Problem with qgraphicsitem_Cast

[kokeroulis]

The problem is that you somehow need to save the relative position of the mousecursor and the item when you start moving. If you just set the position of the item to the mouseCursors position you will move the items origin (0,0) to that position and not the center or wherever you might have clicked.

There are several ways to do that:

1) only use deltas:
item->setPos(item->pos() + event->scenePos() - event->lastScenePos() );

2) store everything:
Wherever you start your move action, store in member variables 1) the item-scenePos (startItemPos) and 2) the event-scenePos (startMousePos). If you want to support moving multiple items, store a list of their startPositions. In mouseMove set the item-position to: item->setPos( startItemPos + event->scenePos() - startMousePos);

HIH

Joh

I am not using the method drug 'n drop but the point 'n click (i select the "piece" and then i click there which i wanted to be moved....) I tried the 1) but the piece doesn't do nothing...because it is moving in the same position....

[JohannesMunk]

I understand your point'n'click well.. that just changes where you start stuff.

The piece does nothing? What do you mean same position?

[kokeroulis]

I understand your point'n'click well.. that just changes where you start stuff.

The piece does nothing? What do you mean same position?

i use the 1) method....I mean that it moves but it goes to the same place....(It is something wrong with the "item->pos() + event->scenePos() - event->lastScenePos() ") because the piece is moving into the current position....E.X. if it is into the (210,150) before the click, after it will be into the (210,150)....So it moves but it goes-reach into the same place....

[JohannesMunk]

The code is fine, but you need to enable Mousetracking and hoverEvents:

class Scene : public QGraphicsScene
{
public:
    Scene() {underMouse = 0;}
protected:
    void mouseMoveEvent(QGraphicsSceneMouseEvent * mouseEvent )
    {
        if (underMouse != 0)
        {
            underMouse->setPos(underMouse->pos() + mouseEvent->scenePos() - mouseEvent->lastScenePos());
            qDebug() << mouseEvent->scenePos() - mouseEvent->lastScenePos();
        }
        QGraphicsScene::mouseMoveEvent(mouseEvent);
    }
 
    void mouseReleaseEvent ( QGraphicsSceneMouseEvent * mouseEvent )
    {
        if (underMouse == 0)
            underMouse = itemAt(mouseEvent->scenePos());
        else
            underMouse = 0;
        QGraphicsScene::mouseReleaseEvent(mouseEvent);
    }
 
private:
    QGraphicsItem* underMouse;
};
 
class Piece : public QGraphicsItem
{
public:
    Piece() {
        setAcceptHoverEvents(true);
    }
    QRectF boundingRect() const{ return QRectF(0, 0, 50, 50); }
 
    void paint(QPainter *painter, const QStyleOptionGraphicsItem *item, QWidget *widget)
    {
        painter->drawRect(boundingRect());
    }
};
 
 
MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent)
{
    scene = new Scene();
 
    Piece* piece = new Piece();
    scene->addItem(piece);
 
    graphicsView = new QGraphicsView(this);
    graphicsView->setMouseTracking(true);
 
    graphicsView->setViewport(new QGLWidget(QGLFormat(QGL::SampleBuffers)));
    graphicsView->setScene(scene);
    graphicsView->show();
 
    graphicsView->setGeometry(QRect(50, 50, 500, 300));
 
    this->setCentralWidget(graphicsView);
 
}

class Scene : public QGraphicsScene
{
public:
    Scene() {underMouse = 0;}
protected:
    void mouseMoveEvent(QGraphicsSceneMouseEvent * mouseEvent )
    {
        if (underMouse != 0)
        {
            underMouse->setPos(underMouse->pos() + mouseEvent->scenePos() - mouseEvent->lastScenePos());
            qDebug() << mouseEvent->scenePos() - mouseEvent->lastScenePos();
        }
        QGraphicsScene::mouseMoveEvent(mouseEvent);
    }

    void mouseReleaseEvent ( QGraphicsSceneMouseEvent * mouseEvent )
    {
        if (underMouse == 0)
            underMouse = itemAt(mouseEvent->scenePos());
        else
            underMouse = 0;
        QGraphicsScene::mouseReleaseEvent(mouseEvent);
    }

private:
    QGraphicsItem* underMouse;
};

class Piece : public QGraphicsItem
{
public:
    Piece() {
        setAcceptHoverEvents(true);
    }
    QRectF boundingRect() const{ return QRectF(0, 0, 50, 50); }

    void paint(QPainter *painter, const QStyleOptionGraphicsItem *item, QWidget *widget)
    {
        painter->drawRect(boundingRect());
    }
};


MainWindow::MainWindow(QWidget *parent) : QMainWindow(parent)
{
    scene = new Scene();

    Piece* piece = new Piece();
    scene->addItem(piece);

    graphicsView = new QGraphicsView(this);
    graphicsView->setMouseTracking(true);

    graphicsView->setViewport(new QGLWidget(QGLFormat(QGL::SampleBuffers)));
    graphicsView->setScene(scene);
    graphicsView->show();

    graphicsView->setGeometry(QRect(50, 50, 500, 300));

    this->setCentralWidget(graphicsView);

}

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Joh