The QOpenGLPaintDevice class enables painting to an OpenGL context using QPainter. More...

Inheritance diagram for QOpenGLPaintDevice:

Public Methods
	QOpenGLPaintDevice ()

	QOpenGLPaintDevice (const QSize &size)

	QOpenGLPaintDevice (int width, int height)

virtual	~QOpenGLPaintDevice ()

QOpenGLContext *	context () const

qreal	dotsPerMeterX () const

qreal	dotsPerMeterY () const

virtual void	ensureActiveTarget ()

QPaintEngine *	paintEngine () const override

bool	paintFlipped () const

void	setDevicePixelRatio (qreal devicePixelRatio)

void	setDotsPerMeterX (qreal dpmx)

void	setDotsPerMeterY (qreal dpmy)

void	setPaintFlipped (bool flipped)

void	setSize (const QSize &size)

QSize	size () 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

Protected Methods inherited from QPaintDevice
	QPaintDevice ()

Additional Inherited Members
Public Types inherited from QPaintDevice
enum	PaintDeviceMetric

Detailed Description

The QOpenGLPaintDevice uses the current QOpenGL context to render QPainter draw commands. The context is captured upon construction. It requires support for OpenGL (ES) 2.0 or higher.

Performance

The QOpenGLPaintDevice is almost always hardware accelerated and has the potential of being much faster than software rasterization. However, it is more sensitive to state changes and requires the drawing commands to be carefully ordered to achieve optimal performance.

Antialiasing and Quality

Antialiasing in the OpenGL paint engine is done using multisampling. Most hardware require significantly more memory to do multisampling and the resulting quality is not on par with the quality of the software paint engine. The OpenGL paint engine's strength lies in its performance, not its visual rendering quality.

State Changes

When painting to a QOpenGLPaintDevice using QPainter, the state of the current OpenGL context will be altered by the paint engine to reflect its needs. Applications should not rely upon the OpenGL state being reset to its original conditions, particularly the current shader program, OpenGL viewport, texture units, and drawing modes.

Mixing QPainter and OpenGL

When intermixing QPainter and OpenGL, it is important to notify QPainter that the OpenGL state may have been cluttered so it can restore its internal state. This is achieved by calling QPainter::beginNativePainting() before starting the OpenGL rendering and calling QPainter::endNativePainting() after finishing.

Constructor & Destructor Documentation

QOpenGLPaintDevice::QOpenGLPaintDevice ( )

Constructs a QOpenGLPaintDevice. The QOpenGLPaintDevice is only valid for the current context.

See also: QOpenGLContext::currentContext()

QOpenGLPaintDevice::QOpenGLPaintDevice ( const QSize & size )

explicit

Constructs a QOpenGLPaintDevice with the given size. The QOpenGLPaintDevice is only valid for the current context.

See also: QOpenGLContext::currentContext()

QOpenGLPaintDevice::QOpenGLPaintDevice	(	int	width,
		int	height
	)

Constructs a QOpenGLPaintDevice with the given width and height. The QOpenGLPaintDevice is only valid for the current context.

See also: QOpenGLContext::currentContext()

QOpenGLPaintDevice::~QOpenGLPaintDevice ( )

virtual

Destroys the QOpenGLPaintDevice.

Method Documentation

QOpenGLContext * QOpenGLPaintDevice::context ( ) const

Returns the OpenGL context associated with the paint device.

qreal QOpenGLPaintDevice::dotsPerMeterX ( ) const

Returns the number of pixels per meter horizontally.

See also: setDotsPerMeterX()

qreal QOpenGLPaintDevice::dotsPerMeterY ( ) const

Returns the number of pixels per meter vertically.

See also: setDotsPerMeterY()

void QOpenGLPaintDevice::ensureActiveTarget ( )

virtual

The default implementation does nothing. Override this method to rebind a target frame buffer object or context when different QOpenGLPaintDevice instances are issuing draw calls alternately.

The method beginNativePainting() will invoke this method.

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

overrideprotectedvirtual

Returns the metric information for the given paint device metric.