Qt Quick 3D - Custom Morphing Animation

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

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Publié le 26 janvier 2024 - Mis à jour le 26 janvier 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 explained in detail. In general: to implement smooth shading, it's neces