Issue with moving QGraphicsItem Fast
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Flickering effect indeed !
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Are the slider and item very close to each other? If so, try out if the effect is still there if you put a bit of distance between then.
What do you actually do in the item's slot?
Since I don't know such flickering effects (at least on typical PC hardware), I suspect the slider being used via proxy item. Can you test what happens when the events are generated some other way, e.g. by a timer, not by the slider?
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Thanks for your help :)
The slider and the item are indeed touching each other as I want the QGraphicsItem ( a custom line) to make the continuation of the slider's handle.
I will try what you are proposing, however, its weird that this only appears from right to left and not from left to right doesnt it? -
bq. What do you actually do in the item's slot?
I dont have item's slot, I just have a slot for my mainwindow which will move this item in the scene by using setPos() according to the slider's signal.
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If all you do is calling setPos(), you shouldn't get this effect.
What type does your QGraphicsItem have? If it's custom, are you sure the boundingRect is calculated correctly? -
Yes it is just what I do... I subclassed QGraphicsItem and added a drawLine in the paint method.
My bounding rect is calculated correctly too .. It is not updated when the item moves but I think it should not, as its a local bouding rect.
I cant have a look at the code right now (I am at work) but I am pretty sure its what I did.But cant it come from the intersection of the item (line) with the slider as you mentionned before?
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what means "convert newposx to pixel value"? how do you do that?
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I used :
int QStyle::sliderPositionFromValue ( int min, int max, int logicalValue, int span, bool upsideDown = false )to have a pixel value from the slider value as I want the line and the slider's header to align.
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Hello,
Asperamanca : after some tests, it looks like its because of the bounding rect you were right ;)
However, I dont know how to set it properly. I was thinking that the bounding rect doesnt need to update if you change the position.I have on my line :
@void Item::paint(QPainter *painter, const QStyleOptionGraphicsItem *option, QWidget *widget)
{
QPen pen(Qt::black);
pen.setWidth(2);QBrush brush(Qt::blue); painter->drawLine(0,0,0,500);}
QRectF Item::boundingRect() const
{
return QRectF(0,0,10,500);
}@and in my window the slot:
@void MainWindow::changeXLinePos(int val)
{
int val2 = slid->style()->sliderPositionFromValue(0,1000,val,slid->width());
qDebug() << "val" << val;
qDebug() << "pix" << val2;
item->setPos(treeWidget->header()->sectionPosition(3)+val2,0);
}@How should I set the bounding rect correctly while the item s moving?
Should I tale the new position as an attribute of the item, update the bounding rect after calling prepareGeometryChange?Thanks for your help !
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no idea? ;)
