Qt Quick 3D - Custom Morphing Animation

Demonstrates writing C++ custom geometry with a morph target.

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Publié le 14 février 2024 - Mis à jour le 14 février 2024

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Qt Quick 3D - Custom Morphing Animation▲

This example shows how to define a complex custom geometry in C++ that contains a base shape and a morph target, with normal vectors for both.

Custom geometry▲

The main part of this example is creating a custom geometry with a morph target. We do this by subclassing QQuick3DGeometry:

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class MorphGeometry : public QQuick3DGeometry
{
    Q_OBJECT
    QML_NAMED_ELEMENT(MorphGeometry)
    Q_PROPERTY(int gridSize READ gridSize WRITE setGridSize NOTIFY gridSizeChanged)

public:
    MorphGeometry(QQuick3DObject *parent = nullptr);

    int gridSize() { return m_gridSize; }
    void setGridSize(int gridSize);

signals:
    void gridSizeChanged();

private:
    void calculateGeometry();
    void updateData();

    QList&lt;QVector3D&gt; m_positions;
    QList&lt;QVector3D&gt; m_normals;

    QList&lt;QVector3D&gt; m_targetPositions;
    QList&lt;QVector3D&gt; m_targetNormals;

    QList&lt;quint32&gt; m_indexes;

    QByteArray m_vertexBuffer;
    QByteArray m_indexBuffer;

    int m_gridSize = 50;
    QVector3D boundsMin;
    QVector3D boundsMax;
};

The constructor defines the layout of the mesh data:

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MorphGeometry::MorphGeometry(QQuick3DObject *parent)
    : QQuick3DGeometry(parent)
{
    updateData();
}

The function updateData performs the actual uploading of the mesh geometry:

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void MorphGeometry::updateData()
{
    clear();
    calculateGeometry();

    addAttribute(QQuick3DGeometry::Attribute::PositionSemantic, 0,
                 QQuick3DGeometry::Attribute::ComponentType::F32Type);
    addAttribute(QQuick3DGeometry::Attribute::NormalSemantic, 3 * sizeof(float),
                 QQuick3DGeometry::Attribute::ComponentType::F32Type);

    addAttribute(QQuick3DGeometry::Attribute::TargetPositionSemantic, 6 * sizeof(float),
                 QQuick3DGeometry::Attribute::ComponentType::F32Type);
    addAttribute(QQuick3DGeometry::Attribute::TargetNormalSemantic, 9 * sizeof(float),
                 QQuick3DGeometry::Attribute::ComponentType::F32Type);

    addAttribute(QQuick3DGeometry::Attribute::IndexSemantic, 0,
                 QQuick3DGeometry::Attribute::ComponentType::U32Type);

    const int numVertexes = m_positions.size();
    m_vertexBuffer.resize(numVertexes * sizeof(Vertex));
    Vertex *vert = reinterpret_cast&lt;Vertex *&gt;(m_vertexBuffer.data());

    for (int i = 0; i &lt; numVertexes; ++i) {
        Vertex &amp;v = vert[i];
        v.position = m_positions[i];
        v.normal = m_normals[i];
        v.targetPosition = m_targetPositions[i];
        v.targetNormal = m_targetNormals[i];
    }

    setStride(sizeof(Vertex));
    setVertexData(m_vertexBuffer);
    setPrimitiveType(QQuick3DGeometry::PrimitiveType::Triangles);
    setBounds(boundsMin, boundsMax);

    m_indexBuffer = QByteArray(reinterpret_cast&lt;char *&gt;(m_indexes.data()), m_indexes.size() * sizeof(quint32));
    setIndexData(m_indexBuffer);
}

We call updateData from the constructor, and when a property has changed.

The function calculateGeometry contains all the tedious mathematics to calculate the shapes and normal vectors. It is specific to this example, and the code will not be