add pixels to qgraphicsitem

**mcarter** · 14th February 2011, 22:42

The item usually knows it changes its own boundingRect()

Well, if its based on its own rect, then not really . . . unless you override the setRect function (which is not a virtual function).

to get the child item working, do I hide/show based on the select state in the paint method of the parent?

**wysota** · 14th February 2011, 23:10

You can call your own method that calls setRect(). setRect() won't be called behind your back, you know.

**mcarter** · 14th February 2011, 23:53

duh . . . I have control of this item . . . way too many long hours . . . thanks, wysota

still would be interested if someone has a resizer item on hand

**spud** · 15th February 2011, 17:53

Well, since you asked so nicely and I haven't posted anything here for ages...

Here's an old example I managed to dig up:
ResizeItem.h

Qt Code:

Switch view

class ResizeItem : public QGraphicsItemGroup
{
	enum Handle{None = -1, TL, T, TR, R, BR, B, BL, L, NrOfHandles};
	QGraphicsRectItem* handles[NrOfHandles];
	Handle _selectedItem;
public:
	ResizeItem()
		: _selectedItem(None)
	{
		for(int i = 0;i<NrOfHandles;i++)
		{
			handles[i] = new QGraphicsRectItem(QRectF(-2,-2,5,5), this);
			handles[i]->setFlags(ItemIgnoresTransformations);
			handles[i]->setPen(Qt::NoPen);
			handles[i]->setBrush(Qt::black);
		}
		handles[TL]->setCursor(QCursor(Qt::SizeFDiagCursor));
		handles[T ]->setCursor(QCursor(Qt::SizeVerCursor));
		handles[TR]->setCursor(QCursor(Qt::SizeBDiagCursor));
		handles[R ]->setCursor(QCursor(Qt::SizeHorCursor));
		handles[BR]->setCursor(QCursor(Qt::SizeFDiagCursor));
		handles[B ]->setCursor(QCursor(Qt::SizeVerCursor));
		handles[BL]->setCursor(QCursor(Qt::SizeBDiagCursor));
		handles[L ]->setCursor(QCursor(Qt::SizeHorCursor));
		hide();
	}
 
protected:
	QVariant itemChange(GraphicsItemChange change, const QVariant &value)
	{
		if (change == ItemParentChange && scene()) 
		{
			QGraphicsRectItem* rectItem = qgraphicsitem_cast<QGraphicsRectItem*>(value.value<QGraphicsItem*>());
			if(rectItem==0){
				hide();
				return 0;
			}
			repositionChildren(rectItem->rect());
			show();
		}
		return QGraphicsItem::itemChange(change, value);
	}
 
	void repositionChildren(QRectF rect)
	{
		handles[TL]->setPos(rect.left(),		rect.top());
		handles[T ]->setPos(rect.center().x(),	rect.top());
		handles[TR]->setPos(rect.right(),		rect.top());
		handles[R ]->setPos(rect.right(),		rect.center().y());
		handles[BR]->setPos(rect.right(),		rect.bottom());
		handles[B ]->setPos(rect.center().x(),	rect.bottom());
		handles[BL]->setPos(rect.left(),		rect.bottom());
		handles[L ]->setPos(rect.left(),		rect.center().y());
	}
 
	void mousePressEvent ( QGraphicsSceneMouseEvent * event )  
	{
		// Find out which handle was clicked
		int minDist = 10000000;
		int closestHandle = None;
		for(int i = 0;i<NrOfHandles;i++)
		{
			int dist = (event->pos()-handles[i]->pos()).manhattanLength();
			if(dist<minDist)
			{
				closestHandle = i;
				minDist = dist;
			}
		}
		_selectedItem = (Handle)closestHandle;
		event->accept();
	}
 
	void mouseMoveEvent ( QGraphicsSceneMouseEvent * event )
	{
		QGraphicsRectItem* rectItem = qgraphicsitem_cast<QGraphicsRectItem*>(parentItem());
		if(rectItem==0)
			return;
 
		QRectF rect = rectItem->rect();
		QPointF pos = event->scenePos()-scenePos();
 
		if(_selectedItem==TR || _selectedItem==R || _selectedItem==BR)
			rect.setRight(qMax(rect.left(), pos.x()));
		else if(_selectedItem==TL || _selectedItem==L || _selectedItem==BL)
			rect.setLeft(qMin(rect.right(), pos.x()));
 
		if(_selectedItem==BL || _selectedItem==B || _selectedItem==BR)
			rect.setBottom(qMax(rect.top(), pos.y()));
		else if(_selectedItem==TL || _selectedItem==T || _selectedItem==TR)
			rect.setTop(qMin(rect.bottom(), pos.y()));
 
		rectItem->setRect(rect);
		repositionChildren(rectItem->boundingRect());
	}
 
	void mouseReleaseEvent ( QGraphicsSceneMouseEvent * ) 
	{
		_selectedItem=None;
	}
};

class ResizeItem : public QGraphicsItemGroup
{
	enum Handle{None = -1, TL, T, TR, R, BR, B, BL, L, NrOfHandles};
	QGraphicsRectItem* handles[NrOfHandles];
	Handle _selectedItem;
public:
	ResizeItem()
		: _selectedItem(None)
	{
		for(int i = 0;i<NrOfHandles;i++)
		{
			handles[i] = new QGraphicsRectItem(QRectF(-2,-2,5,5), this);
			handles[i]->setFlags(ItemIgnoresTransformations);
			handles[i]->setPen(Qt::NoPen);
			handles[i]->setBrush(Qt::black);
		}
		handles[TL]->setCursor(QCursor(Qt::SizeFDiagCursor));
		handles[T ]->setCursor(QCursor(Qt::SizeVerCursor));
		handles[TR]->setCursor(QCursor(Qt::SizeBDiagCursor));
		handles[R ]->setCursor(QCursor(Qt::SizeHorCursor));
		handles[BR]->setCursor(QCursor(Qt::SizeFDiagCursor));
		handles[B ]->setCursor(QCursor(Qt::SizeVerCursor));
		handles[BL]->setCursor(QCursor(Qt::SizeBDiagCursor));
		handles[L ]->setCursor(QCursor(Qt::SizeHorCursor));
		hide();
	}

protected:
	QVariant itemChange(GraphicsItemChange change, const QVariant &value)
	{
		if (change == ItemParentChange && scene()) 
		{
			QGraphicsRectItem* rectItem = qgraphicsitem_cast<QGraphicsRectItem*>(value.value<QGraphicsItem*>());
			if(rectItem==0){
				hide();
				return 0;
			}
			repositionChildren(rectItem->rect());
			show();
		}
		return QGraphicsItem::itemChange(change, value);
	}

	void repositionChildren(QRectF rect)
	{
		handles[TL]->setPos(rect.left(),		rect.top());
		handles[T ]->setPos(rect.center().x(),	rect.top());
		handles[TR]->setPos(rect.right(),		rect.top());
		handles[R ]->setPos(rect.right(),		rect.center().y());
		handles[BR]->setPos(rect.right(),		rect.bottom());
		handles[B ]->setPos(rect.center().x(),	rect.bottom());
		handles[BL]->setPos(rect.left(),		rect.bottom());
		handles[L ]->setPos(rect.left(),		rect.center().y());
	}

	void mousePressEvent ( QGraphicsSceneMouseEvent * event )  
	{
		// Find out which handle was clicked
		int minDist = 10000000;
		int closestHandle = None;
		for(int i = 0;i<NrOfHandles;i++)
		{
			int dist = (event->pos()-handles[i]->pos()).manhattanLength();
			if(dist<minDist)
			{
				closestHandle = i;
				minDist = dist;
			}
		}
		_selectedItem = (Handle)closestHandle;
		event->accept();
	}

	void mouseMoveEvent ( QGraphicsSceneMouseEvent * event )
	{
		QGraphicsRectItem* rectItem = qgraphicsitem_cast<QGraphicsRectItem*>(parentItem());
		if(rectItem==0)
			return;

		QRectF rect = rectItem->rect();
		QPointF pos = event->scenePos()-scenePos();

		if(_selectedItem==TR || _selectedItem==R || _selectedItem==BR)
			rect.setRight(qMax(rect.left(), pos.x()));
		else if(_selectedItem==TL || _selectedItem==L || _selectedItem==BL)
			rect.setLeft(qMin(rect.right(), pos.x()));

		if(_selectedItem==BL || _selectedItem==B || _selectedItem==BR)
			rect.setBottom(qMax(rect.top(), pos.y()));
		else if(_selectedItem==TL || _selectedItem==T || _selectedItem==TR)
			rect.setTop(qMin(rect.bottom(), pos.y()));

		rectItem->setRect(rect);
		repositionChildren(rectItem->boundingRect());
	}

	void mouseReleaseEvent ( QGraphicsSceneMouseEvent * ) 
	{
		_selectedItem=None;
	}
};

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main.cpp

Qt Code:

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#include <QtGui>
 
// There is one global resize item, which stays hidden most of the time.
ResizeItem* resizeItem;
 
class RectItem : public QGraphicsRectItem
{
public:
	RectItem(QRectF rect)
		: QGraphicsRectItem(rect)
	{
		setFlags(ItemIsSelectable|ItemIsMovable);
		setBrush((Qt::GlobalColor)((qrand()%14)+4));
	}
	QVariant itemChange(GraphicsItemChange change, const QVariant &value)
	{
		// When this item is selected, we grab the resizeItem by calling setParentItem(this)
		if (change == ItemSelectedChange)
			resizeItem->setParentItem(value.toBool() ? this : 0);
		return QGraphicsItem::itemChange(change, value);
	}
};
 
int main(int argc, char* argv[])
{
	QApplication app(argc, argv);
 
	QGraphicsScene scene;
	scene.setSceneRect(0, 0, 600, 600);
	scene.addItem(resizeItem = new ResizeItem);
	for(int i=0;i<50;i++)
		scene.addItem(new RectItem(QRectF(qrand()%500, qrand()%500, 100, 100)));
 
	QGraphicsView view;
	view.setScene(&scene);
	view.show();
 
	return app.exec();
}

#include <QtGui>

// There is one global resize item, which stays hidden most of the time.
ResizeItem* resizeItem;

class RectItem : public QGraphicsRectItem
{
public:
	RectItem(QRectF rect)
		: QGraphicsRectItem(rect)
	{
		setFlags(ItemIsSelectable|ItemIsMovable);
		setBrush((Qt::GlobalColor)((qrand()%14)+4));
	}
	QVariant itemChange(GraphicsItemChange change, const QVariant &value)
	{
		// When this item is selected, we grab the resizeItem by calling setParentItem(this)
		if (change == ItemSelectedChange)
			resizeItem->setParentItem(value.toBool() ? this : 0);
		return QGraphicsItem::itemChange(change, value);
	}
};

int main(int argc, char* argv[])
{
	QApplication app(argc, argv);

	QGraphicsScene scene;
	scene.setSceneRect(0, 0, 600, 600);
	scene.addItem(resizeItem = new ResizeItem);
	for(int i=0;i<50;i++)
		scene.addItem(new RectItem(QRectF(qrand()%500, qrand()%500, 100, 100)));

	QGraphicsView view;
	view.setScene(&scene);
	view.show();

	return app.exec();
}

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The idea is that there is only one resize item which get's moved around whenever a rectangle is clicked. The resize item itself is invisible, but it has eight scale invariant children, which stay 5x5 pixel, regardless of view scale.

screen.jpg

**d_stranz** · 15th February 2011, 22:09

Now that's a very clever example of "thinking outside the box".

**mcarter** · 26th February 2011, 17:42

sorry about the late response, been off working other gui issues

spud, I appreciate the post . . . very cool
this has helped in understanding a little more about qgraphicsview and qgraphicsitems

**mcarter** · 28th February 2011, 23:37

I see how the resize items work.

Now lets say i wanted the resizers to be the full-length of the rect I am adjusting.
Something like:

extraction.png

I am trying to create an extraction item for a qgraphicsview that is showing some freq/time pixmaps. The cyan in the picture is where the mouse has entered the resizer edge. Both sides hilite because they would move in unison around the center line (adjusting bandwidth). The top and bottom would be adjusted individually for time.

Once I start resizing the edge items to match the center rect, that is where my problem starts . . . because I am not sure how to exactly go about doing that. Do I get the transformation from parent? Maybe I am just complicating the problem in trying to produce this version of an extraction window that a client has requested.

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