The QGLPixelBuffer class encapsulates an OpenGL pbuffer. More...

Inheritance diagram for QGLPixelBuffer:

Public Methods
	QGLPixelBuffer (const QSize &size, const QGLFormat &format=QGLFormat::defaultFormat (), QGLWidget *shareWidget=nullptr)

	QGLPixelBuffer (int width, int height, const QGLFormat &format=QGLFormat::defaultFormat (), QGLWidget *shareWidget=nullptr)

virtual	~QGLPixelBuffer ()

GLuint	bindTexture (const QImage &image, GLenum target=GL_TEXTURE_2D)

GLuint	bindTexture (const QPixmap &pixmap, GLenum target=GL_TEXTURE_2D)

GLuint	bindTexture (const QString &fileName)

bool	bindToDynamicTexture (GLuint texture_id)

void	deleteTexture (GLuint texture_id)

bool	doneCurrent ()

void	drawTexture (const QPointF &point, GLuint texture_id, GLenum textureTarget=GL_TEXTURE_2D)

void	drawTexture (const QRectF &target, GLuint texture_id, GLenum textureTarget=GL_TEXTURE_2D)

QGLFormat	format () const

GLuint	generateDynamicTexture () const

Qt::HANDLE	handle () const

bool	isValid () const

bool	makeCurrent ()

QPaintEngine *	paintEngine () const override

void	releaseFromDynamicTexture ()

QSize	size () const

QImage	toImage () const

void	updateDynamicTexture (GLuint texture_id) 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

Static Public Methods
static bool	hasOpenGLPbuffers ()

Protected Methods
int	metric (PaintDeviceMetric metric) const override

Protected Methods inherited from QPaintDevice
	QPaintDevice ()

Additional Inherited Members
Public Types inherited from QPaintDevice
enum	PaintDeviceMetric

Detailed Description

The QGLPixelBuffer class encapsulates an OpenGL pbuffer. Rendering into a pbuffer is normally done using full hardware acceleration. This can be significantly faster than rendering into a QPixmap.

There are three approaches to using this class.

We can draw into the pbuffer and convert it to a QImage using toImage(). This is normally much faster than calling QGLWidget::renderPixmap().
We can draw into the pbuffer and copy the contents into an OpenGL texture using updateDynamicTexture(). This allows us to create dynamic textures and works on all systems with pbuffer support.
On systems that support it, we can bind the pbuffer to an OpenGL texture. The texture is then updated automatically when the pbuffer contents change, eliminating the need for additional copy operations. This is supported only on Windows and Mac OS X systems that provide the render_texture extension. Under Windows a multi-sampled pbuffer can not be used in conjunction with the render_texture extension. If a multi-sampled pbuffer is requested under Windows, the render_texture extension is turned off for that pbuffer.

Threading

It is possible to render into a QGLPixelBuffer using a QPainter in a separate thread however OpenGL 2.0 or OpenGL ES 2.0 is required for this to work. Under X11, it iss necessary to set the Qt::AA_X11InitThreads application attribute.

Pbuffers are provided by the OpenGL pbuffer extension, call hasOpenGLPbuffer() to find out if the system provides pbuffers.

See also: size(), format()

Constructor & Destructor Documentation

QGLPixelBuffer::QGLPixelBuffer	(	const QSize &	size,
		const QGLFormat &	format = `QGLFormat::defaultFormat()`,
		QGLWidget *	shareWidget = `nullptr`
	)

Constructs an OpenGL pbuffer of the given size. If no format is specified the default format is used. If the specified shareWidget points to a valid QGLWidget, the pbuffer will share its context with shareWidget.

If you intend to bind this pbuffer as a dynamic texture, the width and height components of size must be powers of two (e.g., 512 x 128).

See also: size(), format()

QGLPixelBuffer::QGLPixelBuffer	(	int	width,
		int	height,
		const QGLFormat &	format = `QGLFormat::defaultFormat()`,
		QGLWidget *	shareWidget = `nullptr`
	)

Constructs an OpenGL pbuffer with the width and height. If no format is specified, the default format is used. If the shareWidget parameter points to a valid QGLWidget, the pbuffer will share its context with shareWidget.

If you intend to bind this pbuffer as a dynamic texture, the width and height components of size must be powers of two (e.g., 512 x 128).

See also: size(), format()

QGLPixelBuffer::~QGLPixelBuffer ( )

virtual

Destroys the pbuffer and frees any allocated resources.

Method Documentation

GLuint QGLPixelBuffer::bindTexture	(	const QImage &	image,
		GLenum	target = `GL_TEXTURE_2D`
	)

Generates and binds a 2D GL texture to the current context, based on image. The generated texture id is returned and can be used in later glBindTexture() calls. The target specifies the texture target.

Equivalent to calling QGLContext::bindTexture().

See also: deleteTexture()

GLuint QGLPixelBuffer::bindTexture	(	const QPixmap &	pixmap,
		GLenum	target = `GL_TEXTURE_2D`
	)

Generates and binds a 2D GL texture based on pixmap.

Equivalent to calling QGLContext::bindTexture().

See also: deleteTexture()

GLuint QGLPixelBuffer::bindTexture ( const QString & fileName )

Reads the DirectDrawSurface (DDS) compressed file fileName and generates a 2D GL texture from it.

Equivalent to calling QGLContext::bindTexture().

See also: deleteTexture()

bool QGLPixelBuffer::bindToDynamicTexture ( GLuint texture_id )

Binds the texture specified by texture_id to this pbuffer. Returns true on success, otherwise returns false. The texture must be of the same size and format as the pbuffer. To unbind the texture, call releaseFromDynamicTexture(). While the texture is bound, it is updated automatically when the pbuffer contents change, eliminating the need for additional copy operations.

QGLPixelBuffer pbuffer(...);
 
// ...
 
pbuffer.makeCurrent();
GLuint dynamicTexture = pbuffer.generateDynamicTexture();
pbuffer.bindToDynamicTexture(dynamicTexture);
 
// ...
 
pbuffer.releaseFromDynamicTexture();

Warning: This method uses the render_texture extension, which is currently not supported under X11. An alternative that works on all systems (including X11) is to manually copy the pbuffer contents to a texture using updateDynamicTexture().; For the bindToDynamicTexture() call to succeed on the Mac OS X, the pbuffer needs a shared context, i.e. the QGLPixelBuffer must be created with a share widget.

See also: generateDynamicTexture(), releaseFromDynamicTexture()

void QGLPixelBuffer::deleteTexture ( GLuint texture_id )

Removes the texture identified by texture_id from the texture cache.

Equivalent to calling QGLContext::deleteTexture().

bool QGLPixelBuffer::doneCurrent ( )

Makes no context the current OpenGL context. Returns true on success, otherwise returns false.

void QGLPixelBuffer::drawTexture	(	const QPointF &	point,
		GLuint	texture_id,
		GLenum	textureTarget = `GL_TEXTURE_2D`
	)

Draws the given texture_id, at the given point in OpenGL model space. The textureTarget parameter should be a 2D texture target.

Equivalent to the corresponding QGLContext::drawTexture().

void QGLPixelBuffer::drawTexture	(	const QRectF &	target,
		GLuint	texture_id,
		GLenum	textureTarget = `GL_TEXTURE_2D`
	)

Draws the given texture_id, to the given target rectangle, target, in OpenGL model space. The textureTarget should be a 2D texture target.

Equivalent to the corresponding QGLContext::drawTexture().

QGLFormat QGLPixelBuffer::format ( ) const

Returns the format of the pbuffer. The format may be different from the one that was requested.

GLuint QGLPixelBuffer::generateDynamicTexture ( ) const

Generates and binds a 2D GL texture that is the same size as the pbuffer, and returns the texture's ID. This can be used in conjunction with bindToDynamicTexture() and updateDynamicTexture().

See also: size()

Qt::HANDLE QGLPixelBuffer::handle ( ) const

Returns the native pbuffer handle.

bool QGLPixelBuffer::hasOpenGLPbuffers ( )

static

Returns true if the OpenGL pbuffer extension is present on this system, otherwise returns false.

bool QGLPixelBuffer::isValid ( ) const

Returns true if this pbuffer is valid, otherwise returns false.

bool QGLPixelBuffer::makeCurrent ( )

Makes this pbuffer the current OpenGL rendering context. Returns true on success, otherwise returns false.

See also: QGLContext::makeCurrent(), doneCurrent()

int QGLPixelBuffer::metric ( PaintDeviceMetric metric ) const

overrideprotectedvirtual

Reimplemented from QPaintDevice::metric()

QPaintEngine * QGLPixelBuffer::paintEngine ( ) const

overridevirtual

Implements QPaintDevice::paintEngine()

void QGLPixelBuffer::releaseFromDynamicTexture ( )

Releases the pbuffer from any previously bound texture.

See also: bindToDynamicTexture()

QSize QGLPixelBuffer::size ( ) const

Returns the size of the pbuffer.

QImage QGLPixelBuffer::toImage ( ) const

Returns the contents of the pbuffer as a QImage.

void QGLPixelBuffer::updateDynamicTexture ( GLuint texture_id ) const

Copies the pbuffer contents into the texture specified with texture_id. The texture must be of the same size and format as the pbuffer.

QGLPixelBuffer pbuffer(...);
 
// ...
 
pbuffer.makeCurrent();
GLuint dynamicTexture = pbuffer.generateDynamicTexture();
 
// ...
 
pbuffer.updateDynamicTexture(dynamicTexture);

An alternative on Windows and Mac OS X systems that support the render_texture extension is to use bindToDynamicTexture() to get dynamic updates of the texture.

See also: generateDynamicTexture(), bindToDynamicTexture()

Public Methods

Static Public Methods

Protected Methods

Additional Inherited Members

Detailed Description

Threading

Constructor & Destructor Documentation

Method Documentation