[Interest] Qt3D/QML How to access a QTransform based property from C++

[Sean Harmer]

Set the properties on the QTransform, not the QTransform itself. But in 
general don't poke up into the QML layer from C++. Much better idea to bind 
the transform in QML to properties on an object you export from C++ to QML.

i.e.

Entity {
    components: [
        Transform {
            translation: _myObject.position
        }
    ]
}

then from C++:

class MyObject : public QObject
{
    Q_OBJECT
    Q_PROPERTY(QVector3D position ...)
    ...
}

auto myObject = new MyObject();
rootContext()->setContextProperty("_myObject", myObject);

Then just update the properties on your myObject and the QML will reflect this.

With this approach, if you change your QML, your lower C++ layer won't break.

Cheers,

Sean

On Wednesday, 30 August 2017 09:07:08 BST Volker Enderlein wrote:
> Hi all,
> 
> for an animation system I try to construct some parameterized QML
> components that provide access to their transformation and material via
> properties. The QML part looks the following way:
> 
> import Qt3D.Core 2.0
> import Qt3D.Render 2.0
> import QtQuick 2.0
> import Qt3D.Extras 2.0
> 
> Entity {
>      id: root
> 
>      property Transform frame: Transform {}
>      property Material mat: PhongMaterial { diffuse: Qt.rgba(0.8, 0.8,
> 0.8, 1.0) }
> ...
> 
> }
> 
> Later I try to update the Transform and Material from C++. But I cannot
> set the properties via qmlEntity->setProperty("Transform",
> QVariant(Qt3DCore::QTransform)); because QTransform is not usable as
> metatype.
> 
> How would I do that, or should I use an entirely different approach?
> 
> 
> Cheers Volker


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--
Dr Sean Harmer | sean.harmer at kdab.com | Managing Director UK
Klarälvdalens Datakonsult AB, a KDAB Group company
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