class QQuick3DGeometry¶

Base class for defining custom geometry. More…

Synopsis¶

Methods¶

def __init__()
def addAttribute()
def addSubset()
def addTargetAttribute()
def attribute()
def attributeCount()
def boundsMax()
def boundsMin()
def clear()
def indexData()
def primitiveType()
def setBounds()
def setIndexData()
def setPrimitiveType()
def setStride()
def setTargetData()
def setVertexData()
def stride()
def subsetBoundsMax()
def subsetBoundsMin()
def subsetCount()
def subsetName()
def subsetOffset()
def targetAttribute()
def targetAttributeCount()
def targetData()
def vertexData()

Note

This documentation may contain snippets that were automatically translated from C++ to Python. We always welcome contributions to the snippet translation. If you see an issue with the translation, you can also let us know by creating a ticket on https:/bugreports.qt.io/projects/PYSIDE

Detailed Description¶

The QQuick3DGeometry can be used to specify custom geometry for a Model in the Qt Quick 3D scene.

While not strictly required, the typical usage is to inherit from this class. The subclass is then exposed to QML by registering it to the type system. The geometry property of a Model can then be set to reference an instance of the registered type.

The high-level structure of such a class is typically similar to the following:

class CustomGeometry : public QQuick3DGeometry
{
public:
    CustomGeometry() { rebuildGeometry(); }

    void setSomething() {
       // Change relevant internal data.
       // ...

       // Then rebuild the vertex and index data and pass it to QQuick3DGeometry.
       rebuildGeometry();

       // Finally, trigger an update. This is relevant in case nothing else
       // is changing in the scene; this way we make sure a new frame will
       // be rendered.
       update();
    }

private:
    void rebuildGeometry()
    {
        QByteArray vertices;
        QByteArray indices;
        ...
        setPrimitiveType(Lines);
        setVertexBuffer(vertices);
        setIndexBuffer(indices);
        setStride(3 * sizeof(float)); // e.g. when having 3 components per vertex
        setBounds(...); // minimum and maximum extents, for picking
        addAttribute(PositionSemantic, 0, F32Type);
        ...
    }
};

This class can then be registered as a QML type and used with Model .

In Qt 5 type registration happened with qmlRegisterType:

qmlRegisterType<CustomGeometry>("Example", 1, 0, "CustomGeometry");

In Qt 6 the default approach is to use automatic registration with the help of the build system. Instead of calling qmlRegisterType, the .pro file can now contain:

CONFIG += qmltypes
QML_IMPORT_NAME = Example
QML_IMPORT_MAJOR_VERSION = 1

With CMake, automatic registration is the default behavior, so no special settings are needed beyond basic QML module setup:

qt_add_qml_module(application
    URI Example
    VERSION 1.0
)

The class implementation should add QML_NAMED_ELEMENT:

class CustomGeometry : public QQuick3DGeometry
{
    Q_OBJECT
    QML_NAMED_ELEMENT(CustomGeometry)
    ...
};

The QML code can then use the custom type:

import Example 1.0

Model {
    id: customModel
    geometry: CustomGeometry {
    }
}

At minimum, a custom geometry should have the following specified:

vertex data,

vertex stride,

primitive type,

an attribute with PositionSemantic.

These are sufficient to render the mesh. For indexed drawing, the index buffer data and an attribute with IndexSemantic needs to be specified as well. In order to support picking (input), the class must specify the bounding volume using setBounds() . For proper lighting, an attribute with NormalSemantic is needed. When the material uses texturing, at least one set of UV coordinates must be provided and described in an TexCoord0Semantic or TexCoord1Semantic attribute. Some materials may require tangents and binormals as well.

As a concrete, minimal example, the following class would provide geometry for a single triangle:

class ExampleGeometry : public QQuick3DGeometry
{
    Q_OBJECT
    QML_NAMED_ELEMENT(ExampleGeometry)

public:
    ExampleGeometry();

private:
    void updateData();
};

ExampleGeometry::ExampleGeometry()
{
    updateData();
}

void ExampleGeometry::updateData()
{
    QByteArray v;
    v.resize(3 * 3 * sizeof(float));
    float *p = reinterpret_cast<float *>(v.data());

    // a triangle, front face = counter-clockwise
    *p++ = -1.0f; *p++ = -1.0f; *p++ = 0.0f;
    *p++ = 1.0f; *p++ = -1.0f; *p++ = 0.0f;
    *p++ = 0.0f; *p++ = 1.0f; *p++ = 0.0f;

    setVertexData(v);
    setStride(3 * sizeof(float));

    setPrimitiveType(QQuick3DGeometry::PrimitiveType::Triangles);

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

Depending on the lighting in the scene, the result of referencing this geometry from a Model:

Note

Vertex data is expected to follow OpenGL conventions. This means the data must be provided with the assumption that the Y axis is pointing up in the normalized device coordinate system, and that front faces have a counter clockwise winding.

See also

Model Geometry

class PrimitiveType¶

__init__([parent=None])¶

Parameters:: parent – QQuick3DObject

addAttribute(att)¶

Parameters:: att – Attribute

This is an overloaded function.

Adds vertex attribute description. Each attribute has a semantic, which specifies the usage of the attribute and the number of components it has, an offset from the beginning to the vertex to the attribute location inside a vertex and a componentType specifying the datatype and size of the attribute.

addAttribute(semantic, offset, componentType)

Parameters:

semantic – Semantic
offset – int
componentType – ComponentType

Adds vertex attribute description. Each attribute has a semantic, which specifies the usage of the attribute and the number of components it has, an offset from the beginning to the vertex to the attribute location inside a vertex and a componentType specifying the datatype and size of the attribute.

The semantic can be one of the following:

PositionSemantic

The attribute is a position. 3 components: x, y, and z

In addition, semantic can be IndexSemantic. In this case the attribute does not represent an entry in the vertex buffer, but rather describes the index data in the index buffer. Since there is always just one index per vertex, offset makes no sense for the index buffer, and should be left at zero.

The component type can be one of the following:

U16Type

The index component type is unsigned 16-bit integer. Only supported for IndexSemantic.

Note

The joint index data is typically I32Type. F32Type is also supported in order to enable functioning with APIs, such as OpenGL ES 2.0, that do not support integer vertex input attributes.

Note

For index data (IndexSemantic) only U16Type and U32Type are sensible and supported.

Note

TargetXXXSemantics will be deprecated. addTargetAttribute can be used for the morph targets. Now these semantics are just supported for backward compatibility. If they are mixed-used with addTargetAttribute and setTargetData , the result cannot be quaranteed.

addSubset(offset, count, boundsMin, boundsMax[, name={}])¶

Parameters:

offset – int
count – int
boundsMin – QVector3D
boundsMax – QVector3D
name – str

Adds new subset to the geometry. Subsets allow rendering parts of the geometry with different materials. The materials are specified in the model .

If the geometry has index buffer, then the offset and count are the primitive offset and count of indices in the subset. If the geometry has only vertex buffer, the offset is the vertex offset and count is the number of vertices in the subset.

The bounds boundsMin and boundsMax should enclose the subset just like geometry bounds. Also the subset can have a name.

addTargetAttribute(att)¶

Parameters:: att – TargetAttribute

This is an overloaded function.

Adds morph target attribute description. Each attribute has a targetId which the attribute belongs to, a semantic, which specifies the usage of the attribute and the number of components it has, an offset from the beginning to the vertex to the attribute location inside a vertex, and a stride which is a byte size between the elements.

addTargetAttribute(targetId, semantic, offset[, stride=0])

Parameters:

targetId – int
semantic – Semantic
offset – int
stride – int

Adds morph target attribute description. Each attribute has a targetId which the attribute belongs to, a semantic, which specifies the usage of the attribute and the number of components it has, an offset from the beginning to the vertex to the attribute location inside a vertex, and a stride which is a byte size between the elements.

Note

The targetId should be increased from 0 without skipping any number and all the targets should have the same attributes.

Note

The semantic is the same as the vertex attribute but IndexSemantic, JointSementic and WeightSemantic are not allowed for target attributes.

Note

The componentTypes of all the target attributes must be F32Type.

Note

If the stride is not given or less than or equal to zero, the attribute is considered to be tightly packed.

See also

addAttribute

attribute(index)¶

Parameters:: index – int
Return type:: Attribute

Returns attribute definition number index

The attribute definitions are numbered from 0 to attributeCount() - 1

attributeCount()¶

Return type:: int

Returns the number of attributes defined for this geometry.

See also

attribute

boundsMax()¶

Return type:: QVector3D

Returns the maximum coordinate of the bounding volume.

See also

setBounds

boundsMin()¶

Return type:: QVector3D

Returns the minimum coordinate of the bounding volume.

See also

setBounds

clear()¶

Resets the geometry to its initial state, clearing previously set vertex and index data as well as attributes.

geometryChanged()¶

geometryNodeDirty()¶

indexData()¶

Return type:: QByteArray

Returns the index buffer data.

See also

setIndexData()

primitiveType()¶

Return type:: PrimitiveType

Returns the primitive type used when rendering. The default is Triangles.

See also

setPrimitiveType

setBounds(min, max)¶

Parameters:

min – QVector3D
max – QVector3D

Sets the bounding volume of the geometry to the cube defined by the points min and max. This is used for picking .

setIndexData(data)¶

Parameters:: data – QByteArray

Sets the index buffer to data. To use indexed drawing, add an attribute with IndexSemantic

See also

indexData() addAttribute

setIndexData(offset, data)

Parameters:

offset – int
data – QByteArray

This is an overloaded function.

Updates a subset of the index buffer. offset specifies the offset in bytes, data specifies the size and the data.

This function will not resize the buffer. If offset + data.size() is greater than the current size of the buffer, the overshooting data will be ignored.

Note

The partial update functions for vertex, index and morph target data do not offer any guarantee on how such changes are implemented internally. Depending on the underlying implementation, even partial changes may lead to updating the entire graphics resource.

setPrimitiveType(type)¶

Parameters:: type – PrimitiveType

Sets the primitive type used for rendering to type.

Points

The primitives are points.

The initial value is Triangles.

Note

Be aware that triangle fans (TriangleFan) may not be supported at run time, depending on the underlying graphics API. For example, with Direct 3D this topology will not be functional at all.

Note

The point size for Points and the line width for Lines and LineStrip are controlled by the material . Be aware however that sizes other than 1 may not be supported at run time, depending on the underlying graphics API.

See also

primitiveType()

setStride(stride)¶

Parameters:: stride – int

Sets the stride of the vertex buffer to stride, measured in bytes. This is the distance between two consecutive vertices in the buffer.

For example, a tightly packed, interleaved vertex buffer for a geometry using PositionSemantic, IndexSemantic, and ColorSemantic will have a stride of 28 (Seven floats in total: Three for position, four for color, and none for indexes, which do not go in the vertex buffer.)

Note

QQuick3DGeometry expects, and works only with, vertex data with an interleaved attribute layout.

See also

stride() addAttribute

setTargetData(data)¶

Parameters:: data – QByteArray

Sets the morph target buffer data. The buffer should hold all the morph target data.

See also

targetData() addTargetAttribute

setTargetData(offset, data)

Parameters:

offset – int
data – QByteArray

This is an overloaded function.

Updates a subset of the morph target buffer. offset specifies the offset in bytes, data specifies the size and the data.

This function will not resize the buffer. If offset + data.size() is greater than the current size of the buffer, the overshooting data will be ignored.

Note

setVertexData(data)¶

Parameters:: data – QByteArray

Sets the vertex buffer data. The buffer should hold all the vertex data packed in the array, as described by the attribute definitions. Note that this does not include attributes with IndexSemantic, which belong in the index buffer.

See also

vertexData() addAttribute setStride setIndexData

setVertexData(offset, data)

Parameters:

offset – int
data – QByteArray

This is an overloaded function.

Updates a subset of the vertex buffer. offset specifies the offset in bytes, data specifies the size and the data.

This function will not resize the buffer. If offset + data.size() is greater than the current size of the buffer, the overshooting data will be ignored.

Note

The partial update functions for vertex, index and morph target data do not offer any guarantee on how such changes are implemented internally. depending on the underlying implementation, even partial changes may lead to updating the entire graphics resource.

stride()¶

Return type:: int

Returns the byte stride of the vertex buffer.

See also

setStride

subsetBoundsMax(subset)¶

Parameters:: subset – int
Return type:: QVector3D

Returns the number of maximum bounds of a subset.

See also

subsetBoundsMin

subsetBoundsMin(subset)¶

Parameters:: subset – int
Return type:: QVector3D

Returns the number of minimum bounds of a subset.

See also

subsetBoundsMax

subsetCount()¶

Return type:: int

Returns the number of subsets.

subsetCount(subset)

Parameters:: subset – int
Return type:: int

Returns the subset primitive count.

See also

subsetOffset

subsetName(subset)¶

Parameters:: subset – int
Return type:: str

Returns the subset name.

subsetOffset(subset)¶

Parameters:: subset – int
Return type:: int

Returns the subset offset to the vertex or index buffer.

See also

subsetCount

targetAttribute(index)¶

Parameters:: index – int
Return type:: TargetAttribute

Returns morph target attribute definition number index

The attribute definitions are numbered from 0 to attributeCount() - 1

targetAttributeCount()¶

Return type:: int

Returns the number of morph target attributes defined for this geometry.

See also

targetAttribute

targetData()¶

Return type:: QByteArray

Returns the target buffer data set by setTargetData .

See also

setTargetData()

vertexData()¶

Return type:: QByteArray

Returns the vertex buffer data set by setVertexData .

See also

setVertexData()