Draw line on image using QPainter

[JohannesMunk]

You just need to setup your pixmap before you assign the painter:

#include <QtCore>
#include <QtGui>
 
int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
 
    QLabel l;
 
    QPixmap pixmap;
    pixmap.load(QString::fromUtf8("E:/2010-02-25_112406.png"));
 
    QPainter painter(&pixmap);
    QPen Red((QColor::QColor(255,0,0)),1);
    painter.setPen(Red);
    painter.drawLine(50,50,250,250);
    l.setPixmap(pixmap);
    l.show();
 
    return a.exec();
}

#include <QtCore>
#include <QtGui>

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);

    QLabel l;

    QPixmap pixmap;
    pixmap.load(QString::fromUtf8("E:/2010-02-25_112406.png"));

    QPainter painter(&pixmap);
    QPen Red((QColor::QColor(255,0,0)),1);
    painter.setPen(Red);
    painter.drawLine(50,50,250,250);
    l.setPixmap(pixmap);
    l.show();

    return a.exec();
}

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Joh