CopperSpice API  1.7.2
QOpenGLWidget Class Reference

The QOpenGLWidget class is a widget for rendering OpenGL graphics. More...

Inheritance diagram for QOpenGLWidget:
QWidget QObject QPaintDevice

Public Signals

void aboutToCompose ()
void aboutToResize ()
void frameSwapped ()
void resized ()
- Public Signals inherited from QWidget
void customContextMenuRequested (const QPoint &pos)
void windowIconChanged (const QIcon &icon)
void windowIconTextChanged (const QString &iconText)
void windowTitleChanged (const QString &title)
- Public Signals inherited from QObject
void destroyed (QObject *obj=nullptr)
void objectNameChanged (const QString &objectName)

Public Methods

 ~QOpenGLWidget ()
QImage grabFramebuffer ()
- Public Methods inherited from QWidget
 QWidget (QWidget *parent=nullptr, Qt::WindowFlags flags=Qt::EmptyFlag)
 ~QWidget ()
bool acceptDrops () const
QString accessibleDescription () const
QString accessibleName () const
QList< QAction * > actions () const
void activateWindow ()
void addAction (QAction *action)
void addActions (const QList< QAction * > &actions)
void adjustSize ()
bool autoFillBackground () const
QPalette::ColorRole backgroundRole () const
QBackingStorebackingStore () const
QSize baseSize () const
QWidget * childAt (const QPoint &position) const
QWidget * childAt (int x, int y) const
QRect childrenRect () const
QRegion childrenRegion () const
void clearFocus ()
void clearMask ()
QMargins contentsMargins () const
QRect contentsRect () const
Qt::ContextMenuPolicy contextMenuPolicy () const
QCursor cursor () const
WId effectiveWinId () const
void ensurePolished () const
Qt::FocusPolicy focusPolicy () const
QWidget * focusProxy () const
QWidget * focusWidget () const
const QFontfont () const
QFontInfo fontInfo () const
QFontMetrics fontMetrics () const
QPalette::ColorRole foregroundRole () const
QRect frameGeometry () const
QSize frameSize () const
const QRectgeometry () const
void getContentsMargins (int *left, int *top, int *right, int *bottom) const
QPixmap grab (const QRect &rectangle=QRect (QPoint (0, 0), QSize (-1,-1)))
void grabGesture (Qt::GestureType gestureType, Qt::GestureFlags flags=Qt::GestureFlags ())
void grabKeyboard ()
void grabMouse ()
void grabMouse (const QCursor &cursor)
int grabShortcut (const QKeySequence &key, Qt::ShortcutContext context=Qt::WindowShortcut)
QGraphicsEffectgraphicsEffect () const
QGraphicsProxyWidgetgraphicsProxyWidget () const
bool hasEditFocus () const
bool hasFocus () const
virtual bool hasHeightForWidth () const
bool hasMouseTracking () const
int height () const
virtual int heightForWidth (int width) const
Qt::InputMethodHints inputMethodHints () const
virtual QVariant inputMethodQuery (Qt::InputMethodQuery query) const
void insertAction (QAction *before, QAction *action)
void insertActions (QAction *before, QList< QAction * > actions)
bool isActiveWindow () const
bool isAncestorOf (const QWidget *child) const
bool isEnabled () const
bool isEnabledTo (const QWidget *parent) const
bool isEnabledToTLW () const
bool isFullScreen () const
bool isHidden () const
bool isMaximized () const
bool isMinimized () const
bool isModal () const
bool isTopLevel () const
bool isVisible () const
bool isVisibleTo (const QWidget *parent) const
bool isWindow () const
bool isWindowModified () const
QLayoutlayout () const
Qt::LayoutDirection layoutDirection () const
QLocale locale () const
QPoint mapFrom (const QWidget *parent, const QPoint &pos) const
QPoint mapFromGlobal (const QPoint &pos) const
QPoint mapFromParent (const QPoint &pos) const
QPoint mapTo (const QWidget *parent, const QPoint &pos) const
QPoint mapToGlobal (const QPoint &pos) const
QPoint mapToParent (const QPoint &pos) const
QRegion mask () const
int maximumHeight () const
QSize maximumSize () const
int maximumWidth () const
int minimumHeight () const
QSize minimumSize () const
virtual QSize minimumSizeHint () const
int minimumWidth () const
void move (const QPoint &point)
void move (int x, int y)
QWidget * nativeParentWidget () const
QWidget * nextInFocusChain () const
QRect normalGeometry () const
void overrideWindowFlags (Qt::WindowFlags flags)
QPaintEnginepaintEngine () const override
const QPalettepalette () const
QWidget * parentWidget () const
QPoint pos () const
QWidget * previousInFocusChain () const
QRect rect () const
void releaseKeyboard ()
void releaseMouse ()
void releaseShortcut (int id)
void removeAction (QAction *action)
void render (QPaintDevice *target, const QPoint &targetOffset=QPoint (), const QRegion &sourceRegion=QRegion (), RenderFlags renderFlags=RenderFlags (DrawWindowBackground|DrawChildren))
void render (QPainter *painter, const QPoint &targetOffset=QPoint (), const QRegion &sourceRegion=QRegion (), RenderFlags renderFlags=RenderFlags (DrawWindowBackground|DrawChildren))
void repaint (const QRect &rect)
void repaint (const QRegion &region)
void repaint (int x, int y, int w, int h)
void resize (const QSize &size)
void resize (int w, int h)
bool restoreGeometry (const QByteArray &geometry)
QByteArray saveGeometry () const
void scroll (int dx, int dy)
void scroll (int dx, int dy, const QRect &rect)
void setAcceptDrops (bool on)
void setAccessibleDescription (const QString &description)
void setAccessibleName (const QString &name)
void setAttribute (Qt::WidgetAttribute attribute, bool enable=true)
void setAutoFillBackground (bool enable)
void setBackgroundRole (QPalette::ColorRole role)
void setBaseSize (const QSize &size)
void setBaseSize (int basew, int baseh)
void setContentsMargins (const QMargins &margins)
void setContentsMargins (int left, int top, int right, int bottom)
void setContextMenuPolicy (Qt::ContextMenuPolicy policy)
void setCursor (const QCursor &cursor)
void setEditFocus (bool enable)
void setFixedHeight (int h)
void setFixedSize (const QSize &size)
void setFixedSize (int w, int h)
void setFixedWidth (int w)
void setFocus (Qt::FocusReason reason)
void setFocusPolicy (Qt::FocusPolicy policy)
void setFocusProxy (QWidget *widget)
void setFont (const QFont &font)
void setForegroundRole (QPalette::ColorRole role)
void setGeometry (const QRect &rect)
void setGeometry (int x, int y, int w, int h)
void setGraphicsEffect (QGraphicsEffect *effect)
void setInputMethodHints (Qt::InputMethodHints hints)
void setLayout (QLayout *layout)
void setLayoutDirection (Qt::LayoutDirection direction)
void setLocale (const QLocale &locale)
void setMask (const QBitmap &bitmap)
void setMask (const QRegion &region)
void setMaximumHeight (int maxh)
void setMaximumSize (const QSize &size)
void setMaximumSize (int maxw, int maxh)
void setMaximumWidth (int maxw)
void setMinimumHeight (int minh)
void setMinimumSize (const QSize &size)
void setMinimumSize (int minw, int minh)
void setMinimumWidth (int minw)
void setMouseTracking (bool enable)
void setPalette (const QPalette &palette)
void setParent (QWidget *parent)
void setParent (QWidget *parent, Qt::WindowFlags flags)
void setShortcutAutoRepeat (int id, bool enable=true)
void setShortcutEnabled (int id, bool enable=true)
void setSizeIncrement (const QSize &size)
void setSizeIncrement (int w, int h)
void setSizePolicy (QSizePolicy policy)
void setSizePolicy (QSizePolicy::Policy horizontal, QSizePolicy::Policy vertical)
void setStatusTip (const QString &data)
void setStyle (QStyle *style)
void setToolTip (const QString &data)
void setToolTipDuration (int msec)
void setUpdatesEnabled (bool enable)
void setWhatsThis (const QString &str)
void setWindowFilePath (const QString &filePath)
void setWindowFlags (Qt::WindowFlags flags)
void setWindowIcon (const QIcon &icon)
void setWindowModality (Qt::WindowModality windowModality)
void setWindowOpacity (qreal level)
void setWindowRole (const QString &role)
void setWindowState (Qt::WindowStates windowState)
QSize size () const
virtual QSize sizeHint () const
QSize sizeIncrement () const
QSizePolicy sizePolicy () const
void stackUnder (QWidget *widget)
QString statusTip () const
QStylestyle () const
QString styleSheet () const
bool testAttribute (Qt::WidgetAttribute attribute) const
QString toolTip () const
int toolTipDuration () const
QWidget * topLevelWidget () const
bool underMouse () const
void ungrabGesture (Qt::GestureType gestureType)
void unsetCursor ()
void unsetLayoutDirection ()
void unsetLocale ()
void update (const QRect &rect)
void update (const QRegion &region)
void update (int x, int y, int w, int h)
void updateGeometry ()
bool updatesEnabled () const
QRegion visibleRegion () const
QString whatsThis () const
int width () const
QWidget * window () const
QString windowFilePath () const
Qt::WindowFlags windowFlags () const
QWindowwindowHandle () const
QIcon windowIcon () const
Qt::WindowModality windowModality () const
qreal windowOpacity () const
QString windowRole () const
Qt::WindowStates windowState () const
QString windowTitle () const
Qt::WindowType windowType () const
WId winId () const
int x () const
int y () const
- Public Methods inherited from QObject
 QObject (QObject *parent=nullptr)
 ~QObject ()
bool blockSignals (bool block)
const QList< QObject * > & children () const
bool connect (const QObject *sender, const QString &signalMethod, const QString &location, const QString &slotMethod, Qt::ConnectionType type=Qt::AutoConnection)
bool connect (const QObject *sender, const QString &signalMethod, const QString &slotMethod, Qt::ConnectionType type=Qt::AutoConnection)
bool disconnect (const QObject *receiver, const QString &slotMethod=QString ()) const
bool disconnect (const QString &signalMethod, const QString &location, const QObject *receiver=nullptr, const QString &slotMethod=QString ()) const
bool disconnect (const QString &signalMethod=QString (), const QObject *receiver=nullptr, const QString &slotMethod=QString ()) const
void dumpObjectInfo ()
void dumpObjectTree ()
QList< QStringdynamicPropertyNames () const
virtual bool event (QEvent *event)
virtual bool eventFilter (QObject *watched, QEvent *event)
template<typename T >
findChild (const QString &childName=QString ()) const
template<class T >
QList< T > findChildren (const QRegularExpression &regExp, Qt::FindChildOptions options=Qt::FindChildrenRecursively) const
template<class T >
QList< T > findChildren (const QString &objName=QString (), Qt::FindChildOptions options=Qt::FindChildrenRecursively) const
bool inherits (const QString &className) const
void installEventFilter (QObject *filterObj)
bool isWidgetType () const
bool isWindowType () const
void killTimer (int id)
const QMetaObjectmetaObject () const
void moveToThread (QThread *targetThread)
QString objectName () const
QObject * parent () const
template<class T = QVariant>
property (const QString &name) const
void removeEventFilter (QObject *obj)
void setObjectName (const QString &name)
void setParent (QObject *parent)
bool setProperty (const QString &name, const QVariant &value)
bool signalsBlocked () const
int startTimer (int interval, Qt::TimerType timerType=Qt::CoarseTimer)
QThreadthread () const
- Public Methods inherited from QPaintDevice
virtual ~QPaintDevice ()
int colorCount () const
int depth () const
int devicePixelRatio () const
qreal devicePixelRatioF () const
int height () const
int heightMM () const
int logicalDpiX () const
int logicalDpiY () const
bool paintingActive () const
int physicalDpiX () const
int physicalDpiY () const
int width () const
int widthMM () const

Protected Methods

int metric (QPaintDevice::PaintDeviceMetric metric) const override
QPaintEnginepaintEngine () const override
void paintEvent (QPaintEvent *event) override
void resizeEvent (QResizeEvent *event) override
- Protected Methods inherited from QWidget
virtual void actionEvent (QActionEvent *event)
virtual void changeEvent (QEvent *event)
virtual void closeEvent (QCloseEvent *event)
virtual void contextMenuEvent (QContextMenuEvent *event)
void create (WId window=0, bool initializeWindow=true, bool destroyOldWindow=true)
void destroy (bool destroyWindow=true, bool destroySubWindows=true)
virtual void dragEnterEvent (QDragEnterEvent *event)
virtual void dragLeaveEvent (QDragLeaveEvent *event)
virtual void dragMoveEvent (QDragMoveEvent *event)
virtual void dropEvent (QDropEvent *event)
virtual void enterEvent (QEvent *event)
bool event (QEvent *event) override
virtual void focusInEvent (QFocusEvent *event)
bool focusNextChild ()
virtual bool focusNextPrevChild (bool next)
virtual void focusOutEvent (QFocusEvent *event)
bool focusPreviousChild ()
virtual void hideEvent (QHideEvent *event)
void initPainter (QPainter *painter) const override
virtual void inputMethodEvent (QInputMethodEvent *event)
virtual void keyPressEvent (QKeyEvent *event)
virtual void keyReleaseEvent (QKeyEvent *event)
virtual void leaveEvent (QEvent *event)
int metric (PaintDeviceMetric metric) const override
virtual void mouseDoubleClickEvent (QMouseEvent *event)
virtual void mouseMoveEvent (QMouseEvent *event)
virtual void mousePressEvent (QMouseEvent *event)
virtual void mouseReleaseEvent (QMouseEvent *event)
virtual void moveEvent (QMoveEvent *event)
virtual bool nativeEvent (const QByteArray &eventType, void *message, long *result)
virtual void showEvent (QShowEvent *event)
virtual void tabletEvent (QTabletEvent *event)
virtual void wheelEvent (QWheelEvent *event)
- Protected Methods inherited from QObject
virtual void childEvent (QChildEvent *event)
virtual void connectNotify (const QMetaMethod &signalMethod) const
virtual void customEvent (QEvent *event)
virtual void disconnectNotify (const QMetaMethod &signalMethod) const
bool isSignalConnected (const QMetaMethod &signalMethod) const
int receivers (const QString &signal) const
QObject * sender () const
int senderSignalIndex () const
virtual void timerEvent (QTimerEvent *event)
- Protected Methods inherited from QPaintDevice
 QPaintDevice ()

Additional Inherited Members

- Public Types inherited from QWidget
enum  RenderFlag
- Public Types inherited from QPaintDevice
enum  PaintDeviceMetric
- Public Slots inherited from QWidget
bool close ()
void hide ()
void lower ()
void raise ()
void repaint ()
void setDisabled (bool disable)
void setEnabled (bool enable)
void setFocus ()
void setHidden (bool hidden)
void setStyleSheet (const QString &styleSheet)
virtual void setVisible (bool visible)
void setWindowModified (bool modified)
void setWindowTitle (const QString &title)
void show ()
void showFullScreen ()
void showMaximized ()
void showMinimized ()
void showNormal ()
void update ()
- Public Slots inherited from QObject
void deleteLater ()
- Static Public Methods inherited from QWidget
static QWidget * createWindowContainer (QWindow *window, QWidget *parent=nullptr, Qt::WindowFlags flags=Qt::EmptyFlag)
static QWidget * find (WId id)
static QWidget * keyboardGrabber ()
static QWidget * mouseGrabber ()
static void setTabOrder (QWidget *firstWidget, QWidget *secondWidget)
- Static Public Methods inherited from QObject
static bool connect (const QObject *sender, const QMetaMethod &signalMethod, const QObject *receiver, const QMetaMethod &slotMethod, Qt::ConnectionType type=Qt::AutoConnection)
static bool connect (const QObject *sender, const QString &signalMethod, const QObject *receiver, const QString &slotMethod, Qt::ConnectionType type=Qt::AutoConnection, const QString &location=QString ())
static bool connect (const QObject *sender, const QString &signalMethod, const QString &location, const QObject *receiver, const QString &slotMethod, Qt::ConnectionType type=Qt::AutoConnection)
template<class Sender , class SignalClass , class... SignalArgs, class Receiver , class SlotClass , class... SlotArgs, class SlotReturn >
static bool connect (const Sender *sender, void (SignalClass::*signalMethod)(SignalArgs...), const Receiver *receiver, SlotReturn (SlotClass::*slotMethod)(SlotArgs...), Qt::ConnectionType type=Qt::AutoConnection)
template<class Sender , class SignalClass , class... SignalArgs, class Receiver , class T >
static bool connect (const Sender *sender, void (SignalClass::*signalMethod)(SignalArgs...), const Receiver *receiver, T slotLambda, Qt::ConnectionType type=Qt::AutoConnection)
static bool disconnect (const QObject *sender, const QMetaMethod &signalMethod, const QObject *receiver, const QMetaMethod &slotMethod)
static bool disconnect (const QObject *sender, const QString &signalMethod, const QObject *receiver, const QString &slotMethod)
static bool disconnect (const QObject *sender, const QString &signalMethod, const QString &location, const QObject *receiver, const QString &slotMethod)
template<class Sender , class SignalClass , class... SignalArgs, class Receiver , class SlotClass , class... SlotArgs, class SlotReturn >
static bool disconnect (const Sender *sender, void (SignalClass::*signalMethod)(SignalArgs...), const Receiver *receiver, SlotReturn (SlotClass::*slotMethod)(SlotArgs...))
template<class Sender , class SignalClass , class... SignalArgs, class Receiver >
static bool disconnect (const Sender *sender, void (SignalClass::*signalMethod)(SignalArgs...), const Receiver *receiver, std::nullptr_t slotMethod=nullptr)
template<class Sender , class SignalClass , class... SignalArgs, class Receiver , class T >
static bool disconnect (const Sender *sender, void (SignalClass::*signalMethod)(SignalArgs...), const Receiver *receiver, T slotMethod)
static QMetaObjectstaticMetaObject ()
static QString tr (const char *text, const char *comment=nullptr, std::optional< int > numArg=std::optional< int >())
- Protected Slots inherited from QWidget
void updateMicroFocus ()
- Properties inherited from QWidget
- Properties inherited from QObject

Detailed Description

The QOpenGLWidget class is a widget for rendering OpenGL graphics.

QOpenGLWidget provides functionality for displaying OpenGL graphics integrated in a CopperSpice application. It is very simple to use: Make your class inherit from it and use the subclass like any other QWidget, except that you have the choice between using QPainter and standard OpenGL rendering commands.

QOpenGLWidget provides three convenient virtual functions you can reimplement in your subclass to perform the typical OpenGL tasks.

Renders the OpenGL scene. Gets called whenever the widget needs to be updated.
Sets up the OpenGL viewport, projection, etc. Gets called whenever the widget has been resized (and also when it is shown for the first time because all newly created widgets get a resize event automatically).
Sets up the OpenGL resources and state. Gets called once before the first time resizeGL() or paintGL() is called.

If you need to trigger a repaint from places other than paintGL() (a typical example is when using timers to animate scenes), you should call the widget's update() function to schedule an update.

Your widget's OpenGL rendering context is made current when paintGL(), resizeGL(), or initializeGL() is called. If you need to call the standard OpenGL API functions from other places (e.g. in your widget's constructor or in your own paint functions), you must call makeCurrent() first.

All rendering happens into an OpenGL framebuffer object. makeCurrent() ensure that it is bound in the context. Keep this in mind when creating and binding additional framebuffer objects in the rendering code in paintGL(). Never re-bind the framebuffer with ID 0. Instead, call defaultFramebufferObject() to get the ID that should be bound.

QOpenGLWidget allows using different OpenGL versions and profiles when the platform supports it. Just set the requested format via setFormat(). Keep in mind however that having multiple QOpenGLWidget instances in the same window requires that they all use the same format, or at least formats that do not make the contexts non-sharable. To overcome this issue, prefer using QSurfaceFormat::setDefaultFormat() instead of setFormat().

Note: Calling QSurfaceFormat::setDefaultFormat() before constructing the QApplication instance is mandatory on some platforms (for example, macOS) when an OpenGL core profile context is requested. This is to ensure that resource sharing between contexts stays functional as all internal contexts are created using the correct version and profile.

Painting Techniques

As described above, subclass QOpenGLWidget to render pure 3D content in the following way.

  • Reimplement the initializeGL() and resizeGL() functions to set up the OpenGL state and provide a perspective transformation.
  • Reimplement paintGL() to paint the 3D scene, calling only OpenGL functions.

It is also possible to draw 2D graphics onto a QOpenGLWidget subclass using QPainter.

  • In paintGL(), instead of issuing OpenGL commands, construct a QPainter object for use on the widget.
  • Draw primitives using QPainter's member functions.
  • Direct OpenGL commands can still be issued. However, you must make sure these are enclosed by a call to the painter's beginNativePainting() and endNativePainting().

When performing drawing using QPainter only, it is also possible to perform the painting like it is done for ordinary widgets by reimplementing paintEvent().

OpenGL Function Calls

When making OpenGL function calls, it is strongly recommended to avoid calling the functions directly. Instead, prefer using QOpenGLFunctions (when making portable applications) or the versioned variants (for example, QOpenGLFunctions_3_2_Core and similar, when targeting modern, desktop-only OpenGL). This way the application will work correctly in all build configurations, including the ones that perform dynamic OpenGL implementation loading which means applications are not directly linking to an GL implementation and thus direct function calls are not feasible.

In paintGL() the current context is always accessible by calling QOpenGLContext::currentContext(). From this context an already initialized, ready-to-be-used QOpenGLFunctions instance is retrievable by calling QOpenGLContext::functions(). An alternative to prefixing every GL call is to inherit from QOpenGLFunctions and call QOpenGLFunctions::initializeOpenGLFunctions() in initializeGL().

As for the OpenGL headers, note that in most cases there will be no need to directly include any headers like GL.h. The OpenGL-related CopperSpice headers will include qopengl.h which will in turn include an appropriate header for the system. This might be an OpenGL ES 3.x or 2.0 header, the highest version that is available, or a system-provided gl.h. In addition, a copy of the extension headers (called glext.h on some systems) is provided as part of CopperSpice both for OpenGL and OpenGL ES. These will get included automatically on platforms where feasible. This means that constants and function pointer typedefs from ARB, EXT, OES extensions are automatically available.

Additional documentation pending.

Constructor & Destructor Documentation

QOpenGLWidget::~QOpenGLWidget ( )

Destroys the QOpenGLWidget instance, freeing its resources.

The QOpenGLWidget's context is made current in the destructor, allowing for safe destruction of any child object that may need to release OpenGL resources belonging to the context provided by this widget.

If you have objects wrapping OpenGL resources (such as QOpenGLBuffer, QOpenGLShaderProgram, etc.) as members of a OpenGLWidget subclass, you may need to add a call to makeCurrent() in that subclass destructor as well. Due to the rules of C++ object destruction, those objects will be destroyed before calling this function (but after that the destructor of the subclass has run), therefore making the OpenGL context current in this function happens too late for their safe disposal.

See also

Method Documentation

void QOpenGLWidget::aboutToCompose ( )

This signal is emitted when the widget's top-level window is about to begin composing the textures of its QOpenGLWidget children and the other widgets.

void QOpenGLWidget::aboutToResize ( )

This signal is emitted when the widget's size is changed and therefore the framebuffer object is going to be recreated.

void QOpenGLWidget::frameSwapped ( )

This signal is emitted after the widget's top-level window has finished composition and returned from its potentially blocking QOpenGLContext::swapBuffers() call.

QImage QOpenGLWidget::grabFramebuffer ( )

Renders and returns a 32-bit RGB image of the framebuffer.

This is a potentially expensive operation because it relies on glReadPixels() to read back the pixels. This may be slow and can stall the GPU pipeline.

int QOpenGLWidget::metric ( QPaintDevice::PaintDeviceMetric  metric) const

Returns the metric information for the given paint device metric.

See also

Reimplemented from QPaintDevice.

QPaintEngine* QOpenGLWidget::paintEngine ( ) const

Returns a pointer to the paint engine used for drawing on the device.

Implements QPaintDevice.

void QOpenGLWidget::paintEvent ( QPaintEvent event)

This event handler can be reimplemented in a subclass to receive paint events passed in event. A paint event is a request to repaint all or part of a widget. It can happen for one of the following reasons.

  • repaint() or update() was invoked
  • widget was obscured and has now been uncovered
  • some other reason

Many widgets can simply repaint their entire surface when asked to, but some slow widgets need to optimize by painting only the requested region: QPaintEvent::region(). This speed optimization does not change the result, as painting is clipped to that region during event processing. QListView and QTableView do this, for example.

CopperSpice also tries to speed up painting by merging multiple paint events into one. When update() is called several times or the window system sends several paint events, CopperSpice merges these events into one event with a larger region (see QRegion::united()). The repaint() function does not permit this optimization, so we suggest using update() whenever possible.

When the paint event occurs, the update region has normally been erased, so you are painting on the widget's background. The background can be set using setBackgroundRole() and setPalette().

QWidget automatically double-buffers its painting, so there is no need to write double-buffering code in paintEvent() to avoid flicker.

For the X11 platform it is possible to toggle global double buffering by calling qt_x11_set_global_double_buffer().

extern void qt_x11_set_global_double_buffer(bool);

Generally you should refrain from calling update() or repaint() inside a paintEvent(). For example, calling update() or repaint() on children inside a paintevent() results in undefined behavior; the child may or may not get a paint event.

If you are using a custom paint engine without the CopperSpice backingstore, Qt::WA_PaintOnScreen must be set. Otherwise, QWidget::paintEngine() will never be called; the backingstore will be used instead.
See also
event(), repaint(), update(), QPainter, QPixmap, QPaintEvent

Reimplemented from QWidget.

void QOpenGLWidget::resized ( )

This signal is emitted right after the framebuffer object has been recreated due to resizing the widget.

void QOpenGLWidget::resizeEvent ( QResizeEvent event)

This event handler can be reimplemented in a subclass to receive widget resize events which are passed in the event parameter. When resizeEvent() is called, the widget already has its new geometry. The old size is accessible through QResizeEvent::oldSize().

The widget will be erased and receive a paint event immediately after processing the resize event. No drawing need be (or should be) done inside this handler.

See also
moveEvent(), event(), resize(), QResizeEvent, paintEvent()

Reimplemented from QWidget.