select a particular area

[jpn]

Use QPainter. Here's an example from the docs:

void SimpleExampleWidget::paintEvent()
    {
        QPainter paint( this );
        paint.setPen( Qt::blue );
        paint.drawText( rect(), AlignCenter, "The Text" );
    }

void SimpleExampleWidget::paintEvent()
    {
        QPainter paint( this );
        paint.setPen( Qt::blue );
        paint.drawText( rect(), AlignCenter, "The Text" );
    }

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Replace QPainter::drawText() with QPainter::drawRect()..