QGLPixelBuffer Class | Qt OpenGL

Qt 5.13 | Qt OpenGL | C++ Classes | QGLPixelBuffer

Qt 5.13.2 Reference Documentation

# QGLPixelBuffer Class

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

Header: | #include <QGLPixelBuffer>
qmake: | QT += opengl
Since: | Qt 4.1
Inherits: | QPaintDevice

This class is obsolete. It is provided to keep old source code working. We strongly advise against using it in new code.

This class was introduced in Qt 4.1.

- List of all members, including inherited members

## Public Functions

| QGLPixelBuffer(int width, int height, const QGLFormat &format = QGLFormat::defaultFormat(), QGLWidget *shareWidget = nullptr)
| QGLPixelBuffer(const QSize &size, 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)
QGLContext * | context() const
void | deleteTexture(GLuint texture_id)
bool | doneCurrent()
void | drawTexture(const QRectF &target, GLuint textureId, GLenum textureTarget = GL_TEXTURE_2D)
void | drawTexture(const QPointF &point, GLuint textureId, GLenum textureTarget = GL_TEXTURE_2D)
QGLFormat | format() const
GLuint | generateDynamicTexture() const
Qt::HANDLE | handle() const
bool | isValid() const
bool | makeCurrent()
void | releaseFromDynamicTexture()
QSize | size() const
QImage | toImage() const
void | updateDynamicTexture(GLuint texture_id) const

## Reimplemented Public Functions

virtual QPaintEngine * | paintEngine() const override

## Static Public Members

bool | hasOpenGLPbuffers()

## Reimplemented Protected Functions

virtual int | metric(QPaintDevice::PaintDeviceMetric metric) const override

## Detailed Description

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 macOS 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.

Note: This class has been deprecated, use QOpenGLFramebufferObject for offscreen rendering.

### Threading

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.

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

## Member Function Documentation

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

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().

### 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 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().

### `[virtual]` QGLPixelBuffer::~QGLPixelBuffer()

Destroys the pbuffer and frees any allocated resources.

### 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 parameter specifies the texture target.

Equivalent to calling QGLContext::bindTexture().

See also deleteTexture().

### GLuint QGLPixelBuffer::bindTexture(const QPixmap &pixmap, GLenum 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().

### GLuint QGLPixelBuffer::bindTexture(const QString &fileName)

This is an overloaded function.

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.

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 macOS, the pbuffer needs a shared context, i.e. the QGLPixelBuffer must be created with a share widget.

See also generateDynamicTexture() and releaseFromDynamicTexture().

### QGLContext *QGLPixelBuffer::context() const

Returns the context of this pixelbuffer.

### 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 QRectF &target, GLuint textureId, GLenum 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.

### void QGLPixelBuffer::drawTexture(const QPointF &point, GLuint textureId, GLenum 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() 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.

### `[static]` bool QGLPixelBuffer::hasOpenGLPbuffers()

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() and doneCurrent().

### `[override virtual protected]` int QGLPixelBuffer::metric(QPaintDevice::PaintDeviceMetric metric) const

Reimplements: QPaintDevice::metric(QPaintDevice::PaintDeviceMetric metric) const.

### `[override virtual]` QPaintEngine *QGLPixelBuffer::paintEngine() const

Reimplements: QPaintDevice::paintEngine() const.

### 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.

Example:

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

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

See also generateDynamicTexture() and bindToDynamicTexture().