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QGLContext(3qt)						       QGLContext(3qt)

NAME
       QGLContext - Encapsulates an OpenGL rendering context

SYNOPSIS
       #include <qgl.h>

       Inherits QGL.

   Public Members
       QGLContext ( const QGLFormat & format, QPaintDevice * device )
       virtual ~QGLContext ()
       virtual bool create ( const QGLContext * shareContext = 0 )
       bool isValid () const
       bool isSharing () const
       virtual void reset ()
       QGLFormat format () const
       QGLFormat requestedFormat () const
       virtual void setFormat ( const QGLFormat & format )
       virtual void makeCurrent ()
       virtual void swapBuffers () const
       QPaintDevice * device () const
       QColor overlayTransparentColor () const

   Static Public Members
       const QGLContext * currentContext ()

   Protected Members
       virtual bool chooseContext ( const QGLContext * shareContext = 0 )
       virtual void doneCurrent ()
       virtual int choosePixelFormat ( void * dummyPfd, HDC pdc )
       virtual void * chooseVisual ()
       virtual void * chooseMacVisual ( GDHandle device )
       bool deviceIsPixmap () const
       bool windowCreated () const
       void setWindowCreated ( bool on )
       bool initialized () const
       void setInitialized ( bool on )
       void generateFontDisplayLists ( const QFont & font, int listBase )

DESCRIPTION
       The QGLContext class encapsulates an OpenGL rendering context.

       An OpenGL<sup>*</sup> 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.

       <sup>*</sup> 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 )
       Constructs an OpenGL context for the paint device device, which can be
       a widget or a pixmap. The format specifies several display options for
       the context.

       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]
       Destroys the OpenGL context and frees its resources.

bool QGLContext::chooseContext ( const QGLContext * shareContext = 0 )
       [virtual protected]
       This semi-internal function is called by create(). It creates a system-
       dependent OpenGL handle that matches the format() of shareContext as
       closely as possible.

       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]
       Mac only: This virtual function tries to find a visual that matches the
       format using the given device handle, reducing the demands if the
       original request cannot be met.

       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]
       Win32 only This virtual function chooses a pixel format that matches
       the OpenGL format. Reimplement this function in a subclass if you need
       a custom context.

       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]
       X11 only: This virtual function tries to find a visual that matches the
       format, reducing the demands if the original request cannot be met.

       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]
       Creates the GL context. Returns TRUE if it was successful in creating a
       valid GL rendering context on the paint device specified in the
       constructor; otherwise returns FALSE (i.e. the context is invalid).

       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]
       Returns the current context, i.e. the context to which any OpenGL
       commands will currently be directed. Returns 0 if no context is
       current.

       See also makeCurrent().

QPaintDevice * QGLContext::device () const
       Returns the paint device set for this context.

       See also QGLContext::QGLContext().

bool QGLContext::deviceIsPixmap () const [protected]
       Returns TRUE if the paint device of this context is a pixmap; otherwise
       returns FALSE.

void QGLContext::doneCurrent () [virtual protected]
       Makes no GL context the current context. Normally, you do not need to
       call this function; QGLContext calls it as necessary.

QGLFormat QGLContext::format () const
       Returns the frame buffer format that was obtained (this may be a subset
       of what was requested).

       See also requestedFormat().

void QGLContext::generateFontDisplayLists ( const QFont & font, int listBase )
       [protected]
       Generates a set of 256 display lists for the 256 first characters in
       the font font. The first list will start at index listBase.

       See also QGLWidget::renderText().

bool QGLContext::initialized () const [protected]
       Returns TRUE if this context has been initialized, i.e. if
       QGLWidget::initializeGL() has been performed on it; otherwise returns
       FALSE.

       See also setInitialized().

bool QGLContext::isSharing () const
       Returns TRUE if display list sharing with another context was requested
       in the create() call and the GL system was able to fulfill this
       request; otherwise returns FALSE. Note that display list sharing might
       not be supported between contexts with different formats.

bool QGLContext::isValid () const
       Returns TRUE if a GL rendering context has been successfully created;
       otherwise returns FALSE.

void QGLContext::makeCurrent () [virtual]
       Makes this context the current OpenGL rendering context. All GL
       functions you call operate on this context until another context is
       made current.

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

QColor QGLContext::overlayTransparentColor () const
       If this context is a valid context in an overlay plane, returns the
       plane's transparent color. Otherwise returns an invalid color.

       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
       Returns the frame buffer format that was originally requested in the
       constructor or setFormat().

       See also format().

void QGLContext::reset () [virtual]
       Resets the context and makes it invalid.

       See also create() and isValid().

void QGLContext::setFormat ( const QGLFormat & format ) [virtual]
       Sets a format for this context. The context is reset.

       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]
       If on is TRUE the context has been initialized, i.e.
       QGLContext::setInitialized() has been called on it. If on is FALSE the
       context has not been initialized.

       See also initialized().

void QGLContext::setWindowCreated ( bool on ) [protected]
       If on is TRUE the context has had a window created for it. If on is
       FALSE no window has been created for the context.

       See also windowCreated().

void QGLContext::swapBuffers () const [virtual]
       Swaps the screen contents with an off-screen buffer. Only works if the
       context is in double buffer mode.

       See also QGLFormat::setDoubleBuffer().

bool QGLContext::windowCreated () const [protected]
       Returns TRUE if a window has been created for this context; otherwise
       returns FALSE.

       See also setWindowCreated().

SEE ALSO
       http://doc.trolltech.com/qglcontext.html
       http://www.trolltech.com/faq/tech.html

COPYRIGHT
       Copyright 1992-2007 Trolltech ASA, http://www.trolltech.com.  See the
       license file included in the distribution for a complete license
       statement.

AUTHOR
       Generated automatically from the source code.

BUGS
       If you find a bug in Qt, please report it as described in
       http://doc.trolltech.com/bughowto.html.	Good bug reports help us to
       help you. Thank you.

       The definitive Qt documentation is provided in HTML format; it is
       located at $QTDIR/doc/html and can be read using Qt Assistant or with a
       web browser. This man page is provided as a convenience for those users
       who prefer man pages, although this format is not officially supported
       by Trolltech.

       If you find errors in this manual page, please report them to qt-
       bugs@trolltech.com.  Please include the name of the manual page
       (qglcontext.3qt) and the Qt version (3.3.8).

Trolltech AS			2 February 2007		       QGLContext(3qt)
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