Hi to all,
I would put in a separate thread a method of my class that actually blocks the gui.
The method is responsible of drawing an audio waveform into a QWidget in the paint event

So:
Qt Code: 
  1. void WaveDisplay::paintEvent( QPaintEvent* pe )
  2. {
  3. 	// Update the ev->rect area with the wave from the rendered QPixmap here
  4. 	if( m_waveCachePixmap.isNull() )
  5. 	{
  6. 		updateWave();// BLOCK MY GUI
  7. 	}
  8.  
  9. 	QPainter p( this );
  10. 	p.setRenderHint( QPainter::Antialiasing, true );
  11. 	QPen pen = QPen( Qt::darkRed, 1 );
  12.  
  13. 	// wave
  14. 	p.drawPixmap( 0, 0, m_waveCachePixmap );
  15.  
  16. 	QWidget::paintEvent(pe);
  17. }
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AND

Qt Code: 
  1. // THIS ROUTINE BLOCK MY GUI
  2. void WaveDisplay::updateWave()
  3. {
  4. 	int h = this->height();
  5. 	int w = this->width();
  6.  
  7. 	// I want another width and height here.
  8. 	// Also, you might to clear the cache at resize events
  9. 	QPixmap temp = QPixmap( w, h );
  10.  
  11. 	QPainter p( &temp );
  12. 	//p.setRenderHint( QPainter::Antialiasing, true );
  13. 	p.fillRect( temp.rect(), bgColor );
  14.  
  15.        ...more code to draw the wave...
  16. }
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I read about threads and QtConcurrent but I don't know how to adapt my code even because I have to pass the painter
and paint on a specific widget.

I hope to get help.

Regards