QPainter does not work though I put them in the paintEvent

Aaron Kim

Canvas is a derived class of QLabel

void Canvas::paintEvent(QPaintEvent*){
    QPainter painter(this);
    painter.setPen(Qt::black);
    painter.setFont(QFont("MaestroTimes", 10));
    std::cout << height() << " " << width() << std::endl;
    painter.drawLine(0, static_cast<int>(height()/2), width()-1, static_cast<int>(height()/2));
}

QLabel* ScoreMaker::makeScore(const QQueue<CommandTimer*>* timers, int interval, int lastInterval, int height){
    int width = 30;
    Canvas* score = new Canvas();
    score->setFixedWidth(static_cast<int>((width + lastInterval) / interval));
    score->setFixedHeight(height);
    score->paintEvent(nullptr);
    return score;
}

Also, update() and repaint() does not trigger paintEvent so I had to use

score->paintEvent(nullptr)

QWidget::paintEngine: Should no longer be called
QPainter::begin: Paint device returned engine == 0, type: 1
QPainter::setPen: Painter not active
QPainter::setFont: Painter not active

Those errors occur even thought I put them in the paintEvent

SGaist

Hi,

Don’t call paintEvent by hand, that’s for the system to do. It will be called automatically when needed. For example, when your widget is shown, when you move it, etc.

Aaron Kim

It seems that I have to set parent of widget before calling repaint(). Otherwise, paintEvent is not called.

SGaist

That’s not mandatory, however you need to call show on the widget depending on how you use it.