Draw rectangle on QImage

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Hi,

I'm trying to draw a rectangle into a QImage using QPainter but I don't know what I'm doing wrong. This code is executed out of the paintEvent

QPainter qPainter(&qImage);
qPainter.setBrush(Qt::NoBrush);
qPainter.setPen(Qt::red);
qPainter.drawRect(iX,iY,iWidth,iHeight);
ui.imageLabel->setPixmap(QPixmap::fromImage(qImage));

QPainter qPainter(&qImage);
qPainter.setBrush(Qt::NoBrush);
qPainter.setPen(Qt::red);
qPainter.drawRect(iX,iY,iWidth,iHeight);
ui.imageLabel->setPixmap(QPixmap::fromImage(qImage));

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The image is showed but not the rectangle.
"iX,iY,iWidth,iHeight" have values into the image size.

Thanks,