ItemClipsToShape doesn't work

Rhadel

Hi,

I have a custom QGraphicsItem class that paints some complexes figures into scene. I have re-implemented boudingRect() member in order to make suitable "click and drag" on these kind of items. But a QRectF is not enough accurate for the precision that I need in clicks.

In my QGraphicsItem custom class I have the following sentences:

@
this->setFlag(QGraphicsItem::ItemClipsToShape, true);
this->setFlag(QGraphicsItem::ItemIsMovable, true);
@

As I understand, ItemClipsToShape flag should replace the call "boundingRect()" to check if item has been clicked, for "shape" (that returns a QPaintPath) with the shape where I want to detect the click.

Shape has been implemented correctly, to check it, I draw it and It's properly drawn in scene:
@
QPainterPath path = shape();
painter->drawPath(path); //Properly drawn.
@

The problem: it seems like Qt is still calling "boundingRect()" to get the area that I want to use to check if item is clicked, even with the flag set.

Any suggestions?

raven-worx

sry, but reading your post the following is not clear to me: did you reimplement QGraphicsItem::shape() in your graphicsitem subclass?

Rhadel

Yes, I did. It returns the shape that I want for click and collision.

raven-worx

can you please post the code of the shape() and paint() method

Rhadel

Sure:

It returns the shape. Its a bit complicated method. Some lines build the entire item:

@
QPainterPath Cable::shape() const
QPainterPath result;
QLineF checkingLine(QPointF(0, 0), QPointF (1, 0));
foreach (CableLine* course, lines){
QLineF current(course->posx, course->posy);
if (current.angleTo(checkingLine) == 0 || current.angleTo(checkingLine) == 180){
QPointF init(current.p1().x(), current.p1().y() - 3);
QPointF ending(current.p2().x(), current.p2().y() + 3);
QRectF rect(init, ending);
result.addRect(rect);
continue;
}
if (current.angleTo(checkingLine) == 90 || current.angleTo(checkingLine) == 270){
QPointF init(current.p1().x() - 3, current.p1().y());
QPointF ending(current.p2().x() + 3, current.p2().y());
QRectF rect(init, ending);
result.addRect(rect);
continue;
}
qDebug() << "Error condition";
}
result.setFillRule(Qt::OddEvenFill);
return result;
}
@

And paint:

@
void Cable::paint(QPainter *painter, const QStyleOptionGraphicsItem *, QWidget *)
{

if (!painter) return;
painter->save();

//Draw connection arrow:
QVector <QPointF> polyPoints;
CableLine* line = lines.last();
QLineF last(line->posx, line->posy);

polyPoints.append(QPointF(last.x2() - _ARROW_CABLE_WIDTH/2, last.y2()));
polyPoints.append(QPointF(last.x2() + _ARROW_CABLE_WIDTH/2, last.y2()));
polyPoints.append(QPointF(last.x2(), last.y2() + _ARROW_CABLE_HEIGHT));
QPolygonF poly(polyPoints);
painter->drawPolygon(poly);


painter->restore();

}
@

raven-worx

are you sure you want to use Qt::OddEvenFill fill rule instead of Qt::WindingFill ?
Nevertheless i couldn't spot any problem in your code on first glance.

But whats exactly the problem? That boundingRect() is called at all? Or that you receive mouse events even outside the shape?

Rhadel

No. The problem is that I want to use shape() instead boundingRect() in order to captura click events.

I tried with Qt::WindingFill, with the same resutl, and I setted this->setFlag(QGraphicsItem::ItemClipsToShape, true).

Even so, click event is only called inside the boundingRect() rectangle, but It's not the exactly area that I want the item to reply to such event. It's the shape area intead.

Shape area is correctly, because when I draw it in paint method, I can see correctly filled and drawn.

Thank you for you reply.

Rhadel

I have some troubles with mapTo.

When shapes colliding, I enter a function: "collisionProduced". But, by calling mapToScene, the shape seems being displaced to left. How it comes? I just changed the coordinate system in order to obtain the coords in scene system, not moving the shape.

JLin

I had same problem. My item is a circle icon, the boundingRect is a square. Clicks within the square but outside the circle area triggers mouse events. I fixed it by defining shape() as constant method, which overrides the parent::shape() const instead of overloading another shape().
@
QPainterPath shape() const;
@