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

List of all members, including inherited members

Public Types

class Renderer

Properties

mirrorVertically : bool
textureFollowsItemSize : bool

24 properties inherited from QQuickItem
1 property inherited from QObject

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

101 public functions inherited from QQuickItem
33 public functions inherited from QObject
2 public functions inherited from QQmlParserStatus

Signals

void	mirrorVerticallyChanged(bool)
void	textureFollowsItemSizeChanged(bool)

2 signals inherited from QQuickItem
2 signals inherited from QObject

Additional Inherited Members

1 public slot inherited from QQuickItem
1 public slot inherited from QObject
1 public variable inherited from QObject
10 static public members inherited from QObject
33 protected functions inherited from QQuickItem
9 protected functions inherited from QObject
2 protected variables inherited from QObject

Detailed Description

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

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.

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.

Property Documentation

mirrorVertically : bool

This property controls if the size of the FBO's contents should be mirrored vertically when drawing. This allows easy integration of third-party rendering code that does not follow the standard expectations.

The default value is false.

This property was introduced in Qt 5.6.

Access functions:

bool	mirrorVertically() const
void	setMirrorVertically(bool enable)

Notifier signal:

void	mirrorVerticallyChanged(bool)

textureFollowsItemSize : bool

This property controls if the size of the FBO's texture should follow the dimensions of the QQuickFramebufferObject item. When this property is false, the FBO will be created once the first time it is displayed. If it is set to true, the FBO will be recreated every time the dimensions of the item change.

The default value is true.

Access functions:

bool	textureFollowsItemSize() const
void	setTextureFollowsItemSize(bool follows)

Notifier signal:

void	textureFollowsItemSizeChanged(bool)

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

Reimplemented from QQuickItem::isTextureProvider().

`[override virtual]` void QQuickFramebufferObject::releaseResources()

Reimplemented from QQuickItem::releaseResources().

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

Reimplemented from QQuickItem::textureProvider().

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