Qt 4.3: QGLWidget Class Reference

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# QGLWidget Class Reference
[QtOpenGL module]

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

     #include <QGLWidget>

Inherits QWidget.

- List of all members, including inherited members
- Obsolete members
- Qt 3 support members

### Public Functions

- QGLWidget ( QWidget * parent = 0, const QGLWidget * shareWidget = 0, Qt::WindowFlags f = 0 )
- QGLWidget ( QGLContext * context, QWidget * parent = 0, const QGLWidget * shareWidget = 0, Qt::WindowFlags f = 0 )
- QGLWidget ( const QGLFormat & format, QWidget * parent = 0, const QGLWidget * shareWidget = 0, Qt::WindowFlags f = 0 )
- ~QGLWidget ()
- GLuint bindTexture ( const QImage & image, GLenum target = GL_TEXTURE_2D, GLint format = GL_RGBA )
- GLuint bindTexture ( const QPixmap & pixmap, GLenum target = GL_TEXTURE_2D, GLint format = GL_RGBA )
- GLuint bindTexture ( const QString & fileName )
- const QGLColormap & colormap () const
- const QGLContext * context () const
- void deleteTexture ( GLuint id )
- void doneCurrent ()
- bool doubleBuffer () const
- QGLFormat format () const
- QImage grabFrameBuffer ( bool withAlpha = false )
- bool isSharing () const
- bool isValid () const
- void makeCurrent ()
- void makeOverlayCurrent ()
- const QGLContext * overlayContext () const
- void qglClearColor ( const QColor & c ) const
- void qglColor ( const QColor & c ) const
- QPixmap renderPixmap ( int w = 0, int h = 0, bool useContext = false )
- void renderText ( int x, int y, const QString & str, const QFont & font = QFont(), int listBase = 2000 )
- void renderText ( double x, double y, double z, const QString & str, const QFont & font = QFont(), int listBase = 2000 )
- void setColormap ( const QGLColormap & cmap )
- void setMouseTracking ( bool enable )
- void swapBuffers ()

- 201 public functions inherited from QWidget
- 29 public functions inherited from QObject
- 12 public functions inherited from QPaintDevice

### Public Slots

- virtual void updateGL ()
- virtual void updateOverlayGL ()

- 19 public slots inherited from QWidget
- 1 public slot inherited from QObject

### Static Public Members

- QImage convertToGLFormat ( const QImage & img )

- 4 static public members inherited from QWidget
- 5 static public members inherited from QObject

### Protected Functions

- bool autoBufferSwap () const
- virtual void glDraw ()
- virtual void glInit ()
- virtual void initializeGL ()
- virtual void initializeOverlayGL ()
- virtual void paintEvent ( QPaintEvent * event )
- virtual void paintGL ()
- virtual void paintOverlayGL ()
- virtual void resizeEvent ( QResizeEvent * event )
- virtual void resizeGL ( int width, int height )
- virtual void resizeOverlayGL ( int width, int height )
- void setAutoBufferSwap ( bool on )

- 38 protected functions inherited from QWidget
- 7 protected functions inherited from QObject
- 1 protected function inherited from QPaintDevice

### Additional Inherited Members

- 56 properties inherited from QWidget
- 1 property inherited from QObject
- 1 signal inherited from QWidget
- 1 signal inherited from QObject
- 1 protected slot inherited from QWidget

## Detailed Description

The QGLWidget class is a widget for rendering OpenGL graphics.

QGLWidget provides functionality for displaying OpenGL graphics integrated into a Qt application. It is very simple to use. You 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.

QGLWidget provides three convenient virtual functions that you can reimplement in your subclass to perform the typical OpenGL tasks:

- paintGL() - Renders the OpenGL scene. Gets called whenever the widget needs to be updated.
- resizeGL() - Sets up the OpenGL viewport, projection, etc. Gets called whenever the 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).
- initializeGL() - Sets up the OpenGL rendering context, defines display lists, etc. Gets called once before the first time resizeGL() or paintGL() is called.

Here is a rough outline of how a QGLWidget subclass might look:

     class MyGLDrawer : public QGLWidget
     {
         Q_OBJECT        // must include this if you use Qt signals/slots

     public:
         MyGLDrawer(QWidget *parent)
             : QGLWidget(parent) {}

     protected:

         void initializeGL()
         {
             // Set up the rendering context, define display lists etc.:
             ...
             glClearColor(0.0, 0.0, 0.0, 0.0);
             glEnable(GL_DEPTH_TEST);
             ...
         }

         void resizeGL(int w, int h)
         {
             // setup viewport, projection etc.:
             glViewport(0, 0, (GLint)w, (GLint)h);
             ...
             glFrustum(...);
             ...
         }

         void paintGL()
         {
             // draw the scene:
             ...
             glRotatef(...);
             glMaterialfv(...);
             glBegin(GL_QUADS);
             glVertex3f(...);
             glVertex3f(...);
             ...
             glEnd();
             ...
         }

     };

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 updateGL() function.

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.

QGLWidget provides functions for requesting a new display format and you can also create widgets with customized rendering contexts.

You can also share OpenGL display lists between QGLWidgets (see the documentation of the QGLWidget constructors for details).

### Overlays

The QGLWidget creates a GL overlay context in addition to the normal context if overlays are supported by the underlying system.

If you want to use overlays, you specify it in the format. (Note: Overlay must be requested in the format passed to the QGLWidget constructor.) Your GL widget should also implement some or all of these virtual methods:

- paintOverlayGL()
- resizeOverlayGL()
- initializeOverlayGL()

These methods work in the same way as the normal paintGL() etc. functions, except that they will be called when the overlay context is made current. You can explicitly make the overlay context current by using makeOverlayCurrent(), and you can access the overlay context directly (e.g. to ask for its transparent color) by calling overlayContext().

On X servers in which the default visual is in an overlay plane, non-GL Qt windows can also be used for overlays.

### Painting Techniques

As described above, subclass QGLWidget to render pure 3D content in the following way:

- Reimplement the QGLWidget::initializeGL() and QGLWidget::resizeGL() to set up the OpenGL state and provide a perspective transformation.
- Reimplement QGLWidget::paintGL() to paint the 3D scene, calling only OpenGL functions to draw on the widget.

It is also possible to draw 2D graphics onto a QGLWidget subclass, it is necessary to reimplement QGLWidget::paintEvent() and do the following:

- Construct a QPainter object.
- Initialize it for use on the widget with the QPainter::begin() function.
- Draw primitives using QPainter's member functions.
- Call QPainter::end() to finish painting.

Overpainting 2D content on top of 3D content takes a little more effort. One approach to doing this is shown in the Overpainting example.

OpenGL is a trademark of Silicon Graphics, Inc. in the United States and other countries.

See also QGLPixelBuffer, Hello GL Example, 2D Painting Example, Overpainting Example, and Grabber Example.

## Member Function Documentation

### QGLWidget::QGLWidget ( QWidget * parent = 0, const QGLWidget * shareWidget = 0, Qt::WindowFlags f = 0 )

Constructs an OpenGL widget with a parent widget.

The default format is used. The widget will be invalid if the system has no OpenGL support.

The parent and widget flag, f, arguments are passed to the QWidget constructor.

If shareWidget is a valid QGLWidget, this widget will share OpenGL display lists and texture objects with shareWidget. But if shareWidget and this widget have different formats, sharing might not be possible. You can check whether sharing is in effect by calling isSharing().

The initialization of OpenGL rendering state, etc. should be done by overriding the initializeGL() function, rather than in the constructor of your QGLWidget subclass.

See also QGLFormat::defaultFormat() and Textures Example.

### QGLWidget::QGLWidget ( QGLContext * context, QWidget * parent = 0, const QGLWidget * shareWidget = 0, Qt::WindowFlags f = 0 )

Constructs an OpenGL widget with parent parent.

The context argument is a pointer to the QGLContext that you wish to be bound to this widget. This allows you to pass in your own QGLContext sub-classes.

The widget will be invalid if the system has no OpenGL support.

The parent and widget flag, f, arguments are passed to the QWidget constructor.

If shareWidget is a valid QGLWidget, this widget will share OpenGL display lists and texture objects with shareWidget. But if shareWidget and this widget have different formats, sharing might not be possible. You can check whether sharing is in effect by calling isSharing().

The initialization of OpenGL rendering state, etc. should be done by overriding the initializeGL() function, rather than in the constructor of your QGLWidget subclass.

See also QGLFormat::defaultFormat() and isValid().

### QGLWidget::QGLWidget ( const QGLFormat & format, QWidget * parent = 0, const QGLWidget * shareWidget = 0, Qt::WindowFlags f = 0 )

Constructs an OpenGL widget with parent parent.

The format argument specifies the desired rendering options. If the underlying OpenGL/Window system cannot satisfy all the features requested in format, the nearest subset of features will be used. After creation, the format() method will return the actual format obtained.

The widget will be invalid if the system has no OpenGL support.

The parent and widget flag, f, arguments are passed to the QWidget constructor.

If shareWidget is a valid QGLWidget, this widget will share OpenGL display lists and texture objects with shareWidget. But if shareWidget and this widget have different formats, sharing might not be possible. You can check whether sharing is in effect by calling isSharing().

The initialization of OpenGL rendering state, etc. should be done by overriding the initializeGL() function, rather than in the constructor of your QGLWidget subclass.

See also QGLFormat::defaultFormat() and isValid().

### QGLWidget::~QGLWidget ()

Destroys the widget.

### bool QGLWidget::autoBufferSwap () const `[protected]`

Returns true if the widget is doing automatic GL buffer swapping; otherwise returns false.

See also setAutoBufferSwap().

### GLuint QGLWidget::bindTexture ( const QImage & image, GLenum target = GL_TEXTURE_2D, GLint format = GL_RGBA )

Calls QGLContext:::bindTexture(image, target, format) on the currently set context.

See also deleteTexture().

### GLuint QGLWidget::bindTexture ( const QPixmap & pixmap, GLenum target = GL_TEXTURE_2D, GLint format = GL_RGBA )

This is an overloaded member function, provided for convenience.

Calls QGLContext:::bindTexture(pixmap, target, format) on the currently set context.

See also deleteTexture().

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

This is an overloaded member function, provided for convenience.

Calls QGLContext::bindTexture(fileName) on the currently set context.

See also deleteTexture().

### const QGLColormap & QGLWidget::colormap () const

Returns the colormap for this widget.

Usually it is only top-level widgets that can have different colormaps installed. Asking for the colormap of a child widget will return the colormap for the child's top-level widget.

If no colormap has been set for this widget, the QColormap returned will be empty.

See also setColormap().

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

Returns the context of this widget.

It is possible that the context is not valid (see isValid()), for example, if the underlying hardware does not support the format attributes that were requested.

### QImage QGLWidget::convertToGLFormat ( const QImage & img ) `[static]`

Converts the image img into the unnamed format expected by OpenGL functions such as glTexImage2D(). The returned image is not usable as a QImage, but QImage::width(), QImage::height() and QImage::bits() may be used with OpenGL.

### void QGLWidget::deleteTexture ( GLuint id )

Calls QGLContext::deleteTexture(id) on the currently set context.

See also bindTexture().

### void QGLWidget::doneCurrent ()

Makes no GL context the current context. Normally, you do not need to call this function; QGLContext calls it as necessary. However, it may be useful in multithreaded environments.

### bool QGLWidget::doubleBuffer () const

Returns true if the contained GL rendering context has double buffering; otherwise returns false.

See also QGLFormat::doubleBuffer().

### QGLFormat QGLWidget::format () const

Returns the format of the contained GL rendering context.

See also setFormat().

### void QGLWidget::glDraw () `[virtual protected]`

Executes the virtual function paintGL().

The widget's rendering context will become the current context and initializeGL() will be called if it hasn't already been called.

### void QGLWidget::glInit () `[virtual protected]`

Initializes OpenGL for this widget's context. Calls the virtual function initializeGL().

### QImage QGLWidget::grabFrameBuffer ( bool withAlpha = false )

Returns an image of the frame buffer. If withAlpha is true the alpha channel is included.

Depending on your hardware, you can explicitly select which color buffer to grab with a glReadBuffer() call before calling this function.

### void QGLWidget::initializeGL () `[virtual protected]`

This virtual function is called once before the first call to paintGL() or resizeGL(), and then once whenever the widget has been assigned a new QGLContext. Reimplement it in a subclass.

This function should set up any required OpenGL context rendering flags, defining display lists, etc.

There is no need to call makeCurrent() because this has already been done when this function is called.

### void QGLWidget::initializeOverlayGL () `[virtual protected]`

This virtual function is used in the same manner as initializeGL() except that it operates on the widget's overlay context instead of the widget's main context. This means that initializeOverlayGL() is called once before the first call to paintOverlayGL() or resizeOverlayGL(). Reimplement it in a subclass.

This function should set up any required OpenGL context rendering flags, defining display lists, etc. for the overlay context.

There is no need to call makeOverlayCurrent() because this has already been done when this function is called.

### bool QGLWidget::isSharing () const

Returns true if this widget's GL context is shared with another GL context, otherwise false is returned. Context sharing might not be possible if the QGLWidgets use different formats.

See also format().

### bool QGLWidget::isValid () const

Returns true if the widget has a valid GL rendering context; otherwise returns false. A widget will be invalid if the system has no OpenGL support.

### void QGLWidget::makeCurrent ()

Makes this widget the current widget for OpenGL operations, i.e. makes the widget's rendering context the current OpenGL rendering context.

### void QGLWidget::makeOverlayCurrent ()

Makes the overlay context of this widget current. Use this if you need to issue OpenGL commands to the overlay context outside of initializeOverlayGL(), resizeOverlayGL(), and paintOverlayGL().

Does nothing if this widget has no overlay.

See also makeCurrent().

### const QGLContext * QGLWidget::overlayContext () const

Returns the overlay context of this widget, or 0 if this widget has no overlay.

See also context().

### void QGLWidget::paintEvent ( QPaintEvent * event ) `[virtual protected]`

Handles paint events passed in the event parameter. Will cause the virtual paintGL() function to be called.

The widget's rendering context will become the current context and initializeGL() will be called if it hasn't already been called.

Reimplemented from QWidget.

### void QGLWidget::paintGL () `[virtual protected]`

This virtual function is called whenever the widget needs to be painted. Reimplement it in a subclass.

There is no need to call makeCurrent() because this has already been done when this function is called.

### void QGLWidget::paintOverlayGL () `[virtual protected]`

This virtual function is used in the same manner as paintGL() except that it operates on the widget's overlay context instead of the widget's main context. This means that paintOverlayGL() is called whenever the widget's overlay needs to be painted. Reimplement it in a subclass.

There is no need to call makeOverlayCurrent() because this has already been done when this function is called.

### void QGLWidget::qglClearColor ( const QColor & c ) const

Convenience function for specifying the clearing color to OpenGL. Calls glClearColor (in RGBA mode) or glClearIndex (in color-index mode) with the color c. Applies to this widgets GL context.

See also qglColor(), QGLContext::currentContext(), and QColor.

### void QGLWidget::qglColor ( const QColor & c ) const

Convenience function for specifying a drawing color to OpenGL. Calls glColor4 (in RGBA mode) or glIndex (in color-index mode) with the color c. Applies to this widgets GL context.

See also qglClearColor(), QGLContext::currentContext(), and QColor.

### QPixmap QGLWidget::renderPixmap ( int w = 0, int h = 0, bool useContext = false )

Renders the current scene on a pixmap and returns the pixmap.

You can use this method on both visible and invisible QGLWidgets.

This method will create a pixmap and a temporary QGLContext to render on the pixmap. It will then call initializeGL(), resizeGL(), and paintGL() on this context. Finally, the widget's original GL context is restored.

The size of the pixmap will be w pixels wide and h pixels high unless one of these parameters is 0 (the default), in which case the pixmap will have the same size as the widget.

If useContext is true, this method will try to be more efficient by using the existing GL context to render the pixmap. The default is false. Only use true if you understand the risks. Note that under Windows a temporary context has to be created and usage of the useContext parameter is not supported.

Overlays are not rendered onto the pixmap.

If the GL rendering context and the desktop have different bit depths, the result will most likely look surprising.

Note that the creation of display lists, modifications of the view frustum etc. should be done from within initializeGL(). If this is not done, the temporary QGLContext will not be initialized properly, and the rendered pixmap may be incomplete/corrupted.

### void QGLWidget::renderText ( int x, int y, const QString & str, const QFont & font = QFont(), int listBase = 2000 )

Renders the string str into the GL context of this widget.

x and y are specified in window coordinates, with the origin in the upper left-hand corner of the window. If font is not specified, the currently set application font will be used to render the string. To change the color of the rendered text you can use the glColor() call (or the qglColor() convenience function), just before the renderText() call.

The listBase parameter is obsolete and will be removed in a future version of Qt.

### void QGLWidget::renderText ( double x, double y, double z, const QString & str, const QFont & font = QFont(), int listBase = 2000 )

This is an overloaded member function, provided for convenience.

x, y and z are specified in scene or object coordinates relative to the currently set projection and model matrices. This can be useful if you want to annotate models with text labels and have the labels move with the model as it is rotated etc.

Note that this function only works properly if `GL_DEPTH_TEST` is enabled, and you have a properly initialized depth buffer.

### void QGLWidget::resizeEvent ( QResizeEvent * event ) `[virtual protected]`

Handles resize events that are passed in the event parameter. Calls the virtual function resizeGL().

Reimplemented from QWidget.

### void QGLWidget::resizeGL ( int width, int height ) `[virtual protected]`

This virtual function is called whenever the widget has been resized. The new size is passed in width and height. Reimplement it in a subclass.

There is no need to call makeCurrent() because this has already been done when this function is called.

### void QGLWidget::resizeOverlayGL ( int width, int height ) `[virtual protected]`

This virtual function is used in the same manner as paintGL() except that it operates on the widget's overlay context instead of the widget's main context. This means that resizeOverlayGL() is called whenever the widget has been resized. The new size is passed in width and height. Reimplement it in a subclass.

There is no need to call makeOverlayCurrent() because this has already been done when this function is called.

### void QGLWidget::setAutoBufferSwap ( bool on ) `[protected]`

If on is true automatic GL buffer swapping is switched on; otherwise it is switched off.

If on is true and the widget is using a double-buffered format, the background and foreground GL buffers will automatically be swapped after each paintGL() call.

The buffer auto-swapping is on by default.

See also autoBufferSwap(), doubleBuffer(), and swapBuffers().

### void QGLWidget::setColormap ( const QGLColormap & cmap )

Set the colormap for this widget to cmap. Usually it is only top-level widgets that can have colormaps installed.

See also colormap().

### void QGLWidget::setMouseTracking ( bool enable )

If enable is true then mouse tracking is enabled; otherwise it is disabled.

### void QGLWidget::swapBuffers ()

Swaps the screen contents with an off-screen buffer. This only works if the widget's format specifies double buffer mode.

Normally, there is no need to explicitly call this function because it is done automatically after each widget repaint, i.e. each time after paintGL() has been executed.

See also doubleBuffer(), setAutoBufferSwap(), and QGLFormat::setDoubleBuffer().

### void QGLWidget::updateGL () `[virtual slot]`

Updates the widget by calling glDraw().

### void QGLWidget::updateOverlayGL () `[virtual slot]`

Updates the widget's overlay (if any). Will cause the virtual function paintOverlayGL() to be executed.

The widget's rendering context will become the current context and initializeGL() will be called if it hasn't already been called.