Qt GraphicsView stop getting paint event

[karankumar1609]

Hello,

I am working with QGraphicsView and QGraphicsScene for drawing of QPixmap data on QGraphicsItem.
What i am doing is start a QTimer on each timeout of QTimer i draw data on QPixmap via QtConcurrent.

QtConcurrent::run(this, &LinePlotter::plotDataOnImage);

QtConcurrent::run(this, &LinePlotter::plotDataOnImage);

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On plotDataOnImage i call update() after drawing on QPixmap.
It works fine but unfortunatly my QGraphicsView and QGraphicsScene stop getting paint events.
but when i click on window it repaint again but it does not repaint on call of update() method.

customizations for QGraphicsView i have made are:

setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
    setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
 
    setRenderHints(QPainter::HighQualityAntialiasing | QPainter::SmoothPixmapTransform | QPainter::TextAntialiasing);
 
    setViewportUpdateMode(QGraphicsView::SmartViewportUpdate);
 
    setCacheMode(QGraphicsView::CacheNone);
 
    setOptimizationFlags(QGraphicsView::DontAdjustForAntialiasing
                         | QGraphicsView::DontClipPainter
                         | QGraphicsView::IndirectPainting);

setHorizontalScrollBarPolicy(Qt::ScrollBarAlwaysOff);
    setVerticalScrollBarPolicy(Qt::ScrollBarAlwaysOff);

    setRenderHints(QPainter::HighQualityAntialiasing | QPainter::SmoothPixmapTransform | QPainter::TextAntialiasing);

    setViewportUpdateMode(QGraphicsView::SmartViewportUpdate);

    setCacheMode(QGraphicsView::CacheNone);

    setOptimizationFlags(QGraphicsView::DontAdjustForAntialiasing
                         | QGraphicsView::DontClipPainter
                         | QGraphicsView::IndirectPainting);

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I have never got this kind of problem before but i dont know why my view not get its paint event properly.
any idea about the problem?


-----------------------------------------------
There is something i have seen i just start my application and keep it opened without any mouse interaction or any other kind of interactions.
Then i start my stop watch and checks the log.

It also got stop painting(stop getting events) when keeping in background (rarely occured)...
What is the issue?
I am using Cent OS 6.4
Qt 5.0

Please tell me what is the issue?

[wysota]

QPixmap cannot be used from threads other than the GUI thread.

[karankumar1609]

i have changed my function to drawing on QImage and then i send it a signal

signals:
     void drawingFinished(const QImage&);

signals:
     void drawingFinished(const QImage&);

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but the same problem occured.
the problem will not occur if i direct call that function.
Somehow it stop getting paint events when i use threads.

[wysota]

Show your exact code related to this call and tell us why you expect a paint event (i.e. where you call update() or sth).

[karankumar1609]

here is my run method implementation of QThread

void LinePlotter::run()
{
    QTime timeSpan;
    timeSpan.start();
 
forever {
    const QRectF& visibleRectL = visibleRect();
 
    qDebug() << "Timer Out : " << visibleRectL;
 
//    *pix = pix->scaled(::max(visibleRectL.width(), 1.0), ::max(visibleRectL.height(), 1.0));
QImage image(visibleRectL.size().toSize(), QImage::Format_ARGB32);
 
    QPainter paint;
 
    paint.begin(&image);
    paint.setRenderHint(QPainter::SmoothPixmapTransform, true);
    paint.setBrush(QBrush(Qt::black));
    paint.setClipRect(visibleRectL);
    paint.drawRect(0, 0, visibleRectL.width(), visibleRectL.height());
 
    const qreal& horizontalPP = horizontalPaddingPixel();
    const qreal& verticalPP = verticalPaddingPixel();
    const qreal& zoomFactorInverse = 1 / zoomFactor();
    const qreal& frontL = front();
    const qreal &gridY0 = 0, &gridY1 = visibleRectL.height();
    const double& height = (this->boundingRect().height() - (2* verticalPP));
    const double& xFactor = zoomFactor(), xPadding = + horizontalPP - ::qCeil(frontL);
    int startPoint = (frontL * zoomFactorInverse) - (horizontalPP * zoomFactorInverse);
    int xPos = mappingLine().x1();
    uint mapperWidth = mapper()->size().width();
    uint date = 00000000, time = 0000;
    QVariantList points;
 
    const QVector<PlotData*>& plotDataVector = plotData();
 
    if(startPoint < 0)
        startPoint = 0;
    int endPoint = startPoint + (visibleRectL.width() * zoomFactorInverse) + 5;
 
 
    foreach (PlotData* plotDataValue, plotDataVector) {
        // Each vector contains the data of one day
        const std::vector<ID_Element> &ID = plotDataValue->ID();
 
        int IDIndex = 0;
        foreach (const ID_Element& idElement, ID) {
            int j = 0;
            const KAxisRange& yRange = plotDataValue->yRange(IDIndex);
            const double yFactor = 1.f / (double(yRange.max() - yRange.min()) / height);
 
            if(endPoint > plotDataValue->totalPixel())
                endPoint = plotDataValue->totalPixel();
 
            const std::vector<Date_Element>& dateElement = idElement.ID_vector;
            int timeSize = dateElement.front().Time_Vector.size();
            qreal min = 0, max = 0;
            bool init = true;
 
            foreach (const Date_Element& dateData, dateElement) {
 
                if((j + timeSize) < startPoint) {
                    j += timeSize;
                } else {
                    const std::vector<Time_Element>& timeElement = dateData.Time_Vector;
                    QPolygonF LineToDraw;
                    QVector<QLineF> gridLines, halfGridLines;
 
                    foreach (const Time_Element& timeData, timeElement) {
                        if(j >= startPoint &&
                                j <= endPoint) {
                            // value contains some data in it
                            const std::vector<float>& value =  timeData.Value;
 
                            qreal x = j;
                            x = (x * xFactor) + xPadding;
 
                            if(value.size() > 0) {
                                qreal y = value[0] - yRange.min();
                                y = height - (y * yFactor) + verticalPP;
                                LineToDraw << QPointF(x, y);
 
                                if(j == xPos) {
                                    // value contains some data in it
                                    date = dateData.Date;
                                    time = timeData.Time;
 
                                    QVariantMap mapVal;
                                    mapVal.insert("color", plotDataValue->IDColor(IDIndex));
                                    mapVal.insert("value", QString::number(value[0]));
 
                                    points.append(mapVal);
                                }
 
                                if(init) {
                                    init = false;
                                    min = value[0];
                                    max = min;
                                } else {
                                    qreal range = value[0];
 
                                    if(min > range)
                                        min = range;
 
                                    if(max < range)
                                        max = range;
                                }
                            }
 
                            {
                                // Draw Grid
                                if(timeData.Time % 100 == 0)
                                    gridLines << QLineF(QPointF(x, gridY0), QPointF(x, gridY1));
                                else if((timeData.Time % 100) % 15 == 0)
                                    halfGridLines << QLineF(QPointF(x, gridY0), QPointF(x, gridY1));
                            }
 
                        } else if(j > endPoint) {
                            break;
                        }
                        ++j;
                    }
 
                    /// Draw graph on pixmap
                    if(!LineToDraw.isEmpty()) {
                        paint.setPen(plotDataValue->IDColor(IDIndex));
                        paint.drawPolyline(LineToDraw);
                    }
 
                    {
                        paint.setPen(QPen(QBrush(Qt::red), 3));
                        paint.drawLines(gridLines);
                    }
 
                    {
                        paint.setPen(QPen(QBrush(Qt::gray), 1, Qt::DotLine));
                        paint.drawLines(halfGridLines);
                    }
                }
            }
 
            // Update the grapg again for new range series
            if(yRange.min() != min ||
                    yRange.max() != max) {
                plotDataValue->setYRange(KAxisRange(min, max), IDIndex);
                emit rangeChanged(min, max, IDIndex);
                //                update();
            }
            ++IDIndex; // increase the ID index number
        }
    }
 
    // Draw pixmap with graph
    // Draw mapper line and set mapper position
    {
        paint.setPen(QPen(QBrush(Qt::green), 1));
        paint.setOpacity(1.0);
 
        // insert date time
        {
            QString dateString = QDateTime::fromString(QString::number(date), "yyyyMMdd").toString("yyyy-MM-dd");
            QString timeString = QTime::fromString(QString::number(time), "hhmm").toString("hh:mm");
 
            QVariantMap dateTimeMap;
            dateTimeMap.insert("date", dateString);
            dateTimeMap.insert("time", timeString);
 
            points.append(dateTimeMap);
        }
 
        // Draw mapper line
        {
            xPos = (xPos * zoomFactor()) + xPadding;
            const QLineF &lineToDraw = QLineF(QPointF(xPos, 0), QPointF(xPos, mappingLine().y2()));
 
            xPos = xPos + 3;
            if((xPos + mapperWidth) > visibleRectL.topRight().x()) { // out from right
                xPos -= mapperWidth + 4;
            }
 
            // use setPos_ for animated positioning
            mapper()->setPos(QPointF(xPos, 0));
 
            mapper()->setDataValues(points);
            paint.drawLine(lineToDraw);
        }
    }
 
    paint.end();
}
 
emit image_changed(image);
}

void LinePlotter::run()
{
    QTime timeSpan;
    timeSpan.start();

forever {
    const QRectF& visibleRectL = visibleRect();

    qDebug() << "Timer Out : " << visibleRectL;

//    *pix = pix->scaled(::max(visibleRectL.width(), 1.0), ::max(visibleRectL.height(), 1.0));
QImage image(visibleRectL.size().toSize(), QImage::Format_ARGB32);

    QPainter paint;

    paint.begin(&image);
    paint.setRenderHint(QPainter::SmoothPixmapTransform, true);
    paint.setBrush(QBrush(Qt::black));
    paint.setClipRect(visibleRectL);
    paint.drawRect(0, 0, visibleRectL.width(), visibleRectL.height());

    const qreal& horizontalPP = horizontalPaddingPixel();
    const qreal& verticalPP = verticalPaddingPixel();
    const qreal& zoomFactorInverse = 1 / zoomFactor();
    const qreal& frontL = front();
    const qreal &gridY0 = 0, &gridY1 = visibleRectL.height();
    const double& height = (this->boundingRect().height() - (2* verticalPP));
    const double& xFactor = zoomFactor(), xPadding = + horizontalPP - ::qCeil(frontL);
    int startPoint = (frontL * zoomFactorInverse) - (horizontalPP * zoomFactorInverse);
    int xPos = mappingLine().x1();
    uint mapperWidth = mapper()->size().width();
    uint date = 00000000, time = 0000;
    QVariantList points;

    const QVector<PlotData*>& plotDataVector = plotData();

    if(startPoint < 0)
        startPoint = 0;
    int endPoint = startPoint + (visibleRectL.width() * zoomFactorInverse) + 5;


    foreach (PlotData* plotDataValue, plotDataVector) {
        // Each vector contains the data of one day
        const std::vector<ID_Element> &ID = plotDataValue->ID();

        int IDIndex = 0;
        foreach (const ID_Element& idElement, ID) {
            int j = 0;
            const KAxisRange& yRange = plotDataValue->yRange(IDIndex);
            const double yFactor = 1.f / (double(yRange.max() - yRange.min()) / height);

            if(endPoint > plotDataValue->totalPixel())
                endPoint = plotDataValue->totalPixel();

            const std::vector<Date_Element>& dateElement = idElement.ID_vector;
            int timeSize = dateElement.front().Time_Vector.size();
            qreal min = 0, max = 0;
            bool init = true;

            foreach (const Date_Element& dateData, dateElement) {

                if((j + timeSize) < startPoint) {
                    j += timeSize;
                } else {
                    const std::vector<Time_Element>& timeElement = dateData.Time_Vector;
                    QPolygonF LineToDraw;
                    QVector<QLineF> gridLines, halfGridLines;

                    foreach (const Time_Element& timeData, timeElement) {
                        if(j >= startPoint &&
                                j <= endPoint) {
                            // value contains some data in it
                            const std::vector<float>& value =  timeData.Value;

                            qreal x = j;
                            x = (x * xFactor) + xPadding;

                            if(value.size() > 0) {
                                qreal y = value[0] - yRange.min();
                                y = height - (y * yFactor) + verticalPP;
                                LineToDraw << QPointF(x, y);

                                if(j == xPos) {
                                    // value contains some data in it
                                    date = dateData.Date;
                                    time = timeData.Time;

                                    QVariantMap mapVal;
                                    mapVal.insert("color", plotDataValue->IDColor(IDIndex));
                                    mapVal.insert("value", QString::number(value[0]));

                                    points.append(mapVal);
                                }

                                if(init) {
                                    init = false;
                                    min = value[0];
                                    max = min;
                                } else {
                                    qreal range = value[0];

                                    if(min > range)
                                        min = range;

                                    if(max < range)
                                        max = range;
                                }
                            }

                            {
                                // Draw Grid
                                if(timeData.Time % 100 == 0)
                                    gridLines << QLineF(QPointF(x, gridY0), QPointF(x, gridY1));
                                else if((timeData.Time % 100) % 15 == 0)
                                    halfGridLines << QLineF(QPointF(x, gridY0), QPointF(x, gridY1));
                            }

                        } else if(j > endPoint) {
                            break;
                        }
                        ++j;
                    }

                    /// Draw graph on pixmap
                    if(!LineToDraw.isEmpty()) {
                        paint.setPen(plotDataValue->IDColor(IDIndex));
                        paint.drawPolyline(LineToDraw);
                    }

                    {
                        paint.setPen(QPen(QBrush(Qt::red), 3));
                        paint.drawLines(gridLines);
                    }

                    {
                        paint.setPen(QPen(QBrush(Qt::gray), 1, Qt::DotLine));
                        paint.drawLines(halfGridLines);
                    }
                }
            }

            // Update the grapg again for new range series
            if(yRange.min() != min ||
                    yRange.max() != max) {
                plotDataValue->setYRange(KAxisRange(min, max), IDIndex);
                emit rangeChanged(min, max, IDIndex);
                //                update();
            }
            ++IDIndex; // increase the ID index number
        }
    }

    // Draw pixmap with graph
    // Draw mapper line and set mapper position
    {
        paint.setPen(QPen(QBrush(Qt::green), 1));
        paint.setOpacity(1.0);

        // insert date time
        {
            QString dateString = QDateTime::fromString(QString::number(date), "yyyyMMdd").toString("yyyy-MM-dd");
            QString timeString = QTime::fromString(QString::number(time), "hhmm").toString("hh:mm");

            QVariantMap dateTimeMap;
            dateTimeMap.insert("date", dateString);
            dateTimeMap.insert("time", timeString);

            points.append(dateTimeMap);
        }

        // Draw mapper line
        {
            xPos = (xPos * zoomFactor()) + xPadding;
            const QLineF &lineToDraw = QLineF(QPointF(xPos, 0), QPointF(xPos, mappingLine().y2()));

            xPos = xPos + 3;
            if((xPos + mapperWidth) > visibleRectL.topRight().x()) { // out from right
                xPos -= mapperWidth + 4;
            }

            // use setPos_ for animated positioning
            mapper()->setPos(QPointF(xPos, 0));

            mapper()->setDataValues(points);
            paint.drawLine(lineToDraw);
        }
    }

    paint.end();
}

emit image_changed(image);
}

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and on SLOT i have done a simple QImage to QPixmap conversion

// pix is the pointer of QPixmap which will draw on QGraphicsItem
*pix = QPixmap::fromImage(image);

// pix is the pointer of QPixmap which will draw on QGraphicsItem
*pix = QPixmap::fromImage(image);

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this is everything i have dont with QThread..

[wysota]

Ok, but where do you call update() to actually update the UI?