Non-scaling image added to scene

[Thomas_Lerman]

I am currently adding a PNG to the scene with addPixmap. It works just find, moving with the scene. However, I do not want the image to scale when the scene gets scaled. Any suggestions?

[wysota]

Set the ItemIgnoresTransformations flag.

[Thomas_Lerman]

Ah, how did I miss that? Thank you very much. The next thing that I need to do is to have the image centered on the position instead of painting from the top-left corner while still not scaling. I hope this is something just as simple that I have missed.

[wysota]

Most likely you mean QGraphicsView::alignment property (set it to Qt::AlignCenter).

[Thomas_Lerman]

I was not very clear with my last message, sorry. I am currently doing the following to add the PNG to the scene:

QPixmap *p = new QPixmap(":/some.png");
QGraphicsPixmapItem *d = NULL;
d = m_graphicsScene->addPixmap(*p);
d->setPos(SceneCoords.x(), SceneCoords.y());
d->setFlag(QGraphicsItem::ItemIgnoresTransformations, true);

QPixmap *p = new QPixmap(":/some.png");
QGraphicsPixmapItem *d = NULL;
d = m_graphicsScene->addPixmap(*p);
d->setPos(SceneCoords.x(), SceneCoords.y());
d->setFlag(QGraphicsItem::ItemIgnoresTransformations, true);

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I would like this PNG centered on the scene coordinates while still not scaling. With the above code, the scene coordinates is the upper-left of the PNG.

[wysota]

Oh, I see. Try calling QGraphicsItem::setTransformOriginPoint() pointing to the center of your pixmap (boundingRect().center()). If it doesn't work then you'll have to subclass your item class.

[Thomas_Lerman]

For the fun of it, I added

d->setTransformOriginPoint((p->width() * 200), (p->height() * 200));

d->setTransformOriginPoint((p->width() * 200), (p->height() * 200));

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between the above lines 4 & 5. I do not see any difference.

[wysota]

So subclass the pixmap item class and redefine the bounding rect to point to the center of the image. Also reimplement paint and translate the painter so that the original paint routine thinks it is still in top-left corner.

[Thomas_Lerman]

I did not find that changing the bounding rect was needed.

class MyGraphicsPixmapItem : public QGraphicsPixmapItem
{
public:
	MyGraphicsPixmapItem(const QPixmap& pixmap, QGraphicsItem* parent = 0) :
	  QGraphicsPixmapItem(pixmap, parent) {};
	void paint(QPainter* painter, const QStyleOptionGraphicsItem* option, QWidget* widget)
	{
		painter->translate(-(option->rect.width() / 2), -(option->rect.height() / 2));
		QGraphicsPixmapItem::paint(painter, option, widget);
	}
};

class MyGraphicsPixmapItem : public QGraphicsPixmapItem
{
public:
	MyGraphicsPixmapItem(const QPixmap& pixmap, QGraphicsItem* parent = 0) :
	  QGraphicsPixmapItem(pixmap, parent) {};
	void paint(QPainter* painter, const QStyleOptionGraphicsItem* option, QWidget* widget)
	{
		painter->translate(-(option->rect.width() / 2), -(option->rect.height() / 2));
		QGraphicsPixmapItem::paint(painter, option, widget);
	}
};

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This is all I had to do. Did I miss anything? Thank you for your direction.

[wysota]

You have to change the bounding rect. Otherwise you'll get artifacts in an area that you paint and that is not inside your bounding rect.

QRectF MyGraphicsPixmapItem::boundingRect() const {
    QRectF r = QGraphicsPixmapItem::boundingRect();
    return r.translated(-r.width()*0.5, -r.height()*.0.5);
};

QRectF MyGraphicsPixmapItem::boundingRect() const {
    QRectF r = QGraphicsPixmapItem::boundingRect();
    return r.translated(-r.width()*0.5, -r.height()*.0.5);
};

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[Thomas_Lerman]

Excellent. I actually already had that in, but did not notice any difference. I now remember reading about the artifacts, so thank you for reminding me and you assistance!