Create a marquee with QGraphicsScene

[plitex]

Hi all,

I'm looking to create a marquee like the ones we could watch on TV, normally horizontal scrolls. What I'm having is a lot of flickering on the animation, and I would like to have other opinions because I'm a newbie on Qt Graphics.

If I resize the window, the animation stops, is there a way to avoid that? I don't know if there is a way to have a thread for the scene.

Here is the main code I'm using, but you can find attached all the project.

Item::Item(QGraphicsItem * parent)
    : QGraphicsItem(parent)
{
    setCacheMode(DeviceCoordinateCache);
    _boundingRect = QRectF(0, 0, 960, 220);
    _animationSpeed = 0.5;
}
 
QRectF Item::boundingRect() const
{
    return _boundingRect;
}
 
void Item::paint(QPainter *painter, const QStyleOptionGraphicsItem *option,
                         QWidget *widget)
{
    painter->setBrush(Qt::yellow);
    painter->drawRoundedRect(2, 2, 84, 84, 4, 4);
    painter->setBrush(QColor(50,50,50));
    painter->drawRoundedRect(90, 2, 84, 84, 4, 4);
    painter->drawRoundedRect(176, 2, 534, 84, 4, 4);
    painter->drawRoundedRect(712, 2, 245, 84, 4, 4);
}
 
void Item::advance(int phase)
{
    if (phase == 1)
    {
        moveBy(-(_animationSpeed), 0.0);
    }
}
 
void Item::setAnimationSpeed(qreal value)
{
    _animationSpeed = value;
}

Item::Item(QGraphicsItem * parent)
    : QGraphicsItem(parent)
{
    setCacheMode(DeviceCoordinateCache);
    _boundingRect = QRectF(0, 0, 960, 220);
    _animationSpeed = 0.5;
}

QRectF Item::boundingRect() const
{
    return _boundingRect;
}

void Item::paint(QPainter *painter, const QStyleOptionGraphicsItem *option,
                         QWidget *widget)
{
    painter->setBrush(Qt::yellow);
    painter->drawRoundedRect(2, 2, 84, 84, 4, 4);
    painter->setBrush(QColor(50,50,50));
    painter->drawRoundedRect(90, 2, 84, 84, 4, 4);
    painter->drawRoundedRect(176, 2, 534, 84, 4, 4);
    painter->drawRoundedRect(712, 2, 245, 84, 4, 4);
}

void Item::advance(int phase)
{
    if (phase == 1)
    {
        moveBy(-(_animationSpeed), 0.0);
    }
}

void Item::setAnimationSpeed(qreal value)
{
    _animationSpeed = value;
}

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MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
 
    QGraphicsScene *scene = new QGraphicsScene();
    scene->setBackgroundBrush(Qt::black);
 
    ui->graphicsView->setViewport(new QGLWidget(QGLFormat(QGL::SampleBuffers)));
    ui->graphicsView->setScene(scene);
    ui->graphicsView->setSceneRect(0,0,960,230);
 
    for (int i = 0; i < 50; i++)
    {
        Item *item = new Item();
        item->setPos(item->boundingRect().width() * i, 0);
        item->setAnimationSpeed(ui->horizontalSlider->value() / 10.0);
        scene->addItem(item);
        _items.append(item);
    }
 
    QTimer *timer = new QTimer();
    connect(timer, SIGNAL(timeout()), this, SLOT(timer_timeout()));
    timer->start(1);
 
    _elapsedTimer = new QElapsedTimer();
    _elapsedTimer->start();
}
 
MainWindow::~MainWindow()
{
    delete ui;
}
 
void MainWindow::timer_timeout()
{
    if (_elapsedTimer->hasExpired(8))
    {
        _elapsedTimer->start();
        ui->graphicsView->scene()->advance();
    }
}
 
void MainWindow::on_horizontalSlider_valueChanged(int value)
{
    foreach(Item *i, _items)
        i->setAnimationSpeed(value / 10.0);
}

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);

    QGraphicsScene *scene = new QGraphicsScene();
    scene->setBackgroundBrush(Qt::black);

    ui->graphicsView->setViewport(new QGLWidget(QGLFormat(QGL::SampleBuffers)));
    ui->graphicsView->setScene(scene);
    ui->graphicsView->setSceneRect(0,0,960,230);

    for (int i = 0; i < 50; i++)
    {
        Item *item = new Item();
        item->setPos(item->boundingRect().width() * i, 0);
        item->setAnimationSpeed(ui->horizontalSlider->value() / 10.0);
        scene->addItem(item);
        _items.append(item);
    }

    QTimer *timer = new QTimer();
    connect(timer, SIGNAL(timeout()), this, SLOT(timer_timeout()));
    timer->start(1);

    _elapsedTimer = new QElapsedTimer();
    _elapsedTimer->start();
}

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

void MainWindow::timer_timeout()
{
    if (_elapsedTimer->hasExpired(8))
    {
        _elapsedTimer->start();
        ui->graphicsView->scene()->advance();
    }
}

void MainWindow::on_horizontalSlider_valueChanged(int value)
{
    foreach(Item *i, _items)
        i->setAnimationSpeed(value / 10.0);
}

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