QGraphicsItem boundingRect coordinates

e_uofu

Hi there,

I am implementing a QGraphicsItem and I'm having trouble understanding the coordinate systems. Particularly, I do not understand in what coordinates the boundingRect should be.

MyItem draws a red rectangle across the middle of the screen (see below). I use QPaintDevice's logical coordinates to find the screen width. (This seems weird. Should the item be able to draw in its own coordinate system?). I store the logical coordinate's width in a member variable. This allows me to compute the bounding rect the same way I paint the rectangle. (This also seems weird. The boundingRect method should return a valid result before MyItem::paint gets executed. )

If the bounding rect were correct I would be able to trigger mouse hover events of MyItem. I cannot do that, however.

I'd appreciate any help or clarification on this. Thanks.

The paint method draws a red rectangle.

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void MyItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
// Device defines the coordinate system
QPaintDevice *device = painter->device();
m_width = (float) device->width();

// Draw stuff
painter->setBrush(Qt::red);
painter->drawRect(-m_width/2, 0, m_width, 10);

}
@

Here is my bounding rect

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QRectF MyItem::boundingRect() const {
return QRectF(-m_width/2, 0, m_width, 10);
}
@

And here is how I setup the scene inside my mainwindow.

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QGraphicsScene *scene = new QGraphicsScene();
MyItem *item = new MyItem();
scene->addItem(item);
ui->graphicsView->setScene(scene);
@