生成QT 打开摄像头的代码

以下是使用QT打开摄像头的代码示例：

#include <QtGui/QApplication>
#include <QtGui/QMainWindow>
#include <QtGui/QLabel>
#include <QtGui/QPixmap>
#include <QtGui/QVBoxLayout>
#include <QtGui/QPushButton>
#include <QtCore/QTimer>
#include <QtCore/QThread>
#include <opencv2/opencv.hpp>

class Camera : public QThread
{
    Q_OBJECT

public:
    Camera(QObject *parent = 0)
        : QThread(parent)
    {
    }

    void run()
    {
        cv::VideoCapture cap(0);
        if (!cap.isOpened())
        {
            emit error("Failed to open camera.");
            return;
        }

        while (true)
        {
            cap >> frame;
            if (frame.empty())
                continue;
            cv::cvtColor(frame, frame, cv::COLOR_BGR2RGB);
            emit newFrame(frame);
            msleep(33);
        }
    }

signals:
    void newFrame(cv::Mat frame);
    void error(QString err);

private:
    cv::Mat frame;
};

class MainWindow : public QMainWindow
{
    Q_OBJECT

public:
    MainWindow(QWidget *parent = 0)
        : QMainWindow(parent)
    {
        QLabel *label = new QLabel(this);
        label->setFixedSize(640, 480);
        QVBoxLayout *layout = new QVBoxLayout;
        layout->addWidget(label);
        QPushButton *button = new QPushButton("Start", this);
        connect(button, SIGNAL(clicked()), this, SLOT(onButtonClicked()));
        layout->addWidget(button);
        QWidget *widget = new QWidget(this);
        widget->setLayout(layout);
        setCentralWidget(widget);
        camera = new Camera(this);
        connect(camera, SIGNAL(newFrame(cv::Mat)), this, SLOT(onNewFrame(cv::Mat)));
        connect(camera, SIGNAL(error(QString)), this, SLOT(onError(QString)));
    }

private slots:
    void onButtonClicked()
    {
        camera->start();
    }

    void onNewFrame(cv::Mat frame)
    {
        QImage image(frame.data, frame.cols, frame.rows, QImage::Format_RGB888);
        QLabel *label = qobject_cast<QLabel *>(centralWidget()->layout()->itemAt(0)->widget());
        label->setPixmap(QPixmap::fromImage(image));
    }

    void onError(QString err)
    {
        QMessageBox::critical(this, "Error", err);
    }

private:
    Camera *camera;
};

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    return a.exec();
}

#include "main.moc"

该代码使用OpenCV库来捕获摄像头数据，并使用QT来显示图像。代码创建了一个`Camera`类，该类继承自`QThread`，以便在单独的线程中运行摄像头捕获循环。该类发出`newFrame`信号，该信号将帧传递给主窗口以显示图像。主窗口显示一个标签，用于显示图像，以及一个按钮，用于启动摄像头。按钮单击将启动`Camera`类的线程。