QGLContext

NAME

SYNOPSIS

Inherits QGL.

Public Members

Static Public Members

Protected Members

DESCRIPTION

An OpenGL^* rendering context is a complete set of OpenGL state variables.

The context's format is set in the constructor or later with setFormat(). The format options that are actually set are returned by format(); the options you asked for are returned by requestedFormat(). Note that after a QGLContext object has been constructed, the actual OpenGL context must be created by explicitly calling the create() function. The makeCurrent() function makes this context the current rendering context. You can make no context current using doneCurrent(). The reset() function will reset the context and make it invalid.

You can examine properties of the context with, e.g. isValid(), isSharing(), initialized(), windowCreated() and overlayTransparentColor().

If you're using double buffering you can swap the screen contents with the off-screen buffer using swapBuffers().

Please note that QGLContext is not thread safe.

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

See also Graphics Classes and Image Processing Classes.  

MEMBER FUNCTION DOCUMENTATION

QGLContext::QGLContext ( const QGLFormat & format, QPaintDevice * device )

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.

Note that after a QGLContext object has been constructed, create() must be called explicitly to create the actual OpenGL context. The context will be invalid if it was not possible to obtain a GL context at all.

See also format() and isValid().  

QGLContext::~QGLContext () [virtual]

bool QGLContext::chooseContext ( const QGLContext * shareContext = 0 ) [virtual protected]

On Windows, it calls the virtual function choosePixelFormat(), which finds a matching pixel format identifier. On X11, it calls the virtual function chooseVisual() which finds an appropriate X visual. On other platforms it may work differently.  

void * QGLContext::chooseMacVisual ( GDHandle device ) [virtual protected]

The algorithm for reducing the demands of the format is quite simple-minded, so override this method in your subclass if your application has specific requirements on visual selection.

See also chooseContext().  

int QGLContext::choosePixelFormat ( void * dummyPfd, HDC pdc ) [virtual protected]

Warning: The dummyPfd pointer and pdc are used as a PIXELFORMATDESCRIPTOR*. We use void to avoid using Windows-specific types in our header files.

See also chooseContext().  

void * QGLContext::chooseVisual () [virtual protected]

The algorithm for reducing the demands of the format is quite simple-minded, so override this method in your subclass if your application has spcific requirements on visual selection.

See also chooseContext().  

bool QGLContext::create ( const QGLContext * shareContext = 0 ) [virtual]

After successful creation, format() returns the set of features of the created GL rendering context.

If shareContext points to a valid QGLContext, this method will try to establish OpenGL display list sharing between this context and the shareContext. Note that this may fail if the two contexts have different formats. Use isSharing() to see if sharing succeeded.

Warning: Implementation note: initialization of C++ class members usually takes place in the class constructor. QGLContext is an exception because it must be simple to customize. The virtual functions chooseContext() (and chooseVisual() for X11) can be reimplemented in a subclass to select a particular context. The problem is that virtual functions are not properly called during construction (even though this is correct C++) because C++ constructs class hierarchies from the bottom up. For this reason we need a create() function.

See also chooseContext(), format(), and isValid().  

const QGLContext * QGLContext::currentContext () [static]

See also makeCurrent().  

QPaintDevice * QGLContext::device () const

See also QGLContext::QGLContext().  

bool QGLContext::deviceIsPixmap () const [protected]

void QGLContext::doneCurrent () [virtual protected]

QGLFormat QGLContext::format () const

See also requestedFormat().  

void QGLContext::generateFontDisplayLists ( const QFont & font, int listBase ) [protected]

See also QGLWidget::renderText().  

bool QGLContext::initialized () const [protected]

See also setInitialized().  

bool QGLContext::isSharing () const

bool QGLContext::isValid () const

void QGLContext::makeCurrent () [virtual]

In some very rare cases the underlying call may fail. If this occurs an error message is output to stderr.  

QColor QGLContext::overlayTransparentColor () const

The returned color's pixel value is the index of the transparent color in the colormap of the overlay plane. (Naturally, the color's RGB values are meaningless.)

The returned QColor object will generally work as expected only when passed as the argument to QGLWidget::qglColor() or QGLWidget::qglClearColor(). Under certain circumstances it can also be used to draw transparent graphics with a QPainter. See the examples/opengl/overlay_x11 example for details.  

QGLFormat QGLContext::requestedFormat () const

See also format().  

void QGLContext::reset () [virtual]

See also create() and isValid().  

void QGLContext::setFormat ( const QGLFormat & format ) [virtual]

Call create() to create a new GL context that tries to match the new format.

    QGLContext *cx;


    //  ...


    QGLFormat f;


    f.setStereo( TRUE );


    cx->setFormat( f );


    if ( !cx->create() )


        exit(); // no OpenGL support, or cannot render on the specified paintdevice


    if ( !cx->format().stereo() )


        exit(); // could not create stereo context

See also format(), reset(), and create().  

void QGLContext::setInitialized ( bool on ) [protected]

See also initialized().  

void QGLContext::setWindowCreated ( bool on ) [protected]

See also windowCreated().  

void QGLContext::swapBuffers () const [virtual]

See also QGLFormat::setDoubleBuffer().  

bool QGLContext::windowCreated () const [protected]

See also setWindowCreated().

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