QGLWidget Class

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

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

protected:

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

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

};

Member Function Documentation

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

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

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

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.

[virtual slot] void QGLWidget::updateGL()

Updates the widget by calling glDraw().

[virtual slot] void QGLWidget::updateOverlayGL()

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.

[virtual] QGLWidget::~QGLWidget()

Destroys the widget.

[protected] bool QGLWidget::autoBufferSwap() const

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 QImage &image, GLenum target, GLint format, QGLContext::BindOptions options)

This is an overloaded function.

The binding options are a set of options used to decide how to bind the texture to the context.

This function was introduced in Qt 4.6.

GLuint QGLWidget::bindTexture(const QPixmap &pixmap, GLenum target, GLint format, QGLContext::BindOptions options)

This is an overloaded function.

Generates and binds a 2D GL texture to the current context, based on pixmap. The generated texture id is returned and can be used in

The binding options are a set of options used to decide how to bind the texture to the context.

This function was introduced in Qt 4.6.

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

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

See also deleteTexture().

GLuint QGLWidget::bindTexture(const QString &fileName)

This is an overloaded function.

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 QGLColormap returned will be empty.

See also setColormap() and QGLColormap::isEmpty().

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.

See also setContext().

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

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. The GL format used is GL_RGBA.

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().

void QGLWidget::drawTexture(const QRectF &target, GLuint textureId, GLenum textureTarget = GL_TEXTURE_2D)

Calls the corresponding QGLContext::drawTexture() with target, textureId, and textureTarget for this widget's context.

This function was introduced in Qt 4.4.

void QGLWidget::drawTexture(const QPointF &point, GLuint textureId, GLenum textureTarget = GL_TEXTURE_2D)

Calls the corresponding QGLContext::drawTexture() with point, textureId, and textureTarget for this widget's context.

This function was introduced in Qt 4.4.

[override virtual protected] bool QGLWidget::event(QEvent *e)

Reimplements: QWidget::event(QEvent *event).

QGLFormat QGLWidget::format() const

Returns the format of the contained GL rendering context.

See also setFormat().

[virtual protected] void QGLWidget::glDraw()

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.

[virtual protected] void QGLWidget::glInit()

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.

On QNX the back buffer is not preserved when swapBuffers() is called. The back buffer where this function reads from, might thus not contain the same content as the front buffer. In order to retrieve what is currently visible on the screen, swapBuffers() has to be executed prior to this function call.

[virtual protected] void QGLWidget::initializeGL()

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.

[virtual protected] void QGLWidget::initializeOverlayGL()

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 widgets 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 nullptr if this widget has no overlay.

See also context().

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

Reimplements: QWidget::paintEvent(QPaintEvent *event).

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.

[virtual protected] void QGLWidget::paintGL()

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.

[virtual protected] void QGLWidget::paintOverlayGL()

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 QGLWidget objects.

Internally the function renders into a framebuffer object and performs pixel readback. This has a performance penalty, meaning that this function is not suitable to be called at a high frequency.

After creating and binding the framebuffer object, the function will call initializeGL(), resizeGL(), and paintGL(). On the next normal update initializeGL() and resizeGL() will be triggered again since the size of the destination pixmap and the QGLWidget's size may differ.

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.

Care must be taken when using framebuffer objects in paintGL() in combination with this function. To switch back to the default framebuffer, use QGLFramebufferObject::bindDefault(). Binding FBO 0 is wrong since renderPixmap() uses a custom framebuffer instead of the one provided by the windowing system.

useContext is ignored. Historically this parameter enabled the usage of the existing GL context. This is not supported anymore since additional contexts are never created.

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())

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.

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

This is an overloaded function.

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.

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

Reimplements: QWidget::resizeEvent(QResizeEvent *event).

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

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

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.

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

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.

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

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::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().