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List:       pykde
Subject:    [PyQt] Handling QGraphicsItem snapping outside of itemChange
From:       Devan Richmond <devan.richmond () gmail ! com>
Date:       2015-02-25 9:45:24
Message-ID: CAJuBzCaTQLcSgH_38Cx+1JviJ40tni1Dfe+OXieGUd_AFNYtRQ () mail ! gmail ! com
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Hi,

I've been trying to create a snap to grid type system for QGraphicsScene and
it seems that most solutions rely on altering the item itself in it's itemChange
method. The problem I have with that solution is that it will also affect
what happens when you use QGraphicsItem::setPos

My ideal solution would decouple the items from any notion of grid snapping such
that the QGraphicsScene deals exclusively with the snapping.

    # QGraphicsScene::mouseMoveEvent
    def mouseMoveEvent(self, event):
        # snapping logic
        event.setScenePos(QtCore.QPointF(x, y))
        super().mouseMoveEvent(event)

I know that QGraphicsSceneMouseEvent::setScenePos is internal and not public but
 it demonstrates what type of functionality I'm aiming for. Similarly, the
 constructor is also internal so I can't subclass or create a new instance to
 inject my own event.

A kick in the right direction about how to implement something like this without
 using undocumented functions would be much appreciated.

 Thanks
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