Collision between QGraphicsItem -

Does it matter if I check collision of a GraphicsItem to every other item in a scene or if I check collision of an item against the parent of these items?

Ex:
Option 1:

Code:

---

QGraphicsItem generic1;
QGraphicsItem generic2;
[...]
QGraphicsItem generic30;
 
 
QGraphicsItem mainItem;
 
mainItem.collidesWithItem(generic1);
mainItem.collidesWithItem(generic2);
[...]
mainItem.collidesWithItem(generic30);

---

Option2:

Code:

---

QGraphicsItem genericItemParent;
QGraphicsItem generic1.setParent(genericItemParent);
QGraphicsItem generic2.setParent(genericItemParent);
[...]
QGraphicsItem generic30.setParent(genericItemParent);
 
 
QGraphicsItem mainItem;
 
mainItem.collidesWithItem(genericItemParent);

---

Which one is faster?

I would partition my scene to minimize the number of objects I am tracking for collision.

How do I partion the scene? Never heard of that...

Did a quick google for you:

http://ubuntu-gamedev.wikispaces.com...sion+Detection

and

http://tinyurl.com/3yu6r3n

Sorry, "how to do it in QT?" should be the question.
So, if I mapToScene() my graphicsView viewport rect, then check any colliding items, then check if those items collide with the "mainItem"?

Example (pseudo-code):

Code:

---

QGraphicsItem generic1;
QGraphicsItem generic2;
[...]
QGraphicsItem generic30;
 
 
QGraphicsItem mainItem;
//-------------------------------------//
QGraphicsView view;
QGraphicsScene scene;
void addSceneItems(){/* add all items to scene */ }
view.setScene(scene);
 
QPolygonF polygon;
polygon = view.mapToScene(0,0,view.width(),view.height);
 
//--> make poligon "invisible" somehow...
 
void itemVSpoli()
{
      for(int i=0;i<scene.items().count();i++)
      {
             if(scene.itemAt(i).collidesWithItem(polygon))
                     //send item to function that checks if 
                     // it collides with mainItem.
       }
}

---

So it was simpler than that:

Code:

---

QPolygonF poli = sceneView->mapToScene(0,0,sceneView->width(),sceneView->height());
    QList<QGraphicsItem *> sceneItems;
    sceneItems = scene->items(poli); //this only returns items that are drawn in the screen

---

And why not just do this?

Code:

---

QGraphicsItem *myItem = ...
//...
QList<QGraphicsItem*> collisions = scene->collidingItems(myItem);

---