBits;
        int srcStep = frame.step, dstStep = lockedRect.Pitch;
        for (int y = 0; y < frame.rows; y++)
            memcpy(dstData + y * dstStep, srcData + y * srcStep, frame.cols * 3);

        texture->UnlockRect(0);

        // 渲染纹理到表面
        d3ddev->BeginScene();

        d3ddev->Clear(0, NULL, D3DCLEAR_TARGET, D3DCOLOR_XRGB(0, 0, 0), 1.0f, 0);

        RECT rect;
        GetClientRect(hwnd, &rect);

        d3ddev->StretchRect(texture, NULL, NULL, &rect, D3DTEXF_LINEAR);

        d3ddev->EndScene();

        texture->Release();

        // 等待一段时间，避免卡UI
        Sleep(20);
    }

    cap.release();
    d3ddev->Release();
    d3d->Release();
}

2. Qt调用代码：

#include <Windows.h>
#include <QWidget>
#include <QHBoxLayout>
#include <QTimer>

typedef void (*RenderVideoFunc)(HWND);

class VideoPlayer : public QWidget
{
public:
    VideoPlayer(QWidget* parent = nullptr) : QWidget(parent)
    {
        QHBoxLayout* layout = new QHBoxLayout(this);
        layout->setMargin(0);

        // 创建一个用于渲染视频的子窗口
        videoWindow = new QWidget(this);
        videoWindow->setFixedSize(640, 360);
        layout->addWidget(videoWindow);

        // 加载动态库并获取函数指针
        renderVideoFunc = nullptr;
        videoLib = LoadLibraryA("video.dll");
        if (videoLib)
            renderVideoFunc = (RenderVideoFunc)GetProcAddress(videoLib, "renderVideo");

        // 创建定时器，定时调用渲染函数
        QTimer* timer = new QTimer(this);
        connect(timer, &QTimer::timeout, this, &VideoPlayer::renderVideo);
        timer->start(33); // 30fps
    }

    ~VideoPlayer()
    {
        FreeLibrary(videoLib);
    }

private:
    void renderVideo()
    {
        if (renderVideoFunc)
            renderVideoFunc((HWND)videoWindow->winId());
    }

    QWidget* videoWindow;
    RenderVideoFunc renderVideoFunc;
    HMODULE videoLib;
};

使用时只需要创建一个VideoPlayer对象，并将其加入到布局中即可。注意需要将test.mp4放在可执行文件同级目录下。