How to move/repaint object in a graphicsscene

[qtgames]

The boundingRect defines the area of your item. If boundingRect() returns (-48,64, 98,24) then your item "starts" at (-48,64) and "lasts" until (50,88).

How can you calculate the end point?

The player can only resize the view, not the scene.

But when the view is resized the scene is also resized.

Please provide a minimal compilable example reproducing this behaviour.

It is a multifile project so I attached it along with this reply

QGraphicsRectItem *item = scene.addItem(QRectF(-100,-50, 200, 100), QPen(Qt::red)); // adds an item to the scene
qDebug() << item->boundingRect() << item->pos() << item->sceneBoundingRect();
item->setPos(50,50);
qDebug() << item->boundingRect() << item->pos() << item->sceneBoundingRect();

QGraphicsRectItem *item = scene.addItem(QRectF(-100,-50, 200, 100), QPen(Qt::red)); // adds an item to the scene
qDebug() << item->boundingRect() << item->pos() << item->sceneBoundingRect();
item->setPos(50,50);
qDebug() << item->boundingRect() << item->pos() << item->sceneBoundingRect();

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The outputs are identical.

[wysota]

How can you calculate the end point?

Please read the docs for QRectF.

But when the view is resized the scene is also resized.

No, it's not.

The outputs are identical.

Did you try it in your application or a verbatim one? Create an application that consists of only a pure scene, pure view and the above calls.

[qtgames]

No, it's not.

When I click to the bottom right corner the event->x() is different than when I resize the window and click bottom right corner and read event->x(). And I pull the scroll bars to the end. How is that possible?

Did you try it in your application or a verbatim one? Create an application that consists of only a pure scene, pure view and the above calls.

The pure one doesn't compile. addItem doesn't have such definition.

[qtgames]

Ok, some progress. The click, vehicle->pos() and the sceneBoundingRect() are at the same location. However, when the items are added into the scene, their vehicle->pos() is at (0,0), but they are 80,80 point below the top left corner.

More progress. The scene was not initialized at 0,0 in the BattleField and that's why there was an offset. Now the only problem is that repaint doesn't work. I have to manually refresh.
And setViewportUpdateMode(FullViewportUpdate) solved this. Thanks.

[qtgames]

Actually there is still a problem with the scroll bars. The movement works ok, when we at the top left corner of the scene. However, in bottom right corner the event->x() gives coordinates relative to the top left corner of the view, even if there is more scene behind the scroll bars. How can I get absolute coordinates in the scene?

[wysota]

When I click to the bottom right corner the event->x() is different than when I resize the window and click bottom right corner and read event->x(). And I pull the scroll bars to the end. How is that possible?

Add this code to your program:

QGraphicsRectItem *item = scene.addRect(scene.sceneRect(), QPen(Qt::red), Qt::yellow));
item->setZValue(-1);

QGraphicsRectItem *item = scene.addRect(scene.sceneRect(), QPen(Qt::red), Qt::yellow));
item->setZValue(-1);

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item->setOpacity(0.5);
This will add an item to the scene which is the size of the scene itself. Then start manipulating the window size and see how the scene is moved in the view (you have to trust me its size doesn't change).

The pure one doesn't compile. addItem doesn't have such definition.

Man...

#include <QtGui>
 
int main(int argc, char **argv){
  QApplication app(argc, argv);
  QGraphicsView view;
  QGraphicsScene scene(-400,-400,800,800);
  view.setScene(&scene);
  QGraphicsRectItem *item = scene.addRect(QRectF(-40, -20, 80, 40), QPen(Qt::red));
  qDebug() << item->pos() << item->boundingRect() << item->sceneBoundingRect();
  item->setPos(QPointF(100,80));
  qDebug() << item->pos() << item->boundingRect() << item->sceneBoundingRect();
  return app.exec();
}

#include <QtGui>

int main(int argc, char **argv){
  QApplication app(argc, argv);
  QGraphicsView view;
  QGraphicsScene scene(-400,-400,800,800);
  view.setScene(&scene);
  QGraphicsRectItem *item = scene.addRect(QRectF(-40, -20, 80, 40), QPen(Qt::red));
  qDebug() << item->pos() << item->boundingRect() << item->sceneBoundingRect();
  item->setPos(QPointF(100,80));
  qDebug() << item->pos() << item->boundingRect() << item->sceneBoundingRect();
  return app.exec();
}

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Now the only problem is that repaint doesn't work. I have to manually refresh.
And setViewportUpdateMode(FullViewportUpdate) solved this. Thanks.

Bad idea. Find out why it doesn't refresh or else you'll have more problems later.

You can add this to your item's paint() routine:

painter->drawRect(boundingRect());

painter->drawRect(boundingRect());

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This will show you if you're drawing in the proper rectangle.