QML or QGraphicsView?

[been_1990]

I'm going to develop a game that relies heavily on animation, hit-testing, state changing, creating/moving/destroying many objects.
Two/four/six/eight views with the same scene and tile based map.
So, should I use QML or QGraphicsView?

[wysota]

Well... strictly speaking QML (or rather QtQuick) is also QGraphicsView so you'll be using Graphics View anyway. If you want multiple views on one scene then as far as I remember you can't use Qt Quick, it's a one-to-one (or one-to-zero) relation only.

[been_1990]

Why does it seem that QML is faster? When I use the Qt Demo QML apps, they work very smooth. But when I use graphics view, updating items positions is so slow...
I think using setPos() might be the culprit. Should I subclass QGraphicsSvgItem and use it's paint() to update it's position?
I saw this example (http://doc.trolltech.com/4.3/tutorial-t11.html) and they subclass a QWidget, reimplement paintEvent() and paint an updated QRect to reflect the items position. Would that help with the speed of QGraphicsView?

[aamer4yu]

I guess with QML comes more of javascript...
Most examples I have seen use javascript for function implementation.

While coding in graphicsview, you will be directly using Qt classes. QML also finally converts the code to Qt graphicsview code.

[wysota]

Why does it seem that QML is faster?
Because QtQuick is fine tuned to some specific use cases.

But when I use graphics view, updating items positions is so slow...
Because your code is not optimal.


I think using setPos() might be the culprit. Should I subclass QGraphicsSvgItem and use it's paint() to update it's position?
No, definitely not. That would break the whole architecture.

[been_1990]

Because your code is not optimal.

What would make my code optimal? The code I use gets the mouse position increment(from raw input), then sets the item with setPos():


QGraphicsSvgItem * redPointer = new QGraphicsSvgItem(QCoreApplication::applicationDirP ath().append("/redPointer.svg"));

void Widget::mouseCoord(int x, int y){
redPointer->setPos(QPointF::QPointF(redPointer->x()+x/3, redPointer->y()+y/3));
}

But that gets awfully slow , any pointers on how to optimize?

[wysota]

What would make my code optimal?
Fixing the slowest parts of it. What the slowest parts are depends on the use case.


The code I use gets the mouse position increment(from raw input), then sets the item with setPos():
setPos() is not the bottleneck.


But that gets awfully slow , any pointers on how to optimize?
I'd start by enabling the item cache.

[steno]

I would also check QGraphicsScene and see what you have set on your ItemIdexMethod. If your scene is highly dynamic and you have BspTreeIndex enabled, it could cause a slow down there.