[Interest] Rotating objects in QML are killing performance

[Michael Andersen]

Hi list,

I have a loading throbber in my application that is completely killing the
performance. If it is rotating then the application does not repaint while
it is being dragged and if more than two or three copies of the application
are running then it starts lagging Unity. I'm on Ubuntu 12.04 with Qt 5.0.1
64-bit. I was going to wait until 5.2 was out and check again, but it's
taking a little longer than I expected for a stable version to be released.

Here is a simple reproducer of the problem, I create a QtQuick2 application
in Qt Creator 2.7. I adjust the QML to look like this:

import QtQuick 2.0

Rectangle {
    width: 400
    height: 400
    Rectangle {
        id: redsquare
        color: "red"
        width: 50
        height: 50
        x: 50
        y: 50
    }
    RotationAnimation {
        loops: Animation.Infinite
        target: redsquare
        properties: "rotation"
        from: 0
        to: 360
        duration: 300*5
        direction: RotationAnimation.Clockwise
        running: true
    }
}

My main.cpp is the default, but that looks like this:

#include <QtGui/QGuiApplication>
#include "qtquick2applicationviewer.h"

int main(int argc, char *argv[])
{
    QGuiApplication app(argc, argv);

    QtQuick2ApplicationViewer viewer;
    viewer.setMainQmlFile(QStringLiteral("qml/SimpleRotator/main.qml"));
    viewer.showExpanded();

    return app.exec();
}

I am new to Qt, so perhaps I am doing something wrong with my animation,
but I have tried a couple other methods of animating and they all lag
equally badly. The PC I develop on is quite a monster, so if it is lagging
on this, I hate to think what it's going to do on my clients' laptops.

Anyone have any ideas?

Regards
Michael
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