highlight QGraphicsItem

user4592357

@kenchan
i reset it after drawing the white line.
it is drawing above red line instead of around it

kenchan

@user4592357
Well I am sorry to say that i just made a test using the same ideas in C++ and it works just fine for me and I don't have to call update :-).
So are we seeing a Python issue here or is it your paint function ?

user4592357

@kenchan
can you please share the code? maybe i am missing something?

kenchan

@user4592357
It is in an app for testing my QGraphicsItems but I can share the code for the subclass.
As a matter of interest what settings do you use for the QGraphicsScene and View? maybe the drawing is being influenced by those settings?

kenchan

@user4592357
Looking at your paint code, I think it is wrong. I think you should separate the line drawing into two if sections.

One draws both lines when hovering and the other draws just one line when not. That is how my code is. I tried it your way and I only saw the the thick lines.

kenchan

@user4592357

Here is my code, i hope it helps.

EDIT: added the code for the shape() member function;
Using a path stroker with the same line thickness as the thin line.
Also, made the highlight line 50% transparent.

The header

class TestItem : public QGraphicsItem
{
public:
    bool hovering;
public:
    explicit TestItem(QGraphicsItem * parent = 0);

    void setHovering(bool flag);
    QRectF boundingRect() const;
    void paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget);
   QPainterPath shape() const;

    virtual void hoverEnterEvent(QGraphicsSceneHoverEvent * event);
    virtual void hoverLeaveEvent(QGraphicsSceneHoverEvent * event);

};

The code

TestItem::TestItem(QGraphicsItem * parent) : QGraphicsItem(parent)
{
    setAcceptHoverEvents(true);
    hovering = false;
}

void TestItem::setHovering(bool flag)
{
    hovering = flag;

}

QRectF TestItem::boundingRect() const
{
    if(hovering)
        return QRectF(-4, -4, 106, 106);
    else
        return QRectF(-2,-2, 102, 102);
}

void TestItem::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
    QPen pen1(QBrush(QColor(0,255,0,128)),8,Qt::SolidLine,Qt::RoundCap);
    QPen pen2(QBrush(QColor(255,0,0)),2,Qt::SolidLine,Qt::RoundCap);

    if(hovering)
    {
        painter->setPen(pen1);
        painter->drawLine(0.0,0.0,100.0,100.0);
        painter->drawLine(0.0,100.0,100.0,00.0);

        painter->setPen(pen2);
        painter->drawLine(0.0,0.0,100.0,100.0);
        painter->drawLine(0.0,100.0,100.0,00.0);
    }
    else
    {
        painter->setPen(pen2);
        painter->drawLine(0.0,0.0,100.0,100.0);
        painter->drawLine(0.0,100.0,100.0,00.0);
    }
}

QPainterPath TestItem::shape() const
{
    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);
}

void TestItem::hoverEnterEvent(QGraphicsSceneHoverEvent * event)
{
    prepareGeometryChange();
    setHovering(true);
}

void TestItem::hoverLeaveEvent(QGraphicsSceneHoverEvent * event)
{
    prepareGeometryChange();
    setHovering(false);
}

kenchan

@user4592357
I edited the code a bit to make it thicker gave it round caps and made the bounding rect a tad bigger. It was leaving crud behind after it was removed :-)
looks nicer now.

user4592357

@kenchan
thnaks.

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!