And here is the code that I want....

Qt Code: 
  1. #include "setrasteroptest.h"
  2. #include <QMouseEvent>
  3. #include <QPainter>
  4.  
  5. //Program to draw a straight line using Qt4
  6. //constructor 
  7. setRasterOpTest::setRasterOpTest(QWidget *parent, Qt::WFlags flags)
  8. 	: QFrame(parent, flags)
  9. {
  10. 	ui.setupUi(this);
  11. 	QColor color( Qt::white );
  12. 	QPalette palette;
  13. 	palette.setColor(backgroundRole(), color);
  14. 	setPalette(palette);
  15. 	setMouseTracking(true);	
  16. 	m_bflag = false;
  17. }
  18.  
  19. setRasterOpTest::~setRasterOpTest()
  20. {}
  21.  
  22. void setRasterOpTest::mousePressEvent( QMouseEvent *e ){ 
  23. 	if (e->button() == Qt::LeftButton){       
  24. 		m_firstpt = e->pos();
  25. 		m_lastpt = e->pos();  
  26. 	}
  27. }
  28.  
  29. void setRasterOpTest::mouseMoveEvent( QMouseEvent *e ){
  30. 	if ((e->buttons() & Qt::LeftButton) ){
  31. 		m_lastpt = e->pos(); 	
  32. 		m_bflag = true;
  33. 		update();    
  34. 	}
  35. }
  36.  
  37. void setRasterOpTest::mouseReleaseEvent(QMouseEvent *e){
  38. 	if (e->button() == Qt::LeftButton )	{
  39. 		m_lastpt = e->pos();
  40. 		m_vectorLine << QLine( m_firstpt, m_lastpt ); 
  41. 		update();
  42. 	}
  43. }
  44.  
  45. void setRasterOpTest::paintEvent(QPaintEvent *e){	
  46. 	QPainter painter(this);
  47. 	painter.setPen( Qt::black );	
  48. 	painter.drawLines( m_vectorLine ); 
  49.  
  50. 	if( m_bflag ){
  51. 		painter.drawLine( m_firstpt, m_lastpt );
  52. 		m_bflag = false;
  53. 	}
  54. }
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Thanks wysota!!!!