Qt3D Qt3DRender:QBuffer update -> No Frame update ?

BillouParis2

Hi guyz,

I created a C++ class to provide vertices data to QML stored in a Qt3DRender::QBuffer.
So the C++ is very basic. I have a qByteArray ready with many vertices.

Header:
    Q_PROPERTY(Qt3DRender::QBuffer *buffer READ buffer WRITE setBuffer NOTIFY bufferChanged)
    Qt3DRender::QBuffer * m_pBuffer;
Source:
    m_pBuffer = new Qt3DRender::QBuffer( nullptr);
    m_pBuffer->setData(qByteArray);

I use the example QML that declares the Geometry as below:
There is a binding with my C++ class property pointsCloud.buffer at the bottom.

Geometry {
       id: idPointsCloudVertexGeometry
       Attribute {
           id: idPointsCloudAttribute
           attributeType: Attribute.VertexAttribute
           vertexBaseType: Attribute.Float
           vertexSize: 3
           byteOffset: 0
           // One float is four bytes, we have 3 coordinates for one vertex
           // Each vertex is close to the next one
           // So the stride is only 3 * 3 * 4
           byteStride:  3 * 3 * 4
           // the vertices count is the array length
           // divided by 3 coordinates for each vertexBaseType:
           count: pointsCloud.pointsCount
           // name found in the vertex shader
           name: "vertexPosition"
           buffer: pointsCloud.buffer
       }
   }

This is working fine (well I have an issue with number of elements, I shall register a Qt Bug later maybe, but if the number is reasonnable, say 20000 vertices, this works fine and display a shape EDIT: I solved this by changing the stride value to 3 * 4 instead of 3 * 3 * 4!)
Now I would like to update the data regularly and have a Frame refresh for the new data.
For this I rely on the updateData method from Qt3DRender::QBuffer
And I override data for the entire buffer, vertex per vertex with a local qByteArray of 3*4 bytes (x, y, and z as float)

m_pBuffer->updateData(iCurrentVertex * 3  * sizeof(float), qByteArraySingle);

But the problem is that I don't get any redraw of the frame, or at least nothing that I can see.
So I added an

emit bufferChanged();

=> It does not help.

I even added a QML Connection in the QML part to make sure the buffer had changed. => it does not help

QQ2.Connections {
        target: pointsCloud
        onBufferChanged: {
            console.log("buffer had changed")
            idPointsCloudAttribute.buffer = pointsCloud.buffer
        }
    }

I even tried to set null to the buffer, and the frame is not refreshed, but I get an error message:

calculateLocalBoundingVolume: Position attribute not referencing a valid buffer

Does any one has any idea why the frame is not refreshed with the new data.
I suspect a CPU/GPU wrong sync at some point, but I don't know how to work this out.
Any help is welcome.
Thank you,

Bill

BillouParis2

Hi guyz,

I finally decided to copy data all the time, for each new data, and then the 3D Frame is refreshed correctly. I wish I knew a better option though.

I will set this topic as solved.
Thank you
Bill

BillouParis2

I shared a sample demo here: https://github.com/billouparis/pointsCloud#readme