highlight QGraphicsItem

user4592357

i was missing the call to prepareGeometryChange() in hoverLeaveEvent

by the way i noticed that when i hover over the bottom (in picture) item, it "goes up". when i hover over the top item, it "goes down".

this happens only after first time hovering. after that they don't move.

what is the reason?

kenchan

@user4592357
that is probably the scene or the view adjusting the scaling for the added items. That is why I asked about the settings you are applying to those before doing the drawing.

kenchan

@user4592357
Please mark the thread as solved if that is the case.

user4592357

@kenchan
the only setting i have is applied to the view:

setRenderHint(QPainter.Antialiasing)
setRenderHint(QPainter.TextAntialiasing)

removing them doesn't solve the problem, however.

kenchan

@user4592357
No they wouldn't, i was thinking more in terms of...

setViewportUpdateMode()
setResizeAnchor()
setDragMode()
setHorizontalScrollBarPolicy()
setSceneRect()

and the like on the QGraphicsView. These things can affect how the scene behaves. It is a good idea to check how they affect yours.

user4592357

@kenchan
setSceneRect() seems to do the job. but how do i tell it to use all the available area as scene rect? because i might have dockable widgets enabled in which case i need the scene rect to be smaller (i hope i could explain it)

kenchan

@user4592357
Yes well that is the tricky bit. the sceneRect is the part of the scene you want to fit into the viewport rectangle.
make it bigger in scene space and it looks smaller in the viewport and so on. You can make it scale automatically to the items in the scene or do it manually.

user4592357

@kenchan
this did the trick ():

view->setSceneRect(scene()->sceneRect())

and my last question. as you could see in the above pictures, the crosses' bounding rects may overlap. in that case, when, for example cursor is in bottom cross's bounding rect, and i try to touch the lower right part of above cross, the highlight for the above cross isn't displayed.

is this issue solvable?

kenchan

@user4592357
Ok, now things might get a bit more complex. The selection is currently using the bounding box so when they overlap you need to do more work if you want to distinguish exactly which cross was hit. In this case the zValue of the items is making the one you drew last get the hit first? You can set the zValue when this is important for picking but I don't think it helps in this case :-).
Please read the documentation about the QGraphicsItem (the c++ docs I guess). If you implement the shape() method you can use a QPainterPath to return a more accurate shape, in your case lines with a thickness. You need to make it look at the thin version of the line because that is what the user will be seeing and trying to pick. You can use contains() and collidesWithPath() etc. to get a more precise picking experience :-). You will probably want to use these different testing functions in the event before you decide that the cursor is actually hovering over your shape. This kind of testing can get slow for complex shapes and when you have many shapes to test, but the bounding box test filters out things pretty quickly.
In the last resort you can implement you own geometric testing algorithms but you probably don't need to go that far, do you?

I hope this all helps :-)

user4592357

@kenchan
something like this?

    def shape():
        path = QPainterPath(QPointF(x(), y()))
        path.setFillRule(Qt.WindingFill)
        update()
        path.lineTo(QPointF(100, 100))
        return path

this doesn't work though. i don't know how to return shape for two lines.

EDIT: what about using two QGraphicsLineItems? how would i return the shape() of the total then?

kenchan

@user4592357
You should draw a path which is exactly the same shape as your two lines. Using the same points and using the painter moveto or lineto functions.

QPainterPath path;
path.moveTo(0,0);
path.lineTo(100,100);
path.moveTo(0,100);
path.lineTo(100,0);
return path;

if you want to include the thickness of the pen you use a QPainterPathStroker like this

QPainterPath path;
path.moveTo(0,0);
path.lineTo(100,100);
path.moveTo(0,100);
path.lineTo(100,0);
QPen pen(QBrush(QColor(255,0,0)),2,Qt::SolidLine,Qt::RoundCap);
QPainterPathStroker stroker(pen);
return stroker.createStroke(path);

I have edited my code in the previous post and added the code for the shape. It works perfectly for me :-)

user4592357

@kenchan
thank you so so much, works perfectly! i wish i was confident (or smart) enough to write that code myself...

kenchan

@user4592357
Glad to hear it worked for you :-)
As you can see in this case just adding the shape function made the hover events respond to the more precise shape without the need for more checking code.
Is that cool or what!