I implemented a QDialog with transparent background, but i move the mouse over QDialog, background becomes dark.

What's the problem?


my code:

Note: numPadDialog is derived class of QDialog.

Qt Code: 
  1. // Constructor, call some functions to implent QDialog
  2. numPadDialog::numPadDialog() {
  3. 	// TODO Auto-generated constructor stub
  4. 	setWallpaper();   //This function try put a background dark semi-transparent
  5. 	setNumericPad();  // This function put the image of numpad
  6. 	configureInterfaceNumericPad();  // This function configure map of the buttons of numpad
  7. 	setInfo("Configure this parameter: ");  //This function put extra information about numPad
  8. 	showDialog();  // This function show the QDialog 
  9. }
  10.  
  11. //This function try put a background dark semi-transparent
  12. void numPadDialog::setWallpaper(){
  13.  
  14. 	mask= new QLabel(this);
  15. 	//set image
  16. 	QString style;
  17. 	style.clear();
  18. 	QString numPadPath;
  19. 	numPadPath.clear();
  20. 	numPadPath.append(QDir::currentPath());
  21. 	numPadPath.append(WALLPAPER_DIRECTORY);
  22. 	numPadPath.append(KEYPAD_BACKGROUND);  // image semi-transparent, dark
  23.  
  24. 	style.append("background-color: transparent;  background: transparent; background-image: url(");
  25. 	style.append(numPadPath);
  26. 	style.append("); ");
  27. 	mask->setStyleSheet(style);
  28. 	mask->setGeometry(0,0,320,240);
  29. 	mask->setFocusPolicy(Qt::NoFocus);
  30. }
  31.  
  32.  
  33. // This function put the image of numpad
  34. void numPadDialog::setNumericPad(){
  35.  
  36. 	numPad= new QLabel(this);
  37. 	//set image
  38. 	QString style;
  39. 	style.clear();
  40. 	QString numPadPath;
  41. 	numPadPath.clear();
  42. 	numPadPath.append(QDir::currentPath());
  43. 	numPadPath.append(WALLPAPER_DIRECTORY);
  44. 	numPadPath.append(KEYPAD_NUMPAD);
  45.  
  46. 	style.append("background-color: transparent;  background: transparent; background-image: url(");
  47. 	style.append(numPadPath);
  48. 	style.append("); ");
  49. 	numPad->setStyleSheet(style);
  50. 	numPad->setGeometry(0,0,320,240);
  51. 	numPad->setFocusPolicy(Qt::NoFocus);
  52. }
  53.  
  54. // This function show the QDialog 
  55. void numPadDialog::showDialog(){
  56. 	this->setWindowFlags(Qt::FramelessWindowHint);
  57. 	this->setAttribute(Qt::WA_NoSystemBackground);
  58. 	//this->setAttribute(Qt::WA_TransparentForMouseEvents);
  59. 	//this->setAttribute(Qt::WA_NoBackground);
  60. 	this->setFixedSize(320,240);  // ( x , y )
  61. 	this->setFocusPolicy(Qt::NoFocus);
  62. 	exec();
  63. }
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