Qt Quick 3D - Custom Geometry Example▲

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This example makes use of QQuick3DGeometry and the geometry property of Model to render a mesh with vertex, normal, and texture coordinates specified from C++ instead of a pre-baked asset.

In addition, the GridGeometry is also demonstrated. GridGeometry is a built-in QQuick3DGeometry implementation that provides a mesh with line primitives suitable for displaying a grid.

The focus on this example will be on the code that provides the custom geometry, so let's first have a look at the ExampleTriangleGeometry C++ header file:

 
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class ExampleTriangleGeometry : public QQuick3DGeometry
{
    Q_OBJECT
    QML_NAMED_ELEMENT(ExampleTriangleGeometry)
    Q_PROPERTY(bool normals READ normals WRITE setNormals NOTIFY normalsChanged)
    Q_PROPERTY(float normalXY READ normalXY WRITE setNormalXY NOTIFY normalXYChanged)
    Q_PROPERTY(bool uv READ uv WRITE setUV NOTIFY uvChanged)
    Q_PROPERTY(float uvAdjust READ uvAdjust WRITE setUVAdjust NOTIFY uvAdjustChanged)

public:
    ExampleTriangleGeometry();

    bool normals() const { return m_hasNormals; }
    void setNormals(bool enable);

    float normalXY() const { return m_normalXY; }
    void setNormalXY(float xy);

    bool uv() const { return m_hasUV; }
    void setUV(bool enable);

    float uvAdjust() const { return m_uvAdjust; }
    void setUVAdjust(float f);

signals:
    void normalsChanged();
    void normalXYChanged();
    void uvChanged();
    void uvAdjustChanged();

private:
    void updateData();

    bool m_hasNormals = false;
    float m_normalXY = 0.0f;
    bool m_hasUV = false;
    float m_uvAdjust = 0.0f;
};

The most important thing to notice is that our ExampleTriangleGeometry class inherits from QQuick3DGeometry and that we call the QML_NAMED_ELEMENT(ExampleTriangleGeometry) macro, making our class accessible in QML. There are also a few properties defined through the Q_PROPERTY macro which are automatically exposed in our QML object. Now, let's look at the QML Model:

 
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Model {
    visible: radioCustGeom.checked
    scale: Qt.vector3d(100, 100, 100)
    geometry: ExampleTriangleGeometry {
        normals: cbNorm.checked
        normalXY: sliderNorm.value
        uv: cbUV.checked
        uvAdjust: sliderUV.value
    }
    materials: [
        DefaultMaterial {
            Texture {
                id: baseColorMap
                source: "qt_logo_rect.png"
            }
            cullMode: DefaultMaterial.NoCulling
            diffuseMap: cbTexture.checked ? baseColorMap : null
            specularAmount: 0.5
        }
    ]
}

Note that we specify the geometry property to use our ExampleTriangleGeometry class, with the relevant properties specified. This is all that is needed on the QML side to use a custom geometry.

Now, lets look at the other important part of the C++ code, namely the updateData() method. This method creates and uploads the data for our custom geometry whenever a ExampleTriangleGeometry class is created or any of its QML properties are updated.

 
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void ExampleTriangleGeometry::updateData()
{
    clear();

    int stride = 3 * sizeof(float);
    if (m_hasNormals)
        stride += 3 * sizeof(float);
    if (m_hasUV)
        stride += 2 * sizeof(float);

    QByteArray vertexData(3 * stride, Qt::Initialization::Uninitialized);
    float *p = reinterpret_cast<float *>(vertexData.data());

    // a triangle, front face = counter-clockwise
    *p++ = -1.0f; *p++ = -1.0f; *p++ = 0.0f;
    if (m_hasNormals) {
        *p++ = m_normalXY; *p++ = m_normalXY; *p++ = 1.0f;
    }
    if (m_hasUV) {
        *p++ = 0.0f + m_uvAdjust; *p++ = 0.0f + m_uvAdjust;
    }
    *p++ = 1.0f; *p++ = -1.0f; *p++ = 0.0f;
    if (m_hasNormals) {
        *p++ = m_normalXY; *p++ = m_normalXY; *p++ = 1.0f;
    }
    if (m_hasUV) {
        *p++ = 1.0f - m_uvAdjust; *p++ = 0.0f + m_uvAdjust;
    }
    *p++ = 0.0f; *p++ = 1.0f; *p++ = 0.0f;
    if (m_hasNormals) {
        *p++ = m_normalXY; *p++ = m_normalXY; *p++ = 1.0f;
    }
    if (m_hasUV) {
        *p++ = 1.0f - m_uvAdjust; *p++ = 1.0f - m_uvAdjust;
    }

    setVertexData(vertexData);
    setStride(stride);
    setBounds(QVector3D(-1.0f, -1.0f, 0.0f), QVector3D(+1.0f, +1.0f, 0.0f));

    setPrimitiveType(QQuick3DGeometry::PrimitiveType::Triangles);

    addAttribute(QQuick3DGeometry::Attribute::PositionSemantic,
                 0,
                 QQuick3DGeometry::Attribute::F32Type);

    if (m_hasNormals) {
        addAttribute(QQuick3DGeometry::Attribute::NormalSemantic,
                     3 * sizeof(float),
                     QQuick3DGeometry::Attribute::F32Type);
    }

    if (m_hasUV) {
        addAttribute(QQuick3DGeometry::Attribute::TexCoordSemantic,
                     m_hasNormals ? 6 * sizeof(float) : 3 * sizeof(float),
                     QQuick3DGeometry::Attribute::F32Type);
    }
}

The method starts by calling clear() to clear all previously uploaded data. It then computes the stride for the vertices, taking into account the pre