CODEWITHSUNDEEP
c++qtqt5qgraphicsviewqgraphicsitem
Haj Ayed Amir
Haj Ayed Amir

Reputation: 197

QGraphicsView/Scene - items are drawn 2x away from mouse click

I've been trying to use the graphic view framework to draw nodes where I click. However, I can't get the position right.

This behaviour happens : I click on the yellow point and the node appears there I click on the yellow point and the node appears there.

So here's the code for mainwindow.cpp : 

MainWindow::MainWindow(QWidget *parent) :
QMainWindow(parent),
ui(new Ui::MainWindow) {

  scene = new GraphScene(this);
  ui->setupUi(this);

  ui->graphicsView->setScene(scene);
  ui->graphicsView->setSceneRect(ui->graphicsView->rect());
  ui->graphicsView->setFrameStyle(0);
  ui->graphicsView->show();
}

the custom scene mousePressEvent: 

void GraphScene::mousePressEvent(QGraphicsSceneMouseEvent *event){
if (!this->itemAt(event->scenePos(), QTransform())){
    this->addItem(new NodeItem(event->scenePos()));
    this->update();
}
}

And the node item : 

NodeItem::NodeItem(QPointF position) {
    this->setPos(position) ;
}

void NodeItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget){
    painter->drawEllipse(pos(), 30.0, 30.0);
}

QRectF NodeItem::boundingRect() const{
    return QRectF(pos(), QSizeF(30,30));
}

I tried my best to fix it but I've stuck for a while and can't fix it. I'll appreciate any help.

Upvotes: 1

Views: 268

Answers (1)

eyllanesc
eyllanesc

Reputation: 243955

QGraphicsView and QGraphicsScene handle different coordinate systems, in the case of boundingRect() and paint() methods they must do in local coordinates with respect to the item and you should not use the pos() method since that refers to coordinates with respect to the scene.

void NodeItem::paint(QPainter *painter, const QStyleOptionGraphicsItem * /*option*/, QWidget * /*widget*/){
    painter->drawEllipse(boundingRect());
}

QRectF NodeItem::boundingRect() const{
    return QRectF(QPointF(-15, -15), QSizeF(30,30));
}

Upvotes: 1

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