QGLFormat(3qt)QGLFormat(3qt)NAME
QGLFormat - The display format of an OpenGL rendering context
SYNOPSIS
#include <qgl.h>
Inherits QGL.
Public Members
QGLFormat ()
QGLFormat ( int options, int plane = 0 )
bool doubleBuffer () const
void setDoubleBuffer ( bool enable )
bool depth () const
void setDepth ( bool enable )
bool rgba () const
void setRgba ( bool enable )
bool alpha () const
void setAlpha ( bool enable )
bool accum () const
void setAccum ( bool enable )
bool stencil () const
void setStencil ( bool enable )
bool stereo () const
void setStereo ( bool enable )
bool directRendering () const
void setDirectRendering ( bool enable )
bool hasOverlay () const
void setOverlay ( bool enable )
int plane () const
void setPlane ( int plane )
void setOption ( FormatOption opt )
bool testOption ( FormatOption opt ) const
Static Public Members
QGLFormat defaultFormat ()
void setDefaultFormat ( const QGLFormat & f )
QGLFormat defaultOverlayFormat ()
void setDefaultOverlayFormat ( const QGLFormat & f )
bool hasOpenGL ()
bool hasOpenGLOverlays ()
DESCRIPTION
The QGLFormat class specifies the display format of an OpenGL rendering
context.
A display format has several characteristics:
Double or single buffering.
Depth buffer.
RGBA or color index mode.
Alpha channel.
Accumulation buffer.
Stencil buffer.
Stereo buffers.
Direct rendering.
Presence of an overlay.
The plane of an overlay format.
You create and tell a QGLFormat object what rendering options you want
from an OpenGL<sup>*</sup> rendering context.
OpenGL drivers or accelerated hardware may or may not support advanced
features such as alpha channel or stereographic viewing. If you request
some features that the driver/hardware does not provide when you create
a QGLWidget, you will get a rendering context with the nearest subset
of features.
There are different ways to define the display characteristics of a
rendering context. One is to create a QGLFormat and make it the default
for the entire application:
QGLFormat f;
f.setAlpha( TRUE );
f.setStereo( TRUE );
QGLFormat::setDefaultFormat( f );
Or you can specify the desired format when creating an object of your
QGLWidget subclass:
QGLFormat f;
f.setDoubleBuffer( FALSE ); // single buffer
f.setDirectRendering( FALSE ); // software rendering
MyGLWidget* myWidget = new MyGLWidget( f, ... );
After the widget has been created, you can find out which of the
requested features the system was able to provide:
QGLFormat f;
f.setOverlay( TRUE );
f.setStereo( TRUE );
MyGLWidget* myWidget = new MyGLWidget( f, ... );
if ( !w->format().stereo() ) {
// ok, goggles off
if ( !w->format().hasOverlay() ) {
qFatal( "Cool hardware required" );
}
}
<sup>*</sup> OpenGL is a trademark of Silicon Graphics, Inc. in the
United States and other countries.
See also QGLContext, QGLWidget, Graphics Classes, and Image Processing
Classes.
MEMBER FUNCTION DOCUMENTATIONQGLFormat::QGLFormat ()
Constructs a QGLFormat object with the factory default settings:
Double buffer: Enabled.
Depth buffer: Enabled.
RGBA: Enabled (i.e., color index disabled).
Alpha channel: Disabled.
Accumulator buffer: Disabled.
Stencil buffer: Disabled.
Stereo: Disabled.
Direct rendering: Enabled.
Overlay: Disabled.
Plane: 0 (i.e., normal plane).
QGLFormat::QGLFormat ( int options, int plane = 0 )
Creates a QGLFormat object that is a copy of the current application
default format.
If options is not 0, this copy is modified by these format options. The
options parameter should be FormatOption values OR'ed together.
This constructor makes it easy to specify a certain desired format in
classes derived from QGLWidget, for example:
// The rendering in MyGLWidget depends on using
// stencil buffer and alpha channel
MyGLWidget::MyGLWidget( QWidget* parent, const char* name )
: QGLWidget( QGLFormat( StencilBuffer | AlphaChannel ), parent, name )
{
if ( !format().stencil() )
qWarning( "Could not get stencil buffer; results will be suboptimal" );
if ( !format().alphaChannel() )
qWarning( "Could not get alpha channel; results will be suboptimal" );
...
}
Note that there are FormatOption values to turn format settings both on
and off, e.g. DepthBuffer and NoDepthBuffer, DirectRendering and
IndirectRendering, etc.
The plane parameter defaults to 0 and is the plane which this format
should be associated with. Not all OpenGL implmentations supports
overlay/underlay rendering planes.
See also defaultFormat() and setOption().
bool QGLFormat::accum () const
Returns TRUE if the accumulation buffer is enabled; otherwise returns
FALSE. The accumulation buffer is disabled by default.
See also setAccum().
bool QGLFormat::alpha () const
Returns TRUE if the alpha channel of the framebuffer is enabled;
otherwise returns FALSE. The alpha channel is disabled by default.
See also setAlpha().
QGLFormat QGLFormat::defaultFormat () [static]
Returns the default QGLFormat for the application. All QGLWidgets that
are created use this format unless another format is specified, e.g.
when they are constructed.
If no special default format has been set using setDefaultFormat(), the
default format is the same as that created with QGLFormat().
See also setDefaultFormat().
QGLFormat QGLFormat::defaultOverlayFormat () [static]
Returns the default QGLFormat for overlay contexts.
The factory default overlay format is:
Double buffer: Disabled.
Depth buffer: Disabled.
RGBA: Disabled (i.e., color index enabled).
Alpha channel: Disabled.
Accumulator buffer: Disabled.
Stencil buffer: Disabled.
Stereo: Disabled.
Direct rendering: Enabled.
Overlay: Disabled.
Plane: 1 (i.e., first overlay plane).
See also setDefaultFormat().
bool QGLFormat::depth () const
Returns TRUE if the depth buffer is enabled; otherwise returns FALSE.
The depth buffer is enabled by default.
See also setDepth().
bool QGLFormat::directRendering () const
Returns TRUE if direct rendering is enabled; otherwise returns FALSE.
Direct rendering is enabled by default.
See also setDirectRendering().
bool QGLFormat::doubleBuffer () const
Returns TRUE if double buffering is enabled; otherwise returns FALSE.
Double buffering is enabled by default.
See also setDoubleBuffer().
bool QGLFormat::hasOpenGL () [static]
Returns TRUE if the window system has any OpenGL support; otherwise
returns FALSE.
Warning: This function must not be called until the QApplication object
has been created.
bool QGLFormat::hasOpenGLOverlays () [static]
Returns TRUE if the window system supports OpenGL overlays; otherwise
returns FALSE.
Warning: This function must not be called until the QApplication object
has been created.
bool QGLFormat::hasOverlay () const
Returns TRUE if overlay plane is enabled; otherwise returns FALSE.
Overlay is disabled by default.
See also setOverlay().
int QGLFormat::plane () const
Returns the plane of this format. The default for normal formats is 0,
which means the normal plane. The default for overlay formats is 1,
which is the first overlay plane.
See also setPlane().
bool QGLFormat::rgba () const
Returns TRUE if RGBA color mode is set. Returns FALSE if color index
mode is set. The default color mode is RGBA.
See also setRgba().
void QGLFormat::setAccum ( bool enable )
If enable is TRUE enables the accumulation buffer; otherwise disables
the accumulation buffer.
The accumulation buffer is disabled by default.
The accumulation buffer is used to create blur effects and multiple
exposures.
See also accum().
void QGLFormat::setAlpha ( bool enable )
If enable is TRUE enables the alpha channel; otherwise disables the
alpha channel.
The alpha buffer is disabled by default.
The alpha channel is typically used for implementing transparency or
translucency. The A in RGBA specifies the transparency of a pixel.
See also alpha().
void QGLFormat::setDefaultFormat ( const QGLFormat & f ) [static]
Sets a new default QGLFormat for the application to f. For example, to
set single buffering as the default instead of double buffering, your
main() might contain code like this:
QApplication a(argc, argv);
QGLFormat f;
f.setDoubleBuffer( FALSE );
QGLFormat::setDefaultFormat( f );
See also defaultFormat().
void QGLFormat::setDefaultOverlayFormat ( const QGLFormat & f ) [static]
Sets a new default QGLFormat for overlay contexts to f. This format is
used whenever a QGLWidget is created with a format that hasOverlay()
enabled.
For example, to get a double buffered overlay context (if available),
use code like this:
QGLFormat f = QGLFormat::defaultOverlayFormat();
f.setDoubleBuffer( TRUE );
QGLFormat::setDefaultOverlayFormat( f );
As usual, you can find out after widget creation whether the underlying
OpenGL system was able to provide the requested specification:
// ...continued from above
MyGLWidget* myWidget = new MyGLWidget( QGLFormat( QGL::HasOverlay ), ... );
if ( myWidget->format().hasOverlay() ) {
// Yes, we got an overlay, let's check _its_ format:
QGLContext* olContext = myWidget->overlayContext();
if ( olContext->format().doubleBuffer() )
; // yes, we got a double buffered overlay
else
; // no, only single buffered overlays are available
}
See also defaultOverlayFormat().
void QGLFormat::setDepth ( bool enable )
If enable is TRUE enables the depth buffer; otherwise disables the
depth buffer.
The depth buffer is enabled by default.
The purpose of a depth buffer (or Z-buffering) is to remove hidden
surfaces. Pixels are assigned Z values based on the distance to the
viewer. A pixel with a high Z value is closer to the viewer than a
pixel with a low Z value. This information is used to decide whether to
draw a pixel or not.
See also depth().
void QGLFormat::setDirectRendering ( bool enable )
If enable is TRUE enables direct rendering; otherwise disables direct
rendering.
Direct rendering is enabled by default.
Enabling this option will make OpenGL bypass the underlying window
system and render directly from hardware to the screen, if this is
supported by the system.
See also directRendering().
void QGLFormat::setDoubleBuffer ( bool enable )
If enable is TRUE sets double buffering; otherwise sets single
buffering.
Double buffering is enabled by default.
Double buffering is a technique where graphics are rendered on an off-
screen buffer and not directly to the screen. When the drawing has been
completed, the program calls a swapBuffers() function to exchange the
screen contents with the buffer. The result is flicker-free drawing and
often better performance.
See also doubleBuffer(), QGLContext::swapBuffers(), and
QGLWidget::swapBuffers().
void QGLFormat::setOption ( FormatOption opt )
Sets the format option to opt.
See also testOption().
void QGLFormat::setOverlay ( bool enable )
If enable is TRUE enables an overlay plane; otherwise disables the
overlay plane.
Enabling the overlay plane will cause QGLWidget to create an additional
context in an overlay plane. See the QGLWidget documentation for
further information.
See also hasOverlay().
void QGLFormat::setPlane ( int plane )
Sets the requested plane to plane. 0 is the normal plane, 1 is the
first overlay plane, 2 is the second overlay plane, etc.; -1, -2, etc.
are underlay planes.
Note that in contrast to other format specifications, the plane
specifications will be matched exactly. This means that if you specify
a plane that the underlying OpenGL system cannot provide, an invalid
QGLWidget will be created.
See also plane().
void QGLFormat::setRgba ( bool enable )
If enable is TRUE sets RGBA mode. If enable is FALSE sets color index
mode.
The default color mode is RGBA.
RGBA is the preferred mode for most OpenGL applications. In RGBA color
mode you specify colors as red + green + blue + alpha quadruplets.
In color index mode you specify an index into a color lookup table.
See also rgba().
void QGLFormat::setStencil ( bool enable )
If enable is TRUE enables the stencil buffer; otherwise disables the
stencil buffer.
The stencil buffer is disabled by default.
The stencil buffer masks certain parts of the drawing area so that
masked parts are not drawn on.
See also stencil().
void QGLFormat::setStereo ( bool enable )
If enable is TRUE enables stereo buffering; otherwise disables stereo
buffering.
Stereo buffering is disabled by default.
Stereo buffering provides extra color buffers to generate left-eye and
right-eye images.
See also stereo().
bool QGLFormat::stencil () const
Returns TRUE if the stencil buffer is enabled; otherwise returns FALSE.
The stencil buffer is disabled by default.
See also setStencil().
bool QGLFormat::stereo () const
Returns TRUE if stereo buffering is enabled; otherwise returns FALSE.
Stereo buffering is disabled by default.
See also setStereo().
bool QGLFormat::testOption ( FormatOption opt ) const
Returns TRUE if format option opt is set; otherwise returns FALSE.
See also setOption().
SEE ALSO
http://doc.trolltech.com/qglformat.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
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If you find errors in this manual page, please report them to qt-
bugs@trolltech.com. Please include the name of the manual page
(qglformat.3qt) and the Qt version (3.3.8).
Trolltech AS 2 February 2007 QGLFormat(3qt)
