[Qt-interest] mouse and polygons

[Mahendra G.R]

Hey Alex,

Thanks for your reply, 4points, i just made it for debugging purposes,
problem is, the application is already heavy on cpu which makes the gui
slower, and when i move the mouse it is really slow, i think there is some
problem with my mouseMove function, i dont know what iäm doing wrong, and
yes, i'm pretty new to c++ as well.  Sorry i didnt get your suggestion, can
you explain it again.


Thanks,
Best regards

On Wed, Nov 17, 2010 at 8:24 PM, Malyushytsky, Alex <alex at wai.com> wrote:

> The easiest way to find why you get segment  fault usually is to use
> debugger.
> At  a glance you have unsafe implementation of  addPolygons()
> which assumes QVector<QPointF> &points has at least 4 points.
> Similar assumptions are made in other place.
>
> With C++ you should be careful with your assumptions.
> Also I would suggest you to review documentation on function before you are
> using them.
> For example:
>     removeItem(tempItem)  will not delete item, as I think you assume each
> time you do it you create memory leak.
>
> As for keeping mouse inside polygon - you can't. User is able to move mouse
> where he wants.
> What you can do is to change way you treat the movement.
>
> For example you could register that user started movement on mount press,
> collect information you need about item in temporary storage and use it
> until you need it (in mouseMove for example).
>
> Alex
>
>
> From: qt-interest-bounces at trolltech.com [mailto:
> qt-interest-bounces at trolltech.com] On Behalf Of Mahendra G.R
> Sent: Wednesday, November 17, 2010 1:25 AM
> To: qt-interest at trolltech.com
> Subject: Re: [Qt-interest] mouse and polygons
>
> Hi all,
>
> anybody?, i just want to know how to contain the mouse pointer within the
> polygon, or avoid seg fault when mouse pointer goes out of my polygon,
>
>
> Regards,
>
> On Fri, Nov 12, 2010 at 5:01 PM, Mahendra G.R <mahendra at mahendragr.com>
> wrote:
> Hello all,
>
> I have implemented drawing polygons in a scene using QpolygonF,
> QGraphicsPolygonItem and QgraphicsScene.  When i click on the scene, i
> collect the points and create a polygon on the double click, until here its
> fine.  When i move/drag the polygon it does move.  But the problem is, i
> have a huge data set, and when i move the polygon with this dataset in the
> background, polygon moves slowly, and when the cursor goes out of the
> polygon, i get a segmentaion fault, how should i restrict cursor to be
> inside the polygon item or is there a better solution for this?
>
>
> My function :
>
>
> void CustomScene::addPolygons( QVector<QPointF> &points )
> {
>
>        QPolygonF polygon1(points), polygon2;
>        MyItem *item1;
>        QPointF p1,p2,p3,p4;
>
>        p1 = points.at(0);
>        p2 = points.at(1);
>        p3 = points.at(2);
>        p4 = points.at(3);
>
>        item1 = new MyItem;
>        item1->setPen(QPen(Qt::red));
>        item1->setPolygon(polygon1);
>        item1->setAcceptDrops(true);
>        item1->setFlag(QGraphicsPolygonItem::ItemIsMovable);
>        item1->setFlag(QGraphicsPolygonItem::ItemSendsGeometryChanges);
>
>
>        this->addItem(item1);
>
>        points.clear();
> }
>
> void CustomScene::mousePressEvent ( QGraphicsSceneMouseEvent * event )
> {
>
>
>
>    if (addPolygonFlag == true && event->button() == Qt::LeftButton)
>    {
>
>        points.append(event->scenePos());
>
>    }
>    else if (event->button() == Qt::RightButton)
>    {
>        QGraphicsPolygonItem *tempItem;
>        tempItem = (QGraphicsPolygonItem*)this->itemAt(event->scenePos());
>        removeItem(tempItem);
>
>    }
>    QGraphicsScene::mousePressEvent(event);
>
> }
> void CustomScene::mouseDoubleClickEvent(QGraphicsSceneMouseEvent *event)
> {
>    addPolygons(points);
>    addPolygonFlag = true;
>    QGraphicsScene::mouseDoubleClickEvent(event);
>
> }
> void CustomScene::mouseMoveEvent ( QGraphicsSceneMouseEvent * event )
> {
>
>        QTextStream out(stdout);
>        MyItem *tempItem;
>
>        tempItem = (MyItem*)this->itemAt(event->scenePos());
>
>
>        if (tempItem == 0)
>        {
>            QGraphicsScene::mouseMoveEvent(event);
>            return;
>
>        }
>
>        tempPoly = tempItem->polygon();
>        //tempPoly1 = tempItem1->polygon();
>
>        QPointF p1,p2,p3,p4;
>        p1 = tempPoly.at(0);
>        p1 = tempItem->mapToParent(p1);
>        p2 = tempPoly.at(1);
>        p2 = tempItem->mapToParent(p2);
>        p3 = tempPoly.at(2);
>        p3 = tempItem->mapToParent(p3);
>        p4 = tempPoly.at(3);
>        p4 = tempItem->mapToParent(p4);
>
>        out <<"p1: "<<p1.x()<<" "<<p1.y()<<endl
>            <<"p2 : "<<" "<<p2.x()<<" "<<p2.y()<<endl
>            <<"p3 : "<<" "<<p3.x()<<" "<<p3.y()<<endl
>            <<"p4 : "<<" "<<p4.x()<<" "<<p4.y()<<endl;
>
>        QGraphicsScene::mouseMoveEvent(event);
>
>
> }
>
> --
> http://www.mahendragr.com
>
>
>
> --
> http://www.mahendragr.com
>
>
>
> ---------------------------------------------------------------------------------------------------
> Weidlinger Associates, Inc. made the following annotations.
>
> “This message and any attachments are solely for the intended recipient and
> may contain confidential or privileged information. If you are not the
> intended recipient, any disclosure, copying, use, or distribution of the
> information included in this message and any attachments is prohibited. If
> you have received this communication in error, please notify us by reply
> e-mail and immediately and permanently delete this message and any
> attachments. Thank you.”
>
> “Please consider our environment before printing this email.”
>
> _______________________________________________
> Qt-interest mailing list
> Qt-interest at trolltech.com
> http://lists.trolltech.com/mailman/listinfo/qt-interest
>



-- 
http://www.mahendragr.com
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.qt-project.org/pipermail/qt-interest-old/attachments/20101117/bb0492c9/attachment.html