Hello, the code is as followed,

I work with the windows default pixtures and
here is the screenshot
when scale factor 25.6289, no problem, when 38.** or 57.6**, the line is not in the correct postion, and when drag the scene with mouse, the pixels blured and changed.

Qt Code: 
  1. #include <QtWidgets>
  2. #include <QGraphicsView>
  3. #include <QWheelEvent>
  4. #include <QApplication>
  5.  
  6.  
  7. class GraphicsView : public QGraphicsView 
  8. {
  9.  
  10. public:
  11. 	GraphicsView ( QWidget* parent = 0 )
  12. 		:QGraphicsView( parent )
  13. 		,m_scale(1.0)
  14. 	{
  15. 	 		setDragMode( QGraphicsView::ScrollHandDrag );
  16. 	}
  17. protected:
  18. 	void wheelEvent(QWheelEvent *ev)
  19. 	{
  20. 		setTransformationAnchor(QGraphicsView::AnchorUnderMouse);
  21. 		setResizeAnchor(QGraphicsView::AnchorUnderMouse);
  22. 		if(ev->delta() > 0) {
  23. 		m_scale *= 1.5;
  24. 		qDebug() << "+1.5" << m_scale;
  25. 		scale(1.5, 1.5);
  26. 		} else {
  27. 		m_scale /= 1.5;
  28. 		qDebug() << "-1.5" << m_scale;
  29. 		scale(1/1.5, 1/1.5);
  30. 	}
  31.  }
  32. private:
  33.  qreal m_scale;
  34. };
  35. int main(int argc, char **argv)
  36. {
  37. 	QApplication app(argc, argv);
  39. 	QPixmap px; 
  40.  
  41. 	QString fileName = QFileDialog::getOpenFileName(0, QString("Open File"), QDir::currentPath(), "Image Files (*.png *.jpg *.bmp)");
  42. 	if (!fileName.isEmpty())
  43. 	{
  44. 		QFileInfo fi( fileName );
  45. 		if( fi.exists())
  46. 		{
  47. 			bool err = px.load( fi.absoluteFilePath());
  48. 			if (!err)
  49. 				return 0;
  50. 		}
  51. 	}
  52.  
  53. 	scene.addPixmap(px);
  54. 	QGraphicsLineItem* line = new QGraphicsLineItem( px.width()-10,px.height()-1,px.width(),px.height()-1 );
  55. 	QPen pen(Qt::red, 1.0 );
  56. 	pen.setCosmetic( true );
  57. 	line->setPen( pen );
  58. 	scene.addItem( line );
  59. 	GraphicsView view;
  60. 	view.setScene(&scene);
  61. 	view.show();
  62. 	return app.exec();
  63. }
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