Using QPainter to 'erase' an area of widget?

[wysota]

Qt::WA_TranslucentBackground

[altec42lansing]

hmm, still cant seem to get this working, basically i have a screen that i draw, and i need to get ride of a portion of it completely, including that 'white box' that is left behind when i erase rect. I basically want to get ride of that white area and any remnants left over after erasing, so i can see whats behind the application, since my widgets are painted over top of everything else.
(here is my current code for erasing it

painter.eraseRect(0,0,width()/2,height()/2);
this->setBackgroundRole(QPalette::Base);
this->setAttribute(Qt::WA_TranslucentBackground);

[Rachol]

Try to test this:

#include <QtGui>
#include <QLabel>
 
//! [main function]
int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
 
    QLabel widget("TEST");
    QFont f = widget.font();
    f.setPointSize(100);
    widget.setFont(f);
    widget.setWindowFlags(Qt::WindowFlags(Qt::FramelessWindowHint));
    widget.setAttribute(Qt::WA_TranslucentBackground);
    widget.show();
 
    return app.exec();
}
//! [main function]

#include <QtGui>
#include <QLabel>

//! [main function]
int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    QLabel widget("TEST");
    QFont f = widget.font();
    f.setPointSize(100);
    widget.setFont(f);
    widget.setWindowFlags(Qt::WindowFlags(Qt::FramelessWindowHint));
    widget.setAttribute(Qt::WA_TranslucentBackground);
    widget.show();

    return app.exec();
}
//! [main function]

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[altec42lansing]

this worked and painted text with a transparent background over my windows, allowing me to see behind it where the text was not, but im not sure how to apply this to my problem

[Rachol]

Does this help? Use your widget as I have used MyWidget in code below. You don't have to erease anything in your paintEvent

#include <QtGui>
#include <QWidget>
 
class MyWidget : public QWidget
{
public:
    explicit MyWidget(QWidget *parent = 0):QWidget(parent){};
 
protected:
    void paintEvent ( QPaintEvent * );
 
};
 
void MyWidget::paintEvent ( QPaintEvent * )
{
    QPainter p(this);
    p.setPen(QPen(Qt::red,5));
 
    p.drawRect(rect());
}
 
//! [main function]
int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
 
    MyWidget widget;
    widget.setFixedSize(300,200);
    widget.setWindowFlags(Qt::WindowFlags(Qt::FramelessWindowHint));
    widget.setAttribute(Qt::WA_TranslucentBackground);
    widget.show();
 
    return app.exec();
}
//! [main function]

#include <QtGui>
#include <QWidget>

class MyWidget : public QWidget
{
public:
    explicit MyWidget(QWidget *parent = 0):QWidget(parent){};

protected:
    void paintEvent ( QPaintEvent * );

};

void MyWidget::paintEvent ( QPaintEvent * )
{
    QPainter p(this);
    p.setPen(QPen(Qt::red,5));

    p.drawRect(rect());
}

//! [main function]
int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    MyWidget widget;
    widget.setFixedSize(300,200);
    widget.setWindowFlags(Qt::WindowFlags(Qt::FramelessWindowHint));
    widget.setAttribute(Qt::WA_TranslucentBackground);
    widget.show();

    return app.exec();
}
//! [main function]

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[altec42lansing]

I hate attached a small file which hopefully demonstrates what i am trying to do

[Rachol]

void MyWidget::paintEvent ( QPaintEvent * )
{
    QPainter p(this);
    p.setPen(QPen(Qt::red,5));
 
    p.fillRect(rect(), Qt::white);
    p.drawText(0,0,width(), height(),Qt::AlignCenter || Qt::TextWordWrap, "THIS IS THE AREA WHERE I DRAW IMG");
 
    p.setCompositionMode(QPainter::CompositionMode_Source);
    p.fillRect(rect().adjusted(0,0,-width()/2,-height()/2), Qt::transparent);
}

void MyWidget::paintEvent ( QPaintEvent * )
{
    QPainter p(this);
    p.setPen(QPen(Qt::red,5));

    p.fillRect(rect(), Qt::white);
    p.drawText(0,0,width(), height(),Qt::AlignCenter || Qt::TextWordWrap, "THIS IS THE AREA WHERE I DRAW IMG");

    p.setCompositionMode(QPainter::CompositionMode_Source);
    p.fillRect(rect().adjusted(0,0,-width()/2,-height()/2), Qt::transparent);
}

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