Qt3D從QGeometry讀取原始頂點數據

Question

我正在開發一個使用Qt3D的應用程序，需要通過C++訪問原始頂點數據。我正在使用QObjectPicker進行射線定位，但由於數據是專用的（我開發了一個導入程序，它爲包含溫度讀數的每個頂點添加了一個額外的屬性），所以我不能使用QObjectPicker來方便地從這個點讀取數據。

3D對象正在通過QMesh加載，所以我相信訪問原始數據的最佳方式是通過QMesh的QGeometry成員。如我錯了請糾正我。 QGeometry具有保存頂點屬性的向量QAttribute。 （再次，糾正我，如果我錯了。）從這一點上，我不知道如何從特定的頂點索引讀取數據。我的猜測是，我需要從某個位置讀取QAttribute::buffer的數據，方法是知道每個頂點數據有多大，然後從偏移量讀取，但我該怎麼做？

這是我想出迄今：

void ES3DScene::handlePickerClicked(QPickEvent *pick) 
{ 
    QPickTriangleEvent *trianglePick = qobject_cast<QPickTriangleEvent*>(pick); 
    // I'd like to get the vertex data from vertex1Index's position. 
    qDebug() << "Clicked " << trianglePick->vertex1Index(); 
    QGeometry *geometry = m_mesh->geometry(); 
    auto attributes = geometry->attributes(); 
    for (auto i = 0; i < attributes.count(); ++i) 
    { 
     if (attributes.at(i)->name() == QAttribute::defaultPositionAttributeName()) 
     { 
      QAttribute *attribute = attributes.at(i); 
      qDebug() << "Attrib " << attribute; 

      //This is where I'm stuck. I need to read the vertex attributes for the 
      //vertex at trianglePick->vertex1Index(); 

      break; 
     } 
    } 
} 

Answer 1

我認爲你必須訪問你感興趣的屬性的QBuffer這可能不符合defaultPositionAttributeName()屬性，但你在進口商給你的名字。獲取實際數據需要您將其從QByteArray轉換爲正確的數據類型，並使用QAttribute的byteStride和byteOffset中包含的信息獲取數據中的正確位置。您可能還想使用vertexSize和vertexBaseType，具體取決於您寫入導入程序的方式。

東西沿着這些路線應該工作（未測試）：

void ES3DScene::handlePickerClicked(QPickEvent *pick) 
{ 
    QPickTriangleEvent *trianglePick = qobject_cast<QPickTriangleEvent*>(pick); 
    QGeometry *geometry = m_mesh->geometry(); 
    auto attributes = geometry->attributes(); 
    int vertexIndex = trianglePick->vertex1Index(); 
    for (auto i = 0; i < attributes.count(); ++i) 
    { 
     if (attributes.at(i)->name() == "yourattributename") 
     { 
      QAttribute *attribute = attributes.at(i); 
      QBuffer *buffer = attribute->buffer(); 
      const QByteArray &data = buffer->data(); 

      int vertexOffset = vertexIndex * attribute->byteStride(); 
      int offset = vertexOffset + attribute.byteOffset(); 

      const char *rawData = &(data.constData()[offset]); 

      // replace float with your data type 
      float *value = reinterpret_cast<float*>(rawData); 

      break; 
     } 
    } 
} 

Answer 2

通過Qt3D來源挖後，我想出了這個：

template<typename T> 
T extractIndexData(QAttribute *attribute, int index) 
{ 
    const T *typedData = reinterpret_cast<const T*>(attribute->buffer()->data().constData()); 
    const T indexValue = *(typedData + index); 
    return indexValue; 
} 

template<typename VT, typename IT> 
VT extractVertexData(QAttribute *attribute, IT index) 
{ 
    const char *buffer = attribute->buffer()->data().constData(); 
    const char *vertexData = buffer + (index * attribute->byteStride() + attribute->byteOffset()); 
    // Construct vertex from from the typed data 
    VT vertex; 
    const QAttribute::VertexBaseType type = attribute->vertexBaseType(); 
    switch (type) 
    { 
    case QAttribute::Float: { 
     const float *typedVertexData = reinterpret_cast<const float*>(vertexData); 
     const int components = attribute->vertexSize(); 
     for (int i = 0; i < components; ++i) 
      vertex[i] = typedVertexData[i]; 
     break; 
    } 
    // TODO: Handle other types as needed. 
    default: { 
     qWarning() << "Unhandled type"; 
     Q_UNREACHABLE(); 
    } 
    } 
    return vertex; 
} 

並稱爲像這樣：

void ES3DScene::handlePickerClicked(QPickEvent *pick) 
{ 
    float *temperature = nullptr; 
    QPickTriangleEvent *trianglePick = qobject_cast<QPickTriangleEvent*>(pick); 
    auto idx = trianglePick->vertex1Index(); 

    QGeometry *geometry = m_mesh->geometry(); 
    for (QAttribute* attribute : geometry->attributes()) 
    { 
     if (attribute->name() == "vertexTemperature") 
     { 
      temperature = extractVertexData<float*>(attribute, idx); 

      break; 
     } 
    } 
}