QT paintEvent for a QWidget

Question

I've a class that inherits QPushButton widget. I want to have custom look of that button so i've overrided paintEvent method. All buttons that I want to paint are childs of QFrame object.

And there I have a problem. I can't repaint those objects.

My paintEvent function:

void Machine::paintEvent(QPaintEvent*) {
    QPainter painter(this);
    QRect geo = this->geometry();

    int x, y, width, height;

    x = geo.x()-10;
    y = geo.y()-10;
    width = geo.width()-3;
    height = geo.height()-5;

    painter.fillRect(x, y, width, height, QColor(220,220,220));

    painter.drawText(x+10, y+10, "Machine " + QString::number(id));
}

When a widget is in top left corner of QFrame, desired effect is ok. But when I move button somewhere else, widget starts to disappear. On images you can see whats going on:

Button is just moved some px down-left. Why it works like this? QFrame which is a container for that button is big enough.

Thanks in advance ;)

Answer 1

The reason is in coordinate system: geometry method returns position relatively to parent, but QPainter::drawRect accepts rectangle in local coordinates. Try this code:

void Machine::paintEvent(QPaintEvent*) {
    QPainter painter(this);

    int width = size().width() - 3;
    int height = size().height() - 5;

    painter.fillRect(0, 0, width, height, QColor(220,220,220));
    painter.drawText(10, 10, "Machine " + QString::number(id));
}