Qt中通过QLabel实时显示图像

Qt中的QLabel控件用于显示文本或图像，不提供用户交互功能。以下测试代码用于从内置摄像头获取图像并实时显示：

Widgets_Test.h：

class Widgets_Test : public QMainWindow
{Q_OBJECTpublic:Widgets_Test(QWidget *parent = nullptr);~Widgets_Test();private slots:void start_capture();void close_caputre();void update_frame(const QImage& image);private:void capture();Ui::Widgets_TestClass ui_;std::thread capture_thread_{};std::atomic<bool> is_running_{ false };
};

Widgets_Test.cpp:

Widgets_Test::Widgets_Test(QWidget *parent): QMainWindow(parent)
{ui_.setupUi(this);connect(ui_.button_close, &QPushButton::clicked, this, &Widgets_Test::close);connect(ui_.open_camera, &QPushButton::clicked, this, &Widgets_Test::start_capture);connect(ui_.close_camera, &QPushButton::clicked, this, & Widgets_Test::close_caputre);connect(ui_.open_camera, &QPushButton::clicked, this, [this] {ui_.button_close->setEnabled(false);});connect(ui_.close_camera, &QPushButton::clicked, this, [this] {ui_.button_close->setEnabled(true);});
}Widgets_Test::~Widgets_Test()
{}void Widgets_Test::start_capture()
{is_running_.store(true);capture_thread_ = std::thread([this] {this->capture();});
}void Widgets_Test::capture()
{cv::VideoCapture cap(0);if (!cap.isOpened()) {qWarning("failed to open camera"); // QMetaObject::invokeMethod, UI操作必须在主线程中执行emit ui_.close_camera->clicked();return;}auto w1 = static_cast<int>(cap.get(cv::CAP_PROP_FRAME_WIDTH));auto h1 = static_cast<int>(cap.get(cv::CAP_PROP_FRAME_HEIGHT));auto w2 = ui_.label_show->width();auto h2 = ui_.label_show->height();qDebug() << w1 << "," << h1 << "," << w2 << "," << h2;cv::Mat frame{}, rgb{};QImage image{}, img_copy{};while (is_running_.load()) {cap >> frame;if (frame.empty())continue;cv::cvtColor(frame, rgb, cv::COLOR_BGR2RGB);cv::resize(rgb, rgb, cv::Size(w2, h2));image = QImage(rgb.data, rgb.cols, rgb.rows, rgb.step, QImage::Format_RGB888);img_copy = image.copy();QMetaObject::invokeMethod(this, "update_frame", Qt::QueuedConnection, Q_ARG(QImage, img_copy));std::this_thread::sleep_for(std::chrono::milliseconds(10));}
}void Widgets_Test::update_frame(const QImage& image)
{ui_.label_show->setPixmap(QPixmap::fromImage(image));
}void Widgets_Test::close_caputre()
{is_running_.store(false);if (capture_thread_.joinable())capture_thread_.join();
}

说明：

1. 在子线程中获取摄像头每帧数据：

(1).因为QLabel中接收数据的类型为QImage，这里需要将cv::Mat转换为QImage。

(2).通过QMetaObject::invokeMethod函数调用对象上的信号或槽函数，支持跨线程调用。这里使用此函数将子线程获取到的图像数据传给主线程上的QLabel控件。使用Qt::QueuedConnection，跨线程异步调用。

2.UI操作必须在主线程中执行：

(1).主线程中通过QLabel的setPixmap函数显示图像。

3.点击"open camera"，开始打开摄像头采集显示图像；点击"close camera"，关闭摄像头。

执行结果如下图所示：