Selection precision problems with QGraphicsScene and scaled content?

**dropkickz** · 13th February 2012, 20:08

Hi,

I got precision problems with the selection in a QGraphicsScene. It is quiet simple to reproduce. Here is my code...

Qt Code:

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//----------------------------------------------------------------------------
//  Includes
//----------------------------------------------------------------------------
 
#include <QApplication>
#include <QGraphicsView>
#include <QGraphicsRectItem>
#include <QHBoxLayout>
 
//----------------------------------------------------------------------------
 
class MyFooView : public QGraphicsView
{
public:
    MyFooView(QWidget* parent = NULL) :
    QGraphicsView(parent)
    {
        setRenderHints(QPainter::Antialiasing | QPainter::SmoothPixmapTransform);
    }
    MyFooView(QGraphicsScene* scene, QWidget* parent = NULL) :
    QGraphicsView(scene, parent)
    {
        setRenderHints(QPainter::Antialiasing | QPainter::SmoothPixmapTransform);
        scale(20.0, 20.0);
    }
	~MyFooView(void)
    {
    }
};
 
int main(int argv, char **args)
{
    QApplication app(argv, args);
 
    QGraphicsScene* scene = new QGraphicsScene();
    scene->setSceneRect(QRectF(0, 0, 5000, 5000));
 
    MyFooView* view = new MyFooView(scene);
 
    QGraphicsRectItem* dummy = new QGraphicsRectItem(50.0, 50.0, 30.0, 30.0);
    dummy->setBrush(QBrush(Qt::red));
    dummy->setAcceptHoverEvents(true);
    dummy->setFlag(QGraphicsItem::ItemIsSelectable, true);
    dummy->setFlag(QGraphicsItem::ItemIgnoresTransformations, true);
    scene->addItem(dummy);
 
    view->centerOn(0.0, 0.0);
 
    QHBoxLayout* l = new QHBoxLayout;
    l->addWidget(view);
 
    QWidget* w = new QWidget();
    w->setLayout(l);
    w->show();
 
    return app.exec();
}

//----------------------------------------------------------------------------
//  Includes
//----------------------------------------------------------------------------

#include <QApplication>
#include <QGraphicsView>
#include <QGraphicsRectItem>
#include <QHBoxLayout>

//----------------------------------------------------------------------------

class MyFooView : public QGraphicsView
{
public:
    MyFooView(QWidget* parent = NULL) :
    QGraphicsView(parent)
    {
        setRenderHints(QPainter::Antialiasing | QPainter::SmoothPixmapTransform);
    }
    MyFooView(QGraphicsScene* scene, QWidget* parent = NULL) :
    QGraphicsView(scene, parent)
    {
        setRenderHints(QPainter::Antialiasing | QPainter::SmoothPixmapTransform);
        scale(20.0, 20.0);
    }
	~MyFooView(void)
    {
    }
};

int main(int argv, char **args)
{
    QApplication app(argv, args);
    
    QGraphicsScene* scene = new QGraphicsScene();
    scene->setSceneRect(QRectF(0, 0, 5000, 5000));
    
    MyFooView* view = new MyFooView(scene);
    
    QGraphicsRectItem* dummy = new QGraphicsRectItem(50.0, 50.0, 30.0, 30.0);
    dummy->setBrush(QBrush(Qt::red));
    dummy->setAcceptHoverEvents(true);
    dummy->setFlag(QGraphicsItem::ItemIsSelectable, true);
    dummy->setFlag(QGraphicsItem::ItemIgnoresTransformations, true);
    scene->addItem(dummy);
    
    view->centerOn(0.0, 0.0);
    
    QHBoxLayout* l = new QHBoxLayout;
    l->addWidget(view);
    
    QWidget* w = new QWidget();
    w->setLayout(l);
    w->show();
    
    return app.exec();
}

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Run the program. For me it is possible to select the rect item a bit above and left of its shape. Can someone confirm and tell me how to solve it?

Best regards,
Marcus