paint in the viewport of a scrollarea

[franco.amato]

Hi to all,
I attached a QWidget to a scrollarea. The widget is scrolled automatically and I draw a text on the position 20, 20.
The problem is that when the widget is scrolled the text disappear. I draw the text in the paint event so:

void WaveDisplay::paintEvent( QPaintEvent* pe )
{
	if( m_waveCachePixmap.isNull() )
	{
		updateWave();
	}
 
	QPainter p( this );
	p.setRenderHint( QPainter::Antialiasing, true );
	QPen pen = QPen( Qt::darkRed, 1 );
 
	// wave
	p.drawPixmap( 0, 0, m_waveCachePixmap );
 
	// timeline
	pen.setColor(Qt::darkRed);
	pen.setStyle(Qt::SolidLine);
	p.setPen( pen );  
	p.drawLine( m_CurrentTimePosition, 0, m_CurrentTimePosition, height() );
 
	// elapsed time
	QWidget* widget = area->viewport(); //HOW CAN I USE THE VIEW PORT
	setElapsedTime( m_CurrentSoundPosition );
	QFont font = p.font();
	font.setPointSize( 24 );
	p.setFont( font );
	p.drawText( QPoint(20, 20), m_elapsedTimeString ); //THE TEXT DISAPPEAR
 
	QWidget::paintEvent(pe);
}

void WaveDisplay::paintEvent( QPaintEvent* pe )
{
	if( m_waveCachePixmap.isNull() )
	{
		updateWave();
	}

	QPainter p( this );
	p.setRenderHint( QPainter::Antialiasing, true );
	QPen pen = QPen( Qt::darkRed, 1 );

	// wave
	p.drawPixmap( 0, 0, m_waveCachePixmap );

	// timeline
	pen.setColor(Qt::darkRed);
	pen.setStyle(Qt::SolidLine);
	p.setPen( pen );  
	p.drawLine( m_CurrentTimePosition, 0, m_CurrentTimePosition, height() );

	// elapsed time
	QWidget* widget = area->viewport(); //HOW CAN I USE THE VIEW PORT
	setElapsedTime( m_CurrentSoundPosition );
	QFont font = p.font();
	font.setPointSize( 24 );
	p.setFont( font );
	p.drawText( QPoint(20, 20), m_elapsedTimeString ); //THE TEXT DISAPPEAR

	QWidget::paintEvent(pe);
}

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I read about the viewport but I don't know how use it for my purpose.
I would always draw at a position of the viewport of my scrollarea.

regards