QQuickFramebufferObject Class

The QQuickFramebufferObject class is a convenience class for integrating OpenGL rendering using a framebuffer object (FBO) with Qt Quick. More...

Header:	#include <QQuickFramebufferObject>
qmake:	QT += quick
Since:	Qt 5.2
Inherits:	QQuickItem

This class was introduced in Qt 5.2.

• List of all members, including inherited members

Public Types

class

Renderer

Properties

• mirrorVertically : bool
• textureFollowsItemSize : bool

Public Functions

	QQuickFramebufferObject(QQuickItem *parent = nullptr)
virtual QQuickFramebufferObject::Renderer *	createRenderer() const = 0
bool	mirrorVertically() const
void	setMirrorVertically(bool enable)
void	setTextureFollowsItemSize(bool follows)
bool	textureFollowsItemSize() const

Reimplemented Public Functions

virtual bool	isTextureProvider() const override
virtual void	releaseResources() override
virtual QSGTextureProvider *	textureProvider() const override

Signals

void	mirrorVerticallyChanged(bool)
void	textureFollowsItemSizeChanged(bool)

Detailed Description

On most platforms, the rendering will occur on a dedicated thread. For this reason, the QQuickFramebufferObject class enforces a strict separation between the item implementation and the FBO rendering. All item logic, such as properties and UI-related helper functions needed by QML should be located in a QQuickFramebufferObject class subclass. Everything that relates to rendering must be located in the QQuickFramebufferObject::Renderer class.

Warning: This class is only functional when Qt Quick is rendering via OpenGL, either directly or through the RHI-based rendering path. It is not compatible with other RHI backends, such as, Vulkan or Metal.

To avoid race conditions and read/write issues from two threads it is important that the renderer and the item never read or write shared variables. Communication between the item and the renderer should primarily happen via the QQuickFramebufferObject::Renderer::synchronize() function. This function will be called on the render thread while the GUI thread is blocked.

Using queued connections or events for communication between item and renderer is also possible.

Both the Renderer and the FBO are memory managed internally.

To render into the FBO, the user should subclass the Renderer class and reimplement its Renderer::render() function. The Renderer subclass is returned from createRenderer().

The size of the FBO will by default adapt to the size of the item. If a fixed size is preferred, set textureFollowsItemSize to false and return a texture of your choosing from QQuickFramebufferObject::Renderer::createFramebufferObject().

Starting Qt 5.4, the QQuickFramebufferObject class is a texture provider and can be used directly in ShaderEffects and other classes that consume texture providers.

See also Scene Graph - Rendering FBOs and Scene Graph and Rendering.

Member Function Documentation

QQuickFramebufferObject::QQuickFramebufferObject(QQuickItem *parent = nullptr)

Constructs a new QQuickFramebufferObject with parent parent.

[pure virtual] QQuickFramebufferObject::Renderer *QQuickFramebufferObject::createRenderer() const

Reimplement this function to create a renderer used to render into the FBO.

This function will be called on the rendering thread while the GUI thread is blocked.

[override virtual] bool QQuickFramebufferObject::isTextureProvider() const

Reimplements: QQuickItem::isTextureProvider() const.

[override virtual] void QQuickFramebufferObject::releaseResources()

Reimplements: QQuickItem::releaseResources().

[override virtual] QSGTextureProvider *QQuickFramebufferObject::textureProvider() const

Reimplements: QQuickItem::textureProvider() const.