I'm trying to locate an item of a tree widget.
Looking up in the doc, I got:
QTreeWidgetItem * QTreeWidget::itemAt ( const QPoint & p ) const
Returns a pointer to the item at the coordinates p. The coordinates are relative to the tree widget's viewport().
The viewport() function does not give definition about viewport either.
So what is a tree widget's viewport ?
QTreeWidget inherits from QAbstractScrollArea, which is where the viewport is defined:
QAbstractScrollArea is a low-level abstraction of a scrolling area. The area provides a central widget called the viewport, in which the contents of the area is to be scrolled (i.e, the visible parts of the contents are rendered in the viewport).
The viewport is essentially the visible part of the tree.
Related
I am trying to limit the movement of QGraphicsItem inside of a parent object inherited from QGraphicsPathItem that has an arbitrary complex shape (not square).
As I understand, I should extract each point of the moving object and check whether each of them is not contained in the parent QPainterPath. Then split the parent QPainterPath into small rectangle-shaped polygons and restrict movement area in the bounding box of each sub polygon.
So, I would like to know if there are any other options to exist. Thanks.
Maybe you can check on QGraphicsItem move event if it is still inside QGraphicsPathItem.
The check itself, you can do it with this QGraphicsItem method:
bool QGraphicsItem::collidesWithItem(const QGraphicsItem * other, Qt::ItemSelectionMode mode = Qt::IntersectsItemShape) const
And to be sure that item is still fully enclosed inside its parent, set the mode to Qt::ContainsItemShape
If it is false, return QGraphicsItem to its previous position
EDIT: this check returns if QGraphicsItems shape is inside other QGraphicsItems shape, not its bounding box.
I've a custom QGraphicsItem which draws nothing but is parent to other QGraphicsItems (like QGraphicsRectItem and so on). My top-level item has (0,0) somewhere "inside" the children Items. This is very inconvenient. I would like to shift the origin to the upper left corner of childrenBoundingRect().
In the picture I've (0,0) of my top-level item somewhere inside of my children items (solid arrow). I would like to shift the origin to the dashed lines. How can I do that?
As result I expect that positioning of the top-level item will be more convenient.
Examples for overriding QGraphicsItem often show the boundingRect() function originating from (0,0). Changing this will change the origin. So, for example, to change it to the centre, where width and height are variables stored internally in the class, you can do this: -
QRectF boundingRect() const
{
return (-width / 2, -height / 2, width, height);
}
in Qt 4.8 i have create a QGraphicsView and a DynamicRadarScene(derived from QGraphicsScene):
QGraphicsView* view = new QGraphicsView;
view->setMinimumSize(800, 600);
DynamicRadarScene* _scene = new DynamicRadarScene(mode, channel_types, this);
view->setScene(_scene);
What is the coordinate system of QGraphicsScene? (0,0) is from upper left corner?
How can i draw an item in the upper right corner of the scene (i have set it 800x600: view->setMinimumSize(800, 600);)?
If i resize the widget and so i resize the QGraphicsView, how can move the item i have drawn before to remain in the upper left corner?
Yes, the upper left corner is generally the coordinate of (0,0) in a graphics scene. What you need to consider is that a QGraphicsView is like a window looking into a world (the QGraphicsScene). You set the view to look at an area or the scene, which may be all or just part of the scene.
Once the scene and view are setup, you can then add QGraphicsItems / QGraphicsObjects or instances of classes derived from those by using functions such as QGraphicsScene::addItem. These items are positioned in the scene and draw themselves.
i (sic) resize the widget and so i resize the QGraphicsView
You can change the QGraphicsView position and dimensions, but then the items in the scene will remain in the same place within the scene. Usually you would set up the scene and view and then move / resize the graphics items / objects within the scene, often with the setPos function: QGraphicsItem::setPos(). This sets the position of the item, relative to its parent. If the item has no parent, it sets the position of the item in the scene.
QGraphicsScene has property sceneRect. If it is not set then it is auto adjusted depending on scene content. This can give a filling that origin of coordinating is in some strange place or even that it is mobile.
Set this property. See also this.
Whenever I add a new item to a QGraphicsScene, the origin of the QGraphicsScene seem to change for the position of the item I have just added.
How to make the QGraphicsScene origin fixed?
Do I need to add the item first in the QGraphicsScene and then specify a position for the item?
Well, by default the content of the scene will be centered in the QGraphicsView. The origin of the graphics scene does not change randomly.
You might want to use setSceneRect() to define the size of the scene, so that the QGraphicsView always centers the scene in the view in a fixed manner. (If you don't set it manually, the rect will be calculated based on the items in the scene, which changes if you add more.)
I answered a related question about a year ago that may be helpful:
How to draw a point (on mouseclick) on a QGraphicsScene?
Ditto to what badcat.
There are a lot of controls for adjusting or manipulating your viewport(s) that you have pointing at your scene. The scene sets what is on the stage. The view is how you look at it. Be sure to set the sceneRect or set it indirectly using centerOn or fitInView or scale or translate from the QGraphicsView class.
http://qt-project.org/doc/qt-4.8/graphicsview.html
http://qt-project.org/doc/qt-4.8/qgraphicsview.html
QGraphicsScene::setSceneRect ( const QRectF & rect ) will make it absolute.
see http://doc.qt.digia.com/qt/qgraphicsscene.html#sceneRect-prop
I'm new to Qt, so I might mangle this question. Having said that-
I'm rendering an image within a subclassed QGraphicsView. I added the image to the scene as a Pixmap with addPixmap(). I'd like to overlay (blit) smaller images on top of the larger one in specific locations. I can add the smaller image to the scene as well by again calling addPixmap(), but it always displays in the upper left corner. I'd like to set those coordinates myself.
How can I accomplish this?
Thanks!
QGraphicsScene::addPixmap returns a pointer to the added QGraphicsPixmapItem. If you want to set its position, you can do something like this:
QGraphicsPixmapItem *item = scene->addPixmap(yourPixmap);
item->setPos(50, 50); // sets position to scene coordinate (50, 50)
If you want to overlay images on top of other images, make sure you know about z-values. See the QGraphicsItem documentation for details. Basically, the z-value determines the stacking order.
Lastly, familiarize yourself with parenting of QGraphicsItems. When a QGraphicsItem has a parent item, it means (among other things) that its coordinates are expressed in terms of its parents' coordinates. So if an item has a position of (0, 0), but it's the child of an item whose scene position is (50, 50), then the child item will be displayed at (50, 50). So, given the above example, you could then do:
QGraphicsPixmapItem *childItem = new QGraphicsPixmapItem(item);
This creates a new item, "childItem", whose parent is "item". Its coordinates are (0, 0), because they haven't been set yet, but its scene coordinates are (50, 50), because it is the child of "item". Note that when you specify an item's parent, you don't need to add the child item to the scene; it is implicitly added.