QTimer acting unreliable with QOpenGLWidget

kloveridge

I have a situation where the QTimer or QBasicTimer will not always start running when I use a QOpenGLWidget or a QGLWidget. If you created a basic project with the code I've provided below, I find that about 1 out of every 5 runs, the QTimer refuses to intiialize. Pretty frustrating. Wonder if anyone has any suggestions?

Here's the code:

// main.cpp
#include "MainWindow.h"
#include <QApplication>

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

#ifndef MAINWINDOW_H
#define MAINWINDOW_H

#include <QMainWindow>

class GLView;
namespace Ui {
    class MainWindow;
}

class MainWindow : public QMainWindow
{
    Q_OBJECT
public:
    explicit MainWindow(QWidget *parent = 0);
    ~MainWindow();
private:
    Ui::MainWindow *ui;
    int m_timerId;

private:
    GLView *m_glview;
};

#endif // MAINWINDOW_H@

#include "MainWindow.h"
#include "ui_MainWindow.h"
#include <QDebug>
#include <QGLFormat>
#include "GLView.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    m_glview = new GLView(this);
    m_glview->setSizePolicy(QSizePolicy::Expanding, QSizePolicy::Expanding);
    setCentralWidget(m_glview);
}

MainWindow::~MainWindow()
{
    delete ui;
}

#ifndef GLVIEW_H
#define GLVIEW_H
#include <QOpenGLWidget>
#include <QOpenGLFunctions>
#include <QBasicTimer>

class Trackball;
class GLView : public QOpenGLWidget, QOpenGLFunctions
{
    Q_OBJECT
    public:
    explicit GLView(QWidget *parent = 0 );
    ~GLView();

protected:
    void initializeGL();
    void resizeGL(int w, int h);
    void paintGL();

    void timerEvent(QTimerEvent *event);

private:
    QBasicTimer   m_timer;
    int m_timerId;
};

#endif // GLVIEW_H

#include "GLView.h"
#include <QDebug>

GLView::GLView(QWidget *parent )
: QOpenGLWidget(parent)
{
}

GLView::~GLView()
{
}

void GLView::initializeGL()
{
    qDebug() << "!!!!!!!!!!!!!!!!!!! Initializing GLView !!!!!!!!!!!!!!!!!!!";
    initializeOpenGLFunctions();
    m_timer.start(16, this);
}

void GLView::resizeGL(int w, int h)
{
}

void GLView::paintGL()
{
    update();
}

void GLView::timerEvent(QTimerEvent *event)
{
    makeCurrent();
    static int count = 0;
    qDebug() << "run: " << count++;

    glClearColor( 255,
            0,
            0,
            255
            );
    glClear(GL_COLOR_BUFFER_BIT | GL_DEPTH_BUFFER_BIT | GL_STENCIL_BUFFER_BIT);
    doneCurrent();
}

[edit: updated code style SGaist]

SGaist

Hi,

Do you have any error message on the console by any chance ?
What about using startTimer directly on your widget ?

JKSH

Hi,

Do you have an infinite loop anywhere in your code? If so, that might block your timer from firing.

Note that QBasicTimer + timerEvent() only uses Qt::CoarseTimer. Depending on your platform, it might not fire precisely every 16 ms. Consider using QTimer and set it to Qt::PreciseTimer instead.