QGraphicsWidgets erased slowly

[Manuka]

I have noticed that also when I resize my widow my texts are corrected, due to the update event.

I've tried to change the ZValue of my elements because I thought that my texts are not visible due to a circle which masks them but even setting the ZValue does not solve the problem.

[Manuka]

Does somebody has an idea , I still could not figure it out?

[ChrisW67]

Without seeing your actual code, or a small, self-contained example that shows the problem it is hard to say. Not sure why you are using a custom painter for the text

[Manuka]

Thank you for your response.

I cannot post my code because it is too large but I wrote a small self-contained example to indicate the problem.

Actually I'm using custom painter for the text because QGraphicsTextItem cannot be inserted in a layout. Hence, first I decided to subclass QGraphicsWidget and override its paint function. With this solution I encountered the problem I've mentioned above. Here is the code:

class GraphicsTextItem : public QGraphicsWidget
{
public:
    QString m_Name;
    QColor m_Color;
 
    GraphicsTextItem(QGraphicsItem * parent = nullptr, const QString& name = QString())
   : QGraphicsWidget(parent)
   , m_Name(name)
   , m_Color(50 + (std::rand() % (255 - 50 + 1)), 50 + (std::rand() % (255 - 50 + 1)), 50 + (std::rand() % (255 - 50 + 1)))
   {
       setMaximumHeight(12);
       setMinimumHeight(12);
   } 
 
    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget) override
    {
       QFont font("Times", 10);
       painter->setFont(font);
       painter->setPen(m_Color);
       painter->drawText(0, 0, m_Name);
    }
};
 
class GraphicsTextItem;
class GraphicsCircleItem : public QGraphicsEllipseItem
{
private:
    const GraphicsTextItem* m_Source;
    bool m_SourceGood;
 
public:
    GraphicsCircleItem(const GraphicsTextItem* source)
    : QGraphicsEllipseItem()
    , m_Source(source)
    , m_SourceGood(false)
    {
        setBrush(QBrush(m_Source->m_Color));
        setPen(QPen(m_Source->m_Color));
        setRect(0, 0, 20, 20);
    }
 
    bool isSourcePositionValid() const { return m_Source->pos().x() != 0.0 || m_Source->pos().y() != 0.0; }
 
    void moveAndShow()
    {
        if(isSourcePositionValid() && m_SourceGood == false)
        {
            m_SourceGood = true;
            setPos(m_Source->scenePos());
            show();
            return;
        }
        else
        {
            if(!m_SourceGood)
                hide();
        }
 
        if(m_SourceGood)
        {
            moveBy(1,6);
        }
    }
};
 
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
 
    QGraphicsWidget* layout_widget = new QGraphicsWidget();
    QGraphicsLinearLayout* layout = new QGraphicsLinearLayout(Qt::Vertical);
    layout_widget->setLayout(layout);
 
    QGraphicsScene* scene  = new QGraphicsScene(&w);
    scene->setItemIndexMethod(QGraphicsScene::NoIndex);
    scene->setBackgroundBrush(Qt::black);
    scene->addItem(layout_widget);
 
    QGraphicsView* scene_view = new QGraphicsView(&w);
    scene_view->setScene(scene);
    scene_view->setSceneRect(0, 0, 1024, 768);
 
    std::vector<GraphicsTextItem*> source_list;
    std::vector<GraphicsCircleItem*> message_list;
    for(int i = 0; i < 1000; i++)
    {
        std::string source = std::string("SourceName_") + std::to_string(i);
        GraphicsTextItem* source_item = new GraphicsTextItem(nullptr, QString(source.c_str()));
        layout->addItem(source_item);
        source_list.push_back(source_item);
 
        GraphicsCircleItem* message_item = new GraphicsCircleItem(source_item);
        scene->addItem(message_item);
        message_list.push_back(message_item);
    }
 
    QTimer timer;
    timer.callOnTimeout([&]()
    {
        static uint64_t counter = 0;
        if(counter == 500)
        {
            for(auto& item : message_list)
            {
                scene->removeItem(item);
                delete item;
            }
            message_list.clear();
 
            for(auto& item : source_list)
            {
                GraphicsCircleItem* message_item = new GraphicsCircleItem(item);
                scene->addItem(message_item);
                message_list.push_back(message_item);
            }
 
            counter = 0;
        }
 
        for(auto& item : message_list)
        {
            item->moveAndShow();
        }
        counter++;
 
    });
    timer.start(10);
 
    w.setCentralWidget(scene_view);
    w.show();
 
    return a.exec();
}

class GraphicsTextItem : public QGraphicsWidget
{
public:
    QString m_Name;
    QColor m_Color;

    GraphicsTextItem(QGraphicsItem * parent = nullptr, const QString& name = QString())
   : QGraphicsWidget(parent)
   , m_Name(name)
   , m_Color(50 + (std::rand() % (255 - 50 + 1)), 50 + (std::rand() % (255 - 50 + 1)), 50 + (std::rand() % (255 - 50 + 1)))
   {
       setMaximumHeight(12);
       setMinimumHeight(12);
   } 

    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget) override
    {
       QFont font("Times", 10);
       painter->setFont(font);
       painter->setPen(m_Color);
       painter->drawText(0, 0, m_Name);
    }
};

class GraphicsTextItem;
class GraphicsCircleItem : public QGraphicsEllipseItem
{
private:
    const GraphicsTextItem* m_Source;
    bool m_SourceGood;

public:
    GraphicsCircleItem(const GraphicsTextItem* source)
    : QGraphicsEllipseItem()
    , m_Source(source)
    , m_SourceGood(false)
    {
        setBrush(QBrush(m_Source->m_Color));
        setPen(QPen(m_Source->m_Color));
        setRect(0, 0, 20, 20);
    }

    bool isSourcePositionValid() const { return m_Source->pos().x() != 0.0 || m_Source->pos().y() != 0.0; }
    
    void moveAndShow()
    {
        if(isSourcePositionValid() && m_SourceGood == false)
        {
            m_SourceGood = true;
            setPos(m_Source->scenePos());
            show();
            return;
        }
        else
        {
            if(!m_SourceGood)
                hide();
        }

        if(m_SourceGood)
        {
            moveBy(1,6);
        }
    }
};

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;

    QGraphicsWidget* layout_widget = new QGraphicsWidget();
    QGraphicsLinearLayout* layout = new QGraphicsLinearLayout(Qt::Vertical);
    layout_widget->setLayout(layout);

    QGraphicsScene* scene  = new QGraphicsScene(&w);
    scene->setItemIndexMethod(QGraphicsScene::NoIndex);
    scene->setBackgroundBrush(Qt::black);
    scene->addItem(layout_widget);

    QGraphicsView* scene_view = new QGraphicsView(&w);
    scene_view->setScene(scene);
    scene_view->setSceneRect(0, 0, 1024, 768);

    std::vector<GraphicsTextItem*> source_list;
    std::vector<GraphicsCircleItem*> message_list;
    for(int i = 0; i < 1000; i++)
    {
        std::string source = std::string("SourceName_") + std::to_string(i);
        GraphicsTextItem* source_item = new GraphicsTextItem(nullptr, QString(source.c_str()));
        layout->addItem(source_item);
        source_list.push_back(source_item);

        GraphicsCircleItem* message_item = new GraphicsCircleItem(source_item);
        scene->addItem(message_item);
        message_list.push_back(message_item);
    }

    QTimer timer;
    timer.callOnTimeout([&]()
    {
        static uint64_t counter = 0;
        if(counter == 500)
        {
            for(auto& item : message_list)
            {
                scene->removeItem(item);
                delete item;
            }
            message_list.clear();

            for(auto& item : source_list)
            {
                GraphicsCircleItem* message_item = new GraphicsCircleItem(item);
                scene->addItem(message_item);
                message_list.push_back(message_item);
            }

            counter = 0;
        }

        for(auto& item : message_list)
        {
            item->moveAndShow();
        }
        counter++;

    });
    timer.start(10);

    w.setCentralWidget(scene_view);
    w.show();

    return a.exec();
}

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I attach also a photo about the issue with the sample code. As I wrote before I have not encountered this problem if I subclass QGraphicsLayoutItem instead of QGraphicsWidget.

Screenshot from 2019-04-25 13-17-55.jpg

I hope the sample code helps.

[Manuka]

Anybody could please advise?