CODEWITHSUNDEEP
c++qtqgraphicsviewqgraphicsscene
sashoalm
sashoalm

Reputation: 79705

Why do the first added item always appear at the center in a graphics scene/view in Qt?

I have a graphics scene and view, and then I'm adding a single element. But no matter what x/y coordinate I give, it always appears at the center of the graphics view.

Why does this happen, and how can I make it appear at, say, the upper left corner?

This is my code:

scene = new QGraphicsScene(this);
ui->graphicsView->setScene(scene);
QGraphicsEllipseItem *ellipseItem = scene->addEllipse(150, 150, 10, 10);

Upvotes: 1

Views: 2271

Answers (2)

Stephen Chu
Stephen Chu

Reputation: 12832

The reason for this is that by default, QGraphicsScene computes its sceneRect by adding all the item rectangles together. When you add the first item, it automatically uses it as the scene rect. And by default QGraphicsView scales and centers on the scene rect.

If you know the final or desired scene rect, set it before you add any item:

scene->setSceneRect(0, 0, 800, 600);
scene->addEllipse(150, 150, 10, 10);

Upvotes: 3

pwuertz
pwuertz

Reputation: 1325

You probably want to define a scene-rectangle that is shown by the QGraphicsView. I think the default view just shows the centered bounding rectangle of the current scene, which is just your ellipse. You can use QGraphicsView::fitInView to define the area to be shown explicitly.

Upvotes: 1

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