QGraphicsItem inheritence

[bajarangi]

I need to subclass an existing QGraphicsItem and change the painting
and size. I started modifying the elasticnodes example and came up with
these changes:

class Node : public QGraphicsItem
{
public:
    Node(GraphWidget *graphWidget);
 
    void addEdge(Edge *edge);
    QList<Edge *> edges() const;
 
    enum { Type = UserType + 1 };
    int type() const { return Type; }
 
    void calculateForces();
    bool advance();
 
    virtual QRectF boundingRect() const;
    QPainterPath shape() const;
    virtual void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);
 
protected:
    QVariant itemChange(GraphicsItemChange change, const QVariant &value);
 
    virtual void mousePressEvent(QGraphicsSceneMouseEvent *event);
    virtual void mouseReleaseEvent(QGraphicsSceneMouseEvent *event);
 
    QList<Edge *> edgeList;
    QPointF newPos;
    GraphWidget *graph;
 
private:
 
};

class Node : public QGraphicsItem
{
public:
    Node(GraphWidget *graphWidget);

    void addEdge(Edge *edge);
    QList<Edge *> edges() const;

    enum { Type = UserType + 1 };
    int type() const { return Type; }

    void calculateForces();
    bool advance();

    virtual QRectF boundingRect() const;
    QPainterPath shape() const;
    virtual void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);

protected:
    QVariant itemChange(GraphicsItemChange change, const QVariant &value);

    virtual void mousePressEvent(QGraphicsSceneMouseEvent *event);
    virtual void mouseReleaseEvent(QGraphicsSceneMouseEvent *event);

    QList<Edge *> edgeList;
    QPointF newPos;
    GraphWidget *graph;
	
private:

};

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So for my derived class, I need to make boundingRect(), paint(), and mousePressEvent() virtual, because I want my class to paint a pixmap
and catch it's own mousePressEvents.
Correct?

So I subclassed Node, loaded a rectangular image in the constructor, implemented boundingRect(), paint(), and mousePressEvent(). Compiles and runs ok.
Just one problem - I can't drag the rectangular image by the mouse!

Some qDebug statements in the relevant methods shows that the derived class
is receiving mousePressEvents, but only in the exact area where a Node (ball) would be (around 0,0 in my pixmap). It looks like I need to make another method in Node virtual to override the default area where a Node accepts mouse events.

I hope this is clear. The attached jpg shows a closeup.
The white circle is some sort of "ghost" node that will accept a mouse press
and allow me to drag the pixmap. I can't drag the pixmap anywhere else.

thanks,
-baj

[wysota]

So for my derived class, I need to make boundingRect(), paint(), and mousePressEvent() virtual, because I want my class to paint a pixmap
and catch it's own mousePressEvents.
Correct?

They already are virtual. You just need to reimplement the methods.

So I subclassed Node, loaded a rectangular image in the constructor, implemented boundingRect(), paint(), and mousePressEvent(). Compiles and runs ok.
Just one problem - I can't drag the rectangular image by the mouse!

Call the base class implementation of mousePressEvent() and mouseReleaseEvent() in your reimplementations.

[bajarangi]

Thanks again, Wysotta. Still no joy here.
So I removed the virtual keywords from the Node class, recompiled and ran. No change.

Here's the derived class declaration:

class CloudNode : public Node
{
public:
	CloudNode(GraphWidget *graphWidget);
 
 protected:
     void paint( QPainter *, const QStyleOptionGraphicsItem *option, QWidget *widget );
	QRectF boundingRect() const;
    void mousePressEvent(QGraphicsSceneMouseEvent *event);
    void mouseReleaseEvent(QGraphicsSceneMouseEvent *event);
 
private:
	QImage *cloudimage;
     QPixmap pixmap;
};
 
CloudNode::CloudNode(GraphWidget *graphWidget) : Node(graphWidget)
{
	qDebug() << "Creating CloudNode";
	cloudimage = new QImage(); // = new QImage();
	bool loadsuccess = cloudimage->load("./images/background.png");
	qDebug() << "CloudNode loaded image = " << loadsuccess;
     setFlag(ItemIsMovable);
     setCacheMode(DeviceCoordinateCache);
     pixmap = QPixmap::fromImage(*cloudimage, Qt::OrderedAlphaDither);
}
 
 
 void CloudNode::paint( QPainter *p, const QStyleOptionGraphicsItem *option, QWidget * )
 {
	qDebug() << "CloudNode::paint";
     p->drawPixmap(0, 0, pixmap);
 }
 
 QRectF CloudNode::boundingRect() const
{
	int adjust = 0;
    QRectF noderect(-adjust, -adjust, cloudimage->width() +10, cloudimage->height()+10);
	//qDebug() << "CloudNode width " << noderect.width() << "  height  " << noderect.height();
	return noderect;
}
 
void CloudNode::mousePressEvent(QGraphicsSceneMouseEvent *event)
{
    update();
    QGraphicsItem::mousePressEvent(event);
	qDebug() << "CloudNode mouse x " << event->pos().x() << "  y " << event->pos().y();
}

class CloudNode : public Node
{
public:
	CloudNode(GraphWidget *graphWidget);

 protected:
     void paint( QPainter *, const QStyleOptionGraphicsItem *option, QWidget *widget );
	QRectF boundingRect() const;
    void mousePressEvent(QGraphicsSceneMouseEvent *event);
    void mouseReleaseEvent(QGraphicsSceneMouseEvent *event);
	
private:
	QImage *cloudimage;
     QPixmap pixmap;
};

CloudNode::CloudNode(GraphWidget *graphWidget) : Node(graphWidget)
{
	qDebug() << "Creating CloudNode";
	cloudimage = new QImage(); // = new QImage();
	bool loadsuccess = cloudimage->load("./images/background.png");
	qDebug() << "CloudNode loaded image = " << loadsuccess;
     setFlag(ItemIsMovable);
     setCacheMode(DeviceCoordinateCache);
     pixmap = QPixmap::fromImage(*cloudimage, Qt::OrderedAlphaDither);
}


 void CloudNode::paint( QPainter *p, const QStyleOptionGraphicsItem *option, QWidget * )
 {
	qDebug() << "CloudNode::paint";
     p->drawPixmap(0, 0, pixmap);
 }

 QRectF CloudNode::boundingRect() const
{
	int adjust = 0;
    QRectF noderect(-adjust, -adjust, cloudimage->width() +10, cloudimage->height()+10);
	//qDebug() << "CloudNode width " << noderect.width() << "  height  " << noderect.height();
	return noderect;
}

void CloudNode::mousePressEvent(QGraphicsSceneMouseEvent *event)
{
    update();
    QGraphicsItem::mousePressEvent(event);
	qDebug() << "CloudNode mouse x " << event->pos().x() << "  y " << event->pos().y();
}

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Problem persists as before. I can click and drag the pixmap in a small area around
0,0 and qDebug output shows:
CloudNode mouse x 2.64032 y 0.489026
But I don't receive the mouse click anywhere else in the pixmap.

Do I have to re-implement itemChange() ? I wouldn't think so, that only
is called after the mouse event is received.

In Graphwidget constructor I have this for a CloudNode:
CloudNode *cnode8 = new CloudNode(this);
scene->addItem(cnode8);
scene->addItem(new Edge(cnode8, node7));
cnode8->setPos(150, 150);

[wysota]

I'd guess your boundingRect() or shape() implementation is incorrect. Try reimplementing shape() to return the result of boundingRect() and see if it changes anything.

[bajarangi]

SUCCESS!

Yea, the runtime was defaulting to the Node implementation of shape(), which
was an elipse around 0,0. Reiplemented shape() in CloudNode like:

QPainterPath CloudNode::shape() const
{
    QPainterPath path;
    path.addRect(0, 0, cloudimage->width(), cloudimage->height());
    return path;
}

QPainterPath CloudNode::shape() const
{
    QPainterPath path;
    path.addRect(0, 0, cloudimage->width(), cloudimage->height());
    return path;
}

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and I can now drag the pixmap from any point in the rectangle.

Thanks again.
-baj