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 DOCUMENTATIONQGLContext::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.
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Trolltech AS 2 February 2007 QGLContext(3qt)