- Qt 5.15
- Qt 3D
- C++ Classes
- QBufferDataGenerator
- Qt 5.15.11 Reference Documentation

# QBufferDataGenerator Class

class Qt3DRender::QBufferDataGenerator

Provides a mechanism to generate buffer data from a job. More...

Header: | #include <QBufferDataGenerator>
qmake: | QT += 3drender
Inherits: | Qt3DRender::QAbstractFunctor

- List of all members, including inherited members

## Public Functions

virtual QByteArray | operator()() = 0
virtual bool | operator==(const QBufferDataGenerator &other) const = 0

## Detailed Description

The Qt3DRender::QBufferDataGenerator should be subclassed to provide a way to fill the data of a Qt3DRender::QBuffer. Such functors are executed at runtime in a Qt 3D job (likely in parallel with many other jobs). When providing a functor you must implement the operator() which will be called to generate the actual data. You must make sure that you have stored copies of anything you might need for it to execute properly. You should also implement the operator==. It will be used to compare with other functors and based on that allow the renderer to decide if a new functor should be executed or not.

Note: functors are useful when you can build data from a few set of attributes (e.g: building a sphere from a radius property). If you already have access to the buffer data, using Qt3DRender::QBuffer::setData() is likely more efficient.

     QByteArray createSphereMeshVertexData(float radius, int rings, int slices)
     {
         ...
     }

     class SphereVertexDataFunctor : public QBufferDataGenerator
     {
     public:
         SphereVertexDataFunctor(int rings, int slices, float radius)
             : m_rings(rings)
             , m_slices(slices)
             , m_radius(radius)
         {}

         QByteArray operator ()() override
         {
             return createSphereMeshVertexData(m_radius, m_rings, m_slices);
         }

         bool operator ==(const QBufferDataGenerator &other) const override
         {
             const SphereVertexDataFunctor *otherFunctor = functor_cast<SphereVertexDataFunctor>(&other);
             if (otherFunctor != nullptr)
                 return (otherFunctor->m_rings == m_rings &&
                         otherFunctor->m_slices == m_slices &&
                         otherFunctor->m_radius == m_radius);
             return false;
         }

         QT3D_FUNCTOR(SphereVertexDataFunctor)

     private:
         int m_rings;
         int m_slices;
         float m_radius;
     };

The QT3D_FUNCTOR macro should be added when subclassing. This allows you to use functor_cast in your comparison operator to make sure that the other functor is of the same type as the one your are trying to compare against.

## Member Function Documentation

### `[pure virtual]` QByteArray QBufferDataGenerator::operator()()

Should be implemented to return the buffer data as a QByteArray when called.

### `[pure virtual]` bool QBufferDataGenerator::operator==(const QBufferDataGenerator &other) const

Should be reimplemented to return true when two generators (the one you are comparing against and the other generator) are identical, false otherwise.

Note: The renderer uses this comparison to decide whether data for a buffer needs to be reuploaded or not when the functor on a Qt3DRender::QBuffer changes.