这是我的 GUI,
我想要在这里做的是一起显示四个不同的视频。用户输入特定视频文件的路径并单击“打开”,应创建一个新线程来播放该视频。
我有一个名为 startThread() 的插槽,以及一个在名为 openCamera() 的线程中调用的函数;
在mainwindow.hpp中,有
public:
static void openCamera(const std::string& address, QLabel* label);
private slots:
void startThread();
在mainwindow.cpp中,有
void MainWindow::startThread() {
std::string address;
QLabel* label;
// Get the input from GUI and assign it to std::string address
// and find the label corresponding to clicked button.
// ...
std::thread t(openCamera, address, label);
}
void MainWindow::openCamera(std::string address, QLabel* label) {
cv::VideoCapture cap(address);
cv::Mat frame;
while (cap.isOpened()) {
cap >> frame;
// cv::imwrite("/Users/wking/Desktop/test.jpg", frame); // This function works!
label->setPixmap(QPixmap::fromImage(QImage(frame.data, frame.cols, frame.rows, frame.step, QImage::Format_RGB888).rgbSwapped()));
}
}
我想通过使用 std::thread 来实现这一点。然而,它什么也没显示。当我单击正确输入的按钮后,程序不会更新标签。我在这里错过了什么吗?谢谢。
最佳答案
只有主线程(GUI线程)可以更新UI。
我有一个类似的项目。我使用 QThread 和 Worker 类。
Worker 类有一个插槽来读取视频文件。读完一帧会发出信号。
在 MainWindow 中,我创建了一些 QThread,将工作对象移动到线程。
将 Worker 的信号框架Finished 与一个函数连接起来,以在标签上显示 cv::Mat。
class Worker : public QObject
{
Q_OBJECT
public:
Worker(QString path, int id);
~Worker();
public slots:
void readVideo(QString path = "");
signals:
// frame and index of label which frame will be displayed
void frameFinished(cv::Mat frame, int index);
void finished(int index);
private:
QString filepath;
int index;
};
这是worker.cpp
#include "worker.h"
#include <QDebug>
#include <QThread>
#include <QTime>
Worker::Worker(QString path, int id) : filepath(path), index(id)
{
}
Worker::~Worker()
{
}
void Worker::readVideo(QString path)
{
if (path.length() > 0)
filepath = path;
cv::VideoCapture cap(filepath.toStdString());
if (! cap.isOpened())
{
qDebug() << "Can't open video file " << filepath;
emit finished(index);
return;
}
cv::Mat frame;
while (true)
{
cap >> frame;
if (frame.empty())
{
frame = cv::Mat(cv::Size(720, 576), CV_8UC3, cv::Scalar(192, 0, 0));
emit frameFinished(frame, index);
break;
}
emit frameFinished(frame.clone(), index);
QThread::msleep(30);
}
emit finished(index);
}
主窗口.h
#ifndef MAINWINDOW_H
#define MAINWINDOW_H
#include <QMainWindow>
#include <opencv2/opencv.hpp>
#include "worker.h"
#define MAX_NUM_CAM 8
namespace Ui {
class MainWindow;
}
class QThread;
class QLabel;
class MainWindow : public QMainWindow
{
Q_OBJECT
public:
explicit MainWindow(QWidget *parent = 0);
~MainWindow();
void init();
private slots:
void displayFrame(cv::Mat frame, int index);
private:
Ui::MainWindow *ui;
int numCams;
QLabel *labels[MAX_NUM_CAM];
QThread* threads[MAX_NUM_CAM];
Worker* workers[MAX_NUM_CAM];
};
#endif // MAINWINDOW_H
主窗口.cpp
#include "mainwindow.h"
#include "ui_mainwindow.h"
#include <QDebug>
#include <QThread>
#include <QLabel>
#include <QGridLayout>
MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow)
{
ui->setupUi(this);
qRegisterMetaType< cv::Mat >("cv::Mat");
qDebug() << "Main thread " << QThread::currentThreadId();
init();
}
MainWindow::~MainWindow()
{
delete ui;
}
void MainWindow::init()
{
QGridLayout *grid = new QGridLayout;
int numCols = 2;
numCams = 4;
int row = 0, col = 0;
for (int i = 0; i < numCams; i++)
{
labels[i] = new QLabel;
row = i / numCols;
col = i % numCols;
grid->addWidget(labels[i], row, col);
threads[i] = new QThread;
workers[i] = new Worker(QString("/home/shang/Videos/%1.mp4").arg(i+1), i);
workers[i]->moveToThread(threads[i]);
connect(workers[i], SIGNAL(frameFinished(cv::Mat, int)), this, SLOT(displayFrame(cv::Mat,int)));
connect(threads[i], SIGNAL(started()), workers[i], SLOT(readVideo()));
connect(workers[i], SIGNAL(finished(int)), threads[i], SLOT(quit()));
connect(workers[i], SIGNAL(finished(int)), workers[i], SLOT(deleteLater()));
connect(threads[i], SIGNAL(finished()), threads[i], SLOT(deleteLater()));
threads[i]->start();
}
this->centralWidget()->setLayout(grid);
}
void MainWindow::displayFrame(cv::Mat frame, int index)
{
QPixmap p = QPixmap::fromImage(QImage(frame.data, frame.cols, frame.rows, frame.step, QImage::Format_RGB888).rgbSwapped());
p = p.scaled(QSize(frame.cols/2, frame.rows/2));
labels[index]->setPixmap(p);
}
关于multithreading - Qt + OpenCV 使用 std::thread 播放视频,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/29338250/