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Qt: QPainter + GDI in the same widget?


Qt: QPainter + GDI in the same widget?

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Qt: QPainter + GDI in the same widget?
Tag : windows , By : JoeCh
Date : January 10 2021, 01:45 PM


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Qt Beginner: QPainter widget not rendering


Tag : cpp , By : Sinisa Ruzin
Date : March 29 2020, 07:55 AM
help you fix your problem In drawGraph(), the call to update() posts an event notifying the widget to paint itself. You then clear the points and the drawGraph() call exits. After that, the event loop will process the update event and trigger a call to the paintEvent() but by then, there are no points in the vector of points to paint.
Don't think of the paintEvent() as painting something permanent onto the widget once that will be displayed forever until you clear it and paint something else. The paintEvent() needs to be able to paint the widget from scratch whenever it needs to be redrawn. This is often due to a request from the system when the widget is moved, minimized and restored etc. This means your vector of points needs to remain until you no longer want a polygon to be displayed or the points are changed.

Why does QPainter clear the widget every time I use it?


Tag : python , By : nhuser
Date : March 29 2020, 07:55 AM
I think the issue was by ths following , you have to redraw the widget content on each paintEvent, there's no other way.
maybe in your case it woule be better to draw on a other paint device (QImage, QPixmap, QPicture, ...), and just paint that on each paint event.

How to draw QImage on QScrollArea? Did this, but have some minor problems QPainter::begin: Widget painting can only begi


Tag : cpp , By : user182548
Date : March 29 2020, 07:55 AM
With these it helps Question is, where do you want to paint: on ImageWidget, on imgDisplayLabel, or on scrollArea.
If I interpret correctly, the warning is basically saying that, if you want to begin a painter on a widget, you should do it in THE same widget's paint event.

QPainter fillRect over geometry of widget in grid cell


Tag : cpp , By : pepper
Date : March 29 2020, 07:55 AM
will help you Check the difference between geometry() and e->rect(). It works with e->rect().
qDebug() << "paint" << text() << geometry() << e->rect();
painter.fillRect(e->rect(), QColor(200, 200, 200, 200 * (delta < 1.0f ? delta : 2.0f - delta)));
paint "Registry" QRect(0,0 381x24) QRect(0,0 381x24)
paint "Exit" QRect(0,217 381x24) QRect(0,0 381x24)

How to draw with QPainter on a specific widget from a group of widgets in QMainWindow?


Tag : cpp , By : user185283
Date : March 29 2020, 07:55 AM
seems to work fine
How to draw with QPainter on a specific widget from a group of widgets in QMainWindow?
void Rectangle::paintEvent(QPaintEvent * e)
{
    QRect rectangle(5, 5, width() - 5, height() - 5);

    QPainter painter(this);
    painter.drawRect(rectangle);
}
void MainWindow::paintEvent(QPaintEvent *event)
{
    QMainWindow::paintEvent(event); // Let QMainWindow draw itself
    QPainter painter(this);
    painter.setPen(Qt::white);
    painter.setFont(QFont("Arial", 30));
    painter.drawText(rect(), Qt::AlignCenter, "Qt");
}
class ViewFinderHolder: public QWidget {
    Q_OBJECT
    public:
        explicit ViewFinder(QWidget *parent = 0)
    ...
}

Reimplement the paintEvent() function:


class ViewFinderHolder: public QWidget {
    Q_OBJECT
    public:
        explicit ViewFinderHolder(QWidget *parent = 0)
    ...
    protected:
        void paintEvent(QPaintEvent *e);
}

void ViewFinderHolder::paintEvent(QPaintEvent *event)
{
    QLineF line(10.0, 80.0, 90.0, 20.0);

    QPainter(this);
    painter.drawLine(line);
}
m_QWidget_viewfinder_holder    = new QWidget;
m_QWidget_viewfinder_holder    = new ViewFinder();
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