Rubberband relative to QGraphicsScene

[Gopala Krishna]

I had a look at the sources of qt and was shocked to see their own rubberband implementation for the QGView! They are drawing the rubberband from a QPainter manually in paintEvent() and updating manually. They aren;t using QRubberBand widget at all now!

Anyways i really feel there is something related to hovering which is giving you pains. Have you tried my example and checked performance issue ?
It would be better if you could post a minimal working example.

[pherthyl]

I had a look at the sources of qt and was shocked to see their own rubberband implementation for the QGView! They are drawing the rubberband from a QPainter manually in paintEvent() and updating manually. They aren;t using QRubberBand widget at all now!

Ah yes, I suspected something like that.

Anyways i really feel there is something related to hovering which is giving you pains. Have you tried my example and checked performance issue ?
It would be better if you could post a minimal working example.

Yes, that's next on the list. I tried your example on my work machine and there are no problems with performance or weird selection behaviour. I'll modify that minimal example to handle the rubber band in the view and check if it still works.

[pherthyl]

I'll modify that minimal example to handle the rubber band in the view and check if it still works.

Ok, so with the following code it works fine on my work computer. I saw the "no mouse release event" bug once or twice but now I can't reproduce it anymore. I will try this same code at home and see what the situation is there.

#include <QtGui>
 
class View : public QGraphicsView
{
public:
  View() : QGraphicsView()
  {
	rubberBand = new QRubberBand(QRubberBand::Rectangle, this);
  }
 
protected:
void mouseMoveEvent(QMouseEvent* evt) {
	if(evt->buttons().testFlag(Qt::LeftButton)) {
		// handle the rubberband
		if(rubberBand->isVisible()) {
			QPoint mouseDownView = mapFromScene(mouseDownPos);
			lastMouseViewPos = evt->pos();
			QRect rubberRect(mouseDownView, lastMouseViewPos);
			rubberRect = rubberRect.normalized();
			rubberBand->setGeometry(rubberRect);
			QPolygonF p = mapToScene(rubberRect);
			QPainterPath path;
			path.addPolygon(p);
			scene()->setSelectionArea(path, Qt::IntersectsItemShape);
		}
	}
	QGraphicsView::mouseMoveEvent(evt);
}
 
void mouseReleaseEvent(QMouseEvent* evt) {
	qDebug() << "release";
	rubberBand->hide();
	QGraphicsView::mouseReleaseEvent(evt);
}
 
void mousePressEvent(QMouseEvent* evt) {
	qDebug() << "press";
	QGraphicsView::mousePressEvent(evt);
	if(!scene()->itemAt(mapToScene(evt->pos()))) {
		mouseDownPos = mapToScene(evt->pos()).toPoint();
		lastMouseViewPos = evt->pos();
		rubberBand->setGeometry(mapFromScene(mouseDownPos).x(), mapFromScene(mouseDownPos).y(), 0,0);
		rubberBand->show();
	}
}
  private:
	QPoint mouseDownPos;
	QPoint lastMouseViewPos;
	QRubberBand *rubberBand;
};
 
void addItems(View *s)
{
  QGraphicsEllipseItem *item = s->scene()->addEllipse(10,10, 150, 150);
  item->setFlags(QGraphicsItem::ItemIsMovable | QGraphicsItem::ItemIsSelectable);
 
  item = s->scene()->addEllipse(100,210, 50, 150);
  item->setFlags(QGraphicsItem::ItemIsSelectable);
 
}
 
int main(int argc, char *argv[])
{
  QApplication app(argc, argv);
  QRectF rect = QRectF(0,0, 1024,768);
  QGraphicsScene* scene = new QGraphicsScene(rect);
  View *s = new View();
  s->setScene(scene);
  addItems(s);
 
  s->show();
  return app.exec();
}

#include <QtGui>

class View : public QGraphicsView
{
public:
  View() : QGraphicsView()
  {
	rubberBand = new QRubberBand(QRubberBand::Rectangle, this);
  }

protected:
void mouseMoveEvent(QMouseEvent* evt) {
	if(evt->buttons().testFlag(Qt::LeftButton)) {
		// handle the rubberband
		if(rubberBand->isVisible()) {
			QPoint mouseDownView = mapFromScene(mouseDownPos);
			lastMouseViewPos = evt->pos();
			QRect rubberRect(mouseDownView, lastMouseViewPos);
			rubberRect = rubberRect.normalized();
			rubberBand->setGeometry(rubberRect);
			QPolygonF p = mapToScene(rubberRect);
			QPainterPath path;
			path.addPolygon(p);
			scene()->setSelectionArea(path, Qt::IntersectsItemShape);
		}
	}
	QGraphicsView::mouseMoveEvent(evt);
}

void mouseReleaseEvent(QMouseEvent* evt) {
	qDebug() << "release";
	rubberBand->hide();
	QGraphicsView::mouseReleaseEvent(evt);
}

void mousePressEvent(QMouseEvent* evt) {
	qDebug() << "press";
	QGraphicsView::mousePressEvent(evt);
	if(!scene()->itemAt(mapToScene(evt->pos()))) {
		mouseDownPos = mapToScene(evt->pos()).toPoint();
		lastMouseViewPos = evt->pos();
		rubberBand->setGeometry(mapFromScene(mouseDownPos).x(), mapFromScene(mouseDownPos).y(), 0,0);
		rubberBand->show();
	}
}
  private:
	QPoint mouseDownPos;
	QPoint lastMouseViewPos;
	QRubberBand *rubberBand;
};

void addItems(View *s)
{
  QGraphicsEllipseItem *item = s->scene()->addEllipse(10,10, 150, 150);
  item->setFlags(QGraphicsItem::ItemIsMovable | QGraphicsItem::ItemIsSelectable);

  item = s->scene()->addEllipse(100,210, 50, 150);
  item->setFlags(QGraphicsItem::ItemIsSelectable);

}

int main(int argc, char *argv[])
{
  QApplication app(argc, argv);
  QRectF rect = QRectF(0,0, 1024,768);
  QGraphicsScene* scene = new QGraphicsScene(rect);
  View *s = new View();
  s->setScene(scene);
  addItems(s);

  s->show();
  return app.exec();
}

To copy to clipboard, switch view to plain text mode 

[pherthyl]

I tried your example on my work machine and there are no problems with performance or weird selection behaviour.

No performance problems on my home machine with that simple example either.

Turns out the problem in my app wasn't the rubberband but the drawing of the background. In my drawbackground I was drawing borders for pages, in a not-so-efficient way.

void ProjectScene::drawBackground(QPainter *painter, const QRectF &rect) {
	if(renderBackground) {
		painter->setBrush(Qt::white);
		painter->setPen(Qt::black);
 
		int hPages = getNumHorizontalPages();
		int vPages = getNumVerticalPages();
		QRectF currPage;
		for(int h = 0; h < hPages; h++) {
			for(int v = 0; v < vPages; v++) {
				currPage.setRect(h*pageSize.width(), v*pageSize.height(), pageSize.width(), pageSize.height());
				if(currPage.intersects(rect)) {
					painter->drawRect(currPage);
				}
			}
		}
	}
}

void ProjectScene::drawBackground(QPainter *painter, const QRectF &rect) {
	if(renderBackground) {
		painter->setBrush(Qt::white);
		painter->setPen(Qt::black);

		int hPages = getNumHorizontalPages();
		int vPages = getNumVerticalPages();
		QRectF currPage;
		for(int h = 0; h < hPages; h++) {
			for(int v = 0; v < vPages; v++) {
				currPage.setRect(h*pageSize.width(), v*pageSize.height(), pageSize.width(), pageSize.height());
				if(currPage.intersects(rect)) {
					painter->drawRect(currPage);
				}
			}
		}
	}
}

To copy to clipboard, switch view to plain text mode 

I'll have to rethink that function.

So now I just have to figure out the strange selection bug...

[pherthyl]

So now I just have to figure out the strange selection bug...

Aha! Now I've isolated the problem.

Can someone please try out the attached code and select the items as shown in the screenshot? The ellipse is correctly selected, while the rectangle is not. Not sure where this is coming from yet. Something to do with that the rect item has a default shape implementation?

[pherthyl]

Well I fixed the selection bug by implementing my own version of setSelectionArea and reporting the bug to Trolltech. Now everything works.

[Gopala Krishna]

Nice, but what bug was there in qt's setSelectionArea function ?

[pherthyl]

Nice, but what bug was there in qt's setSelectionArea function ?

No idea. I just gave them the compileable example and let them figure it out
But I wrote my own that just iterates through all the items and uses either shape().intersects() (for line items) and sceneBoundingRect().intersects() for my boxes. Maybe not so great for large numbers of items (haven't checked how qt does it), but I don't anticipate having more than about 100 on the scene at once.

[pherthyl]

Got a response from Trolltech support:

This does indeed look like a bug in Qt. The problem is most likely the
same as the one reported here

http://trolltech.com/developer/task-...ntry&id=191706

as QGraphicsScene uses QPainterPath for calculating whether the
rectangle intersects with the selection rectangle.

We'll verify that fixing this also solves your problem.

Thanks for reporting.

[pherthyl]

I'll have to rethink that function.

CacheBackground fixed this problem.