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QGLPixelBuffer Class Reference
^{[QtOpenGL module]}

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

Inherits QPaintDevice.

Methods

• __init__ (self, QSize size, QGLFormat format = QGLFormat.defaultFormat(), QGLWidget shareWidget = None)
• __init__ (self, int width, int height, QGLFormat format = QGLFormat.defaultFormat(), QGLWidget shareWidget = None)
• int bindTexture (self, QImage image, int target = GL_TEXTURE_2D)
• int bindTexture (self, QPixmap pixmap, int target = GL_TEXTURE_2D)
• int bindTexture (self, QString fileName)
• bool bindToDynamicTexture (self, int texture)
• deleteTexture (self, int texture_id)
• int devType (self)
• bool doneCurrent (self)
• drawTexture (self, QRectF target, int textureId, int textureTarget = GL_TEXTURE_2D)
• drawTexture (self, QPointF point, int textureId, int textureTarget = GL_TEXTURE_2D)
• QGLFormat format (self)
• int generateDynamicTexture (self)
• int handle (self)
• bool isValid (self)
• bool makeCurrent (self)
• int metric (self, QPaintDevice.PaintDeviceMetric metric)
• QPaintEngine paintEngine (self)
• releaseFromDynamicTexture (self)
• QSize size (self)
• QImage toImage (self)
• updateDynamicTexture (self, int texture_id)

Static Methods

• bool hasOpenGLPbuffers ()

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:

1. We can draw into the pbuffer and convert it to a QImage using toImage(). This is normally much faster than calling QGLWidget.renderPixmap().
2. 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.
3. 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. Note that under Windows, a multi-sampled pbuffer can't 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.

As of Qt 4.8, it's possible to render into a QGLPixelBuffer using a QPainter in a separate thread. Note that OpenGL 2.0 or OpenGL ES 2.0 is required for this to work. Also, under X11, it's 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.

Method Documentation

QGLPixelBuffer.__init__ (self, QSize size, QGLFormat format = QGLFormat.defaultFormat(), QGLWidget shareWidget = None)

Constructs an OpenGL pbuffer of the given size. 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() and format().

QGLPixelBuffer.__init__ (self, int width, int height, QGLFormat format = QGLFormat.defaultFormat(), QGLWidget shareWidget = None)

This is an overloaded function.

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() and format().

int QGLPixelBuffer.bindTexture (self, QImage image, int 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 parameter specifies the texture target.

Equivalent to calling QGLContext.bindTexture().

See also deleteTexture().

int QGLPixelBuffer.bindTexture (self, QPixmap pixmap, int target = GL_TEXTURE_2D)

This is an overloaded function.

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

Equivalent to calling QGLContext.bindTexture().

See also deleteTexture().

int QGLPixelBuffer.bindTexture (self, QString fileName)

This is an overloaded function.

Equivalent to calling QGLContext.bindTexture().

See also deleteTexture().

bool QGLPixelBuffer.bindToDynamicTexture (self, int texture)

Binds the texture specified by texture_id to this pbuffer. Returns true on success; otherwise returns false.

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.

Example:

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

Warning: This function 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().

Warning: 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() and releaseFromDynamicTexture().

QGLPixelBuffer.deleteTexture (self, int texture_id)

Removes the texture identified by texture_id from the texture cache.

Equivalent to calling QGLContext.deleteTexture().

int QGLPixelBuffer.devType (self)

bool QGLPixelBuffer.doneCurrent (self)

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

QGLPixelBuffer.drawTexture (self, QRectF target, int textureId, int textureTarget = GL_TEXTURE_2D)

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

Equivalent to the corresponding QGLContext.drawTexture().

This function was introduced in Qt 4.4.

QGLPixelBuffer.drawTexture (self, QPointF point, int textureId, int textureTarget = GL_TEXTURE_2D)

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

Equivalent to the corresponding QGLContext.drawTexture().

This function was introduced in Qt 4.4.

QGLFormat QGLPixelBuffer.format (self)

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

int QGLPixelBuffer.generateDynamicTexture (self)

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().

int QGLPixelBuffer.handle (self)

Returns the native pbuffer handle.

bool QGLPixelBuffer.hasOpenGLPbuffers ()

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

bool QGLPixelBuffer.isValid (self)

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

bool QGLPixelBuffer.makeCurrent (self)

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

See also QGLContext.makeCurrent() and doneCurrent().

int QGLPixelBuffer.metric (self, QPaintDevice.PaintDeviceMetric metric)

Reimplemented from QPaintDevice.metric().

QPaintEngine QGLPixelBuffer.paintEngine (self)

Reimplemented from QPaintDevice.paintEngine().

QGLPixelBuffer.releaseFromDynamicTexture (self)

Releases the pbuffer from any previously bound texture.

See also bindToDynamicTexture().

QSize QGLPixelBuffer.size (self)

Returns the size of the pbuffer.

QImage QGLPixelBuffer.toImage (self)

Returns the contents of the pbuffer as a QImage.

QGLPixelBuffer.updateDynamicTexture (self, int texture_id)

Copies the pbuffer contents into the texture specified with texture_id.

 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() and bindToDynamicTexture().