Thanks Jérôme for pushing me into the right direction.
Now I see where I went wrong.
The buffers data assignment must be done as follows:
data: { var vertexArray = new Float32Array([ -1., 1., 0., 1., 1., 0.,
-1., -1., 0., 1., -1., 0. ]); return vertexArray; }
Cheers, Volker
Am 10.04.2019 um 15:57 schrieb Jérôme Godbout:
The new is not something you should do into binding for sure. If I look at the
Qml Buffer doc:
https://doc.qt.io/qt-5/qml-qt3d-render-buffer.html
Not much seem to be expose to Qml, syncData, usage
https://doc.qt.io/qt-5/qt3drender-qbuffer.html
and the sub class QBuffer offer the following properties accessType.
Seem like you will need to fill the data into C++ from what the doc is saying.
Maybe make your own QmlBuffer inherited class where you can expose QByteArray
to expose the data, the dataChanged signal is already present. Just need a
property exposure, wonder why this was not already exposed. You can make static
Q_INVOKABLE to create QByteArray from JS array type into that class:
Q_INVOKABLE QByteArray MakeVector3F(const QVariantList& data);
Q_INVOKABLE QByteArray MakeVector2D(const QVariantList& data);
...
Maybe add the data type, so you could have a call that push/pop data into your
buffer QByteArray
Q_INVOKABLE void pushData(const QVariant& data);
with the proper C++ call to convert the QVariant into the Buffer data type.
Those buffer class seem a bit anemic into functionality, wonder how they should
be normally be used?!? The Qml exposure seem incomplete to me. Maybe someone
with deeper knowledge can pitch in, but the only way I see it, they are fully
managed into C++ only to be plug in Qml at best, no containing data
manipulation into Qml from what I see. You use case seem legit to me, you have
some property you need to assign to a Buffer, you probably don't want to do
this with huge data set, but for simple and debugging buffer this will come in
handy to do so. In the real world, making C++ producer to generate you data
Buffer would be better performance wise.
I haven't play much with Qt3D, but we did a lot of rendering to texture at my
previous place, and we did have a Qml Buffer implementation way before Qt3D and
we did needed those data type and everything was named attribs to the rendering
actor and we could set the shader programs (vertex, geometry, fragment...) from
the Qml, we could attachs as many attribs Buffer and a draw call to the actors
for the rendering. I would expect something similar for a real 3D rendering
engine.
-----Original Message-----
From: Interest <interest-boun...@qt-project.org> On Behalf Of Volker Enderlein
Sent: April 10, 2019 3:48 AM
To: Qt Project <interest@qt-project.org>
Subject: [Interest] Initialization of Buffer entity property in QML
Hi,
in a QML file I try to initialize a property of type Buffer, but unfortunately
it does not work.
There's no error but in the MyMesh Entity the vertices Buffer always has zero
length.
import Qt3D.Core 2.0
import Qt3D.Render 2.0
import QtQuick 2.0
import Qt3D.Extras 2.10
Entity {
id: root
property Buffer vertices: Buffer { type: Buffer.VertexBuffer; data:
new Float32Array([ -1., 1., 0., 1., 1., 0., -1., -1., 0., 1., -1., 0. ]) }
MyMesh {
id: mesh
vertices: root.vertices
}
}
How is the correct way?
Cheers, Volker
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