- Qt 5.15
- Qt GUI
- C++ Classes
- QBackingStore
- Qt 5.15.18 Reference Documentation

# QBackingStore Class

The QBackingStore class provides a drawing area for QWindow. More...

Header: | #include <QBackingStore>
qmake: | QT += gui
Since: | Qt 5.0

This class was introduced in Qt 5.0.

- List of all members, including inherited members

## Public Functions

| QBackingStore(QWindow *window)
| ~QBackingStore()
void | beginPaint(const QRegion &region)
void | endPaint()
void | flush(const QRegion &region, QWindow *window = nullptr, const QPoint &offset = QPoint())
QPlatformBackingStore * | handle() const
bool | hasStaticContents() const
QPaintDevice * | paintDevice()
void | resize(const QSize &size)
bool | scroll(const QRegion &area, int dx, int dy)
void | setStaticContents(const QRegion &region)
QSize | size() const
QRegion | staticContents() const
QWindow * | window() const

## Detailed Description

QBackingStore enables the use of QPainter to paint on a QWindow with type RasterSurface. The other way of rendering to a QWindow is through the use of OpenGL with QOpenGLContext.

A QBackingStore contains a buffered representation of the window contents, and thus supports partial updates by using QPainter to only update a sub region of the window contents.

QBackingStore might be used by an application that wants to use QPainter without OpenGL acceleration and without the extra overhead of using the QWidget or QGraphicsView UI stacks. For an example of how to use QBackingStore see the Raster Window Example.

## Member Function Documentation

### QBackingStore::QBackingStore(QWindow *window)

Constructs an empty surface for the given top-level window.

### QBackingStore::~QBackingStore()

Destroys this surface.

### void QBackingStore::beginPaint(const QRegion &region)

Begins painting on the backing store surface in the given region.

You should call this function before using the paintDevice() to paint.

See also endPaint() and paintDevice().

### void QBackingStore::endPaint()

Ends painting.

You should call this function after painting with the paintDevice() has ended.

See also beginPaint() and paintDevice().

### void QBackingStore::flush(const QRegion &region, QWindow *window = nullptr, const QPoint &offset = QPoint())

Flushes the given region from the specified window onto the screen.

The window must either be the top level window represented by this backingstore, or a non-transient child of that window. Passing `nullptr` falls back to using the backingstore's top level window.

If the window is a child window, the region should be in child window coordinates, and the offset should be the child window's offset in relation to the backingstore's top level window.

You should call this function after ending painting with endPaint().

### QPlatformBackingStore *QBackingStore::handle() const

Returns a pointer to the QPlatformBackingStore implementation

### bool QBackingStore::hasStaticContents() const

Returns a boolean indicating if this window has static contents or not.

### QPaintDevice *QBackingStore::paintDevice()

Returns the paint device for this surface.

Warning: The device is only valid between calls to beginPaint() and endPaint(). You should not cache the returned value.

### void QBackingStore::resize(const QSize &size)

Sets the size of the window surface to size.

See also size().

### bool QBackingStore::scroll(const QRegion &area, int dx, int dy)

Scrolls the given area dx pixels to the right and dy downward; both dx and dy may be negative.

Returns `true` if the area was scrolled successfully; false otherwise.

### void QBackingStore::setStaticContents(const QRegion &region)

Set region as the static contents of this window.

See also staticContents().

### QSize QBackingStore::size() const

Returns the current size of the window surface.

### QRegion QBackingStore::staticContents() const

Returns a QRegion representing the area of the window that has static contents.

See also setStaticContents().

### QWindow *QBackingStore::window() const

Returns a pointer to the top-level window associated with this surface.