Hi to all,
I'm trying to write an audio editor with waveform visualizer.
The number of audio samples I have to draw is ~10E6 or more. This is the code where I draw them:
Qt Code: 
  1. void WaveWidget::updateWave()
  2. {
  3. 	int h = height();
  4. 	int w = width();
  5. 	// I need width and height here.
  6. 	// Also, I clear the cache at resize events
  7. 	QPixmap temp = QPixmap( w, h );
  8.  
  9. 	QPainter p( &temp );
  10. 	p.setRenderHint( QPainter::Antialiasing );
  11. 	p.fillRect( temp.rect(), Qt::white );
  12.  
  13. 	QPen pen( Qt::blue, 1 ); // blue solid line, 1 pixels wide
  14. 	p.setPen( pen );
  15. 	short* audio = reinterpret_cast<short*>(soundStream);
  16. 	for( unsigned int i = 0; i < numSamples; i++ )// numSamples very big (~10e6 or more)
  17. 	{
  18. 		int startY = maxHeight;
  19. 		for( int k = 0; k < channels; k++ )
  20. 		{
  21. 			short* value1 = audio + k;
  22. 			int x = i / ( numSamples / w); 
  23. 			int y = *value1 * maxHeight / 0x0000FFFF * 2;
  24. 			QLine line( x, startY, x, startY + y );
  25. 			p.drawLine(line);
  26. 			startY += increment;
  27. 		}
  28. 		audio += sampleSize;
  29. 	}
  30. 	m_waveCachePixmap = temp;
  31. }
To copy to clipboard, switch view to plain text mode 

and the paintEvent
Qt Code: 
  1. void WaveWidget::paintEvent( QPaintEvent* pe )
  2. {
  3. 	// call updateWave only if necesary, if not I draw what is in cache
  4. 	if( m_waveCachePixmap.isNull() )
  5. 	{
  6. 		updateWave();
  7. 	}
  8.  
  9. 	QPainter p( this );
  10. 	p.setRenderHint( QPainter::Antialiasing );
  11. 	p.drawPixmap( 0, 0, m_waveCachePixmap );
  12. }
To copy to clipboard, switch view to plain text mode 

where waveWidget inherits from QWidget.
The problem is that the draw process is very slow as I have to draw more that 10 millions of lines. Is not a fast way do draw something? For example the same audio file in audacity is displayed very fast.

Best Regards