Hi to all, I'm writing an audio editor. I have to draw the waveform.
The paint event of my wavewidget is so done:

Qt Code: 
  1. /***************************************************************/
  2. /* Paint event                                                 */
  3. /***************************************************************/
  4. void WaveWidget::paintEvent( QPaintEvent* pe )
  5. {
  6. 	// I call updateWave only if necessary if not I draw what is in cache
  7. 	if( m_waveCachePixmap.isNull() )
  8. 	{
  9. 		updateWave();
  10. 	}
  11.  
  12. 	QPainter p( this );
  13. 	p.setRenderHint( QPainter::Antialiasing );
  14. 	p.drawPixmap( 0, 0, m_waveCachePixmap );
  15. }
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where the updateWave() is so done:

Qt Code: 
  1. /************************************************************************/
  2. /* updateWave                                                           */
  3. /* call this only when the wave is changed,                             */
  4. /************************************************************************/ 
  5. void WaveWidget::updateWave()
  6. {
  7. 	int h = height();
  8. 	int w = width();
  9.  
  10. 	// I want another width and height here.
  11. 	// Also, you might to clear the cache at resize events
  12. 	QPixmap temp = QPixmap( w, h );
  13.  
  14. 	QPainter p( &temp );
  15. 	p.fillRect( temp.rect(), Qt::white );
  16. 	p.setRenderHint( QPainter::Antialiasing );
  17.  
  18.  
  19. 	QPen pen( Qt::blue, 1 ); // blue solid line, 1 pixels wide
  20. 	p.setPen( pen );
  21.  
  22. 	// Draw the waveform or no data thingie
  23. 	if( m_wave )
  24. 	{
  25. 		unsigned int numSamples = m_wave->getNumSamples();
  26. 		int channels = m_wave->getNumChannels();
  27. 		FMOD_SOUND_TYPE soundType = m_wave->getSoundType();
  28. 		FMOD_SOUND_FORMAT soundFormat = m_wave->getSoundFormat();
  29.  
  30. 		int sampleSize = channels * ( soundFormat == PCM8 ) ? 1 : 2;
  31.  
  32. 		//char* stream = sound->stream;
  33. 		void* soundStream = m_wave->getSoundStream();
  34. 		int maxHeight = (h / 2) / channels;
  35. 		int increment = (h / 2);
  36.  
  37. 		switch( soundFormat )
  38. 		{
  39. 		case PCM8: //8 bits mono
  40. 			{
  41. 				qDebug("PCM8 sound file");
  42. 				char* audio = reinterpret_cast<char*>(soundStream);
  43. 				for( unsigned int i =  0; i < numSamples ; i++ )
  44. 				{
  45. 					char* current = (audio) + (i * sampleSize);
  46. 					char audio = *current;
  47. 					float reproc = audio / (float)(1 << 8);
  48. 					//DrawLine( i, 0, i, height * reproc );
  49. 					//QLine line( x, startY, x, startY + Y);
  50. 					//p.drawLine(line);
  51. 					//startY += increment;
  52. 				}
  53. 				break;
  54. 			}
  55. 		case PCM16: //16 bits stereo (LRLRLRLR...LRLR)
  56. 			{
  57. 				qDebug("PCM16 sound file");
  58. 				short* audio = reinterpret_cast<short*>(soundStream);
  59. 				for( unsigned int i = 0; i < numSamples; i++ )
  60. 				{
  61. 					int startY = maxHeight;
  62. 					for( int k = 0; k < channels; k++ )
  63. 					{
  64. 						//short* value1 = reinterpret_cast<short*>(stream + k * 2);
  65.                         //short* value1 = audio + k * 2;
  66. 						short* value1 = audio + k;
  67. 						int x = i / ( numSamples / w);//?
  68. 						int y = *value1 * maxHeight / 0x0000FFFF * 2;
  69. 						QLine line( x, startY, x, startY + y );
  70. 						//std::cout << "Drawing at x: " << x << "startY: " << startY << "y: " << y << "\n";
  71. 						p.drawLine(line);
  72. 						startY += increment;
  73. 					}
  74. 					//std::cout << audio[i] << "\n";
  75. 					audio += sampleSize;
  76. 				}
  77. 				break;
  78. 			}
  79.  
  80. 		default:
  81. 			{
  82. 				qDebug("Undefined sound type");
  83. 				break;
  84. 			}
  85. 		}
  86. 	}
  87. 	else
  88. 	{
  89. 		// Inform the user that no file has been loaded - perhaps using a
  90. 		// no-data icon or something
  91. 		qDebug("No data");
  92. 	}
  93.  
  94. 	m_waveCachePixmap = temp;
  95. }
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I have some problems:
1) It doesn't draw nothing
2) I get the follow strange errors that with my poor experience in Qt I can not solve:
QPainter::begin: Paint device returned engine == 0, type: 2
QPainter::setRenderHint: painter must be active to set rendering hints
QPainter::setPen: Painter not active
3) The step of drawing ( that doesn't work ) blok the application.

I hope to get help.
Best Regards